Note: Descriptions are shown in the official language in which they were submitted.
1 3 1 1 02~
INSTRUllENTATION AND MONITORING SYSTEMS
EMPLOYING DIPFERENTIAL TE:MPERAqllR~ SENSORS
This invention relates to instrumentation and
monitoringsystems employingdiff~rentialtemperature sensing,
or detecting, devices and, more particularly, to such systems
employing improved, split-well differential temperature
sensors, or detectors, for detecting the presence of water in
a pressure vessel, such as a steam extraction pipe of a steam
turbine system.
Differential temperature sensors, a~ are well known
in the art, employ thermodynamic and fluid principles for
selectively sensing the presence or absence of, and/or the
creation or cessation of the flow of materials in a liquid or
gaseous form. U.S. Patent No. 3,366,942 - Deane, illustrates
one form of a prior art differential temperature sensor, used
as a flow stoppage detector. The sensor, or probe, comprises
a pair of heat sensing probes with a heater probe thermally
connected therewith. The sensing and heater probes are
adapted for being introduced
~;, .. .
1 31 ~ ~2~
into a conduit through which a material may flow. The
heater probe is spaced more closely to one than to the
other of the sensing probes. In the absence of flow, the
sensing probe closer to the heater probe is at a higher
temperature than the other sensing probe; conversely, when
a fluid material flows past the probes, heat is conducted
away from the heater probe and thus the temperature
difference between the two sensing probes decreases, or
disappears.
U.S. Patent No. 3,898,638 - Deane et al.,
illustra~es another such differential temperature sensor,
having the same basic configuration as that of the earlier
Deane Patent 3,366,942 but represented to have an improved
internal structure of the temperature sensing probes which
affords increased accuracy of measurements. As noted
therein, differential heating of the two temperature
sensing probes by the heater probe may be accomplished in
part by, for example, the heat shunt running between the
heater probe and the more adjacent of the two temperature
sensing probes; further, both convection and/or conduction
in the medium at rest, and conduction in the shunt, serve
to carry heat differentially between the probes.
Another form of such differential temperature
~ sensing probes, again having the same basic configuration
- 25 of a pair of temperature sensors and a heater element
disposed adjacent to one of the two temperature sensors,
is disclosed in U.S. Patent No. 4,449,403 - McQueen. The
particular application of the McQueen device entails
utilizing plural such sensors in a vertically stacked
array within a guide tube disposed within a reactor
vessel, the outputs from the plurality of sensors
providing an indication of the wet/dry condition of the
coolant in the region of the fuel rods, among other
purposes and functions. A particular concern in such
reactor vessels is the presence of voids, e.g., a steam
void, displacing the reactor coolant from the nuclear fuel
rods, which then are inadequately cooled and may overhaat.
The composite device most specifically is disclosed for
3 t31 102~
use in sensing the coolant properties under three regimes:
subcooled (the normal operating condition); saturated
liquid (the boiling condition); and saturated vapor (a
voided condition). As noted therein, the improper
conditions may result in "water hammer" effects producing
pressure pulses which can break pipes, pipe supports,
tanks, valves and other such vital equipment.
U.S. Patent No. 4,440,717 - Bevilacqua et al.
likewise discloses an instrumentation system employing
plural sensors at vertically spaced elevations and
positioned within a nuclear reactor vessel, each sensor
comprising a heater for heating one of a pair of thermo-
couples wired to provide both absolute temperatures and
differential temperatures therebetween, for detecting the
liquid coolant level within the vessel, again employing
the difference in heat transfer characteristics between
heat transfer to a liquid and heat transfer to a gas or
vapor to senge the liquid level. Similar such sensors and
related systems for use in nuclear reactor vessels or
other pressurized water systems are disclosed in U.S.
Patents 4,418,035 - Smith and 4,439,396 - Rolstad. The
Smith '035 patent moreover illustrates a block diagram
form of a multiple function monitoring system employing
such sensors.
While the differential temperature sensors, or
detectors, as disclosed in the above cross-referenced
applications, and the instrumentation systems of the
present invention have broad application, including use in
sensing and monitoring pressure vessels of nuclear reactor
systems as in the above-referenced patents, they have been
developed wi~h specific reference to the operation and
preventive maintenance of steam turbine generators.
Problems with such generators arising out of the induction
of water or cool vapor into the steam turbines become more
3S critical as the units age and particularly as they are
used, increasingly, for cyclic and/or shift operation.
Malfunctions of the equipment in the heat cycle can cause
such induction to occur at various locations, including
~ 3 ~ 1 32~
the main-steam inlet piping, the hot-reheat steam inlet
piping, the cold-reheat steam piping, extraction connec-
tions, gland steam-sealing system, and turbine drains.
Beyond the resulting structural damage and mechanical
malfunctions caused by the induction of water or cool
vapor, the resulting unscheduled down time of the
equipment is a matter of serious concern.
In addition to the particular locations at which
induction occurs, it is important to identify the various
types of induction, i.e., the types of water induction
events, which may occur. For example, induction may occur
as a flow of a water film on the side of a pipe associated
with the turbine produced typically by condensation of
steam on the side of a cold pipe or from an overspray
condition. Droplet or "chunk" flow may occur, visualized
as a continuous projectile of water which may vary from
the size of drops to walnuts and which may be mixed with
steam. Slug ~low may be produced, i.e., a slug of water
which completely fills a section of pipe and is projected
down the pipe, presumably by the flash-off of water. Two-
phase flow as well has been identified, comprising
generally an ill-defined "water-steam" mixture that may
result from flash-off of high energy water, and may
involve a core flow of solid water. Finally, a broad
category exists wherein water may rise within a pipe, due
to such sources as condensation, spray or flow, feed water
heater tube leaks, and/or design deficiencies in the drain
system, an~ to combinations thereof. It appears, however,
that the vast majority of water induction events are of
the slow rise type of the last category described, and
; which, moreover, may be the precursor to the other
categories of water induction events. Thus, while not
necessarily so limited in its scope, the sensors, or
detectors of the present invention and the associated
instrumentation systems are directed to this broader,
last-mentioned category and thus to monitoring the
condition within a pipe and more specifically for the
detection of the relatively slow rise of water within a
s 1311~2~
pipe associated with a turbine system. As noted, the
sources of such water may be the boiler and feed water
heaters, accumulation due to condensation, faulty sprayers
and broXen pipes, and accumulation arising from condensa-
tion within the turbine itself, in stages that operate inth~ wet region.
Beyond the specific sensors as disclosed in the
foregoing patents, commercially available systems
incorporating such differential temperature sensors for
monitoring and detecting the presence of water have been
developed. Solartron Protective Systems, a division of
Solartron Transducers, owned by Schlumberger, offers a
"Self-Validating Water Induction Monitoring System~' under
its registered trademark HYDRATECT - 2455D. Resistivity
measurements are made inside of a manifold by means of
electrodes, which serve to discriminate between the
resistivities of water and steam (or air). As described
in its sales literature, the energized tip of an electrode
is referenced to the body of the manifold, and the tip is
insulated from the body by a high purity insulator. Pairs
of such electrodes may be mounted in two-port manifolds in
conduits, such as drain lines, to be monitored, each
electrode detecting the presence of either water or steam,
and its output being routed by independent connections to
an electronic discrimination circuit. A discriminator
circuit purportedly checks for component failures and
declares same as occurring, within each electrode channel.
A validation check between two electrode channels
subjected to the same conditions is described as being
performed, as a basis for indicating whether a fault
exists. The HYDR.ATECT - 2455D system of Solartron,
however, is deficient in many respects and inherently
incapable of providing reliable, long-life character-
istics. For example, the sensor is of generally cylindri-
cal configuration and is adapted to be inserted through apenetration in the sidewall of a pressure vessel and
secured thereto, as is conventional. A segment of the
cylindrical structure comprises an annular band of
6 131102~
insulating material, which insulates the electrode tip of
the sensor from the remainder of the structure. A tight
pressure seal, e.g., a porcelain to metal weld, must be
provided at the respective interfaces of the insulating
band with the electrode and with the remainder of the
cylindrical sidewall of the sensor. The interfaces of
dissimilar materials, i.e., porcelain and metal, renders
in the sensor structure highly susceptible to leakage and
eventually breaking, particularly in view of the rather
hostile environment to which it is subjected (e.g.,
temperature cycling, vibration and the like). In typical
experience, such sensors have a reliable lifetime only of
from one to three years, at most. Not only do sensors of
this type fail to provide the long-life characteristics
essential to an effective monitoring system, their
tendency to leak and break presents a serious threat to
personnel. Moreover, because of their structure, as
described and as will be appreciated, the sensors cannot
be repaired or replaced while the system, which they are
int0nded to monitor, is on-line.
Another commercial system is offered by Fluid
Components, Inc. and set forth in its brochure entitled
"Li~uid Level & Interface Controllers," that brochure
citing protection for the disclosed systems under the
above-referenced Patents 3,366,942, 3,898,638 and
4,449,403. Sensors incorporating probes as disclosed in
those patents are employed for measuring temperature
differentials. The specific values of the output signals
are stated to be governed by the media in contact with the
probes and thus, for example, liquid/gas and li~uidlliquid
interfaces as well as wet/dry conditions purportedly may
be detected. Monitoring and calibration circuits for the
~ uid level and interface controllers associated with the
sensors are indicated to be available. These sensors and
associated controllers, however, are not suitable for the
hostile environment of steam turbine systems and,
particularly, for performing the requisite sensing
functions for anticipating problems of water induction.
131 102~
For example, the sensors cannot withstand the involved
high pressure and temperature conditions. The sensors,
moreover, are asymmetric and inherently lack any duplex
functional capabilit~ as has been determined, in accor-
dance with the present invention, to be essential to theeffective and reliable monitoring and control of such
systems. For example, an important fouling test,
performed by the sensox and related system of the present
invention, is incapable of being performed by an asym-
metric sensor and a system incorporating same; moreover,since lacking any duplex configuration, there necessarily
is no capability of on-line, automatic substitution for a
failed element, e.g., a heater element. The specific
structure of the sensors, moreover, does not permit
physical replacement of failed heater and/or thermocouple
elements while on-line. Moreover, such sensors and
necessarily the related systems will not work in a steam
flow environment in the absence of a shield surrounding
the heater and thermocouple elements, since even low steam
velocities will remove heat more rapidly than water.
Despite incorporating advances in technology,
currently available sensors and monitoring and alarm
systems employing same, as reported in the literature
above-identified, have failed to satisfy critical needs in
the industry. For example, the above-noted problem of
water induction in steam turbines, while recognized and
studied since the early 1970's, has yet to be adequately
resolved.
Water induction incidents have become of such
concern that the ASME (American Society of Mechanical
~ngineers) established a Committee on Turbine Water-Damage
Prevention; plant design recommendations to prevent water
damage are contained in ANSIIASME Standard No. TDP-1-1985.
More recently, studies done by the assignee of the
present invention for EPRI in actual operating power
generating facilities are set forth in a final report
prepared and released by EPRI as report CS-4285, "Detec-
tion of Water Induction in Steam Turbines. Phase III:
8 131 102~
Field Demonstration." These studies emphasiZe the
continuiny, critical need for reliable sensors and
monitoring systems for use in the environment of steam
tur~ines, to detect the severe problem of water induction.
Accordingly, there remains a critical need for
improved instrumentation and monitoring systems employing
differential temperature sensors for reliably detecting
the potentially serious water induction problems in steam
turbine installations, as well as for detecting a
liquid/gas (vapor) condition and/or any change therein in
other high pressure and high temperature environments such
as those which exist in nuclear reactor vessels. Perhaps
~ost critical to water induction monitor systems for use
with steam turbines, is the fact that the sensors and
associated control systems typically remain inactive for
many years, before the system is called upon to generate a
response indicating that a water induction event may take
place. Over such extended time periods, however, it is
predictable that periodic failure of the electrical
elements, i.e., both the heater and the thermocouple
elements, will occur, due to the vibration and cycling
conditions to which they are exposed. It follows that the
sensor device itself must be of rugged construction and
sufficient mechanical strength so as to withstand, over
essentially indefinite time periods, the high temperature
and pressure conditions, and cycling thereof, as well as
the vibrations to which it is subjected, while neverthe-
less affording highly accurate and reliable outputs.
Because of the potential of failure of both the heating
and the temperature sensing elements in such sensors, the
sensors and the associated monitoring and control
circuitry must afford on-line test capabilities, as well
as the capability of on-line replacement of the heater and
thermocouple elements of the sensors. Each sensor,
moreover, should afford duplex, or redundant, components;
likewise, the associated control and monitoring circuitry
should produce automatic alarm indications upon detection
of such failures, as well as automatic toggling or
9 131 102~
switching to the duplex or redundant elements upon
detection of failures.
A closely related concern is that the number of
penetrations through the sidewall of the vessel within
which conditions are to be monitored, i.e., to accommodate
the sensor~, be minimized, fxom both structural integrity
and installation efficiency standpoints. Further, taking
into account the desired duplex capability, assuring
accuracy of the sensor outputs dictates that substantially
the same conditions be monitored by the respective, duplex
elements of each sensor.
The differential temperature sensors as
disclosed in the above, cross-referenced applications and
incorporated in the instrumentation and monitoring systems
of the present invention, overcome the foregoing and other
problems and deficiencies of the prior art, and satisfy
the objectives above-noted.
The sensors, or detectors, in accordance with
various different disclosed embodiments thereof, uniformly
are of rugged design and afford reliable and safe pressure
vessel penetration -- and a minimum number of such
penetrations for a given level of accuracy and verified
monitoring capability by the associated instrumentation
system. The various disclosed embodiments accommodate the
requisite heater and thermocouple elements to afford the
desired differential temperature sensing, or detecting
operation, along with on-line testability and on-line
replaceability of those elements; moreover, in certain
preferred sensor embodiments of duplex character,
automatic substitution of failed elements may be performed
by the associated instrumentation system, in actual
operation. All share a basic, or generic structural
configuration of a generally cylindrical thermowell body
which is split by a small gap along a bilateral plane
forming, effectively, two identical half-cylinder probes
which are integrally joined to and extend from a common,
cylindrical shank portion. In another embodiment, the
body is split by a second bilateral plane, crossed, or
lo ~ 3 1 l ~28
transverse, relative to the first and thus defining four
identical ~uarter-cylinder probes. Accordingly, the
expression part-cylinder, generic to both, is adopted,
where applicable. The shank portion is threaded on a
section of its exterior circumference for being received
and secured in a boss welded to a steam line or other
pressure vessel; alternatively, a socket weld connection
may be made. Tha part-cylinder probes thus project into
the interior of the line, or may be recessed into a boss,
and in either such installation, are in communication with
the fluid condition in the line, or vessel, for performing
the sensing/detecting function. Accordingly, the generic
expression is adopted that the detector, or sensor, is
mounted to a pressure vessel with the probes in communica-
tion with the fluid in the pressure vessel, the condition
of which is to be monitored. The shank is bored from its
upper~ free end to define a generally cylindrical access
chamber therein, terminating in a base wall at the
juncture of the shank and the half-cylinder probes.
In accordance with a first preferred embodiment
of the sensors, a central bore and a pair of bores
symmetrically displaced relatively to the central bore
extend in parallel-axial relationship into each half-
cylinder probe from the base wall; within each half-
cylinder probe, the heater element is inserted into the
central bore and a pair of thermocouple sensor elements is
inserted into the corresponding pair of symmetrically
displaced bores. Thus, the sensor is of duplex configura-
tion and functional capability, either probe being
selectable as the heated probe/thermocouple and according-
ly the heater element thereof being supplied with
electrical power, and the other probe with the inactive
heater element providing the nonheated thermocouple
element, thereby to function as a differential temperature
sensor. As will be more fully described in the following,
the opposite complementary elements of the two probes may
be selected in the alternative; this duplex configuration
affords many advantages, including automatic switching or
1 .'~1 1 0'~
toggling between the complementary sets of heater elements
for performing verification and fouling tests and for
automatic substitution of complementary elements upon
detection of element failure, thereby to afford continuous
monitoring functions despite individual element failure.
By virtue of the connection of the shank to the
pipe or vessel wall, the latter funstions as a temperature
sink affording thermal isolation between the heated and
unheated half-cylinder probes, enhancing the accuracy of
the thermocouple outputs. ~ connector box is affixed to
the upper, free end of the shank for connecting the
electrical leads of the heaters and the thermocouples
through a cable to external monitoring, control and po~er
circuits. The sensor design provides for securing the
elements in their inserted positions, while permitting
ready, on-line access to the heater and thermocouple
elements for replacement, without any need for removing
the thermowell housing.
Instrumentation and monitoring system, as herein
disclosed and claimed, perform continuity checks of both
the heater and the associated pair of thermocouple
elements of each sensor probe on a continuous basis, and
provide suitable indications of failure of any of these
elements. When a failed element is detected, the system
automatically switches to the complementary set of
elements, as is required to correct for and thus exclude
the failed element. This insures continued operation of
the sensor and prevents false alarms that would otherwise
result upon a component failure. More specifically, the
sensor functions as a differential temperature sensor, as
above explained. Thus, identifying the two half-cylinder
probes as A and B, heater A may be initially energized.
one of the symmetrically disposed thermocouples Al and A2,
for example Al, then is employed in conjunction with one
of the thermocouples B1 and B2 of probe B, for example,
thermocouple Bl. Should either of thermo-couples Al and
B1 fail, the system automatically switches to the
respecti~e, complementary thermo-couples A2 and B2.
12 1 31 1 028
Similarly, should heater A fail, the system automatically
switches to heater B. As will be appreciated, the
differential temperature indication (8T) should be of the
same value but opposite sign. The switching or toggling
capability, afforded by the duplex character of the
sensor, thus enables automatic correction for failed
elements, without loss of continuous monitoring and
without producing a false alarm. Moreover, the validity
of testing operations is enhanced, since by toggling
between heater ~ and heater B during on-line testing, and
comparing the resulting, respective outputs, i.e., T
indications of equal value but opposite signs should be
produced, the system can confirm that the sensor has not
been fouled by accumulation of material the probes and
that the calibration remains valid.
A second, integrated detector, or sensor,
embodiment similarly employs a generally cylindrical
thermowell body having two (or four) identical part-
cylinder probes but only a single bore is formed in each
of the probes. A single heater/thermometer element,
effective to simultaneously heat and measure the tempera-
ture of the probe, is received in each bore. The
heater/thermometer element is of nickel, iron or other
similar, pure metal, having a value of electrical
resistance which is substantially linearly dependent on
temperature. As to each related pair of probes, the
heater/thermometer element of one is supplied with
sufficient current for heating its corresponding probe and
the other with a much smaller current, the former
~unctioning as the heated element, or probe, and the
latter as the reference element, or probe. Conveniently,
the two heater/thermometer elements are connected as
corresponding arms of a bridge and predetermined,
proportionately related currents are supplied thereto, the
voltage drop across the heater/thermometer element of the
reference probe being correspondingly multiplied by the
same proportionality factor and the multiplied value
being compared, in opposite sense, with the voltage drop
13 l 31~28
across the heated element by a differential amplifier.
The resultant differential voltage ( V) thus obtained
represents the value of the temperature differential ( T)
between the selected pair of problems (i.e., T = k( V)
where "k" is a known constant). Similarly to the first
embodiment, a high level differential is maintained when
the sensor probes are exposed to steam, and is substan-
tially reduced when the probes are surrounded by water.
This embodiment has a duplex character, permitting
toggling, as above-described, for enhanced monitoring/tes-
ting operations.
In accordance with another embodiment of an in-
tegrated sensor, or detector, two bores are symmetrically
disposed in each of the two half-cylinder probes and four
such heater/thermometer elements are received in the
respective bores. There thus are provided two pairs of
heater and reference elements, each such pair comprising
one element from each of the two half-cylinder probes.
Preferably, the bores are formed in symmetrical relation-
ship in the respective probes and the two sets of,effectively, diagonally-related elements are associated as
the respective two pairs. This embodiment thus has a
duplex character affording the switching or toggling
capability above-described, thus enhancing the validity of
the monitoring/testing operations and enabling automatic
corrections/substitutions upon element failure.
In accordance with yet another embodiment of the
integrated sensor, or detector, the cylindrical thermowell
body is split by two small, crossed gaps along correspond-
ing, crossed bilateral planes, the planes preferably beingperpendicular and intersecting along the axis of the
cylindrical thermowell body so as to define, effecti~ely,
four identical half-cylinder probes. This embodiment
affords the same duplex character and the related
switching or toggling capability as that just above
described, and the further capabilities of parallel,
independent operation, with "voting" as to the dual,
monitored condition T outputs. Relating the four
14 131 1023
elements as before, i.e., as two corresponding pairs,
redundant, high temperature differential outputs from ~oth
pairs enhance the assurance of the detected condition
indication of steam, i.e., no water; likewise, redundant
low temperature differential outputs enhance the reliabil-
ity of the detected condition of the presence of water.
Conflicting high and low temperature differential output
indications of the respective pairs in either sense, on
the other hand, indicate a failed or possibly fouled
sensor.
The integrated sensors, or detectors, in
addition to affording expanded and more versatile
detection functions in the successively more complex
configurations, offer the added advantage of a reduction
in size with concomitar.t reduction in the costs of
manufacture and installation and, even more significantly,
an improvement in thermal performance and mechanical
strength.
Instrumentation and monitoring systems incorpor-
ating the integrated sensors perform functionally as the
first system embodiment, discussed above, yet are of
simplified internal organization and both simplified and
reduced interconnecting wiring, contributing to further
cost of manufacture and installation, and maintenance.
A more detailed understanding of the invention
may be had from the following description of preferred
embodiments, given by way of example, and to be understood
in conjunction with the accompanying drawings wherein:
Fig. 1 is an elevational view of the split-well
thermowell housing of a first sensor embodiment utilizable
in a first instrumentation and monitoring system embodi-
ment in accordance with the present invention;
Fig. 2 is a bottom plan view of the split-well
thermowell housing of Fig. l;
Fig. 3 is a top plan view of the split-well
thermowell housing of Fig. l;
Fig. 4 is an elevational and cross-sectional
view of the assembly of the sensor of the first embodi-
131 1~2~
ment, taken in a plane through the axis of the split-well
thermowell housing as shown in Fig. 1, and further
including an electrical connector box and related
structure~;
Fig. 5 is a top plan view, partially in cross-
section, taken along a broken plane passing through the
line 5-5 in Fig. 4;
Fig. 6 is an end elevational view of a cover
component of the connector box, shown in cross-section in
Figs. 4 and 5;
Figs. 7 and 8 are plan views of heater and
thermocouple components, respectively, utilized in the
sensor of the first embodiment;
Fig. 9 is a schematic block diagram of an
instrumentation and monitoring system employing multiple
sensors of the split-well type of the first embodiment of
the present invention;
Fig. 10 is a schematic, partially in block
diagram form, of the instrumentation and monitoring
system of Fig. 9;
Figs. llA, llB and llC are plan views of
components of a display and operator control panel of a
first instrumentation and monitoring system embodiment in
accordance with the present invention;
Fig. 12A is a simplified, perspective view of a
split-well thermowell housing which, in more detail, may
be substantially similar to that of Fig. 1 but has
differing internal configurations in accordance with
second and third sensor embodiments;
Fig. 12B is a cross-sectional view of the probe
portion of the sensor housing of Fig. 12A, taken in a
plane transverse to the central axis thereof, and
illustrating the internal configuration thereof in
accordance with a second sensor embodiment;
Fig. 12C is a cross-sectional view of the probe
portion of the sensor housing of Fig. 12A, taken in a
plane transverse to the central axis thereof, and
illustrating the internal configuration thereof in
,
:
16 131 t028
accordance with a third sensor embodiment;
Fig. 13A is a simplified perspecti~e view of a
thermowell housing in accordance with a fourth sensor
embodiment having four symmetrical part-cylinder probes
defined by crossed bilateral planes;
Fig. 13B is a cross-sectional view of the probes
of the thermowell housing of Fig. 13A, taken in a plane
transverse to the central axis of the latter;
Fig. 14 is a simplified schematic of the current
lo supplies and bridge circuit arrangement for both anergiz-
ing and detecting a differential voltage, or voltage
difference, representative of the differen~ial between the
temperatures sensed by the heater/thermometer elements
associated as a pair in the integrated sensors of the
embodiments of the invention shown variously in Figs. 12A
through 13B;
Fig. 15 is a temperature diagram used for
explaining the temperature levels sensed by, and the
corresponding differential produced by an associated pair
of heater/thermometer elements in accordance with, the
integrated sensor embodiments;
Fig. 16 is a temperature diagram illustrating
the basis for setting a trigger level for delineating
between the differential voltage outputs of the circuit of
Fig. 14, respectively representative of an indication of
steam and water;
Fig. 17 is a schematic block diagram of a
monitor system in accordance with a second embodiment,
employing multiple sensors of the integrated split-well
type of the above, second through fourth embodiments
thereof; and
Fig. 18 is a schematic, partially in block
diagram form, of the instrumentation and monitoring
system of Fig. 9.
Fig. 1 is an elevational view of the housing 10
of a first embodiment of a split-well thermowell sensor
suita~le for use in an instrumentation and monitoring
system in accordance with the present invention and is
17 131 102~
described concurrently with reference to the bottom plan
and top plan views thereof shown in Fig ~ 2 and 3. The
sensor housing 10 preferably is formed of a cylindrical
bar of stainless steel or other, mechanically strong but
poor heat-conducting metal, which is machined to the
configuration illustrated in the drawings and herein
described. One end of th~ bar is machined to define two
identical, substantially half-cylinder sensor probes 12A
and 12B delineated by a bilateral plane, identified at 13,
which is c~t therebetween. The ends, or tips, 14A and 14B
of the probes 12A and 12B further are machined to define
chambers 15A and 1ss. The opposite ends, or bases, of the
probes 12A and 12B thus extend integrally from a shank
portion 20 of the sensor housing 10, a collar 18 of
slightly larger diameter than the exterior circumference
of the probes 12A and 12B is formed at approximately the
juncture of the shank 20 and the probes 12A and 12B, Por a
purpose to be explained. A pipe thread is formed on
section 22 of the shank 20, for mounting the housing 10 in
a correspondingly threaded boss that is welded into the
steam line, in a conventional manner. An annular mounting
ledge 24 is formed on the outer surface of the upper, free
end of the shank 20, and threaded holes 26 and 27 are
formed in the annular end surface 28 of the shank 20, for
purposes to be described.
Shank 20 is bored from its upper free end to
define a generally cylindrical chamber 30 extending
coaxially through a substantial portion of the length of
the shank 20 and terminating in a base wall 32, adjacent
~; 30 the juncture of the base ends of the probes 12A and 12B.
; Central bores 34A and 34B extend in parallel axial
relationship from the base wall 32 into the probes 12A and
12B, respectively, to a position closely adjacent the tips
14A and 14B thereof. The bores 34A and 34B are provided
to accommodate generally elongated and cylindrical heater
elements (not shown in Figs. 1 to 3), as later described.
Symmetrically disposed about the bores 34A and 34B are
further bores 36A1, 36A2 and 36B1, 36B2, respectively,
18 l 31 1 02~
which extend approximately two-thirds of the axial length
of the probes 12A and 12B, respectively, and which are
provided for receiving corresponding thermocouple elements
(not shown in Figs. 1 to 3).
The overall axial length of the sensor housing
10 may be apprsximately (six inches) 150 mm and the
maximum diameter approximately (two inches) 50 mm, the
threaded portion 22 corresponding to a standard (one and
one-half inch) 40 mm pipe tap which is formed in the boss,
for mounting the housing 10 as before described. The
bilateral planar gap 13 separating the sensor probes 12A
and 12B may be approximately (one-eighth of an inch) 3 mm
thick and the diameter of the outer circumference of the
probes 12A and 12B may be approximately (one and one-
quarter inches) 32 mm. The bores 34a and 34B for the
heater elements may be 0.257 inch diameter by (2.5 inch)
63 mm depth, measured from the base wall 32 ~nd the bores
36A1, 36A2 and 36B1, 36B2 for the thermocouple elements
may be 0.136 inch diameter and 2.00 in~hes deep. Each of
these bores further is counterbored to a slightly larger
diameter and about (one-quarter of an inch) 6.5 mm in
depth, as identified by identical, but primed numerals
34A', 34B', 36Al' ... 36B2'.
Fig. 4 is an elevational and cross-sectional
view, taken in a broken plane along the line 4-4 in Fig.
5, of the sensor housing 10, illustrating the completed
assembly of the sensor. A protective shield 40 having
apertures 42 in its cylindrical sidewall 43 and, typical-
ly, a base 44, which may also contain apertures, is
disposed about the sensor probes 12A and 12B and secured
at its upper, free end at the collar 18 of the shank 20 of
the sensor housing 10 by a weld bead 46. The primary
function of the shield 40 is to reduce the velocity of the
steam flow around the split wells, or probes, of the
sensor and yet allow water to enter. A high steam flow
velocity may cause the heated sensor probe to be cooled as
effectively as water. Thus, the apertures 42 are arranged
symmetrically in the shield 40 so as to permit a minimum
19 ~31 1(~28
or limited amount of flow in immediate contact with the
sensor probes and thus within the sensor chamber defined
within the interior of the shield 40, when the sensor is
disposed in the steam flow path. Since the apertures 42,
while symmetric relative to the probes 12A and 12B, are
not necessarily uniformly disposed about the cylindrical
sidewall 43 of the shield 40 and instead are aligned
perpendicularly to the direction of flow, the sensor must
be properly oriented with respect to the direction of
steam flow, when installed. ~oles may also be placed in
the base of the shield.
Extension assembly 50 releasakly mounts an
electrical connector box 60 to the upper free end of the
housing lO. The assembly 50 comprises a cylindrical
sleeve 51 which is telescopingly received at its lower end
in the annular ledge 24 of the housing 10 and is welded at
its upper end to the base wall 61 of box 60 ! aS indicated
by weld bead 52. To better appreciate the illustration of
Fig. 4, it is taken in a segmented plane along the line
4-4 in Fig. 5. The extension assembly 50 thus comprises
two elongated tubes 53A and 53B which are received at
their bottom ends, as seen in Fig. 4, in the counterbores
34A' and 34B' which accommodate the heater elements A and
B (not shown) and extend at their upper ends to a position
flush with the interior surface of base wall 61 of
connector box 60. Similar, but smaller diameter tubes
54Al, 54A2 and 54B1, 54B2 are received at their lower ends
in the corresponding counterbores 36Al', 36A2' and 36B1',
36B2' and similarly extend to the upper surface of the
base wall 61 and connector box 60. The base wall 61
includes a central aperture 62 to accommodate the various
tubes, just described.
Within the connector box 60, plate 63 is
disposed over and spans aperture 62. Threaded rods 64 are
received in the threaded bores 26 of the sensor housing 10
and are received through holes 65 in the plate 63,
extending thereabove so as to receive nuts 66 for securing
the plate 63 and, through it, the connector box 6Q and
1 31 1 n~
extension assembly 50 to the ~ensor housing 10. Holes 66A
and 66B are formed in the plate 63 for permitting passage
therethrough of the electrical connections (not shown) to
the heater elements; similarly, holes 67Al, 67A2 and 67Bl,
67B2 are formed in the plate 63, corresponding to the four
thermocouples to be received in the sensor housing 10.
Fig. 4 illustrates an illustrative thermocouple 70, as
received in and passing through plate 63, the upper end
being broken-away. A true arc ring 72 is received about
the upper end of the thermocouple 70 and engaged by the
under surface of plate 63, thereby to secure the thermo-
couple 70 in position. Spring-type snap rings 74A and 74s
are received through slots formed in the sidewall of the
corresponding tubes 53A and 53B, which secure the heater
elements (not shown in Figs. 4 and 5) within the cor-
responding tubes 53A and 53B. Terminal strips 80A and 80B
are secured on the base plate 61 by screws and nuts 82A
and 82B; sufficient terminal screws 8~A and 84B are
provided on the respective strips 80A and 80B for
connection to the leads from the respective thermocouples
and heaters of the probes 12A and 12B -- which will be
understood to be six (6) in number, for each probe half.
With concurrent reference to Figs. 4, 5 and 6, a
cover plate 86 has four ~4) downwardly depending sides 87
and is received over the up-turned ends 61a of the base
plate 61 and secured in position by self-tapping screws
88. Mating openings 89 and 66b are provided to accom-
modate a cable (not shown) for connection to the connector
screws 84A and 84B of the terminal strips 80A and 80B.
Fig. 7 is an illustration of a heater element 90
for use in the sensor of Figs. 1 to 6. It comprises a
generally cylindrical heater element portion 91 having a
grooved tip portion 92 from which leads 93 extend. With
reference to Figs. 4 and 5, clip 74 is received in the
groove portion 92 for securing the heater element 90 in
position. A preferred heater element is of a commercially
available type known as a FIREROD CARTRIDGE HEATER,
manufactured by the Watlow Company of St. Louis, Missouri
1 Jl 1 02~
21
and identified by code ElA51; it is of one-quarter inch
diameter and three inches in length, rated at 120 volts
and 80 watts of power.
Fig. 8 illustrates a plan view ~f a thermocouple
95 as is contemplated for use in the sensor of Figs. 1 to
6, havin~ a gen~rally elongated cylindrical body and leads
96. Commercially available thermocouples may be used, a
preferred one being Model CAIN-18U-lORP manufactured by
Marlin Manufacturing Company of Cleveland, Ohio. The
structure is approximately ~10 inches long) 255 mm long
which correspondingly is accommodated by the sensor
housing 10 and extension assembly 50, as seen in the
preceding Figs. 4 and 5.
In addition to the rugged construction and low
cost of manufacture and installation, the duplex ~haracter
of the sensor 10 affords significant operational ad-
vantages as well as simplifying maintenance operations by
on-line replacement of defective or failed elements.
These aspects of the duplex sensor will be more readily
appreciated by the following description, taken in
relation to Figs. 9, 10 and llA to llC, of a system and
related circuitry utilizing the aforesaid sensors in
accordance with the present invention.
Fig. 9 is a block diagram of a first embodiment
of the instrumentation and monitoring systems of the
present invention, as particularly designed for use with
plural sensors of the type of Figs. 1 through 8. In Fig.
9, two such sensors, designated sensor I and sensor II,
are illustrated, it being understood that numerous sensors
typically would be accommodated in the system. Sin~e each
sensor is of identical construction, the duplex, internal
elementQ of the probes are schematically illustrated only
for sensor I; consistent with the element number/letter
designations in Figs. 1 through 8, sensor I comprises the
dual probes A and B respectively comprising heater (~TR) A
and heater (HTR) B, and thermocouples (TC) Al, A2, and
thermocouples (TC) Bl, B2. In similar fashion, processor
I for sensor I includes a heater controller 100 and a
22 1 31 1 02~
thermocouple (TC) controller 102, respectively intercon-
nected through bidirectional buses I (HC) and I (TC) to a
system control unit 104. Unit 104 further is connected
over plural such buses II (HC), ... and II (TC), ... to
corresponding controllers (HC and TC) of plural, respec-
tive processors II, ... and associated sensors II, ....
and over a bidirectional bus 106 to a central display and
operator control panel 108. As more fully described
hereafter, heater controller 100, under controls from
system control unit 104, provides for calibration, on-line
testing (e.g., continuity checking and shorts and grounds,
processing of alarm indications, and toggling of heaters A
and B of sensor I. Similarly, under control of the system
control unit 104, the thermocouple (TC) controller 102
performs corresponding functions for the respective
thermocouples A1 and A2, and B1 and B2, e.g., on-line
testing and automatic switching functions upon element
failure.
Fig. 10 is a schematic illustration, partially
in block diagram form, of details of the components of the
instrumentation and monitoring system of the invention for
a single processor I (i.e., as in Fig. 9) including a
heater controller 100 and a TC controller 102. As shown,
interface circuits 118 and 129 in ths controllers lOO and
102, respectively, interface between the internal
components of the latter and the system control unit 104.
Heater elements HTR A and HTR B are independently
connected through a continuity check, current flow check,
and calibration ("CCCFCC") unit 110 and through a switch,
or toggle, selection circuit (SELECTOR) 112, to an
adjustable power supply 116. Display unit 114 includes
alarm lamps 116 and 118, respectively corrçsponding to the
heater elements ~TR A and HTR B, and which are respective-
ly and independently illuminated when the corresponding
heater element has failed, by corresponding outputs from
the unit 110. The associated units 110 and 114, unit 112
and the adjustable DC supply unit 116 are connected
through interfac~ circuits 118 and appropriate buses, as
1 3 1 1 02~
23
shown, to a system control unit 104.
System control un:it 104 automatically adjusts
the output of the ~C supply unit 11~ in accordance with
conditions determined by the CCCFCC unit 110 and further
in accordance with the selection of heater element HTR A
or HTR B, as effected by operation of selector 112 by the
system control unit 104, to assure that identical heat
outputs are produced by heaters A and B. Unit 104 also
produces a heater failure display on central display panel
108, as later described.
The illustratiYe sensor of Fig. 10 includes four
thermocouples TC Al, TC A2, TC B1 and TC B2; in conven-
tional fashion for a differential temperature sensor, one
thermocouple of probe A is associated with a corresponding
thermocouple of probe B and the two are connected in
series as a pair and in a bucking, or opposed, relation-
ship. Thermocouple ~lements TC A1 and TC ~ 1 are
connected as a first pair and the thermocouple elements TC
A2 and TC B2 are connected as a second, or complementary,
such pair in the described series, bucking or opposed
relationship. In Fig. 10, the two ~uch pairs are
designated TCP-1 and TCP-2. Continuity check unit 121
checks the continuity of the respective pairs of thermo-
couples on an on-going basis and, should lacX of con-
tinuity indicating an element failure be detected,provides an output to TC failure alarm unit 120 for
lighting the corresponding alarm lamp 120-1 or 120-2
corresponding to the respective, failed thermocouple pair
TCP-1 or TCP-2, and to system control unit 104 for
producing a failure display on central display panel 108,
as later described.
Selector unit 122 is controlled to select the
outputs of one or the other of the two TC TEMP CIRCUITS
124-1 and 124~2 to supply the selec~ed one of said
respective outputs T1 and T2 to the interface circuits
129. The selected one of the TC TEMP CIRCUITS 124-1 and
124-2 produces an output voltage signal STEMP proportional
to the temperature differential ( T) sensed by the
1 3 1 1 0~
24
selected thermocouple pair. Interface circuits 129
interconnect the units 120, 121, 122, 124-1 and
124-2 with the system control unit 104 through appropriate
buses, as indicated. Unit 104 also produces a selectable
T display on central display unit 108 during normal
monitoring, displays of a failed sensor and failed
heater/thermocouple pair, and an automatic and verified
indication of an alarm condition for each sensor on the
control display panel 108.
Figs. llA, llB and llC illustrate panel configura-
tions of various display and control modules of the
display ard operator control panel 108 of Figs. 9 and 10.
Readout and control module 130 of Fig. llA includes a
digital display 132 for indicating the valua and sign of
the temperature differential T (in Fahrenheit degrees)
currently measured by a given sensor, selected for display
~s hereinafter described.
Under operator control of switch 140, the system
may be placed in an automatic test mode, evidenced by
lighting of lamp 138 or in a selective test mode,
evidenced by lighting of lamp 139; in the latter mode, the
operator may test a selected one of the plural sensors,
again, as more fully hereinafter described. Momentary
actuation of switch 142 produces a "Test All Sensors" or
"Single Sensor ~est" mode of operation, later described.
The digital display 132 is enabled only by the operator
for producing a display of the T for a selected sensor.
Finally, a "failed sensor" lamp 135 and a "failed heater
or TC (thermocouple) lamp" 136 are provided to give
corresponding alarms, described in more detail hereafter.
Finally, switch 137 may be depressed for testing all
display lamps in the system.
Fig. llB illustrates an extraction monitor 150;
numerous such monitors are employed in a typical turbine
system and thus plate 152 is provided to identify the
particular, monitored function and thus the location of
the associated sensors. As illustrated in the schematic
on the monitor panel 150, sensors are positioned in the
25 1311028
extraction piping and heater associated with a turbine at
the positions of the corre ponding alarm lamps/switches
155, 156, 157 and 160. Particularly, alarm lamp/switch
155 corresponds to a sensor positioned at the turbine side
of an isolation valve 158; alarm lamp/switch 156, to a
sensor positioned between the isolation valve 158 and a
nonreturn ~alve 159; alarm lamp/switch 157, to a sensor
positioned at a low point in the extraction line; and
alarm lamp/switch 160, to a sensor positioned in the
heater for detecting a high water level condi~ion in the
heater. When water is detected by a given sensor, the
corresponding alarm lamp/switch on panel 150 is automatic-
ally illuminated.
A number of different types of monitors may be
incorporated in the system and corresponding monitor
display and control panels incorporating similar alarm
lamps/switches are provided therefore, as for monitor
panel 150. Illustrative thereof is a water monitor panel
170 shown in Fig. llC, having alarm lamps/switches 1001
through 1004. It thus is to be understood that the
invention encompasses monitors of various, different types
and of a sufficient number of each type, with correspond-
ing monitor display and control panels, as required. For
convenience, reference hereafter shall be limited to the
extraction monitor panel 150 of Fig. 12B, as exemplary of
all such panels.
The duplex character of the sensors enables sig-
nificant system operations facilitating more meaningful
monitoring and verification capabilities. With reference
to the schematic presentation of sensor I in Fig. 10,
assume that selector 112 normally selects heater HTR A and
selector 122 normally selects thermocouple pair TCP-l
comprising the thermocouples TC Al and TC B1. Under
normal operating conditions (and thus in the absence of
water surrounding the dual probes A and B of sensor I), TC
Al will be heated by HTR A and sense a higher temperature,
relatively to that sensed by TC Bl and, for an assumed
polarity or sense in which the respective outputs are
,
26 t31 IQ2g
paired, an output STEMP of a positive T is produced.
Conversely, if complementary heater B were selected and
e~ergized and thus substituted for heater A, under this
same analysis, the STEMP output would be a negative T,
i.e., the same numerical or absolute temperature differen-
tial value, but of opposite sign. As will be appreciated
and as above-noted, the calibration circuit of unit 110,
under direction of system control unit 104 and through
adjustment thereby of the adjustable DC supply 116,
provides for controlling the respective power levels
supplied to heater A and to heater B, to assure that the
same heater power is developed in HTR A and HTR B,
resulting in the same absolute values of T being produced
if the sensor is not fouled.
The system further uses the capability of the
duplex sensor by automatically toggling, or switching,
between heater A and heater B for substituting heater B
for heater A upon failure of heater A (or vice versa), 50
as to provide continuous monitoring functions and so as to
prevent false alarm that would otherwise result from a
heater failure. For example, if heater A fails, unit 104
will operate through selector 112 to switch to heater B.
With reference to the TC controller 102 in Fig.
10, the duplex nature of the sensor also affords signifi-
cant capabilities in the system encompassing the thermo-
couples, as well. Thus, if one or both of the thermo-
couple elements of pair TCP-1 should fail, as detected by
continuity check circuit 121, system control unit 104
causes selector 122 to switch automatically to the second
pair TCP-2, for supplying the output through TC TEMP
circuit 124-2 and thus deriving the value STEMP ( T)
therefrom. As shown in Fig. 10, TC A2 and TC B2 of the
pair TCP-2 are connected in the same sense as the
complementary, first pair Trp-l of thermocouples TC A1 and
TC ~1. Thus, the same effective sign of T is produced
upon the alternative selection of the complementary pair
TCP-2 of heater elements HTR A and HTR B. It will be
appreciated that a more complex, or sophisticated,
27 131 102~
arrangement with greater failure indicating capabilities
could be achieved by reversing the sense of TC A2 and TC
B2, and thus of the pair TCP-~ relative to the pair TCP-1.
Thus, for example, when using a given heater, e.g., H~R A,
if a first pair TCP-l fails and the system automatically
switches to a second pair TCP-2, and the sensor i8
otherwise operative, there results a negative T, i.e., a
temperature differential output o~ the same numeric value
but opposite sign. This then would indicate which
thermocouple pair had failed, facilitating maintenance
operations.
Physical replacement (i.e., as distinguished
from automatic substitution) of the heater elements and of
the thermocouple elements of the sensor may be made on-
line, following specific identification of the failed
element at the processor I which may be located remotely
from the central panel 108. Thus, HTR and TC failure
alarm displays 114 and 120 are shown as incorporated in
the heater controller 100 and TC controller 102, respec-
tively, it being understood that the displays 114 and 120
would be positioned at a convenient location for viewing
by maintenance personnel. In the event that a failed
element is detected, the corresponding alarm lamp/switch
116 or 118 for heater A or heater B, or alarm lamp/switch
12~-1 or 120-2 for the thermocouple pairs TCP-1 and TCP-2,
respectively, is illuminated.
Should both heaters, A and B, and/or both
thermocouple pairs, TCP-1 and TCP-2, fail, that sensor
channel is disabled so as to prevent a false alarm.
Further, an in-phase blinking of lamp/ switch 135 (Fig.
llA) and the alarm lamp/switch for the failed channel
informs the user that this channel has failed and has been
disabled. Automatic toggling is performed for verifica-
tion of a sensed alarm condition. Specifically, should
the water level rise and surround both probes A and B, the
normal T value will be reduced significantly to less than
an alarm threshold value, but typically to a nonzero
value. The alarm condition is automatically verifiable,
1 31 I n2~
28
therefore, by toggling to heaters and comparing the
corresponding T value of STEMP. If not of the same
numerical value (but of opposite sign), the conclusion may
be reached that sensor I has been fouled and that the
reduced T value is a false alarm. On the other hand, the
failure of the sensor to pass the verification test, as
thus conducted, serves to alert the operator to the need
for system maintenance.
With the foregoing background, the system
operation, as displayed at and controlled from the central
display and operator control panel 108, will be now more
readily understood.
Considering first a normal operating condition,
and in either of the "auto" and "selective" test modes, an
operator may determine the T of each sensor in the system
by depressing the corresponding alarm lamptswitch, e.g.,
alarm lamp/switch 155 in the monitor panel 150. A time
delay circuit, triggered by actuation of the alarm
lamp/switch, e.g. 155, maintains the T display in
display 132 of module 130 for a predetermined time
interval, e.g., two minutes. The time delay circuit is
reset upon actuation of a further alarm lamp/switch, e.g.,
156, in monitor panel 150 or in any other monitor panel.
These same alarm lamps/switches, as previously
noted, are illuminated in the event that an alarm
condition is sensed by the corresponding sensor. As
likewise before noted, the system, in the automatic test
mode as selected by switch 140, performs an automatic
verification test on the sensor channel issuing an alarm
condition by toggling of the heaters, before producing the
alarm indication; the toggling function for verification,
however, is disabled as to any sensor in which one of its
heaters has already failed. The toggling function, in
fact, is performed in each of three different formats, one
in the "auto-test" mode and two in manual, or operator-
controlled test modes, as now described.
Particularly, with switch 140 set to the auto-
test mode position and thereby illuminating lamp/switch
1 31 1 02~
29
138, system control unit 104 responds to an alarm
condition as detected by a given sensor to perform the
toggle function as a verification test on ~ha~ sensor
(unless, as before noted, the toggle test is inhibited by
a heater ailure in that sensor channel, in which event an
alarm is issued based solely on the single functioning
heater of the sensor). In the event that the same, but
opposite sign, values of T (and thus the absolute values
of both being below the alarm threshold) are prodused, an
alarm is issued. If the two T magnitudes disagree by
more than a preset value, e.g., 3F, a failed sensor alarm
is issued as described above. This alarm is cleared by
switching switch 140 to the central neutral position or to
the Selective Test Mode (139). In a preferred embodiment
of the system, in the l'auto-test mode," the toggle test is
performed only for sensor channels indicating an alarm,
for verification thereo~ on the basis specified; further,
only one cycle of the toggle test is performed in the
auto-test mode in response to an alarm indication.
Moreover, upon returning from either of the neutral or the
"selective test mode" positions of switch 140 to the
"auto-test mode" position, any channel cllrrently indicat-
ing an alarm will undergo the toggle test before the alarm
is reissued.
The second format of the toggle test is
selectable by the operator, by placing switch 140 to the
"selective test mode" position (thereby illuminating
lamp/switch 139), and then simultaneously, momentarily
depressing switch 142 to the Single Sensor Test position
(143) and the alarm lamp/switch for the desired channel,
e.g., alarm lamp/switch 155 in monitor panel 150. The T
for the toggled sensor then is displayed in panel 132 of
monitor 130. As before explained, a time delay circuit
maintains this display for two minutes, or until another
switch prompting a display is pushed.
The toggle test, in the third format, is
performed on all channels simultaneously by placing switch
140 in the 139 posi~ion and momentarily depressing switch
1 3 1 1 978
142 to the "test all sensors" position (illuminating
lamp/switch 144). This switches all sensors from heater A
to heater B (or, conversely, from B to A in the event of
an opposite initial orientation). After a two minute
period, the operator then manually depresses the alarm
lamp/switches in indi~idual succession (e.g., 155, 156,
157 ~O~ as in monitor panel 150) to produce the corres-
ponding succession of T displays on display panel 132 of
module 130. The resulting T displays for the succession
of sensor channels may be compared with previously
recorded T values of those same channels before all
heaters were switched.
In either of these manual test modes, the
operator may then verify the existence of an actual alarm
condition, i.e., the T displays are of the absolute same
value (but opposite sign~ which is below a predetermined
threshold, or of fouling of the sensor, i.e., T displays
of different numerical values for the toggled positions.
The manual formats of the toggle test provide
other operability checks, as well. For example, as before
noted, in the event that one heater of a given sensor
(e.g., sensor I) has failed, the toggle test is inhibited
and no change in T is observed in either of the manual
test nodes. ~his will identify sensors with a single
failed heater. Specific failed heater and thermocouple
pair failures can be identified by lamps/switches on
displays 114 and 120, respectively.
A failed sensor is identified by a blinking
illumination of both the failed sensor lamp/switch 135 and
the corresponding alarm ~amp/switch for that sensor
channel, e.g., alarm lamp/switch 155 of control panel 150.
The failed sensor indication is produced by unit 104 as a
result of any of (1) the loss of continuity in both
thermocouple pairs ~CP-l and TCP-2 of a given sensor as
detected by unit 121; (2) failure of both heater elements
A and B of a given sensor as detected by unit 110; and (3)
failure of a sensor to pass the toggle test in the "auto-
test mode," as above-described.
31 131 102~
Finally, button 137 on the module 130 may be
depressed to test all lamps and lamp/switches of the
central display and operator control panel 108 (Fig. lO)
and thus including the specific indicator, alarm lamps and
lamp/switch~s of the individual modules, e.g., 130, 152,
170 (Figs. llA-llC~.
Fig. 12A is a perspective view of a split-well
thermowell housing 219 representing the external con-
figuration of both second and third sensor embodiments,
the latter being differentiated by their respective
internal configurations, as will be described. The
external configuration of the sensor 210 may be substan-
tially identical to the housing 10 of the Fig. 1, but
because of the integrated feature, to be described, may be
substantially smaller in size and thus have reduced
heater power requirements; moreover, the integrated
character reduces the number of heating and sensing
elements, with concomitant savings in material, reduced
electronic circuit complexity and reduced costs of
manufacture and installation. For example, whereas the
sensor housing 10 of Fig. 1 may be implemented for use as
a one and one-half inch (l-l/2") nipple pipe thread size,
the sensor housing 210 instead may be constructed for use
as a one inch (1") nipple pipe thread size device.
Similarly to housing 10 of Fig. 1, the housing
210 of Fig. 12A includes a pair of substantiallv half-
cylinder probes 212A and 212B separated by a gap 213
defined by a bilateral plane symmetrical with respect to
the axis of the housing 210. It will be understood that
the housing 210, similarly to that of Fig. 1, comprises a
shank portion 220 having a pipe thread 222 formed thereon
or other alternative means for mounting the housing 210
through a suitable boss in a pipe or other pressure
vessel. The shank 220 furthermore is bored to define a
generally cylindrical chamber therewithin (not shown in
Fig. 12A) substantially corresponding to the chamber 30
with base wall 32 in the housing 10 of Fig. 1.
Fig. 12B is a cross-sectional view taken in a
1 31 1 0~3
32
plane perpendicular to the axis of the housing 210 through
the probes 212A and 212B, for illus~rating bores 224A and
224B disposed centrally and generally symmetrically within
the respective pro~es 212A and 212B and extending in
parallel axial relationship therethrough to positions
adjacent the free ends 214A and 214B of the respective
probes. In accordance with this embodiment of the
invention, an integrated heater/thermometer element having
a outward appearance and external dimensions which may be
substantially identical to the heater element 95 of Fig. 8
is received in each of the bores 224A and 224B; the
latter, correspondingly, may be of (0.257 inch) 6.5 mm
diameter and (2.5 inch) 63.5 mm depth, as for the sensor
10 of Fig. 1. Such heater elements are not illustrated in
Fig. 12B, but their locations are designated by the
parenthetical expressions H/T A and H/T B adjacent the
respective bores 224A and 224B.
The elements H/T A and H/T B comprise heater
elements of nickel, iron or other similar pure metal
which exhibits a substantially linear relationship, or
dependence, of electrical resistance to temperature. As
explained hereinafter with reference to Figs. 14 through
16, one of the elements, for example, H/T A, is supplied
with current of a sufficient level to function as a
heater and simultaneously as a thermometer and thus as the
heated element; the other element, H/T B in the example,
is supplied with a much lower current so as to render it
negligible in effect as a heater element but to function
nevertheless as a thermometer and thus as the reference
element. Correspondingly, for the example, probe 212A is
the heated probe and probe 212~ is the reference probe.
As will be understood from the description of the first
embodiment of the invention, the alternative presence of
steam or water will result in respective, high and lsw
temperature differentials being produced as the output of
the specified sensor element pair, as later discussed.
Fig. 12C is a cross-sectional view taken in a
plane transverse to the axis of housing 210 through the
33 l 3ll 02~
probes 212A and 212B, but wherein the internal configura-
tion of the housing 210 is altered in accordance with a
third embodiment of the invention so as to include four
identical bores, bores 224Al and 224A2 being disposed in
probe 212A' and bores 224B1 and 224B2 being disposed in
probe 212B', the bores each being of identical dimensions,
as above, and spaced in symmetrical and equidistant
relationship from the sidewalls of the respective probes
212A' and 212B'. Four heater/thermometer H/T (elements
Al, A2, B1 and B2 are received in the correspondingly
designated bores. The embodiment of Fig. 12C affords the
full duplex capabilities of the sensor 10 of the first
embodiment of the invention disclosed in Figs. 1 through 8
and thus may be employed in lieu thereof in the system as
disclosed and discussed above in relation to Figs. 9 to
llC, with modifications thereto as required to accommodate
the integrated heater/thermometer character of the H/T
elements. A system specifically designed to utilize the
integrated sensor of Fig. 12C (and of a fourth embodiment,
described hereinafter) moreover is disclosed in Figs. 17
to 18, discussed hereafter.
Fig. 13A is a perspective ~liew of a sensor
housing 310 of a fourth embodiment, substantially
corresponding to the housing 210 of Fig. 12A but having
four part-cylinder (i.e., four symmetrical, substantially
quarter-cylinder) probes 312A1 through 312B2, spaced by
intersecting gaps 313-1 and 313-2 defined by crossed
bilateral planes of mutually perpendicular relationship
and symmetric with the axis of the housing 310. As seen
in the cross-sectional view of Fig. 13B and adopting
similar nomenclature as in Fig. 12C, bores 324A1 and 324A2
; are formed in the respective probes 312A1 and 312A2, and
bores 324B1 and 324B2 are formed in the respective probes
312B1 and 312B~, corresponding in respective heater/-
thermometer elements being received in the respective
bores. The sensor employing the housing 310 permits
operation of the respective diagonally related pairs of
heater/thermometer elements (i.e., the pair HIT Al and H/T
1 31 1 0~
34
B1, and the pair H/T A2 and H/T ~2) as two fully indepen-
dent, differential temperature sensors.
The sensors of Figs. 12A to 13B furthermore may
be provided with an electrical connector box and related
structures substantially as disclosed for the first
embodiment, but of simplified construction in view of the
reduced number of electrical elements and related circuit
connections required thereby.
~ig. 14 is a simplified schematic of a circuit
for both energizing a selected one of a related pair of
heater/thermometer (~/T) elements A and B and for deriving
from the respective voltage outputs thereof a differential
voltage representative of the differential temperature
sensed thereby; while illustrated for a single pair of
related elements H~T A and H/T B such as employed in the
housing 210 when internally configured as Fig. llB, it
will be understood that each of the diagonally related H/T
element pairs, in each of the configurations of Figs. 12C
and 13B, would be similarly connected. Further, whereas
typically a single such related H/T pair in the configura-
tion of Fig. 12C would be selected at a time for such
circuit connection and operation, both such pairs in the
configuration of Fig. 13B may be so connected in respec-
tive such circuits for performing simultaneous sensing
operations.
The operation of the circuit of Fig. 13 will now
be discussed with reference to Figs. 14 and 15. In Fig.
13, constant current sources 97' and 94' respectively
supplying currents Io and Io ~ 50 are connected in
respective first and second legs of a bridge circuit in
series with corresponding elements H/T A and ~/T B, the
two legs being interconnected in parallel at the vertical-
ly related, first set of diagonally opposite junctions.
The external circuit between those junctions accordingly
carries the current 51/50 Io. Ths voltage outputs Va and
Vb at the horizontal, second set of diagonally opposite
junctions are supplied to the inputs of differential
amplifier 98', the voltage Vb first being multiplied by a
.~
1311~2~
proportionality factor ("x50") by circuit 94". The
proportionality factor is the inverse of the current
differential supplied through the two legs by the sources
97' and 94' so as to enable comparison of the voltage
outputs Va and Vb, circuit 94 " accordingly producing the
output 50Vb supplied to the second input of the differen-
tial amplifier 98'. The differential voltage output of
the differential amplifier 98', V = Va ~ ~~b~ thus is
representative of the temperature differential between the
temperatures sensed by the elements H/T A and H/T B, i.e.,
T = k( V). The V output from differential amplifier 98'
is applied to a trigger and alarm circuit 99 which
produces outputs indicating the sensed condition of steam
(normal) or water (alarm), and which may be the respec-
tive, actual T values.
Because of the complementary functions ofcircuits 94' and 94", the temperature sensing function of
heater element H/T B is equivalent to that of element H/T
A, but whereas H/T A functions additionally as the heated
element, su~stantially no heating, i.e., insignificant
heating, of H/T B occurs and the latter thus serves as the
reference element.
The thermal function of an H/T element pair of
the integrated sensors 210 and 310 is explained using the
following definitions of temperature and di~ferential
temperatures:
T(H20) - temperature of the steam or water
within the pipe or vessel.
T(IWDI-STEAM) - temperature drop between the outer
surface of the probes 212A and 212B
and steam. This is typically 60F.
T(IWDI-WATER) - temperature drop between the outer
surface of the probes 212A and 212B
and water. This is typicall~ 0F.
T(METAL) - temperature drop across the metal
surrounding the bore ~e.g., 224A) of
the heated probe (212A). This is
small and is assumed to be zero.
T(IWDI-H/T) - temperature drop across the (air) gap
between the inner surface of the bore
224A in the probe 212A and the heated
1 3 1 1 ~
36
element, ~/T A, typically 20F.
The changes in the respective, sensed temperatures of
H/T A and H/T B (Ta and Tb) in steam and water ars shown
in Fig. 14. The di~ferential amplifier 98' shown in Fig.
13 subtracts out T(H2O) which is common to H/T A and H/~
B. T(IWDI-H/T3 depends solely on the power dissipated in
H/T A for bore H/T gaps < 10 mils. Since power level
supplied to H/T A (i.e., current Io~ and that supplied to
H/T B (i.e., current Io - 50) are held nearly constant by
10 the respecti~e sources 97' and 94', T(IWDI-H/T) remains
nearly constant.
The temperature of H/T A in steam is then:
TA = T(H2O))+ T(IWDI-STEAM)+ T(IWDI-H/T) (1)
In water, TA falls to:
TA = T(H20)+ T(IWDI-H/~) (2)
The temperature of H/T B remains:
TB = T (H2O)
in steam and in water. The differential temperature is
thus:
T = Ta-Tb = k~Va-50Vb) =
T(IWDI-STEAM)+ T(IWDI-H/T) (4)
in steam; and
T = T(IWDI-H/T) (5)
in water. This represents a change in T of, typically,
T = 80F in steam to T = 20F in water.
Fig. 16 is a temperature diagram indicating the
above, typical values of the temperature differentials T
of 80F in the case of steam and 20F in the case of water
being present and sensed and, particularly, graphically
illustrating the typical, 60F variation in those
respective differential temperatures. Fig. 16 moreover
illustrates a trigger level value of T = 35F, a drop of
somewhat less than the temperature range between the
respective steam- and water-temperature differential
values, for rendering a determination of the alarm
condition that water is present. As implemented in Fig.
14, the trigger and alarm circuit 99 may utiliæe a voltage
threshold value corresponding to T = 35F as a trigger
37
level for automatically delineating between and providing,
as an output, either a steam (normal) condition indication
or a water talarm) condition indication.
The sensor 310 of Figs. 13A and 13B has the same
functional capabilities as that of Fig. 12C and that of
Figs. 1-8 and thus may function as a full duplex sensor as
described in relation to Figs. 1-8. In fact, because the
sensor 310 additionally has the capability o~ functioning
as two independent temperature differential sensors, it
may provide, by a logical combination of the respective
temperature differential indications of the two indepen-
dent H/T element pairs, a "voting" function as to the
condition detected, thus affording a self-verification
capability. Adopting, for simplicity, solely the
designations A1, A2, B1, and B2 for the four H/T elements:
: : Detected
Pair A1-Bl : Pair A2-B2 : Condition
Indication
high T : high T : Normal
high T : low T : Fault
low T : high T : Fault
low T : low T : Alarm
It will be understood that the operations of the
embodiments of Figs. 12C and 13B as to each related H/T
pair thereof, when selected for operation, i5 as well
fully explained by the foregoing equations (1) through
(5), with the minor ~ualification that certain of the
typical temperature drops specified in the definitions may
vary somewhat, particularly for the configuration of Fig.
13B due to the reduced mass and wall thickness of the
individual probes, assuming same to be formed in a housing
310 corresponding otherwise in dimensions and material to
the housing 210.
A control system and related components, such as
a display and operator control panel utilizing the in-
tegrated, duplex split-well sensors of the second through
fourth embodiments are shown variously in Figs. 17 and 18.
As will be recalled, the embodiment of Fig. 12B has the
1 3 1 1 02~
38
duplex capability of togglin~, whereas the embodiment of
Fig. 12C has both that duple~ capability and redundancy,
permitting automatic substitution of elements and
functionally being similar to the first embodiment of
Figs. 1 through 8. The embodiment of Figs. 13A and 13B,
on the other hand, offers yet further capabilities
inasmuch as it can function essentially as two independent
differential temperature sensors, or detectors. Referring
first to Fig. 17, a plurality of integrated sensors,
10 illustratively sensors 1, 2, 48, are connected to
respective and correspondingly numbered channels 410 of a
sensor controller unit 400, each of the channels 410 in
turn being connected to a system control unit 402 and a
display and operator control panel 404. Each channel unit
of the sensor control unit 400 preferably includes alarm
lamps/switches 401 and 403 respectively designating the
conditions of a failed H/T Al-Bl pair and of a failed H/T
A2-B2 pair, facilitating the identification of the failed
such pair for simplifying maintenance. If both H/T pairs
of a given sensor have failed, the channel correspondingly
is disabled and is so displayed at the panel 404,
described earlier.
The display and operator control panel 404
includes a number of modules thereon which may correspond
substantially identically to the modules 130, 152 and 170
of Figs. llA through llC, the principal exception being
that the read-out control module 130 of Fig. llA for the
integrated sensors has an indication merely of a "failed
H/T element" in lieu of the "failed heater or TC"
designation associated with lamp/switch 136. It will be
understood in this regard that since the integrated
sensors of the third and fourth embodiments duplicate the
differential temperature sensing functions of the first
embodiment, all of the operating functions of the latter
likèwise may ~e performed with essentially the identical
manual and/or automatic controls, all as hereinbefore
described. The system control unit 402 of Fig. 17
interfaces be~ween panel 404 and effects selection of the
39 131102~
H/T pairs of the individual channels of the sensor
controller unit 400, either automatically or in response
to operator-selected manual control inputs at the display
and operator control panel 404, as described previously
with respect to the monitor system of Figs. 9, 10 and llA-
llC.
Fig. 18 illustrates the control circuitry of a
single sensor control channel 410, e.g., channel number 1,
of the sensor controller unit 400 of Fig. 17. Recalling
the duplex nature of the integrated sensors, a single such
channel controller 410 comprises two identical sub-
channels, as delineated in Fig. 18 and identified by the
designations "H/T pair Al-B1 channel 410-1 and H/T pair
A2-B2 sub-channel 410-2." Since the sub-channels 410-1
and 410-2 are identical, only the Al-Bl sub-channel is
shown in detail. The sensor channel controller 410
selects between and controls the operations of the two
associated sub-channels 410-1 and 410-2 and interfaces
directly with the system control unit 402 of Fig. 18, in a
manner to be described.
Current select switch 412 selectively connects
the Io current source 414 and the Io-50 current source 416
to the H/T elements Al and Bl, under control of the
- channel controller 410 over leads 418 and 420. The H/T
temperature select switch 422 receives the voltage level
signals from ~/~ Al and H/T Bl over signal lines 424 and
426 and processes same, in a manner to be described, under
control of the sensor channel controller 410 through
corresponding signals ~ver the lines 418 and 420.
Particularly, when the control signal on line
418 is high (418' is low), the H/T element pair Al Bl is
selected to be operational, whereas the H/T element pair
A2-B2 is on standby. (Conversely, when line 418' is high
and line 418 is low, then H/T element pair A2-B2 (i.e.,
sub-channel 410-2) is selected to be operational.~ A high
signal on line 420 then causes switch 412 to supply
current Io from source 414 to H/T element Al and the Io-50
current from source 416 to H/T element Bl. (If the signal
~3~102~
on line 420 is low, the reverse connection is made.)
Accordingly, channel controller 410 can selectively
toggle the H/T element pair Al-Bl (when 418 is high) as
between which element is the heated element and which is
the reference element. (The signal on line 420' performs
a similar role for H/T A2-B2 of sub-channel 410-2.)
Typically, sensor channel controller 410 will normally
select a given element pair, e.g., H/T Al-Bl (i.e., line
418 is high) with element Al carrying Io (line 420 being
high), and will respond to an input over input lines 471
and 474 from the system control unit 402 (Fig. 18) to
toggle to the opposite selection, i.e., to H/T Bl carrying
Io (heated) or to H/T A2-B2 being active. When the
signals on lines 418' and 420' are high (418 and 420 low),
switch 412 supplies the Io~50 current from source 416' to
both H/T elements A2 and B2.
Assuming that H/T element pair Al-Bl is selected
by the high signal on line 418, and element Al carries Io
(line 420 is also high) the temperature selection switch
422 supplies the respective, higher and lower voltage
outputs of the H/T element pair Al-Bl, as received over
lines 424 and 426, to the output lines 428 and 430,
respectively, those outputs being processed by multiplying
circuits 432 and 434, which may be operational amplifiers
having respective multiplication factors of "xl" (i.e.,
"times 1") and "x50" (i.e., "times 50") as indicated. The
respective outputs on lines 436 and 438 thus are made to
correspond in magnitude, with the exception of any
temperature difference sensed by the respective H/T
elements Al and Blp for differential comparison by
differential amplifier 440. These circuit operations
correspond to those described with reference to Fig. 14
hereinabove, the multiplying circuit 434 and the differen-
tial amplifier 440 corresponding to elements 94'' and
98', respectively, in Fig. 14. The temperature select
switch 422 of course directs the outputs of the H/~ Al, Bl
in accordance with their selection as reference and heated
elements. Thus, for example, if line 420 goes low, the
1 31 1 !32~
41
voltage output of H/T Bl on line 426 is larger than that
on line 424 and accordingly the switch 422 directs the
former to output line 428 and the latter to output line
430. Thus, amplifier 434 always receives the output
voltage of the elements of the reference probe as defined
by the supply of the Io.50 current to the E/T element of
that reference probe.
The resultant output of differential amplifier
440 is a signal representative of the temperature
differential T, of the respective temperatures sensed by
the H/T element pair Al, B1, where T = k V. The T
output further is supplied over line 440 to switch 442
which is operated over control line 444 by the sensor
channel controller 410 to selectively connect the output
of the corresponding sub-channel 410-1 or 410-2, which
currently is selected for operation, to the channel
out~ut line 446 by the 474 input line to controller 410
and thus to supply the T signal on that line for
transmission to the system control unit 402 and the
2~ display and operator control panel 404 in accordance with
Fig. 17.
The sensor channel controller 410 simultaneously
performs an error check and verification function, as to
the operating channel and the T output condition produced
thereby, and monitors and verifies the operational status
of all four H/T elements of its associated, integrated
sensor and the respective support circuits thereof.
The error check and channel operability
verification functions take into account the normal range
of voltage levels in both operational and standby
conditions of the H/T element pairs of both sub-channels.
; Considering first the most typical source of error, namely
breaking of electrical leads or burn out and disablement
of the heater elements, and as may be visualized from the
schematic of Fig. 14, there results essentially an open
circuit condition. Because of the character of the
constant current sources 97' and 94', the corresponding
bridge output voltage Va or Vb, corresponding to the
1 31 1 02~
42
respective H/T element and/or its supporting circuitry
which is now in an open circuit condition, approaches the
so-called "rail voltage" o~ the current sources 97' and
94', i.e., the highest voltage to which that source will
rise in attempting to maintain the constant current
condition. With reference to Fig. 14, the rail voltage
for example may be 150 volts for the Va output in the
branch receiving Io and 12 volts for the Vb output for the
leg receiving Io~50. The normal operating voltage range
for Va on the other hand would be 50 to 125 volts and for
Vb, 1 to 2.5 volts. Conversely, a short circuit of either
or both of the H/T elements will produce an output Va and
Vb at or approaching zero (0) volts. Accordingly, an
operative range of the output voltage Va may be defined as
that range extending from a lower limit threshold voltage
of 25 volts to an upper limit threshold voltage of 125
volts. Similarly, for the output voltage Vb, the
operative range would be defined by a lower limit
threshold voltage of approximately 0.5 volts and an upper
limit threshold voltage of 2.5 volts. As will be
recalled, however, the lower level output voltage Vb is
normalized relatively to the voltage Va by the (x50)
circuits 434 and 462 in Fig. 18. Thus, the reference
voltages VREFl AND VREF2 supplied to comparator circuits
450 and 452 in Fig. 18 both define lower and upper limits
of 25 and 125 volts, respectively, as the respective
operative range references for the voltage outputs of the
H/T elements A1 and B1.
Considerîng first the circumstance in which the
H/T element pair A1-B1 is operational, and further that
the signal on line 420 is high such that element Al
receives the high level current Io, temperature select
switch 422, in addition to supplying the voltage output of
element Al on line 428, supplies that same voltage output
on line 464 to comparator 450. The low level output of
element B1, which is supplied with the Io.50 current, is
applied through line 430 to multiplier 434, as before, and
the multiplied output is supplied to comparator 452 over
43 13110~
line 439. Both voltages on lines 464 and 434 should thus
be within the range established by VREF1 and VREF2 (i-e-~
25 to 125 volts). If either is not, the corresponding
comparator 450 or 452 produces an error signal on the
respective outputs 451 and 453. OR gate 454 passes any
such error output through line 458 to the controller 410.
When elements Al and Bl are toggled, the opposite circuit
paths for the respective outputs are followed, with the
same result.
In the circumstance that the signal on line 418
is low, the element pair Al-Bl is not selected and thus is
in a standby condition. Both elements Al and Bl are
supplied with the Io.50 current from source 416 by switch
412 and thus the respective voltage outputs should be of
1~ the same low level. Under that circumstance, switch 422
transfers the output voltage on line 424 to line 428 and
that on line 426 to line 430 Temperature selection
switch 422 in this instance now selects input 460, which
receives the signal on line 436 through line 437 and a x50
multiplying circuit 462, and supplies the multiplied
signal over line 464 to comparator 450 for comparison
against the reference VREFl. The output vol~age on line
430 from switch 422 corresponds in its normal range of
values to that for the unheated element of the reference
probe when the element pair H/T A1-Bl was selected; thus,
as before, that output signal is multiplied by the (x50)
circuit 434 and applied through line 435 to comparator
452. Correspondingly, the same lower limit and upper
limit threshold voltages and range therebetween, as
supplied by VREFl and VRE~2~ remain applicable for
determining operability of the H/T elements Al and Bl in
the standby condition, as well.
As will ~e apparent, any failure of the
operational and supporting circuits for the H/T elements
Al and Bl, e.g., the current supplies 414 and 416, the
switches 412 and 422, or the like -- whether the element
pair Al-Bl is selected for operation or is in standby, and
correspondingly for the pair A2-B2 -- will result in an
1 ~ 1 1 02~
44
error signal on line 458. Sensor channel controller 410
sends the corresponding error signal over output lead 470
to the system control unit 402 (Fig. 18), to indicate the
failure of an H/T pair of a given sub-channel (e.g., sub-
channel 410-1 as element pair H/T Al-Bl and sub-channel
410-2 as element pair H/T A2-B2). Similarly, an error
signal is transmitted over output line 472 to indicate
failure of the entire sensor channel, in the event that
both sub-channels of a given channel fail. Sensor channel
controller 410, moreover, either internally upon detection
of a failure of an element pair of one sub-channel, or in
response to a request to switch H/T element pair control
signal received over line 474 from the system control unit
402, switches to the other sub-channel currently in
standby. ~f course, where both sub-channels are in a
failure condition, operator intervention is required.
Sub-channel 410-2, as before-noted, is effec-
tively identical to sub-channel 410-1 and thus undergoes
the same operations and signal communic~tions over the
corresponding signal lines, as are similarly oriented in
Fig. 18 and identified by identical, but primed, reference
numbers. Error checking functions as between the two sub-
channels 410-1 and 410-2 are performed continuously.
As will be apparent, the system of Fig. 20
provides the same condition-indicating signals for the
respective sub-channels 410-1 and 410-2 and H/T element
pairs as does the monitoring system of the system of Figs.
9 to 12C, and thus is fully operational in the automatic
and operator control modes as described hereinabove. The
integrated sensors, however, afford simplified intercon-
nections and signal processing relative to the prior
described system, contributing to improved reliability and
lower costs of installation, maintenance and operation
while affording the same flexibili~y and reliability of
the monitoring and veri~ication functions.
In conclusion, the monitoring systems of the
invention provide a display of an alarm condition for a
given sensor, as produced by the first, normally selected
1 3 1 1 02~
and activ~ element pair but subject to automatic verifica-
tion thereof by the toggle test utilizing the complemen-
tary, second heater element, while performing continuous
on-line testing and both automatic detection of element
failures with issuance of appropriate failure indications
and automatic substitution of the complementary elements,
such that all sensor locations are constantly monitored
and diagnosed and in a ready condition to provide alarm
indications, while furthermore eliminating false alarms
lo that may otherwise result from component failure. In
addition to the automatic and continuous on-line testing,
operator-controlled selective testing modes are provided.
Important to these capabilities of the systems is the
duplex character and toggling capability of the sensors of
the invention. In addition to their rugged construction
assuring lon~ life, the sensors afford on-line replace-
ability of failed heater and sensor elements~ the duplex
and redundant sensors remaining fully functional by
automatic substitution of the complementary elements
thereof. Numerous modifications and adaptations of the
sensors and the instrumentation system of the present
invention will be apparent to those of skill in the art
and thus it is intended by the following claims to cover
all such modifications and adaptations.
13~ ~)2~
Page 45-1 53,671I2
IDENTIFICATION OF REFERENCE NUMERALS USED IN THE DRAWINGS
LEGEND REF. NO. FICURE
HTR FAILURE ALARM DISPLAY
HTR A ~_ 116
HTR B ~ 118 114 10
TC FAILURE ALARM DISPLAY
TCP-l 120-1
TCP-2 120-2 120 10
