Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02816881 2013-05-24
FLOW METER AND METHOD FOR DETECTING A CABLE FAULT IN A
CABLING OF THE FLOW METER
Background of the Invention
This application is a divisional application of co-pending application Serial
No.
2,768,991 filed February 21, 2012, which is a divisional of 2,642,611, filed
August 13,
2008, which is the National Phase Entry of PCT/US2006/006818 filed February
27,
2006.
1. Field of the Invention
The present invention relates to a flow meter and method for detecting a cable
fault in a cabling of the flow meter.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flow meters, typically
operate
by detecting motion of a vibrating conduit that contains a flowing material.
Properties
associated with the material in the conduit, such as mass flow, density and
the like, can
be determined by processing measurement signals received from motion
transducers
associated with the conduit. The vibration modes of the vibrating material-
filled system
generally are affected by the combined mass, stiffness and damping
characteristics of
the containing conduit and the material contained therein.
A typical Coriolis mass flow meter includes one or more conduits that are
connected inline in a pipeline or other transport system and convey material,
e.g., fluids,
slurries and the like, in the system. Each conduit may be viewed as having a
set of
natural vibration modes including, for example, simple bending, torsional,
radial, and
coupled modes. In a typical Coriolis mass flow measurement application, a
conduit is
excited in one or more vibration modes as a material flows through the
conduit, and
motion of the conduit is measured at points spaced along the conduit.
Excitation is
typically provided by an actuator, e.g., an electromechanical device, such as
a voice
coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow
rate may be
determined by measuring time delay or phase differences between motions at the
transducer locations. Two such transducers (or pickoff sensors) are typically
employed
in order to measure a vibrational response of the flow conduit or conduits,
and are
typically located at positions upstream and downstream of the actuator. The
two pickoff
sensors are connected to electronic instrumentation by cabling, such as two
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independent pairs of wires. The instrumentation receives signals from the two
pickoff
sensors and processes the signals in order to derive a mass flow rate
measurement.
When the flow conduit or conduits of a Coriolis flow meter are empty, then the
phase difference between the two pickoff signals is ideally zero. In contrast,
during
normal operation, the flow through the flow meter induces a phase shift
between the two
pickoff signals due to the Coriolis effect. The phase shift is directly
proportional to the
material flow through the conduits. Therefore, by making an accurate
measurement of
the signal difference, the flow meter can accurately measure the mass flow
rate.
A Coriolis flow meter typically uses coils to drive a flow conduit(s) and to
measure resulting flow conduit vibrations. In many cases, the flow sensor
apparatus
(L e., the flow conduit(s), pickoff sensors, and driver), is not integrally
mounted with the
transmitter electronics. A typical Coriolis meter includes 9 wires bundled in
a cable
between the transmitter/meter electronics and the flow sensor apparatus. The
cabling
typically includes 3 wires for a Resistance Temperature Detector (RTD) sensor,
2 wires
for a first pickoff sensor, 2 wires for a second pickoff sensor, and 2 wires
for a driver.
The cabling is typically connected in the field and by the customer. This can
lead to problems in the cabling. Pairs of wires can be swapped. Wires can be
mixed
up. Bad terminal connections or a failed coil can result in an open circuit.
For example,
if a first pickoff sensor is connected in a first orientation and the second
pickoff sensor is
connected in a second, opposite orientation, then a measured phase shift
during a
zeroing operation will be excessively large. Similarly, where the wires
connecting to the
driver are switched, then an expected phase characteristic will not be
observed and a
feedback loop of the driver circuit may drive the response toward zero instead
of driving
the response to a fundamental frequency.
Another problem that can occur is a broken or unconnected wire between
components. A broken or unconnected wire may not be detected until the unit is
put
into operation. Troubleshooting the problem at the customer's location is
costly and
time-consuming. In addition, the customer will experience downtime, expense,
and
frustration.
It is desirable for the transmitter to automatically determine if the sensor
is wired
correctly, and if not, correct for the encountered problem. Additionally, it
is desirable to
determine this independently of process variations.
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Summary of the Solution
Meter electronics for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The meter electronics
comprises
first and second pickoff sensors and the cabling coupled to the first and
second pickoff
sensors. The cabling includes one or more first pickoff wires and one or more
second
pickoff wires. The meter electronics further comprises a signal injection
device coupled
to the cabling. The signal injection device is configured to generate an
injection signal
and communicate the injection signal into the cabling and to the first and
second pickoff
sensors. The meter electronics further comprises a signal conditioning circuit
coupled to
the cabling. The signal conditioning circuit is configured to receive at least
one
response signal from at least one of the first and second pickoff sensors in
response to
the injection signal and determine one or more of a pickoff open wire fault
and a pickoff
connection orientation fault in one or both of the one or more first pickoff
wires and the
one or more second pickoff wires of the cabling.
Meter electronics for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The meter electronics
comprises
a driver, first and second pickoff sensors, and the cabling coupled to the
first and
second pickoff sensors and to the driver. The meter electronics further
comprises a
driver circuit coupled to the cabling and configured to generate a drive
signal and
communicate the drive signal into the cabling and to the driver. The meter
electronics
further comprises a signal conditioning circuit coupled to the cabling. The
signal
conditioning circuit is configured to receive at least one response signal
from at least
one of the first and second pickoff sensors in response to the drive signal
and determine
one or more of a driver open wire fault and a driver connection orientation
fault in one or
more driver wires of the cabling.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises comparing an
injection signal component of a response signal received from at least one of
a first
pickoff sensor and a second pickoff sensor to a predetermined pickoff
amplitude
threshold and determining a pickoff open wire fault in a corresponding one or
more first
pickoff wires or in a corresponding one or more second pickoff wires if the
injection
signal component does not exceed the predetermined pickoff amplitude
threshold.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises comparing a
phase difference between a first pickoff response phase of a first pickoff
response signal
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and a second pickoff response phase of a second pickoff response signal to a
predetermined pickoff phase difference threshold. The first pickoff response
signal and
the second pickoff response signal are received from the first pickoff sensor
and the
second pickoff sensor via the cabling. The method further comprises
determining a
pickoff connection orientation fault if the phase difference exceeds the
predetermined
pickoff phase difference threshold.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises comparing a
drive
resistor voltage across a drive resistor RD at an output of the driver circuit
to a
predetermined voltage threshold and determining a driver open wire fault in
the one or
more driver wires if the drive resistor voltage does not exceed the
predetermined
voltage threshold.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises comparing a
response signal phase difference to a predetermined driver phase difference
threshold.
The response signal phase difference comprises a difference between a response
signal phase and a drive signal phase. The response signal phase is received
from at
least one of a first pickoff sensor and a second pickoff sensor. The method
further
comprises determining a driver connection orientation fault in the one or more
driver
wires if the response signal phase difference exceeds the predetermined driver
phase
difference threshold.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises determining
a
vibrational response amplitude of a vibrational response and determining a
driver
connection orientation fault in the one or more driver wires if the
vibrational response
amplitude does not substantially track a drive signal amplitude.
A method for detecting a cable fault in a cabling of a flow meter is provided
according to an embodiment of the invention. The method comprises testing one
or
more first pickoff wires and one or more second pickoff wires of the cabling
for pickoff
open wire faults. The one or more first pickoff wires and the one or more
second pickoff
wires are included in the cabling and connect to a first pickoff sensor and to
a second
pickoff sensor respectively. The method further comprises testing the one or
more first
pickoff wires and the one or more second pickoff wires for a pickoff
connection
orientation fault if no pickoff open wire faults are determined in the one or
more first
pickoff wires and the one or more second pickoff wires. The method further
comprises
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testing one or more driver wires of the cabling for a driver open wire fault.
The one or
more driver wires connect to a driver. The method further comprises testing
the one or
more driver wires for a driver connection orientation fault if no driver open
wire faults are
determined in the one or more driver wires.
ASPECTS
In one aspect of the meter electronics, the signal conditioning circuit is
configured to compare an injection signal component of the at least one
response signal
to a predetermined pickoff amplitude threshold and determine a pickoff open
wire fault
in the corresponding one or more first pickoff wires or in the corresponding
one or more
second pickoff wires if the injection signal component does not exceed the
predetermined pickoff amplitude threshold.
In another aspect of the meter electronics, the signal conditioning circuit
receives
a first pickoff response signal and a second pickoff response signal and the
signal
conditioning circuit is configured to compare a phase difference between a
first pickoff
response phase and a second pickoff response phase to a predetermined pickoff
phase
difference threshold and determine a pickoff connection orientation fault in
the
corresponding one or more first pickoff wires or in the corresponding one or
more
second pickoff wires if the phase difference exceeds the predetermined pickoff
phase
difference threshold.
In yet another aspect of the meter electronics, the signal injection device
comprises a digital-to-analog (D/A) converter configured to receive a digital
frequency
command and output a frequency input, an injection signal generator that
receives the
frequency input from the D/A converter and outputs an injection signal of a
frequency
specified by the frequency input, and a transformer that communicates the
injection
signal into the cabling.
In yet another aspect of the meter electronics, the signal conditioning
circuit is
further configured to invert a received response signal from one pickoff
sensor if a
pickoff connection orientation fault is determined to exist.
In yet another aspect of the meter electronics, the signal conditioning
circuit is
configured to compare a drive resistor voltage across a drive resistor RD at
an output of
the driver circuit to a predetermined voltage threshold and determine a driver
open wire
fault in the one or more driver wires if the drive resistor voltage does not
exceed the
predetermined voltage threshold.
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In yet another aspect of the meter electronics, the signal conditioning
circuit is
configured to compare a response signal phase difference to a predetermined
driver
phase difference threshold and determine a driver connection orientation fault
in the one
or more driver wires if the response signal phase difference exceeds the
predetermined
driver phase difference threshold, with the response signal phase difference
comprising
a difference between a response signal phase and a drive signal phase and with
the
response signal phase being received from at least one of the first pickoff
sensor and
the second pickoff sensor.
In yet another aspect of the meter electronics, the meter electronics is
further
configured to determine a vibrational response amplitude of a vibrational
response and
determine a driver connection orientation fault in the one or more driver
wires if the
vibrational response amplitude does not substantially track a drive signal
amplitude.
In yet another aspect of the meter electronics, the driver circuit is further
configured to invert a drive signal if the driver connection orientation fault
is determined
to exist.
In one embodiment of the method, the method further comprises generating an
alarm if the pickoff open wire fault is determined to exist.
In another embodiment of the method, the comparing and determining further
comprise comparing a first injection signal component of a first response
signal from the
first pickoff sensor to the predetermined pickoff amplitude threshold,
determining a first
pickoff open wire fault in the one or more first pickoff wires if the first
injection signal
component does not exceed the predetermined pickoff amplitude threshold,
comparing
a second injection signal component of a second response signal from the
second
pickoff sensor to the predetermined pickoff amplitude threshold, and
determining a
second pickoff open wire fault in the one or more second pickoff wires if the
second
injection signal component does not exceed the predetermined pickoff amplitude
threshold.
In yet another embodiment of the method, the method further comprises
generating an alarm if the pickoff connection orientation fault is determined
to exist.
In yet another embodiment of the method, the method further comprises, after
the determining, inverting a received response signal from one pickoff sensor
if a pickoff
connection orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if the driver open wire fault is determined to exist.
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In yet another embodiment of the method, the method further comprises
generating an alarm if the driver connection orientation fault is determined
to exist.
In yet another embodiment of the method, the method further comprises, after
the determining, inverting a drive signal from the driver circuit if the
driver connection
orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if the driver connection orientation fault is determined
to exist.
In yet another embodiment of the method, the method further comprises, after
the determining, inverting a drive signal from the driver circuit if the
driver connection
orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if an open wire fault is determined to exist in the one or
more first
pickoff wires, in the one or more second pickoff wires, or in the one or more
driver wires.
In yet another embodiment of the method, the method further comprises
generating an alarm if a connection orientation fault is determined to exist
in the one or
more first pickoff wires, in the one or more second pickoff wires, or in the
one or more
driver wires.
In yet another embodiment of the method, the testing the one or more pickoff
sensors for pickoff open wire faults comprises comparing an injection signal
component
of a response signal received from at least one of the first pickoff sensor
and the second
pickoff sensor to a predetermined pickoff amplitude threshold and determining
a pickoff
open wire fault in a corresponding one or more first pickoff wires or in a
corresponding
one or more second pickoff wires if the injection signal component does not
exceed the
predetermined pickoff amplitude threshold.
In yet another embodiment of the method, testing the one or more first pickoff
wires and the one or more second pickoff wires for pickoff connection
orientation faults
comprises comparing a phase difference between a first pickoff response phase
of a
first pickoff response signal and a second pickoff response phase of a second
pickoff
response signal to a predetermined pickoff phase difference threshold, with
the first
pickoff response signal and the second pickoff response signal being received
from the
first pickoff sensor and the second pickoff sensor via the cabling, and
determining a
pickoff connection orientation fault if the phase difference exceeds the
predetermined
pickoff phase difference threshold.
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In yet another embodiment of the method, the method further comprises, after
testing for the pickoff connection orientation fault, inverting the response
signal from one
pickoff sensor if a pickoff connection orientation fault is determined to
exist.
In yet another embodiment of the method, testing the driver for open wires
comprises comparing a drive resistor voltage across a drive resistor RD at an
output of
the driver circuit to a predetermined voltage threshold and determining a
driver open
wire fault in the one or more driver wires if the drive resistor voltage does
not exceed the
predetermined voltage threshold.
In yet another embodiment of the method, testing the one or more driver wires
for a driver connection orientation fault comprises comparing a response
signal phase
difference to a predetermined driver phase difference threshold, with the
response
signal phase difference comprising a difference between a response signal
phase and a
drive signal phase and with the response signal phase being received from at
least one
of the first pickoff sensor and the second pickoff sensor, and determining a
driver
connection orientation fault in the one or more driver wires if the response
signal phase
difference exceeds the predetermined driver phase difference threshold.
In yet another embodiment of the method, testing the one or more driver wires
for a driver connection orientation fault comprises determining a vibrational
response
amplitude of a vibrational response and determining a driver connection
orientation fault
in the one or more driver wires if the vibrational response amplitude does not
substantially track a drive signal amplitude.
In yet another embodiment of the method, the method further comprises, after
testing the one or more driver wires for the driver connection orientation
fault, inverting
the drive signal from the driver if the driver connection orientation fault is
determined to
exist.
Description of the Drawings
FIG. 1 illustrates a Coriolis flow meter comprising a flow meter assembly and
meter electronics.
FIG. 2 is a diagram of a portion of the flow meter according to an embodiment
of
the invention.
FIG. 3 is a flowchart of a method for detecting a cable fault in a cabling of
a flow
meter according to an embodiment of the invention.
FIG. 4 is a flowchart of a method for detecting a cable fault in a cabling of
a flow
meter according to an embodiment of the invention.
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FIG. 5 is a flowchart of a method for detecting a cable fault in a cabling of
a flow
meter according to an embodiment of the invention.
FIG. 6 is a flowchart of a method for detecting a cable fault in a cabling of
a flow
meter according to an embodiment of the invention.
FIG. 7 is a flowchart of a method for detecting a cable fault in a cabling of
a flow
meter according to an embodiment of the invention.
FIG. 8 shows the flow meter according to an embodiment of the invention.
Detailed Description of the Invention
FIGS. 1-8 and the following description depict specific examples to teach
those
skilled in the art how to make and use the best mode of the invention. For the
purpose
of teaching inventive principles, some conventional aspects have been
simplified or
omitted. Those skilled in the art will appreciate variations from these
examples that fall
within the scope of the invention. Those skilled in the art will appreciate
that the
features described below can be combined in various ways to form multiple
variations of
the invention. As a result, the invention is not limited to the specific
examples described
below, but only by the claims and their equivalents.
FIG. 1 illustrates a Coriolis flow meter 5 comprising a flow meter assembly 10
and meter electronics 20. Meter electronics 20 is connected to meter assembly
10 via
leads 100 to provide density, mass flow rate, volume flow rate, totalized mass
flow,
temperature, and other information over path 26. It should be apparent to
those skilled
in the art that the present invention can be used by any type of Coriolis flow
meter
regardless of the number of drivers, pickoff sensors, flow conduits, or the
operating
mode of vibration. A Coriolis flow meter structure is described although it is
apparent to
those skilled in the art that the present invention could be practiced as a
vibrating tube
densitometer without the additional measurement capability provided by a
Coriolis mass
flow meter.
Flow meter assembly 10 includes a pair of flanges 101 and 101', manifolds 102
and 102', driver 104, pickoff sensors 105-105', and flow conduits 103A and
103B.
Driver 104 and pickoff sensors 105 and 105' are connected to flow conduits
103A and
103B.
Flanges 101 and 101' are affixed to manifolds 102 and 102'. Manifolds 102 and
102' are affixed to opposite ends of spacer 106. Spacer 106 maintains the
spacing
between manifolds 102 and 102' to prevent undesired vibrations in flow
conduits 103A
and 103B. When flow meter assembly 10 is inserted into a pipeline system (not
shown)
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. .
which carries the material being measured, material enters flow meter assembly
10
through flange 101, passes through inlet manifold 102 where the total amount
of
material is directed to enter flow conduits 103A and 103B, flows through flow
conduits
103A and 103B and back into outlet manifold 102' where it exits meter assembly
10
through flange 101'.
Flow conduits 103A and 103B are selected and appropriately mounted to inlet
manifold 102 and outlet manifold 102' so as to have substantially the same
mass
distribution, moments of inertia, and elastic modules about bending axes W--W
and
W'--W' respectively. The flow conduits extend outwardly from the manifolds in
an
essentially parallel fashion.
Flow conduits 103A-B are driven by driver 104 in opposite directions about
their
respective bending axes W and W' and at what is termed the first out of
bending mode
of the flow meter. Driver 104 may comprise one of many well known
arrangements,
such as a magnet mounted to flow conduit 103A and an opposing coil mounted to
flow
conduit 103B. An alternating current is passed through the opposing coil to
cause both
conduits to oscillate. A suitable drive signal is applied by meter electronics
20, via lead
110 to driver 104.
Meter electronics 20 receives sensor signals on leads 111 and 111',
respectively. Meter electronics 20 produces a drive signal on lead 110 which
causes
driver 104 to oscillate flow conduits 103A and 103B. Meter electronics 20
processes left
and right velocity signals from pickoff sensors 105 and 105' in order to
compute a mass
flow rate. Path 26 provides an input and an output means that allows meter
electronics
20 to interface with an operator. The description of FIG. 1 is provided merely
as an
example of the operation of a flow meter and is not intended to limit the
teaching of the
present invention.
FIG. 2 is a diagram of a portion of the flow meter 5 according to an
embodiment
of the invention. The flow meter 5 includes a first pickoff sensor 201a, a
second pickoff
sensor 201b, a driver 204, and the meter electronics 20. The meter electronics
20 can
operate as a mass flow meter or can operate as a densitometer, including
operating as
a Coriolis flow meter. The meter electronics 20 can include, among other
things, a
driver circuit 220, a signal injection device 203, and a signal conditioning
circuit 202.
The meter electronics 20 is connected to the pickoff sensors 201 and to the
driver 204
by cabling 205. The cabling 205 connects the first pickoff sensor 201a and the
second
pickoff sensor 201b to a signal conditioning circuit 202 and to a signal
injection device
203. The cabling 205 connects the driver 204 to the driver circuit 220. In one
CA 02816881 2013-05-24
embodiment, the signal conditioning circuit 202 and the signal injection
device 203 are
interconnected by a link 210.
The cabling 205 can comprise any manner of wires, cables, fibers, etc., that
electrically connect the first and second pickoff sensors 201a and 201b to the
signal
conditioning circuit 202. The cabling 205 in one embodiment comprises at least
a
portion of the leads 100 of FIG. 1.
A typical flow meter includes 9 wires bundled in the cabling 205 between the
transmitter/meter electronics 20 and the flow meter assembly 10. The cabling
205
typically includes 3 wires for a Resistance Temperature Detector (RTD) sensor,
2 wires
for a first pickoff sensor, 2 wires for a second pickoff sensor, and 2 wires
for the driver.
The meter electronics 20 in one embodiment can perform cable fault
determinations for the cabling 205 between the meter electronics 20 and the
pickoff
sensors 201a and 201b. The meter electronics 20 in one embodiment can perform
cable fault determinations for the cabling 205 between the meter electronics
20 and the
driver 204.
The driver circuit 220 generates a drive signal and communicates the drive
signal to the driver 204. The driver 204 vibrates the flow conduits 103A and
103B
according to the drive signal. The drive signal therefore includes an
amplitude
characteristic and a frequency characteristic. Where the meter electronics 20
implements a closed-loop drive, a difference between a drive signal and a
response
signal is employed as feedback for modifying the drive signal. For example, a
phase
difference between the drive signal and a response signal can comprise the
feedback.
Ideally, under no-flow conditions the phase difference will be substantially
zero if the
flow meter is accurately calibrated.
The driver circuit 220 can generate a drive signal. The drive signal in one
embodiment comprises an operational drive signal that is generated by the
driver circuit
220, wherein the signal vibrates a flow conduit(s) 103. A resulting response
signal to
the drive signal can be received in the signal conditioning circuit 202.
Alternatively, the
drive signal can be generated specifically for a fault test according to the
invention.
The signal injection device 203 can generate an injection signal and can
communicate the injection signal to one or both of the first pickoff sensor
201a and the
second pickoff sensor 201b via the cabling 205. The signal injection device
203 can
generate an injection signal according to an injection signal command that can
be
received from the signal conditioning circuit 202 over the link 210. The
injection signal
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can comprise any desired frequency or frequencies. The injection signal can
include
frequencies above, below, or the same as a drive signal.
The signal conditioning circuit 202 receives response signals from both
pickoff
sensors 201a and 201b. The signal conditioning circuit 202 can detect and/or
process
the response signals. The signal conditioning circuit 202 can process the
response
signals in order to produce appropriate flow measurements. In addition, the
signal
conditioning circuit 202 can process the response signals in order to detect
faults in the
cabling 205 according to embodiments of the invention.
The response signals can be generated by the pickoff sensors 201 according to
normal operation of the flow meter 5. Alternatively, the response signals can
be
generated by the pickoff sensors 201 in response to any manner of test
vibration of the
flow conduits 103. In yet another alternative, the response signals can be
generated by
the pickoff sensor 201 in response to an injection signal from the signal
injection device
203.
The signal conditioning circuit 202 can determine a response signal amplitude
for each pickoff sensor. The signal conditioning circuit 202 can determine a
phase
difference between the response signals received from the first pickoff sensor
201a and
the second pickoff sensor 201b. The amplitude and phase difference can be used
to
determine a connection orientation faults in the cabling 205.
In one embodiment, the meter electronics 20 can include a processor (not
shown) and a cable troubleshooting software routine. The processor can execute
the
cable troubleshooting software routine and can initiate and supervise open
wire and
connection orientation fault determinations for the cabling 205. The processor
and
cable troubleshooting software routine can initiate signals into the pickoff
sensors 201a
and 201b. The processor and routine can receive measurements/data from the
open
wire and connection orientation fault tests and can perform appropriate fault
determinations. The processor and routine can generate alarms if problems are
detected. In addition, the processor and routine can perform compensation
techniques,
including inverting signals or signal responses in order to compensate for
improper
wiring orientations. Alternatively, the signal conditioning circuit 202, the
signal injection
device 203, the driver circuit 220, and the processor can include equivalent
circuitry
and/or specialized circuit components that perform the above operations.
FIG. 3 is a flowchart 300 of a method for detecting a cable fault in a cabling
of a
flow meter according to an embodiment of the invention. In this method, a
pickoff open
wire fault determination is performed. The pickoff open wire fault test can
detect open
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wire faults such as a wire break or an unconnected wire in corresponding
pickoff wires
of the cabling 205.
In step 301, an injection signal is communicated into one or more pickoff
wires of
the cabling 205. As a result, the injection signal is communicated to at least
one of the
first pickoff sensor 201a and the second pickoff sensor 201b. The injection
signal can
be generated by the signal injection device 203, for example. When an
injection signal
is generated by the signal injection device 203, the signal conditioning
circuit 202 should
substantially simultaneously receive response signals from both pickoff
sensors 201a
and 201b.
In step 302, a response signal is compared to a predetermined pickoff
amplitude
threshold. The injection signal sent to the pickoff sensor 201 will generate
two different,
returning signals to the signal conditioning circuit 202, but only if the
pickoff wires are
not open. The first signal, an injection signal component, is a reflection of
the injection
signal and is at substantially the same frequency as the injection signal. If
the pickoff
wires are not open, then this injection signal component should be similar in
amplitude
to the injection signal and therefore can be compared to a threshold. The
second signal
is a response signal component and differs in frequency from the original
injection signal
due to the effects of vibration of the flow conduit(s) 103 and due to the
effects of a flow
material in the flow conduit(s) 103. However, this response signal component
may vary
in amplitude and may be undetectable in some cases. Therefore, in one
embodiment,
the injection signal component of the response signal is used for the
comparing.
In step 303, if the injection signal component does not exceed the
predetermined
pickoff amplitude threshold, then the method proceeds to step 304. Here, it is
determined that a response signal was not received and that a wire of the
corresponding pickoff sensor is either broken or not connected. Otherwise, if
the
injection signal component does exceed the predetermined pickoff amplitude
threshold,
then the method branches around step 304. Therefore, it is determined that a
response
signal was received and that the corresponding pickoff wires are not broken or
disconnected.
In step 304, because the injection signal component did not exceed the
predetermined pickoff amplitude threshold, the corresponding pickoff wires are
determined to have an open wire fault. Subsequently, the meter electronics 20
can
perform other actions, including generating an alarm that indicates the open
wire fault.
The above steps are discussed in the context of a single pickoff sensor and a
single response signal amplitude. However, it should be understood that the
steps 302-
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CA 02816881 2013-05-24
304 can be performed on the response signals from both pickoff sensors 201a
and
201b.
FIG. 4 is a flowchart 400 of a method for detecting a cable fault in a cabling
of a
flow meter according to an embodiment of the invention. In this method, a
pickoff
sensor connection orientation fault determination is performed.
In step 401, a response signal is received from one or both pickoff sensors
via
the cabling 205 in response to a drive signal applied by the driver 204.
Under no-flow conditions in the flow meter 5, the phase difference between the
left and right (or first and second) pickoff signals will be substantially
zero. Under flow
conditions, the phase of the first pickoff signal will differ from the phase
of the second
pickoff signal by a relatively small amount, according to a mass flow rate of
flow material
through the flow meter 5. However, if the phase difference between the two
pickoff
signals is too great, then a connection orientation fault exists.
In step 402, a phase difference is compared to a predetermined pickoff phase
difference threshold. The phase difference comprises a difference between a
response
signal phase and a drive signal phase.
In step 403, if the phase difference exceeds the predetermined pickoff phase
difference threshold, then the method proceeds to step 404. If the phase
difference
does not exceed the predetermined pickoff phase difference threshold, then the
method
branches around step 404.
In step 404, because the phase difference exceeded the predetermined pickoff
phase difference threshold, then it is determined that a connection
orientation fault
exists in corresponding pickoff wires. For example, the two response signals
can be
around 180 degrees out of phase, plus or minus a relatively small phase
difference
portion caused by a response to a flow material in the flow conduit(s) 103. As
before,
an alarm condition can be generated if the connection orientation fault is
determined to
exist. In addition, the meter electronics 20 can invert all subsequent
response signals
received from the affected pickoff sensor. In this manner, the improper
connection
orientation can be remediated.
The above steps are discussed in the context of a single pickoff sensor and a
single phase difference. However, it should be understood that the steps 402-
404 can
be performed on the response signals from both pickoff sensors 201a and 201b.
FIG. 5 is a flowchart 500 of a method for detecting a cable fault in a cabling
205
of a flow meter according to an embodiment of the invention. In this method, a
driver
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CA 02816881 2013-05-24
open wire fault determination is performed. The driver open wire fault test
can detect
open wire faults such as a wire break or an unconnected wire.
In step 501, a drive signal is communicated into one or more driver wires of
the
cabling 205 and to the driver 204. The drive signal can be generated by the
driver
circuit 220, as previously discussed. The drive signal can comprise a normal
operational drive signal or can comprise any generated signal that is suitable
for the
wire open fault testing.
Referring back to FIG. 2, the driver circuit 220 includes a drive resistor RD
in the
output. An op-amp 221 is connected across the drive resistor RD. In one
embodiment,
the op-amp 221 amplifies a voltage across the drive resistor RD and outputs a
drive
resistor voltage. The drive resistor voltage can comprise an analog voltage
signal that
can be compared to a predetermined voltage threshold.
Referring again to FIG. 5, in step 502 the drive resistor voltage across the
drive
resistor RD is compared to a predetermined voltage threshold. If the drive
resistor
voltage at the output of the op-amp 221 exceeds the predetermined voltage
threshold,
then an expected level of electrical current is flowing through the cabling
205 to the
driver 204.
In step 503, if the drive resistor voltage does not exceed the predetermined
voltage threshold, then the method proceeds to step 504. Otherwise, if the
drive resistor
voltage exceeds the predetermined voltage threshold, then it can be determined
that no
open wire condition exists and therefore the method branches around step 504.
In step 504, because the drive resistor voltage did not exceed the
predetermined
voltage threshold, then it can be determined that a driver open wire fault
condition exists
in the cabling 205 to the driver 204. This step can include generating an
alarm
condition, as previously discussed.
Alternatively, the op-amp 221 can comprise a comparator device that compares
the voltage at the cabling side of the drive resistor RD to a voltage (L e.,
to the
predetermined voltage threshold) and generates a digital true or false output.
The
digital output therefore comprises a first digital output level if the drive
resistor voltage
exceeds the predetermined voltage and a second digital output level if the
drive resistor
voltage does not exceed the predetermined voltage. The comparison of step 502
therefore can comprise a comparison internal to the comparator device, wherein
the
predetermined voltage threshold comprises a voltage input to the comparator
device.
CA 02816881 2013-05-24
FIG. 6 is a flowchart 600 of a method for detecting a cable fault in a cabling
of a
flow meter according to an embodiment of the invention. In this method, a
driver
connection orientation fault determination is performed.
In step 601, the driver circuit 220 generates a drive signal and communicates
the
drive signal to the driver 204 via the cabling 205, as previously discussed.
As a result,
the driver 204 generates a physical excitation in the flow conduits 103A and
103B using
the drive signal. Consequently, the signal conditioning circuit 202 receives
first and
second response signals from the first and second pickoff sensors 201a and
201b via
the cabling 205 in response to the vibration of the flow conduits by the
driver 204.
In step 602, a response signal phase difference is compared to a predetermined
driver phase difference threshold. The response signal phase difference
comprises a
difference between a response signal phase and a drive signal phase. The drive
signal
phase is the phase characteristic provided to the driver circuit 220, i.e., it
s the drive
phase that the driver circuit 220 and the drive 204 are targeted to achieve.
The actual
phase of the response should be close to the phase, and will typically differ
in relation to
a mass flow rate of flow material in the flow conduits 103.
In step 603, if the response signal phase difference exceeds the predetermined
driver phase difference threshold, then a driver connection orientation fault
is
determined in the driver wires and the method proceeds to step 604. Otherwise,
if the
response signal phase difference does not exceed the predetermined driver
phase
difference threshold, then the driver connection orientation is determined to
be correct
and the method branches around step 604.
In step 604, because the response signal phase difference exceeded the
predetermined driver phase difference threshold, then it is determined that a
driver
connection orientation fault exists in the driver wires. For example, the
phase difference
can be around 180 degrees, plus or minus a relatively small phase difference
portion
caused by a response to a flow material in the flow conduit(s) 103. As before,
an alarm
condition can be generated if the connection orientation fault is determined
to exist. In
addition, the meter electronics 20 can invert the drive signal. For example,
the drive
signal can be inverted before it is sent to the driver 204. In this manner,
the improper
driver connection orientation can be remediated.
It should be understood that either method of FIG. 6 or FIG. 7 can be used to
make a driver connection orientation fault determination.
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CA 02816881 2013-05-24
FIG. 7 is a flowchart 700 of a method for detecting a cable fault in a cabling
of a
flow meter according to an embodiment of the invention. In this method, a
driver
connection orientation fault determination is performed.
In step 701, a vibrational response amplitude is determined. The vibrational
response amplitude can comprise an amplitude of a response signal from either
pickoff.
In step 702, the vibrational response amplitude is compared to a drive signal
amplitude. The comparison can be a comparison of the two amplitudes at one or
more
instantaneous points in time. Alternatively, the comparison can compare
averaged or
filtered values, etc.
In step 703, if the vibrational response amplitude is substantially tracking
the
drive signal amplitude, then the method exits. If the vibrational response
amplitude is
not substantially tracking the drive signal amplitude, then the method
proceeds to step
704.
In step 704, because the vibrational response amplitude is not substantially
tracking the drive signal amplitude, then it is determined that a driver
connection
orientation fault exists in the driver wires. As before, an alarm condition
can be
generated if the driver connection orientation fault is determined to exist.
In addition,
the meter electronics 20 can invert the drive signal. For example, the drive
signal can
be inverted before it is sent to the drive 204. In this manner, the improper
driver
connection orientation can be remediated.
FIG. 8 shows the flow meter 5 according to an embodiment of the invention.
Components in common with FIG. 2 share the same reference numbers. In this
embodiment, the signal injection device 203 comprises a digital-to-analog
(D/A)
converter 808, an injection signal generator 806, and a transformer 807. The
D/A 808 is
connected to the signal conditioning circuit 202 and to the injection signal
generator
806. The injection signal generator 806 is further connected to the
transformer 807.
The D/A 808 receives a digital frequency command from the signal conditioning
circuit 202. The D/A 808 converts the digital frequency command into a
frequency input
into the injection signal generator 806, wherein the frequency input specifies
the
frequency of a (single) injection signal to be generated. The injection signal
generator
806 generates the injection signal and transmits the injection signal to
primary windings
810 of the transformer 807.
The transformer 807 creates the first and second injection signals through the
use of a split transformer secondary, wherein the secondary windings 811 of
the
transformer 807 comprise substantially equal pairs of secondary windings. In
this
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CA 02816881 2013-05-24
manner, the injection signal at the primary windings 810 of the transformer
807 is
converted into the first and second injection signals at the secondary
windings 811. The
two secondary windings 811 are connected to the cabling 205 and to the first
and
second pickoff sensors 201a and 201b, wherein signals can be injected into the
pickoff
sensors. As before, the signal conditioning circuit 202 receives the first and
second
response signals that are created as a result of the injection of the first
and second
injection signals.
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