Note: Descriptions are shown in the official language in which they were submitted.
3Z
METHOD AND APPARATUS FOR MEASURING AND PROVIDING
CO~RECTED GAS FLOW
~b~
ield of the Invention:
This invention relates ~o systems and methods
for measuring gas flow, flow temperature and flow pressure
and for determining with a high degree of accuracy the
supercompressibility factor, from which a value of gas
volume at base conditions of tempexature and pressure may
be calculated.
Descrlption o~ the Prior Art:
Gas is compressible, the volume of which changes
as a unction of temperature and pressure in accordance
with the well known ideal gas laws. Natural gas is widely
used as a fuel and, typically, is ~ransmitted via pipe-
lines from a source to an end user. Conditions of temper-
ature and pressure may vary widely throughout such a gas
distribution system. To distribute and sell gas that is
exposed to ~arying conditions of temperature and pressure,
calculations must be made to convert the measured flow or
line volume ~f of gas, in terms of cubic feet at varying
flow or line conditions of flow or line temparature Tf and
pressure Pf, to a standard cubic feet volume Vb at spec-
ified, previously agreed upon base temperature Tb and base
pressure Pb.
The basic gas law relationship can be expressed
as:
PV - NRTZ (1)
where:
332
--2--
P is absolute pressure
V is volume
N is mols of gas
R is the universal gas constant
T is the absolute ~emperature
Z is the compressibility factor.
When dealing with a simple gas, such as N2 or 2~ the
ideal gas laws serve very well, and Z may not be needed.
~Iowever, when ~here are mixtures of gases and complex
hydrocarbons, it has been found that Boyle's and Charles'
laws are in error~ Fuel gases tend to be easier to
compress, up to around 2000 psig, than these laws would
suggest. Above this pressure, the trend is reversed. The
exact values are functions of the pressure, ~emperature
and the gas composition. The ideal gas law is extended to
the real conditions by the use of the compressibility
factor Z.
From equation (1), the following relationship
between base and flowing conditions may be derived:
. .
Pf Pa Tb
Vb ~ Vf pv ~2)
Pb Tf
, where:
Vb is base volume
Vf is flowing volume
Pf is flowing pressure, gage
P~ is atmospheric pressure
Pb is base pxessure, absolute
Tb is base temper2ture, absolute
Tf is flowing temperature, absolute
Fpv is supercompressibility factor
,
.
,
.
~3~33~
--3--
The diffic~lt part of calculating base volume in accor-
dance with equation (2) is to determine the
supercompressibility factor Fpv which is a function of the
flowing temperature and pressure, as well as the specific
gravity and the compositi.on of the gas being measured.
One way of determining the supercompressibility
factor Fpv is to utilize the equations and tables as those
set forth in the "Manual for the Determination of
Supercompressibility Factors for Natural Gas", PAR Re-
search Projects WX;l9, published by the American Gas
Associaticn (AGA). The supercompressibility factor Fpv is
complex to calculate, as will be seen below, since it is a
function of five variables: pressure, temperature,
speciic gravity of the gas and the composition of the
gas, in terms of mol ~ of the constituent gases such as
nitrogen and carbon dioxide. The AGA NX-l9 method for
determining the supercompressibility factor Fpv is as
~ollows:
r D + n
Fpv= ~ --F--Dirl~-- (3)
-3.25
- 1 681 M (4)
, where
Mc is mol % of CO2 and
Mn is mol ~ of N.
F = __ 226.29 _ (5)
T (99.15 + 211.9 G - Kt).
, where G is specific gravity
= tadj + 460 ~6)
500
' ' , .
~0IL3~
--4--
" . .
, where tadj = [(t + 460)FT] - 460 and t is gas
temperature, E'
Kp = Mc ~ 0.392 Mn (7)
F = 156.47
P (160.8 - 7.22 G + Kp) (8
i ~ 14 - 7
, 1000 (9)
, where Padj = P Fp and P is gas pressure, psig
m = .0330378 (T) 2 _ 0.0221323(~) 3 + 0.016353 (~) 5 (10)
n = 0.265827(.) 2 + 0.0457697(~ ) 4 -0.133185 (~) 1
B = 3 - mn2
9 m ~2 (12)
b = 9 n - 2 m n 3 - _ E
54 m ~3 2 m ~ ~13)
D = [b + ~+ B3] 1/3 (14)
The value of E is calculated based upon one of a
number o equations, the particular equation being select-
ed ~for a particular range of adjusted pressure and
adjusted temperature. For example, E2 is calculated
according to the following equation for an adjusted
pressure range of 0 to 1300 psia and an adjusted
temperature rate of -40F. to +8 5 F:
E2 ~ 1. - .00075k )2 3[2. - e 20(1.09 , )] _
1.317 (1.09 ~ 4 ( ~ (1.69 _ ~ 2) (15~
U.S. Patent 4,173,891 of Johnson, assigned to
the assignee of this invention, discloses a gas flow
measuring and calculating sys~em for measuring values of
~;~V1332
line pressure, temperature and gas flow and for providing
corrected indications of gas flow at base conditions of
temperature and pressure. The Johnson system employs
calculation means in the form of a microprocessor utiliz-
ing the ideal gas laws and calculates the super-
compressibility factor Fpv in accordance with equations
(3) to (15) as set out above. These calculations comprise
a number of computing steps, each step using an in_tially
approximated value of the supercompressibility factor or
the previously-calculated value. The Johnson system
calculates these supercompressibility factors exactly, but
at the expense of employing a lengthy and time consuming
program to execute.
U.S. Patent 4,390,956 of Cornforth et al.
discloses a system employing the following simplified
expression for the supercompressiblity factor Fpv:
Fpv ~ 1 = (Pf/QTf) (16)
, where
Q = P~
(F ~ 1) Tf (17)
~y considering only values of the supercomprèssibility
factor Fpv for a limited range of flow temperature Tf, a
linear fit of Q may be made as a function of T~. In
particular, two rits or linear equations are required as a
function of Tf permitting Q to be expressed as fcllows:
Q = S + CTf (18)
~3t~:133~
,where C and S may be expressed as linear equations as a
function of the flow pressure Tf. Cornforth et al. states
that the use of their simplified equations (16) to (18),
as expxessed above, produces calculations of the corrected
volume with an accuracy to within plus or minus 0.1~.
Thus, the prior art is left on the horns of a dilemma
having either to program the lengthy equations of the AGA
NX-19 set or to use less complex equations that fit or
approximate the values of supercompressibility with an
appreciable sacrifice in accuracy. As the cost of natural
gas has risen, the commercial necessity of accurately
measuring and calculating gas flow to a set of base con-
ditions, becomes more important.
The prior art, as exemplified by U.S. Patent
4,056,717 of Cornforth et al. and U.S. Patent 4,093,871 of
Plumb et al., have further recognized the problem of
employing a gas flow measuring and correcting circuit at
remote locations, where power lines are not readily
available, thus normally requiring the use of batteries as
the energization source. If batteries are used, the
energized circuitry needs to be designed to minimize power
r~quirements or, otherwise, frequent battery replacement
may be necessary, which would be, at least, inconvenient
where the measuring and correcting circuitry is employed
at remote locations. The Plumb et al. patent '871 dis-
closes a measuring and correction circuit, which includes
a first, relatively high power consuming portion and a
second, relatively low power consuming portion. To
minimize battery drainage, the battery is selectively
connected for limited periods of time to the first por-
tion. The Plumb et al. circuit employs a reed switch
coupled to a gas flow meter to open and close, thus
producing a train of pulses dependent upon the uncorrected
gas fIow. Each of these pulses not only indicates a unit
volume of uncorrected fluid flow, but also serves to apply
~V~3~2
--7--
~`
the battery for a limlted period of time to the first
portionj while the battery is continuously connected to
the second portion.
The use of batteries to energize such measuring
and correcting circuits not only ralses problems of
battery drainage, but also problems of achieving accurate
measurement of temperature and pressure as a result of the
varying voltage levels produced by batteries due to
fluctuations of ambient conditions, namely temperature,
and to extended use. To some degree, complex and expen-
sive voltage regulating circuits could be employed to
ensure the supply of a substantially constant voltage
level to such measuring and correcting circuits; however,
such accurate voltage regulators are expensive and do not
of themselves compensate for voltage fluctuations as would
be applied to the temperature and pressure measuring
elements. Such pressure and temperature elements may be
resistive in nature and, thus, produce fluctuations in
voltage thereacross; thus, such resistive devices output
signals that not only vary as a function of pressure and
temperature, but also as a function of the voltage supply
level.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to
provide a new and improved system for measuring and
corrscti~g measurements of flow volume as a function of
pressure and temperature of the flow gas.
It is a more particular object of this invention
to achieve a calculation of the gas supercompressibility
factor to an accuracy within 0.06%, over applicable
temperature and pressure ranges, of the results obtained
by the AGA NX-l9 method.`
It is a still further object of this invention
to provide a new and improved system for measuring a
~3(:~L33~2
corrected gas flow employing a processor for executing a
simplified, shortened program.
It is a further object of this invention to
provide a new and improved measuring and correcting system
employing a processor executing a simplified, shortened
program avoiding calculations using fractional ex-
ponentiation.
It is stiLl another object of this invention to
provide a new and improved system for measuring and
correcting gas flow that avoids the problems of the prior
art associated with fluc~uating voltage levels as would
otherwise affect the accuracy with which pressure and
temperature are measured.
It is a still further object of this invention
to provide a new and improved method of deriving measure-
ments of variables such as temperature and pressure that
avoids or negates the effects of varying voltage levels.
It is a further object of this invention to
provide a new and improved system employing variable
measuring elements, whose output signals are dependent
upon voltage levels, in a circuit that compensates for
varying levels of voLtage to provide accurate indications
of the measured variables.
In accordance with these and other objects, this
invention is related to a method and apparatus for measur-
ing flowing gas and at least one variable for calculating
gas flow corrected to a base value of that variable.
Illustratively, the measured variahles are temperature and
pressure, and devices are employed for measuring the
temperature Tf and Pf of the gas flowing through a con-
duit, and means in the illustrative form of a flow meter
for measuring the volume Vf of the gas flowing through the
conduit. Calculating means in the illustrative form of a
microprocessor is employed to calculate th~ corrected gas
volume to base conditions in accordance with an expression
.
.
L3~
_9_
~,
including the supercompressibility factor. The super-
compressibility factor is calculated according to an
equation lnvolving only whole number exponentiation and a
selected set of coefficients. The calculation means
selects a particular set of these coefficients in ac-
cordance with lndications of pressure and/or temperature.
A second aspect of this invention involves a
method of taking measurements of variables with element(s)
whose impedance varies as a function of the measured
variable, and of a voltage derived from a fluc~uating
supply source, e.g. a battery. A calibration process is
ùsed, whereby the variable measuring element is exposed to
a first calibration temperature, and ~irst and second
signals are derived from ~he variable measuring element
and a reference element. The variable measuring element
is also exposed to a second, higher calibration variable,
and corresponding third and fourth signals are derived
fr~m the variable measuring element and the reference
element. First and second calibra~ion ratios are taken as
the ratios of the first and second, and third and fourth
signals. Subsequently, the variable measuring element is
exposed tc a present, unknown variable, and corresponding
fifth and sixth signals are similarly derived to provide a
present ratio of the fifth to sixth signals. The present
ratio is interpolated with respect to the ~irst and second
calibration ratios to provide a manifestation or signal
indicative of the rneasured variable, which is substan-
tially free of any fluctuation of the level of voltage
applied thereto.
In a still further aspect of this invention,
t~ere is disclosed a system for minimizing current drain
in a battery energized system, comprising a first volatile
memory energized by the battery at a first, relatively low
power consumption rate, for storing a set of calculation
variables, and a second, non-volatile memory energizable
. --
~3~33Z
-- 10 --
by the battery at a second relatively high power
consumption rate, for storing a back-up set of the
calibrat.ion variables. A control mechanism in the form
of a programmed microprocessor reviews the set of
calculation variables stored in the first, volatile
memory and, if any portion of the set is not correctly
retained, the non-volatile memory is energized and the
back up set of calibration variables is transferred to
the first, volatile memory.
.In accordance with an embodiment of the
invention, a process of measuring a variable employing a
:voltage dependent element whose impedance varies as a
function of the measured variable for providing a
manifestation indiaative of the measured variable,
wherein the process is comprised of the steps of applying
a voltage to the variable measuring element and a
reference element, whose impedance is relatively stable
across at least a range of the variable between first and
second calibration variables; exposing the variable
measuring element to the first calibration variable, and
deriving from the variable measuring element and the
reference element corresponding fi.rst and seaond signals;
exposing the variable measuring element to the second
calibrati.on variable, and deriving from the variable
:measuring element and the reference element corresponding
third and fourth signals; obtaining a first caIibration
ratio of the first to the second signals and a second
calibration ratio of the third to the fourth signals;
exposing the variable measuring element to an unknown
variable and deriving from the variable measuring element
and the reference element corresponding fifth and sixth
signals, a fluctuating voltage being applied commonly to
the variable measuring element and the reference element;
~3~332
- lOa -
: deriving a present ratio of the fifth to sixth signals;
interpolating the present ratio with respect to the first
S and second calibration ratios to provide the
manifestation of the measured variable substantially free
of any fluctuation of the level of the voltage.
In accordance with another embodiment, a
measuring and calculating system for providing with high
accuracy a manifestation of gas volume Vb corrected to
give base conditions of pressure Pb and temperature Tb of
a gas flowing through a conduit, wherein the system is
comprised of first apparatus for measuring the
temperature Tf of the gas flowing through the conduit and
for providing a first signal indicative thereof; second
apparatus for measuring the pressure Tf of the gas
` flowing through the conduit and providing a second signal
indicative thereof; third apparatus for measuring the
volume Vf of the yas flowing through the conduit
providing a third signal indicative thereof; calculating
apparatus for calculating gas volume Vb corrected to the
given base conditions in accordance with the following
equation:
b = (V~) Pf Tb (Fpv)
Pb Tf
where Fpv is the supercompressibility factor; and
supercompressibility calculating apparatus comprising
apparatus for calculating the supercompressibility factor
in accordance with an equation involving only whole
number exponentiation and a selected set of coefficients
from a plurality of coefficient sets, and apparatus for
selecting the set in accordance with the first and second
signals.
In accordance with another embodiment,
apparatus for measuring a variable is comprised of a
variable measuring element having an impedance which
L3~332
- lOb -
varies as a function of the vari.able; a reference element
whose impedance is relatively stable with respect to that
of the variable measuring element across a range of the
variable between first and second calibration variables;
apparatus for applying a voltage to each of the variable
measuring element and the reference element; calibration
apparatus for deriving from the variable measuring
element and the reference element first and second
signals respectively when the variable measuring element
is exposed to the first calibration variable, and third
and fourt~ signals respectively when the variable
measuring device is exposed to the second, calibration
variable, and for obtaining a first calibration ratio of
the first to the second signals and a second calibration
ratio of the third to the fourth signals; and control
apparatus including measuring apparatus for deriving
fi~th and sixth signals respectively from the variable
measuring element and the reference element when the
variable measuring element is exposed to a present
variable to be measured and for obtaining a present ratio
of the fifth to the sixth signals, and interpolation
apparatus for interpolating the present ratio with
respect to the first and second calibration ratios to
provide a manifestation of the variable free of
variations in the level of the voltage.
In accordance with another embodiment, a
battery energized system for measuring a variable and for
performing calculations involving the measured variable
and a set of calculation variables, wherein the system is
comprised of apparatus for measuring the variable and for
providing a signal indicative thereof; first volatile
apparatus energizable by the battery at a first,
relatively low power consumption rate, for storing the
~3C~3;~
-- lOc --
set of calculation variables; second non-volatile
apparatus energizable by the battery at a second,
S relatively high power consumption rate, for storing a
back-up set of the calculation variables; and control
apparatus comprising apparatus coupled to the measuring
apparatus and the first memory apparatus for effecting
the calculations involving the variable signal and the
set of calculation variables, apparatus for reviewing the
set of calculation variables as stored in the first
memory apparatus to provide a first manifestation
indicative that the set of calculation variables is
intact and to provide a second manifestation indicative
15 that at least one of the set of calculation variables has
been lost, and apparatus responsive to the second
manifestation for energizing and transferring from the
second memory apparatus the back-up set of calculation
variables to the first memory apparatus.
BRIEF DESCRIPqlION OF THE DRAWINGS
A detailed description of the preferred
embodiment of this invention is hereafter made with
specific reference to the drawings, in which:
Figure 1 i5 a ~unctional block diagram of the
apparatus or system for measuring and correcting gas flow
as a function of measured temperature and pressure in
accordance with the teachings of this invention;
Figures 2A-2F are detailed schematic diagrams
of the circuit elements of the system as shown in Figure
1;.
Figure 3 is a high level flow diagram of the
program as executed by the microprocessor incorporated in
the system as shown in Figures 1/ 2A and 2B;
Figure 4 is a chart showing the 11 regions
determined in accordance with measurements of temperature
-` ~3~)1332
~ lOd -
and pressure, for selecting one of a corresponding 11
sets of coefficients to be used n the calculation of the
S supercompressibility factor Fpv by the micxoprocessor
incorporated in the system as shown in Figures 1, 2A and
2B; and
Figure 5 is a chart of the 11 sets of
coefficients, one set of which is selected in accordance
with the chart of Figure 4.
~3~L332
DE~AILED DESCRIPTION OF THE PRE~ERRED EMBODIMENT
Referring now to the drawin~s and in particular
to Figure 1, a corrected gas flow measuring system is
indicated by the general numeral 10. In a preferred
embodiment of ~his invention, this system 10 is implement-
ed by a programmed microprocessor 11 for receiving and
processing a series of pulses generated by a gas flow
meter 13 coupled to a gas conduit or line, each meter
pulse indicative of a unit volume of the gas flow through
the line. The receipt of each meter pulse by the pro-
grammed microprocessor 11 provides an uncorrected in-
dication of the gas unit volume of gas flow through the
line for the presen~ measurements of the flow pressure Pf
within the line, as taken by a pressure measuring device
28, and of the flow temperature Tf of the gas within the
line, as measured by a temperature measuring device 30.
As will be explained, the application of each meter pulse
to the microprocessor 11 initiates the calculation in
accordance with a simplified algorithm or equation to
correct the measured gas flow to base conditions of
pressure Pb and temperature Tb. The resultant calcu-
lations are outputted by a general terminal interface 14
to a portable recorder 27. The gas flow meter 13 is
coupled to a general input/output 16, whereby the series
of meter pulses is applied via the input/output 16 and a
turn-on logic circuit 12 to the microprocessor 11.
Resultant calculations of corrected volume for this line
volume increment, are outputted through the general
input/output 16 to a totalizer 54, which accumulates
corrected volume.
The corrected gas flow measuring system 10 is
battory powered so that it may be used in remote loca-
tions, where normal AC power is not available. To reduce
battery drainage, each pulse of the gas flow meter 13 is
applied to a turn-on logic circuit 12 to initiate the
13C1133~
-12-
operation of the microprocessor 11, the sampling or the
outputs of the pressure and ternperature measuring ~evices
28 and 30 and the calculation of corrected yas volume at
base conditions. The samples of flow temperature Tf and
flow pressure Pf are taken by an analog input circuit 21
and are converted from analog to digital values by an
analog-to-digital (A/D) conver~er 19.
Further, the calculation of the
supercompressibility factor Fp~ requires the st~rage and
availability of a set of calculation variables including
specific gravity G, Mc and Mn, indicative of the mol ~'s
of carbon dioxide and nitrogen, i.e., the illustrative
constituents of the natural gas measured by this system
10, and a plurality of sets of coefficients to be entered
into the simplified equation or algorithm used for the
calculation of the supercompressibility factor ~pv In
accordance with the teachings of this invention, there are
a plurality of sets of coefficients, each set correspond-
ing to particular range o~ measured pressure and tempera-
ture. These coe~ficients and caLculation variables are
stored within a low power memory 34, as shown in Figure 2B
and included generally within the block of the micropro-
cessor 11 as shown in Figure 1. A backup set of the
calculation variables is also stored in a high power,
non-volatile memory 18, in case they are lost from the low
power memory 34. Lightning or accidentaL discharge of
static electricity in the vicinity of the corrected gas
flow measuring system 10, can possibly effect data loss
from the low power memory 34. In the course of performing
a calculation, the microprocessor 11 performs an error
check of these constants and coefficients within the low
power memory 34 and, if there is an error, a power switch
24 is closed to energize the high power, non-volatile
memory 18 and to effect a dump of these constants and
coefficients into the low power memory 34. After the
~L3C)~L33:~
-13-
,
memory dump, the power switch 24 is opened, thus reducing
battery drainage. In a similar fashion, a power switch 26
is closed to energize the A/D converter 19 for a relative-
ly brief period sufficient to permit the A/D conversion o.
the sampled line temperature and line pressure measure-
ments. The A/D converter l9 is a relatively high power
consuming device and its brief energization extends the
battery life.
As illustrated in Figure 1, the pressure measur-
ing and temperature measuring devices 28 and 30 ara
coupled to a pressure and temperature input circuit 21,
which in turn is coupled to the A/D converter 19~ Fur-
ther, the system 10 employs a real time clock 38 shown in
Figure 2B, whereby an array or histogram of daily or
hourly measurements of pressure, temperature and gas
volume may be stored in the low power memory 34 and, upon
interrogation, may be read through the terminal interface
14 to the portable terminal 27.
Reerring now to Figures 2A - 2F, there is
shown a detailed schematic o~ the elemen~s comprising the
corrected gas flow and measuring system 10. For the sake
of clarity, many interconnections between the elements of
the system 10 are not shown, but rather indicated by
identi~ying the terminal(s) associated with one or more
elements by the same designation, understanding that the
interconnection couples those elements together. For
example, ~he microprocessor 11, as shown in Figure 2A, is
interconnected by a data bus 32 from its outputs D0 to D7,
to the turn-on logic 12~ and to the low power memory 34,
among other elements. In particular, the data bus 32 is
coupled to a decoder 64 o' the turn-on logic 12b and ls
coupled to the low power memory 34. The low power memory
34 comprises a pair of read-only-memories (ROM) 34a and
34b for storing the program, as will be explained with
respect to Figure 3, and a plurality of sets of
'
:
~30~33Z
coefficients used in the calculation of the supercom-
pressibility factor Fpv, and a random-access-memory (R~M)
34c for providing short term storage of the measured
variables and calculation variables. The non-volatile
memory 18 stores a back-up set of the parameters used for
volume calculation as stored in the RAM 34c. Further, the
microprocessor 11 includes 16 address terminals A0 to A15,
which are coupled by an address bus 36 to each of the
ROM's 34a and 34b, and the RAM 34c of the low power memory
34 and to an address decoder 40, among other elements. In
particular, selected lines of the address bus 36 are
variously connected to selected of a plurality of decoders
66a, 66b and 66c that comprise the address decoder 40.
The outputs of the decoders 66a, 66b and 66c generate a
number of control signals that are applied throughout the
system 10 to control data processing, output signals and
transfer data between the elements of system 10. In a
similar fashion, selected lines of the address bus 36 are
coupled to inputs of a real tlme clock 44, whiah is
coupled to receive the output of an oscillator 28, as
shown in Figure 2A.
As shown in Figure 2C, the microprocessor 11 is
connected via the data bus 32 and a latch 17 to the power
switch 2~, which selectively energizes the high power,
non-volatile memory 18. The memory 18 is also coupled by
the address bus 36 and the data bus 32 to the micropro-
cessor 11. The turn-on logic 12 is illustrated in Figures
2B and 2C as being comprised oE a number of elements
generally grouped within the blocks 12a and 12b.
The gas flow meter 13, as generally shown in
Figure 1 and in de~ail in Figure 2~, comprlses a volume
switch 46, which is closed in response to the passage of a
unit of volume of the gas to be measured. The volume
switch 46 is coupled by the gas meter input 16, which
comprises a 5chmitt Trigger 76, to supply a pulse-like
~ 3V~332
signal VTON to the turn-on logic 12b and in particular, to
the clock input C of the flip-flop 68a, as shown in Figure
2C. In turn, the Q output of the flip-flop 68a goes high,
and a corresponding output ON is generated by a NOR gate
70 and applied to a one-shot multi-vibrator 72 of the turn
on logic 12a. The multi-vibrator 72 actuates an AND gate
74 after a suitable delay to generate and apply a signal
to the interrupt terminal RES of the microprocessor 11, to
initiate the next set of calculations of the supercom-
pressibility factor Fpv and the corrected gas flow. In
effect, each closing of the volume switch 46 initiates
execution of ~he program as will be explained with respect
to Figure 3.
A main oscillator 15 includes a crystal 22 for
generating a 3.6 MHz signal, which i5 divided down and
applied to the microprocessor 11 to time various events
thereinl and an ADCLOCK to the A/D converter 19 to time
its operations. The ON signal is applied to the main
osclllator 15 to initiate its operation.
A write-enable switch 19 is shown in Figure 2C
and, upon closing, permits writing of data into the
non-volatile, high power memory 18. The write-enable
switch 19 is ~hrown by the operator and is a protection
mechanism to prevent undesired writing ir.to the memory 18.
The closing o the swltch 19 sends a signal through the
latch 64 of the turn-on logic 12b to the microprocessor 11
indicating that the switch 19 is closed. In turn, the
microprocessor 11 causes a 02W signal to be generated,
which is applied through switch 19 to the write-enable
terminal WE of the non-volatile, high power memory 18,
thus permitting data to be written therein.
Referring now to Figure 2E, there is shown a
power supply 37 coupled to a battery pack for providing a
voltage, e.g., +5 volts, to the various elements of the
system lO. A negative power supply 39 is provided, as
:'
~ .
-16- ~3~3~2
shown in Figure 2D, to provide a negative voltage to the
analog input circuit 21 and the A/D converter 19, thus
serviny to actuate and energize these circuits. The
battery pack is also connected to a voltage regulating
switch 26, which when actuated by an ~ON signal applied a
regulated, switched voltage 5S to the temperature an~
pressure measuring devices 30 and 28, the analog input
circuit 21, a pair of operational amplifiers 80a and 80b,
and the AID converter 19. As will be explained later, it
is not necessary that the switch 26 be of a relatively
high precision and, thus, a costly piece of equipment, but
may be of conventional design as may be secured at
relatively low cost.
When the microprocessor 11 has completed executins
the program, as shown in Figure 3, it commands via the
data bus 32 the address decoder 66, to cause decoder 66b
to generate a signal VTOF~, which resets the flip-flop 68a
of the turn-on logic 12b, thus causing the QN signal to go
high. As a result, the main oscillator 15 is turned off
and the CLOCK and ADCLOCK signals as applied respectively
to the microprocessor 11 and the A/D converter 19, are
turned off~ Furthex, the -5 OSC signal is likewise
deenergized and removed from the negative power supply 39,
whereby the -S volts is removed from the analog input
circuit 21~ Thus, after the program has been run to take
measurements of flow temperature Tf and flow pressure Pf,
to calculate the supercompressibility factor Fpv and to
calculate the base gas volume Vb, power and clock signals
are removed from the analog input circuit 21, the A/D
converter 19 and the microprocessor 11, whereby these
relatively high power consuming elements are disposed in a
"sleep" mode, until the next unit volume of gas flows
through the gas flow meter 13 and its volume switch 46
closes. The closing of the volume switch 46, as explained
above, initiates the application of power and clock
3~332
signals to ~he analog lnput circuit 21, the A/D converte~
19 and the microprocessor 11 causing them once agair. to
operate ln their "run" mode. In this fashion, the power
drained from the battery is reduced and its life extended.
A battery check circuit 41 monitors the output
; VBAT out of the battery and, if below a preset limit e.g.,
6.4 volts, a turn-off signal PORL is generated. The PORL
signal is applied to the set terminal of the flip-flop 68b
of the turn-on logic 12b, which is set to render high the
ON signal, thus removing the clock signal and disposing
the microprocessor 11 in its "sleep" mode.
As shown in Figure 2D, the analog input circuit
21 takes the form of a multiplexer having four inputs; the
first input to terminals X3 and Y3 is derived from the
temperature measuring device 30, which assumes the form of
a temperature sensitive resistor. The second input to
terminals X2 and Y2 of the circuit 21 is taken from the
pressure measuring device 28, which takes the form of a
strain gauge-type devlce. The third input to terminals Xl
and Yl is connected to ground, whereby an offset voltage
as would be indicative o that residual or error voltage
as added onto the input signals applied to the other three
inputs of ~he analog input circuit 21. A ~ourth input to
terminals X0 and Y0 is coupled to a reference voltage
divider 58 comprising series connected resistors R53 and
R54, which couple the voltage SS to ground; the resistors
R53 and R54 are temperature stable resistors, whose
resistance vary but slightly over at least the extended
ambient temperature range of interest, e.g., -40 to
+160F. The resistances of the resistors R53 and R54 do
vary slightly with temperature, but are deemed temperature
stable relative to the devices 28 and 30, whose impedances
vary greatly with temperature. The analog input circuit
21 is controlled by a pair of signals M0 and Ml to con=rol
:
:
:
, . .
..
. . ~
-18- 13~332
which of the four lnputs is applied to the input circuit's
output X and Y.
The output of the analog input circuit 21 is in
turn connected via the pair of operational amplifiers 80a
and 80b to the inputs INHI and INLO of the A/D converter
19. In a fashion similar to that of the analog input
circuit 21, a reference voltage divider 62 comprised of
series connected reference resistors R58 and R59, is
connected to the inputs RIN+ and RIN- of the A/D converter
19, whereby a comparison of a reference voltage developed
across a reference resistor R59 of the voltage divider 62
may be made with the output of the analog input circuit 21
to provide a digital signal indicative of the analog input
circuit's output. The A/D converter 19 is coupled by the
data bus 32 to the microprocessor 11 and is commanded by
an ADRUN signal from the microprocessor 11 to effect an
A/D conversion; thereafter, the A/D converter 19 applies
an ADSTAT signal to the microprocessor 11, indica~ing the
completion of the commanded A/D conversion. In
particular, the microprocessor 11 executes the program, as
shown in Figure 3, to send a command signal via the data
bus 32 to the latch 17 to first generate the enabling
signal XON, which in turn actuates the switch 26, thereby
energizing the pressure and temperature measuring devices
28 and 30, the analog input circuit 21 and the A/D
converter 19. In particular, the enabling signal XON is
applied via an inverter to the power switch 26, as shown
in Figure 2D. The power switch 26 not only functions as a
switch but as a voltage regulator to apply a regulated
reerence voltage 5S, upon being actuated by the enabling
signal XON, to the devices 28 and 30, the aralog input
circuit 21 and the A/D converter 19. Next, the
microprocessor 11 trar.smits a command signal via the data
bus 32 to the latch 17, to generate the ADRUN signal as
applied to the A/D converter 19, thus actuating the A/D
. --
-19- ~3~L33;~
.
converter 19 to convert the input analog signal to a
corresponding digital signal. Upon completion o~ the A/D
conversion, the ~/D converter 19 generates the ADS~AT
signal, which is applied via the latch 64 and the data bus
32 to inform the microprocessor 11 of the completion of
the A/D conversion. Tha inverted XON signal is also
applied to the I input of the analog input circuit 21,
enabling this circuit~
The details of the terminal interface 14 are
shown in Figure 2E The microprocessor 11 is connected to
a UART 48 via the data bus 32, which in turn supplies a
series of autputs to the portable recorder 27, a~s -hown in
Figure 1. The portable terminal 27 includes a keyboard
and a suitable display, whereby the operator may enter
various constants to be used in the calculations performed
by the program. The terminal 27 is illustratively an
RS-232 compatible terminal.
The general input/output 16 includes a latch 50
coupled to the data bus 32 to receive inpu~ signals, to a
fault indicator 52 and to the mechanical counter or
totalizer 54, whereby a total or accumulated indication of
corrected flow may be provided. The microprocessor 11
transmits a command via the data bus 32 to the latch 50,
which outputs the command signals M0 and Ml, whereby the
analog input circuit 21 is commanded to select one of its
four input3 to be applied to the A/D converter 19. The
fault indicator 52 provides a visual indication to the
operator that the pressure and temperature measuring
devices 28 and 30 are operating out of range, that the
constants stored in the non-volatile, high power memory 18
have been lost, that the battery is low, and other
malfunctions of the system 10.
Figure 3 is a high level flow diagram of the
pxogram s~ored in ~he ROM's 34a and 34b of the low power
memory 34, as shown in Figure 2 B, and executed by the
` -20- ~3~33%
microprocessor 11 for accumulating the pulses of the gas
flow meter 13, for taking samples of flow temperature Tf
and fLow pressure Pf and for calculating an indication or
manifestation indicative of gas flow corrected to base
temperature Tb and pressure Pb. Initially, step 100
responds to the measurement by the gas flow meter 13 of a
unit volume of gas flow and, in particular, to the closing
of the volume switch 46 as shown in Figure 2E to generate
a VTON signal as applied to the turn-on logic 12a, which
in turn applies after an appropriate delay provided by the
one-shot ~ulti-vibrator 72 an RES signal to the micropro-
cessor 11, whereby the following steps 102 to 132 are
executed as will be explained with respect to Figure 3.
The closing of the volume switch 46 initiates the exe-
cution of the program by the microprocessor 11. In that
period between the completion of the execution of the
program and its next execution, the corrected gas flow
measuring system 10 is disposed in its "sleep" mode,
wherein relatively little current is drawn from the
battery. On the alo~ing o~ the vol~me switch 46, the
system 10 is operated in its "run" mode, wherein samples
of flow temperature T and pressure P~ are taken, these
analo~ samples are converted into digital ~orm, and
calculatlons of the supercompressibility factor Fpv and
the base gas volume Vb axe made. In the "run" mode, the
system draws increased power from the battery for that
limited period of time corresponding to the execution of
the program. Upon completing the execution of the pro-
gram, the system returns to its "sleep" mode.
Next, step 102 provides a warm-up period before
step 104 tests the low power memory 34 and, in particular,
the RAM 34c, which stores the constants and coefficients
to be used subsequen~ly in calculations of the super-
compressiblity factor Fpv and base gas flow Vb. Each gas
or mixture of gases to be measured has a particular set Qf
~" -21- ~3~332
constants, which are stored within the RAM 34c. Once a
particular mixture of gas is determined to be measured and
the corresponding set of calculation variables is stored
within the RAM 34c, the values of the stored calculation
variables are summed in an initialization or calibration
procedure and that sum is stored in a known location
within the ~AM 34c and the non-volatile, high power memory
18. In order to ensure the integrity of the calculation
variables as stored within the RAM 34c, step 104 executes
a CHECR SUM subroutine, whereby the coefficients and
constants as stored within the RAM 34c are again summed
and the sum compared with the previous sum as stored in
the known location. The CHECK SUM subroutine searches for
the first in a sequence of locations where the constants
and coe~ficients are stored, and repeatedly addresses each
o the sequence of these locations adding that value to
the previously summed value until the las~ known address
is accessed.
At that point, the current sum is compared with
the previously obtained sum and if there is a match,
indicating the integrity of the RAM 34c, the program
continues wi~h step 112, wherein the flow temperature Tf
and flow pressure Pf may be sampled. Otherwise, as shown
in Figure 3, the program moves to step 106 as shown in
Figure 3, which effects an energization of the relatively
high power, non~voltage memory 18 and, thereafter, a
downloading of a backup set of the calculation variables
from the memory 18 to the RAM 34c. Initially, the power
switch 24 is closed, whereby an energizing voltage is
applied to the non-volatile memory 187 thereafter, the
CHECK SUM subroutine is again run on the contents of the
non-volatile memory 18, i.e., each location, where the
calculation variables are stored, is sequentially summed
until the last storage locatlon within the memory 18 is
accessed; the final sum is then compared with the
, .
I 22 ~3~3~
prede~ermined sum and if there is an agreement, indicating
the integrity of the set of calculation variables stored
within the non-volatile, high power memory 18, the backup
set of calculation variables is downloaded into the RAM
34c. If the sum of the calculation variables within the
non-volatile, high power memory 18 does not agree with the
predetermined sum, the program moves to its standard
turn-off procedure, whereby the system 10 is disposed in
its "sleep" mode. If the CHECK SUM subroutine fails to
indicate that the contents of the memory 18 are intact,
the microprocessor 11 commands via the data bus 32 and the
latch 50 for the fault indicator 52 to provide a visual
manlfestation o~ such failure.
After the backup set of calculation variables
has been downloaded in step 108 from the non-volatile,
high power memory 18 to the RAM 34c, a further CHECK SUM
subroutine is executed on the newly entered contents of
the RAM 34c. If the obtained sum agrees with the pre-
determined sum, step 110 opens the power switch 24,
whereby the non-volatile, high power rnemory 18 is de-
energized, and the program continues with step 112.~
However, if either the sacond CHECK SUM subroutine check
of the non-volatile, high power memory 18 or the CHECK SUM
subroutine check of the RAM 34c after the backup set o~
constants and coef~icients have been downloaded to the RAM
34c fails, then the system 10 goes into its "sleep" mode,
wherein non volatile memory 18, the A/D converter 19, the
analog input circuit 21 and the pressure and temperature
measuring devices 28 and 30 are deenergized, and further
the fault indicator 52 is energized to provide an alarm
manifestation indicative of system shutdown.
Next, step 112 determines whether ~he sample
outputs of the pressure and temperature measuring devices
28 and 30 are to be used and, if so, the program moves to
step 114. If the devices 28 and/or 30 are not to be used,
13~33~
-23-
the program moves to step 122, wherein the supercom-
presslbility factor Fpv is calculated using previously
entered values of flow pressure Pf and/or temperature T~.
One or both of the devices 28 and 30 may have failed and
the programming of step 112 permits the system to still be
used. Further, the system 10 may be employed where the
pressure and/or temperature may he known to be relative
constant values and therefore need not be measured. If
the pressure and temperature measuring devices 28 and 30
are used, step 114 actuates the power switch 26, applying
the switched voltage 5S to the A/D converter 19 and the
analog input circuit 21. The microprocessor 11 applies
its M0 and Ml signals to command the analog input circuit
21 to sequentially sample i~s X3-Y3 input to obtain an in-
dication of the flow temperature T~, its X2-Y2 input to
obtain a value of line pressure P~, its Xl-Yl input to
obtain the offset voltage appearing at ground and,
~inally, its X0-Y0 terminal to sample the reference
voltage appearing across resistor R54 of the reference
voltage di~ider 58. After each sampling, the analog
values as derived from the analog input circuit 21 are
applied to the ~/D converter 19 to derive corresponding,
digital samples or coun~s indicative of flow temperature
Tf , flow pressure P~, the ofset voltage and a tempera-
ture independent reference voltage.
~ he integrity of these samples is double checked
in a number of ways. First the level of the switched
voltage 5S is checked to determine whether i~ is overrange
and of the correct polarity. In addi~ion, the operation
of the A/D converter 19 is checked by measuring the time
of conversion and if the A/D conYersion has taken too
long, there is indication of the faulty operation of the
A/D converter 19. If either the voltage level of the
switched voltage 5S is not within predefined limits or the
A/D conversion takes too long, predetermined values of
-24- ~3~1332
pressure and temperature, e.g., 0 pounds per square inch
and 60F., are used in the subsequent calculations of the
supercompressibility factor Fpv.
Thereaf~er, step 118 opens the power switch 26,
whereby ~he voltage provided by the switch 26 is removed
from the A/D converter 19. By energizing the A/D convert-
er 19 and the analog input circuit 21 for limited periods
of time, the battery drainage is minimized and battery
life extended. The measurements of pressure, temperature
and reference voltage as obtained in step 118 are
processed in step 120 to compare or interpolate these
measurements of temperature and pressure with initially
derived, calibrated values of temperature and pressure
taken at predetermined, calibration conditions. The
interpolation procedure provides accurate measurements of
pressure and temperature that substantially eLiminates any
errors caused by variations in the level of the output
voltage of the switch 26. Such variation or fluctuation
occurs often as temperature varies. In particular, the
outputs of step 120 are digital signals or counts indica-
tive o~ flow pressure P either in lbs./in.~ or kilo
pascals (a metric measurement o pressure) or of flow
temperature T either in degrees centigrade or Fahrenheit.
;~eore the system 10 is run to execute the
program shown in Figure 3, an initial calibration
;procedure is carried out to obtain ratios of a temperature
count to reference voltage count at two predetermined
calibration temperatures. Typically, if the system is to
be used in a temperature range of 32 to 70F, the
calibration temperatures are selected to be 32 and 70F,
and coxresponding count ratios are obtained, as will now
be discussed. First, the temperature transducer 30 is
disposed at the relatively low calibration temperature,
e.g., 32F, which is precisely measured by any of well
known, precision temperature measuring devices. The
~ ~25 ~3~33Z
operator enters the measured temperature through the
portable terminal 27 and the terminal interface 14 to the
microprocessor 11, which then commands the A/D converter
19 to obtain analog slgnals from the temperature measuring
device 30 and the voltage reference divider 58, and to
provide corresponding digital signals or counts; the ratio
of these two counts is stored in the high power, known
volatile memory 18 and the RAM 34c, along with the
operator input value of the corresponding, measured low
calibration temperature. A similar ratio of the output of
the temperature m~asuring device and th~ voltage reference
divider 58 and an operator input value of the
corresponding temperature is obtained at the higher
calibration temperature, e.g., 70F. At the end of the
temperature calibration procedure, there are two pairs of
ratios stored in the high power, non-volatile memory 18
and the RAM 34c. A similar calibration procedure is
carried out for the pressure measuring device 28, whereby
the ratios of the low and high pressure counts to the
reference voltage counts are stored in the memory 18 and
the RAM 34c, along with operator input values of cali-
bration pressure as precisely measured by the operator.
Illustratlvely, the low and high calibration pressures are
0 and 100 lbs./in.~. The calibration temperature and
pressure ratios are thus obtained during the calibration
procedure and are stored in the high power, non-volatile
memory 18 and the R~M 34c for later use in step 120.
~ eturning now to a consideration of the program
shown in Figure 3, step 118 deactivates the switch 26,
thus removing the switched voltage 5S from the analog
input circuit 21 and the A/D convertex 19. Then, step 120
takes the current counts indicative of the measured flow
temperature Tf and pressure Pf, and the reference voltage
level from the A/D conver~er 19 and, firs~, forms ratios
of pressure to reference voltage and temperature to
~ -26- ~3V~332
reference voltage, before interpolating these count ratios
with respect to the calibration ratios or pressure and
temparature obtained in the manner described above. The
details of the step or subroutine 120 to obtain a precise
value of pressure will now be explained. First, a sample
output Pf of the pressure measuring device 28 is obtained
and is converted by the A/D converter 19 to a
corresponding digital value or count. A check is made to
determine whether the A/D converter 19 has operated
improperly, i.e., has the A/D conversion taken too long,
and, if not, the digital output of the A/D converter 19 is
converted into an appropriate numerical form that can be
operated on by the program executed by the microprocessor
11. Then the polarity and magnitude of the pressure count
are checked. If correct, a count corresponding to the
offset voltage is subtracted from each of the pressure
count, the temperature count and the reference count.
Then a ratio of the count corresponding to the pressure
measuxement less voltage offset, to the voltage reference
level is obtained. Then, the difference between the
presently measured pre~sure and the low calibration
pressure is obtained, before the difference between the
high and Low calibration pressures, i.e., the pressure
range, is obtained. Next, the fraction of present
pre~sure ~o the pressuro ranye is obtained as the ratio of
the dif~erence between the current pressure and the low
calibration pressure, to the pressure range~ Next, that
fraction is multiplied times the pressure range and, then,
added to the low calibration pressure to provide an
interpolated, highly accurate measurement of the value of
pressure that is independen~ of the level of the switched
voltage 5S of the switch 26 and is substantially
independent of the differences from one system 10 to the
next. Subroutine 120 also operates on the sampled output
of the temperature measuring device 30 to obtain similar
-27-
133%
ratios of temperature Tf to reference voltage, and then,
subsequently interpolates that present temperature ratio
between two cali~ration ratios obtained at the low and
high cali~ratlon temperatures, to provide a precise value
of temperature that is substantially independent of the
output level of the switched voltage 5S from switch 26.
Next, step 122 calculates the supercom-
pressibility factor Fpv. The AGA NX~l9 procedure for
calculating the supercompressibility factor Fpv i5 a
lengthly series of equations (see equations 3 to 15, set
out above) that use fractional exponen~iation and covers
pressure and temperature ranges of 0 to 5Q00 psig and -40
to +240F, respectively. These equations are used to
generate a table by sectioning the P-T range into eight
smaller regions. Observation of equation (15) above
indicates that fractional exponentiation, i.e., the
calculation of 2.3, requires a lengthy program requiring
extended time for a microprocessor to execute. In accor~
dance with the teachings of this invention, a least
squares curve-fitting routine was developed to fit the
supercompressibility factor Fpv generated by the AGA NX-l9
procedure to provide the following 9-coefficient,
equation:
F = A + ~x ~ Cy2 + Dy + Ey3 + Fxy
+ Gxy2 + Hxy3 + I~2 (16)
, where:
KT = Mc + 1.681 Mn (17)
F = _ 226.29
T 99O15 + 211.9 SG - KT (18)
` -28- ~3~
adj ((~f + 460) FT) - 460 (19)
Kp = Mc ~ .392 Mn (20)
F = _ 156.47 (21)
P 160.8 - 7.22 SG + K2
Padj ~ Pf . Fp (22)
.
y Pad; 123)
x =
Tad~ 70 (24)
, where A to I are the equation coefficients as discussed
above, Kp is a diluent pressure cons~ant, Fp is a pressure
adjusting factor, Padj is ~he adjusted pressure in psig,
K~ is the diluent temperature constant, Ft is the pressure
adjusting factor, Tadj is the adjusted temperature in
degrees Fahrenheit, and SG i.s the specific gravity of the
10wing~gas. The measured values of flowing pressure Pf
and flowing temperature Tf are inserted into equations
(19) and t22), and the subroutine 122 effects a series of
calculations starting irst with equation (17) and con-
tinulng in sequence to equatio~ 4), until the values of
x and y are derived and inserted into equation (1~). The
values of mol ~ o carbon dioxide Mc and mole % of
nitrogen Mn, and specific gravity SG are stored in the
non-volatile memory 18 and the RAM 34c and are entered
into the equations (17j, ~18), (20) and ~21) as noted
above.
One equation could not fit the entire pressure
and temperature range ~or the calculations of the super-
compressibility factor Fp~. As a result, the pressure and
temperature range was divided into 11 regions, as shown in
Figure 4, each of the 11 regions defining a set of A to I
..
13~L3;3;2
-29-
" ~
coefficients as shown in Figure 5. Referring to Figure 4,
region 1 includes values of adjusted temperature Tadj of
116 to 240F., and adjusted pressure in the range of 0 to
1500 psig. If the values of Tadj and Padj as calculated
by equations (19) and (2Z), respectively, fall within
those ranges, the coefficients A to I of region 1 are
accessed as stored in the ROM's 34a and 34b and that set
is entered into equation (16), and the supercompres-
sibili~y factor Fpv is calculated. In particular, the
subroutine 122 compares the calculated values of Tadj and
Padj with a sequence of sets of Iimits, whereby through a
process of elimination, the corresponding one region is
determined. For example, if the value of adjusted temper-
ature Tadj is greater than 116, the first region is
determined and that set of coefficients is taken from the
table reproduced above and inserted into the above
equation (16). However, if the adjusted pressure Tadj is
less than 116F. and the adjusted pressure Padj is less
than 75 psig, region 11 is determined. In a similar
fashion, each of the remaining regions is determined by
~his logical process of elimination.
The sets of coefficients A to I for expression
(16) and th~ constant terms o~ the expressions (17 to 24)
are stored in the ROMs 34a and 34b. The particular values
of base temperature Tb, base pressure Pb, the calibration
temperatures and pressures, and the mol %'s of the gas
constituents for a particular situation, are entered by
the portable terminal 27 to be stored in the RAM 34c. The
corresponding calibration ratios are calculated by the
microprocessor 11 and then stored in the RAM 34c~ As
explained above, a back-up set of these calculation
variables is also stored in the non-volatile memory 18.
In order to check the accuracy of the values of
the supercompressibility factor Fpv as obtained from the
least squares fi~ted expression 16, reproduced above, with
-30- ~3~332
those values obtained from the AGA NX-l9 procedure, a
computer program was written to effect calculations of
values by both procedures, at every O.S psig and 0.~F.
over a range of adjusted temperature of -30 to 240F. and
adjusted pressure of 0 to lS00 psig. The maximum error
between these two procedures of 0.06%.
Next, step 124 inserts the value of the super-
compressibility factor Fpv calculated in step 122,
into the following equation to calculate base volume Vb
from line volume Vf corrected for conditions of base
pressure Pb and temperature Tb:
~b Vf Pf Tb FPV 2 (25)
Pb f
The number of pulses from the gas flow meter 13 is ac-
cumulated to provide an indication of measured uncorrected
gas volume V~ In order to distribute and sell natural
gas, it is necessary to agree upon the base conditions
including base pressure Pb and base temperature Tb.
Further, the line and base gas flow rates are calculated
using the calculations o~ measured and base volume alony
with time rom the real time clock 44.
~ ext, step 128 stores measured values o~ pres-
sure, temperature and volume as a function of time into a
volume survey memory as stored in RAM 34c. The micropro-
cessor 11 responds to the indication of real time as
provided by the real time clock 44, ~o periodically store
measurements of pressure, temperature and volume for each
regular period of time, e.g., daily or hourly. There-
after, the microprocessor 11 transmits a command via the
data bus 32 to increment the mechanical counter or
totalizer 54 and an external totalizer as coupled to the
general input/output 16, as shown in Figure 2F. There-
after, step 132 turns off the system 10, deenergizing ~he
, .
~3~33Z
-31-
main oscillator 15, thus removing the CLOCK and ADCLOCK
signals from and disposing the microprocessor 11 into a
low power state, to wait for the next pulse received from
the gas flow meter 13, i.e., the system 10 is returned to
its "sleep" mode. In this fashion, the system 10 is only
disposed briefly in its "run" mode, wherein samples of
pressure and temperature are taken and calculations of the
supercompressibility factor Fpv and corrected gas flow are
calculated, to minimize battery drainage and increace
battery life.
In considering this invention, it should be
remembered that the presen~ disclosure is illustrative
8~1y and the scope of the invention should be determined
solely by the appended claims.
