Method for performing temperature compensation of maximum sensor current and test tone amplitude during meter verification
A method of determining optimal resistance and compensating for temperature variations in determining a test tone is presented. The optimal resistance in a drive circuit amplifier and drive coil and using the optimal resistance to improve the accuracy of a test tone used in the calibration of a flow meter is presented. The optimal resistance is calculated using a linear extrapolation of the resistance change of the circuit with respect to temperature. The optimal resistance is then used to calculate the proper maximum sensor current (MSC) value using an equation derived from Ohm's law, and from the MSC a test tone level is calculated.
1 . A method for determining and employing a test tone level during a meter verification of a vibrating flow meter, the method comprising:
calculating an electrical resistance of a coil wire of a driver, the coil wire receiving a plurality of drive currents to test an integrity of flow tubes of the vibrating flow meter;
calculating a maximum sensor current (MSC) using the electrical resistance, the maximum sensor current (MSC) being the maximum current a drive amplifier can deliver to the coil wire;
measuring the plurality of drive currents during an appropriate period of time;
averaging the plurality of drive currents;
calculating a buffer value using the average of the plurality of drive currents;
calculating the test tone level of a test tone on either side of a drive frequency of the vibrating flow tubes using the maximum sensor current (MSC) and the buffer value; and
operating the vibrating flow meter at the test tone level calculated during meter verification, the test tone level being within a range that avoids voltage clipping, thereby reducing stiffness uncertainty in the vibrating flow meter.
2 . The method of claim 1 , wherein calculating an electrical resistance further comprises using a curve-fit of test data.
3 . The method of claim 1 , wherein calculating an electrical resistance further comprises using the known resistance change of the coil wire with temperature.
4 . The method of claim 1 , wherein calculating the maximum sensor current (MSC) comprises using the formula:
MSC
=
[
V
max
-
(
V
emf
x
rf
)
R
T
]
×
1000.
where:
V max is the maximum voltage supplied by an amplifier;
V emf is a back electro-motive force of the driver;
x rf is a reduction factor for a drive set-point used during meter verification;
R T is an electrical resistance.
5 . The method of claim 1 , wherein the buffer value is calculated using the formula:
Buffer
Value
=
x
ptl
(
MSC
-
i
Drive
)
;
where:
i Drive is a drive current for the driver; and
x ptl is a reduction factor for drive set-point used during meter verification.
6 . The method of claim 1 , wherein the buffer value is calculated using the formula:
Buffer
Value
=
x
ndev
σ
;
where:
x ndev is a factor of the standard deviation of the drive current; and
σ is a standard deviation.
7 . The method of claim 1 , wherein the test tone level is calculated by the formula:
Test
Tone
Level
=
MSC
-
i
Drive
-
Buffer
Value
;
where:
i Drive is a drive current for the driver.
8 . The method of claim 1 , wherein if the test tone level is negative, then the meter verification will abort due to unstable process conditions.
9 . The method of claim 1 , wherein if the test tone level is positive, then the recently calculated maximum sensor current (MSC) and tone level values are written into the appropriate registers and meter verification is initiated.
10 . A method of performing temperature compensation of a test tone amplitude during meter verification in a vibrating flow meter with a test tone level, comprising:
calculating an electrical resistance using one of a curve-fit of test data and the known resistance change of a coil wire of a driver with temperature, the coil wire receiving a plurality of drive currents to test an integrity of a flow tube of the vibrating flow meter;
calculating a maximum sensor current (MSC) using the electrical resistance, maximum voltage and an EMF voltage, the maximum sensor current (MSC) being the maximum current a drive amplifier can deliver to the coil wire;
measuring the plurality of drive currents for an appropriate period of time;
averaging the plurality of drive currents;
calculating a buffer value using the average of the drive currents;
calculating the test tone level of a test tone on either side of a drive frequency of the vibrating flow tubes using the maximum sensor current (MSC) and the buffer value; and
operating the vibrating flow meter at the test tone level calculated during meter verification, the test tone level being within a range that avoids voltage clipping, thereby reducing stiffness uncertainty in the vibrating flow meter.
11 . The method of claim 10 , wherein calculating a test tone level using the maximum sensor current (MSC), the buffer value, and the formula:
Test
Tone
Level
=
MSC
-
i
Drive
-
Buffer
Value
;
where:
i Drive is a drive current for the driver.
12 . The method of claim 10 , wherein the maximum sensor current (MSC) is calculated using the formula:
MSC
=
[
V
max
-
(
V
emf
x
rf
)
R
T
]
×
1000.
where:
V max is the maximum voltage supplied by an amplifier;
V emf is the back electro-motive force of the driver;
R T is a drive circuit resistance of a drive circuit including the driver; and
x rf is a reduction factor for drive set-point used during meter verification.
13 . The method of claim 10 , wherein the buffer value is calculated using the formula:
Buffer
Value
=
x
ptl
(
MSC
-
i
Drive
)
;
where:
i Drive is a drive current for the driver; and
x ptl is a reduction factor for drive set-point used during meter verification.
14 . The method of claim 10 , wherein the buffer value is calculated using the formula:
Buffer
Value
=
x
ndev
σ
;
where:
x ndev is a factor of the standard deviation of the drive current; and
σ is a standard deviation.
15 . The method of claim 10 , wherein if the test tone level is negative, then the meter verification will abort due to unstable process conditions.
16 . The method of claim 10 , wherein if the test tone level is positive, then the recently calculated maximum sensor current (MSC) and tone level values are written into the appropriate computer operable memory registers and meter verification is initiated.
17 . A meter electronics for dynamically optimizing maximum sensor current in a vibrating flow meter with a test tone level, comprising:
an interface for receiving a plurality of temperature values and corresponding electrical resistance values, sensor current, maximum voltage, EMF voltage and drive currents;
a storage system for storing and retrieving the plurality of temperature values and the corresponding electrical resistance values, sensor current, maximum voltage, EMF voltage and drive currents; and
a processing system for measuring a plurality of drive currents to test an integrity of flow tubes of the vibrating flow meter for an appropriate period of time and for performing calculations using the interface, the calculation comprising:
extrapolation calculations using the plurality of temperature values and the corresponding electrical resistance values and produce an optimal resistance;
maximum sensor current calculations using the electrical resistance, a maximum voltage and an EMF voltage computed;
averaging the plurality of drive currents;
buffer value calculations using the average of the drive currents in the processing system; and
calculation of the test tone level of a test tone on either side of a drive frequency of the vibrating flow tubes using the maximum sensor current (MSC),
wherein the processing system is configured to operate the vibrating flow meter at the test tone level calculated during meter verification, the test tone level being within a range that avoids voltage clipping, thereby reducing stiffness uncertainty in the vibrating flow meter.
18 . The apparatus of claim 17 , wherein the buffer value is calculated using one of:
Buffer
Value
=
x
ptl
(
MSC
-
i
Drive
)
and
Buffer
Value
=
x
ndev
σ
;
where:
i Drive is a drive current for the driver;
x ptl is a reduction factor for drive set-point used during meter verification;
x ndev is a factor of the standard deviation of the drive current; and
σ is a standard deviation.
19 . The meter electronics of claim 17 , wherein if the test tone level is negative, then the meter verification will abort due to unstable process conditions and if the test tone level is positive, then the recently calculated maximum sensor current and tone level values are written into the appropriate computer operable memory registers and meter verification is initiated.