Compensating for frequency change in flowmeters
View Patent ↗Motion is induced in a conduit that contains a fluid. The motion is induced such that the conduit oscillates in a first mode of vibration and a second mode of vibration. The first mode of vibration has a corresponding first frequency of vibration and the second mode of vibration has a corresponding second frequency of vibration. At least one of the first frequency of vibration or the second frequency of vibration is determined. A phase difference between the motion of the conduit at a first point of the conduit and the motion of the conduit at a second point of the conduit is determined. A quantity based on the phase difference and the determined frequency is determined. The quantity includes a ratio between the first frequency during a zero-flow condition and the second frequency during the zero-flow condition. A property of the fluid is determined based on the quantity.
1. A method comprising:
inducing motion in a flowtube containing a fluid such that the flowtube oscillates in a first mode of vibration and a second mode of vibration, the first mode of vibration having a corresponding frequency of vibration and the second mode of vibration having a corresponding frequency of vibration;
determining the first frequency of vibration;
determining the second frequency of vibration;
determining a property of said fluid in the flowtube based on the determined first and second frequencies, wherein determining said property comprises compensating for a mass flow rate-induced variation of at least one of the first frequency and second frequency.
2. A method as set forth in claim 1 wherein the first mode of vibration is a Coriolis mode and the second mode of vibration is a driven mode.
3. A method as set forth in claim 2 wherein the determining comprises compensating for mass flow rate-induced variation in the frequency of the Coriolis mode.
4. A method as set forth in claim 2 wherein the determining comprises compensating for mass flow rate-induced variation in the frequency of the driven mode.
5. A method as set forth in claim 2 wherein the determining comprises compensating for mass flow rate-induced variation in the frequency of the Coriolis mode and compensating for mass flow rate-induced variation in the frequency of the driven mode.
6. A method as set forth in claim 1 wherein the property is a mass flow rate of said fluid through the flowtube.
7. A method as set forth in claim 6 wherein compensating for mass flow rate-induced variation of at least one of the first frequency and second frequency comprises multiplying a non-fully compensated mass flow measurement by the following:
(
1
+
k
m
tan
2
(
φ
2
)
)
wherein k m is a coefficient obtained from a massflow calibration procedure and φ is a phase difference between motion of two different locations on the flowtube.
8. A method as set forth in claim 1 wherein the non-fully compensated mass flow rate is compensated to account for the influence temperature on the mass flow measurement.
9. A method as set forth in claim 1 wherein determining said property further comprises compensating for a pressure of said fluid in the flowtube.
10. A Coriolis flowmeter comprising:
a vibratable flowtube for containing a fluid;
a driver configured to impart motion to the conduit such that the conduit oscillates in a first mode of vibration having a first frequency of vibration and a second mode of vibration having a second frequency of vibration;
a sensor configured to detect motion of the conduit and generate a sensor signal;
a controller configured to:
receive the sensor signal;
determine the first and second frequencies of vibration; and
determine a property of the fluid in the flowtube based on the determined first and second frequencies, wherein determining said property comprises compensating for a mass flow rate-induced variation of at least one of the first frequency and second frequency.
11. A flowmeter as set forth in claim 10 wherein the first mode of vibration is a Coriolis mode and the second mode of vibration is a driven mode.
12. A flowmeter as set forth in claim 11 wherein the controller is configured to compensate for mass flow rate-induced variation in the frequency of the Coriolis mode when determining said property.
13. A flowmeter as set forth in claim 11 wherein the controller is configured to compensate for mass flow rate-induced variation in the frequency of the driven mode when determining said property.
14. A flowmeter as set forth in claim 11 wherein the controller is configured to compensate for mass flow rate-induced variation in the frequency of the Coriolis mode and compensate for mass flow rate-induced variation in the frequency of the driven mode when determining said property.
15. A flowmeter as set forth in claim 14 wherein the property is a mass flow rate of said fluid through the flowtube.
16. A flowmeter as set forth in claim 15 wherein the controller is configured to compensate for mass flow rate-induced variation of at least one of the first frequency and second frequency by multiplying a non-fully compensated mass flow measurement by the following:
(
1
+
k
m
tan
2
(
φ
2
)
)
wherein k m is a coefficient obtained from a massflow calibration procedure and φ is a phase difference between motion of two different locations on the flowtube.
17. A flowmeter as set forth in claim 16 wherein the controller is configured to compensate a raw mass flow measurement to account for influence temperature on the mass flow measurement to produce said non-fully compensated mass flow measurement.
18. A flowmeter as set forth in claim 10 wherein the controller is configured to compensate for a pressure of said fluid in the flowtube when determining said property.