HK1156101B - Method for generating a diagnostic from a deviation of a flow meter parameter - Google Patents

Description

Method for diagnosing based on deviations of flow meter parameters

Technical Field

The present invention relates to flow meters, and more particularly to methods for diagnosing with deviations in flow meter parameters.

Background

It is known to use coriolis effect mass flowmeters to measure mass flow and other information for materials flowing through conduits inside the flowmeter. Exemplary coriolis flowmeters are disclosed in U.S. patent 4109524, U.S. patent 4491025, and re.31450, all issued to j.e.smith et al. These flow meters have one or more conduits in a straight or curved configuration. Each conduit structure in a coriolis mass flowmeter has a set of natural vibration modes, which may be simple bending, torsional, or coupled types. Each conduit may be driven to oscillate at resonance in one of these natural modes. Material flowing into the meter from an associated conduit on the inlet side of the meter is directed through one or more conduits and then exits the meter through the outlet side of the meter. The natural vibration modes of a vibrating material filled system are determined in part by the total mass of the conduit and the material flowing within the conduit.

In the absence of flow through the flowmeter, all locations along the conduit will oscillate due to the applied actuator force having the same phase or an initial small fixed phase deviation that can be corrected. As material begins to flow through the flowmeter, coriolis forces cause each location along the conduit to have a different phase. For example, the phase at the inlet end of the flow meter lags the driver, while the phase at the outlet leads the driver. Pickoff sensors on one or more of the conduits generate sinusoidal signals indicative of the motion of the one or more conduits. The signal outputs from the pickoff sensors are processed to determine the phase difference between the pickoff sensors. The phase difference between the two or more pickoff sensors is proportional to the mass flow rate of material flowing through the one or more conduits.

Coriolis mass flowmeters have enjoyed great success in a wide range of industrial applications. However, like many other flow meters, coriolis flow meters suffer from the problem of deposit buildup left behind by the process fluid. This accumulation is commonly referred to in the art as a "coating". Depending on the characteristics of the process fluid, the fluid coating may or may not affect the performance and accuracy of the flow meter. While the coating typically does not affect the stability of the meter nor cause measurement errors in the flow, it can affect other aspects of the meter characteristics. For example, the coating layer may have a different density than the process fluid. This may adversely affect the density readings obtained from the flow meter. For some process fluids, the coating may build up to a certain thickness within the meter and then break down into small fragments. These small debris may affect other process components connected to the flow meter. In extreme cases, the coating may build up sufficiently that the meter becomes clogged and requires a complete shutdown or, in some cases, a complete replacement of the meter.

Other problems may result from coating, clogging, unstable process fluid components, temperature changes of the process fluid, and the like. For example, in the paint industry, the same flow meter may be used for multiple paint colors. Thus, even if the coating does not cause meter reading errors, the coating can negatively impact the final product.

Because of the above-mentioned problems, as well as other problems caused by coatings, it is desirable to perform diagnostics in the presence of meter coatings. The diagnostic methods for detecting the coating of a flow meter in the prior art have many problems. First, many prior art methods are limited to coating detection in the active portion of the flow tube, i.e., the vibrating portion. Other limitations in the prior art stem from the fact that the coating density is substantially similar to the process fluid. In this case, the density-based coating layer detection cannot be performed. Accordingly, there is a need in the art for a coating layer detection method that overcomes the above limitations. Moreover, in applications where it is known that process fluid can coat the flow meter, it is desirable to be able to detect when the flow meter has been completely coated during cleaning of the flow meter.

Disclosure of Invention

According to one aspect of the invention, a method for detecting a deviation in a flow meter parameter includes the steps of:

measuring a differential pressure across at least a portion of the flow meter;

comparing the measured differential pressure to an expected differential pressure based on the measured flow rate; and

if the difference between the measured differential pressure and the expected differential pressure exceeds a threshold limit, a deviation in a flow meter parameter is detected.

Preferably, the method further comprises the step of measuring the differential pressure across the flow meter.

Preferably, the expected pressure differential is based on a known fixed fluid viscosity.

Preferably, the expected pressure difference is obtained by a pressure difference-flow curve prepared in advance.

Preferably, the method further comprises the step of storing the expected differential pressure within meter electronics.

Preferably, the threshold limit comprises a predetermined value.

Preferably, the flow meter comprises a coriolis flow meter.

Preferably, the deviation in the flow meter parameter is indicative of a coating within the flow meter.

In accordance with another aspect of the invention, a method for detecting a deviation in a flow meter parameter includes the steps of:

measuring a differential pressure across the flow meter;

calculating an expected fluid flow based on the pressure differential; and

the measured fluid flow rate is compared to the calculated fluid flow rate and a deviation in a flowmeter parameter is detected if a difference between the measured fluid flow rate and the calculated fluid flow rate exceeds a threshold limit.

Preferably, the step of calculating the expected fluid flow rate includes the step of characterizing the flow meter as an orifice plate flow meter.

Preferably, the method further comprises the step of determining a flow coefficient of the flow meter.

Preferably, the method further comprises the step of storing the expected fluid flow within meter electronics.

Preferably, the threshold limit comprises a predetermined value.

Preferably, the flow meter comprises a coriolis flow meter.

Preferably, the deviation in the flow meter parameter is indicative of a coating within the flow meter.

In accordance with another aspect of the invention, a method for detecting a deviation in a flow meter parameter includes the steps of:

measuring a differential pressure across at least a portion of the flow meter;

calculating a friction coefficient based on the measured flow rate and the measured differential pressure; and

the calculated coefficient of friction is compared to an expected coefficient of friction based on the measured flow and a deviation in the flow meter parameter is detected if the difference between the calculated coefficient of friction and the expected coefficient of friction exceeds a threshold limit.

Preferably, the step of calculating the coefficient of friction comprises using the formula:

preferably, the expected coefficient of friction is obtained from previous measurements.

Preferably, the differential pressure is measured across the entire flow meter.

Preferably, the expected friction coefficient is calculated based on the reynolds number used to measure the flow rate.

Preferably, the method further comprises the step of storing the expected coefficient of friction within meter electronics.

Preferably, the flow meter comprises a coriolis flow meter.

Preferably, the deviation in the flow meter parameter is indicative of a coating within the flow meter.

In accordance with another aspect of the invention, a method for detecting a deviation in a flow meter parameter includes the steps of:

measuring flow tube temperature at a plurality of locations; and

a temperature gradient is calculated based on the measured temperature, and a deviation in a flow meter parameter is detected if the calculated temperature gradient exceeds a temperature gradient threshold.

Preferably, the step of calculating a temperature gradient comprises calculating a temperature gradient from an inlet of the flow meter to an outlet of the flow meter.

Preferably, the step of calculating a temperature gradient comprises calculating a temperature gradient from the first flow tube to the second flow tube.

Preferably, the method further comprises the step of detecting a coating within the flow meter if the calculated temperature gradient changes beyond a threshold limit.

Preferably, the temperature gradient threshold is predetermined.

Preferably, the flow meter comprises a coriolis flow meter.

Preferably, the deviation in the flow meter parameter is indicative of a coating within the flow meter.

Drawings

FIG. 1 shows a flow meter according to an embodiment of the invention.

FIG. 2 shows a partial cross-sectional view of a flow meter according to an embodiment of the invention.

FIG. 3 shows a cross-sectional view of a flow tube with a coating formed inside the flow tube.

FIG. 4 shows a block diagram of a flow meter according to an embodiment of the invention.

Detailed Description

Fig. 1-4 and the following description present 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 matters have been simplified or omitted. From these examples, a person skilled in the art will appreciate variations 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. Accordingly, the present invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 shows a flow meter 100 according to an embodiment of the invention. According to one embodiment of the invention, the flow meter 100 comprises a coriolis flow meter. However, the present invention is not limited to applications incorporating coriolis flowmeters, but rather it should be understood that the present invention may be used with other types of flowmeters. Flowmeter 100 includes a sleeve 103 and a manifold 107 enclosing the lower portions of flow tubes 101, 102, flow tubes 101, 102 being internally connected at their left ends to flange 104 by neck 108 and at their right ends to flange 105 by neck 120. Also shown in fig. 1 are the outlet 106 of the flange 105, the left pickoff LPO, the right pickoff RPO and the driver D. The right hand pick-off RPO is shown in partial detail and comprises a magnet structure 115 and a coil structure 116. The element 114 at the bottom of the manifold sleeve 103 is an opening for receiving wiring (not shown) from meter electronics (not shown) that extends internally to the driver D and the pickoffs LPO and RPO. The flow meter 100 is adapted to be connected in use to a pipeline or the like by flanges 104 and 105.

Fig. 2 shows a cross-sectional view of the flow meter 100. This view removes the front of the manifold sleeve 103 so that the internal components of the manifold sleeve can be shown. The components shown in fig. 2 but not shown in fig. 1 include outer end brace bars 201 and 204, inner brace bars 202 and 203, right end flow tube exhaust ports 205 and 212, flow tubes 101 and 102, and curved flow tube portions 214, 215, 216 and 217. In use, the flow tubes 101 and 102 vibrate about their bending axes W and W'. The outer end struts 201 and 204 and the inner struts 202 and 203 help to locate the bending axes W and W'.

According to the embodiment shown in fig. 2, the flow meter 100 includes a pressure sensor 230. According to an embodiment of the present invention, the pressure sensor 230 comprises a differential pressure sensor. Pressure sensor 230 is connected to flow meter 100 via pressure taps 231 and 232 to take pressure readings. Taps 231 and 232 allow pressure sensor 230 to continuously monitor the material pressure drop across flow meter 100. It should be noted that while taps 231, 232 may be connected to flow meter 100 at any desired location, according to the embodiment shown in fig. 2, taps 231, 232 are connected at flanges 104, 105, respectively. Advantageously, the pressure sensor 230 can acquire differential pressure measurements for the entire flow meter 100, not just the active portion of the flow meter 100. In other embodiments, such as shown below in fig. 4, pressure taps 231, 232 may be provided in a line connecting the flow meters. The differential pressure measurement is described further below.

Fig. 2 also shows a plurality of temperature measuring devices 240. According to the embodiment shown in fig. 2, the temperature measuring device comprises an RTD sensor. It should be understood that other temperature measuring devices may be used and the invention should not be limited to RTD sensors. Similarly, although six RTD sensors 240 are shown, it should be understood that any number of RTD sensors may be used and still fall within the scope of the present invention.

Pressure sensor 230 and RTD sensor 240 are shown connected to meter electronics 20 by a Δ P signal and an RTD signal in the leads, respectively. As illustrated in fig. 1, the left pickoff LPO and right pickoff RPO and driver D shown in fig. 1 are also connected to meter electronics 20. The meter electronics 20 provides information of the mass flow and the accumulated mass flow. In addition, mass flow information, density, temperature, pressure, and other flow characteristics may be sent to downstream process control and/or measurement devices via leads 26. Meter electronics 20 may also include a user interface that allows a user to input information such as fluid viscosity and other known values. According to an embodiment of the present invention, meter electronics 20 includes a hard drive capable of storing known information or calculated information for future recall. These stored information will be further described below.

Fig. 3 shows a cross-sectional view of a portion of flow tube 101 with a coating 310. Although only a portion of the flow tube 101 is shown, it should be understood that the coating 310 can also be formed on the interior of the flow tube 102 and other components of the flow meter 100 exposed to the process fluid. As the process fluid flows through flow tube 101, deposits in the process fluid may remain. Over time, these deposits form coating layer 310. The coating 310 may cover the entire inner diameter of the flow tube 101 as shown, or alternatively the coating 310 may cover the entire inner diameter of the flow tube 101While other areas are free of coating 310. Moreover, although the coating 310 may not be as thick as shown in FIG. 3 in a particular application, the coating 310 may become thick enough to severely clog the flow meter 100 in some processes. Even though coating 310 is not thick enough to block flow meter 100, it reduces the cross-sectional area available for process fluid to flow through. For example, flow tube 101 can have an inner diameter D₁(ii) a However, in the presence of coating 310, the actual allowable diameter through which process fluid can flow is reduced to D₂。

Because the coating 310 may have a negative impact on the performance of the flow meter 100, the present invention provides an alternative method for determining the presence of the coating 310 within the flow meter 100. Moreover, while the prior art method is limited to detecting the coating 310 only in the active portion, i.e., the vibrating portion of the flow tubes 101, 102, the present invention is capable of detecting the coating 310 in all portions of the flow meter 100 including the manifolds 104, 105. It should be understood, however, that the present invention is not limited to detecting coating layers and that the present invention also provides an alternative method for detecting deviations in flow meter parameters. The flow meter parameter may be any measurement obtained by the flow meter. In certain embodiments, the deviation in the flow meter parameter is caused by the coating 310. However, other factors can also cause a deviation in the flow meter measurements, such as clogging of the flow meter, unstable temperatures, unstable process fluid mixtures, bubbles formed within the flow meter, and the like. Thus, in accordance with an embodiment of the present invention, the method provided below detects deviations in flow meter parameters, which can provide diagnostics needed for further analysis.

The deviation in the flow meter parameter can be detected according to one of the methods described below. According to an embodiment of the present invention, the deviation in the flow meter parameter is detected directly from the differential pressure measurement obtained by the pressure sensor 230. When the absence of the coating 310 within the flow meter 100 is known at the factory or alternatively in the field, for example, a portion of the profile of the differential pressure and mass flow rate across the flow meter 100 can be prepared for a known fixed fluid viscosity. From this curve, the expected pressure differential for a given flow rate can be determined. The pressure sensor 230 may then be utilized to continuously monitor the actual differential pressure and compare it to the expected differential pressure for measuring flow. If the actual pressure differential is within the threshold limits of the expected pressure differential, the meter electronics 20 may send a signal that no deviation in the parameter has been detected, or alternatively, that a slight deviation in the flow meter parameter has been detected. On the other hand, if the measured differential pressure falls outside the threshold limit, meter electronics 20 may flag the measurement for further analysis. According to one embodiment of the invention, the threshold limit comprises a predetermined value. According to another embodiment of the invention, the threshold limit is set by the user or operator.

Although this method provides satisfactory results, there are still many limitations to using this direct comparison method. First, the user must know the viscosity of the process fluid. In addition, the viscosity must remain substantially constant. This is because the expected pressure differential, as well as the actual pressure differential, obtained from previous measurements, are dependent on the viscosity of the process fluid. Due to this limitation, a change in the pressure difference may be indicative of other conditions than coating, giving a false coating indication.

Another method for detecting deviations in flow meter parameters is to characterize the flow meter 100 as an orifice plate flow meter. Orifice plate flow meters are well known and are used to measure fluid flow from differential pressure. Orifice plate flow meters have certain advantages over other flow meters that measure fluid flow based on differential pressure because they take up much less space. Orifice plate flow meters operate by providing a plate with an orifice in the tube, where the orifice is smaller than the diameter of the tube. This reduction in cross-sectional area increases the fluid flow by a velocity head at the expense of a pressure head. The pressure difference can be measured by pressure tapping pipes in front of the plate and behind the plate. Using the measured differential pressure, the fluid velocity can be calculated according to, for example, the following equation:

wherein:

V₀speed of passing through a hole

Beta is the ratio of the aperture to the diameter of the pipe

Δ P ═ pressure difference across the orifice

Rho ═ fluid density

C₀Hole flow coefficient

It should be understood that other equations for calculating fluid flow using bore diameter are known, and equation (1) is merely an example and should not limit the scope of the present invention. In general, except for the orifice flow coefficient C₀In addition, all unknowns can be measured or known, the pore flow coefficient C₀Are typically determined experimentally and will vary from flow meter to flow meter. It generally depends on β and the reynolds number, which is a dimensionless number and is defined as follows:

wherein:

d-diameter

Fluid viscosity

Rho ═ fluid density

v-kinematic fluid viscosity

Orifice flow coefficient C for multiple orifice plate flowmeters₀Remains nearly constant and is independent of reynolds numbers greater than about 30000. Like the orifice plate flow meter, the flow meter 100 experiences a measurable pressure drop and can be considered to be the orifice plate flow meter shown in fig. 4.

Fig. 4 shows the flow meter 100 positioned within a conduit 410 and connected to meter electronics 20. In fig. 4, the internal structure of the flow meter 100 is not shown, but the flow meter 100 is shown as a simple block diagram. During experimental testing, the flow meter 100 may be characterized as an orifice plate flow meter. In other words, the pressure sensor 430 may measure the pressure differential between the inlet 410 and the outlet 411 of the flow meter 100 using the pressure taps 431, 432, respectively. Since the variables in equation (1) are either known or readily available by measurement, and the flow meter 100 determines the flow rate, the flow coefficient of the flow meter can be determined experimentally. The flow coefficient of the flow meter is similar to the orifice flow coefficient. Once the flow coefficient of the flow meter is known, the flow rate can be calculated based on the differential pressure across the flow meter 100 on the same principles as the flow rate is determined using an orifice plate flow meter.

During normal operation, the flow rate measured by the flow meter 100 can be compared to an expected flow rate obtained by calculation using equation (1) or a similar equation for calculating flow based on orifice plate flow meters. If the expected flow rate falls outside of the threshold difference in flow rate achieved by the meter 100, the meter electronics 20 can signal a deviation in the meter parameter. The deviation may be caused by the presence of the coating 310 within the flow meter 100. However, the deterioration may be caused by some reason other than the coating layer 310. On the other hand, if the expected flow rate obtained by characterizing the flow meter as an orifice plate flow meter falls within the threshold difference of the measured flow rate obtained by the flow meter 100, the meter electronics 20 can signal little or no deviation in the flow meter parameters. It should be understood that the threshold difference may be predetermined or may be determined by an operator on a case-by-case basis.

Another method for detecting a deviation in a flow meter parameter is to use a coefficient of friction, such as fanning coefficient of friction f, which provides greater accuracy and wider applicability than the previously described methods. Other coefficients of friction are also known in the art, such as a Darcy Weissbach coefficient of friction of about 4 f. It should be understood that the particular coefficient of friction used is not critical to the invention, as any applicable formula may be adjusted depending on the coefficient of friction used.

It is well known in the art that the pressure drop through a line can be quantified and adjusted by using the coefficient of friction f. First, it is important to understand how to characterize the process fluid flowing through a circular pipe. For this embodiment, the flow meter 100 can be characterized as a circular pipe having a known inner diameter and length. An important value in characterizing the fluid flowing through the pipeline is the reynolds number Re used in equation (2) above. It should be noted that the pipe diameter D can be easily determined and is generally known in the factory. Many flow meters, including coriolis flow meters, are capable of measuring fluid characteristics such as fluid density and mass flow. Root of herbaceous plantFrom these two quantities, the average fluid velocity can be calculated. The fluid viscosity may also be determined from known, calculated or measured values. The coefficient of friction of a system is defined as the product of wall shear stress and the density and velocity head differenceThe ratio of (a) to (b). For flow systems of incompressible fluids, it is often very effective to characterize the friction coefficient f with the reynolds number Re. The specific formula varies depending on the characteristics of the fluid and the conduit through which the fluid flows. It should be understood that the following formulas are merely examples and that other similar formulas are known in the art. Therefore, the formulas listed below do not limit the scope of the present invention. For laminar flow through a smooth pipe, the coefficient of friction f can be described as:

by contrast, for turbulent flow through smooth pipelines, the coefficient of friction f can be described as:

the formula (4) canAt 10⁴＜Re＜10⁶Is used with reasonable accuracy. Other formulas for relating the friction coefficient to the reynolds number are also known, such as:

f＝.046Re^-2 (5)

equation (5) is generally applicable to 50000 < Re < 10⁶While equation (6) is generally applicable to 3000 < Re < 3X 10⁶. According to any one of the formula (1) and the formulas (3) to (6), the friction coefficient of the system can be determined, wherein only the viscosity is an unknown quantity. Depending on the flow rate, the change in viscosity may not be significant. Alternatively, the user may enter a nominal viscosity.

It is also well known in the art that the coefficient of friction f can be described in terms of the pressure drop Δ P across the system as follows:

wherein:

Δ P ═ pressure drop

L is the length of the pipe between the pressure tapping pipes

Coefficient of friction

Rho ═ fluid density

D is the pipe diameter

The pressure drop may be obtained by the pressure sensor 230; the length of the flow meter 100 between the pressure taps 231, 232 can be easily measured; the pipe diameter can be easily measured; the fluid density can be obtained from the flow meter 100 and the average velocity can be obtained from the mass flow rate and the density measured by the flow meter. Thus, all variables on the right side of equation (7) are known.

According to an embodiment of the invention, the friction coefficient f is calculated by calculating a friction coefficient f based on the pressure difference_cCoefficient of friction with expected f_eThe comparison allows for diagnostics based on deviations that exist within the flow meter parameters. The desired coefficient of friction f can be obtained in a number of different ways_e. According to one embodiment of the invention, the expected coefficient of friction f may be determined at the factory or alternatively at the site when it is known that only a small or no coating layer is present_e. The expected coefficient of friction f can be obtained from various flow measurements_eAnd thus the coefficient of friction versus flow can be prepared. Expected coefficient of friction f_eMay be prepared in advance and stored in meter electronics 20. According to another embodiment of the invention, the expected friction coefficient f may be calculated from a correlation with the Reynolds number obtained during normal operation_e。

During normal operation, pressure sensor 230 can obtain differential pressure measurements of flow meter 100 according to an embodiment of the present invention. Additionally, the flow meter 100 can obtain flow measurements. Calculating the friction coefficient f from the measured flow and the measured differential pressure_cThat is, it can be calculated from the formula (7). This calculated coefficient of friction f can be used_cCoefficient of friction with expected f_eAnd (6) comparing. The difference between the two coefficients of friction indicates a deviation in the flow meter parameter. According to one embodiment, the deviation may be caused by the coating 300 within the flow meter 100. However, in other embodiments, the deviation may be caused by other conditions such as blockages, unstable process fluid mixtures, bubbles within the process fluid, and the like. If the calculated coefficient of friction f_cFalling within the expected coefficient of friction f_eWithin the threshold limits of (a), meter electronics 20 can determine that there is no deviation or only a slight deviation in the flow meter parameters. On the other hand, if the calculated coefficient of friction f_cFalling within the expected coefficient of friction f_eBeyond the threshold limit of (a), the meter electronics 20 can send a warning that there may be a deviation in the flow meter parameters. According to one embodiment of the invention, the threshold limit may be predetermined based on the particular flow meter or flow characteristics. According to another embodiment of the invention, the threshold limit may be determined on-site by a user or operator.

In addition to providing an accurate prediction of the coating 230, the method may additionally determine deviations in flow meter parameters in the absence of an accurately known fluid viscosity. Depending on the flow rate of the fluid, small changes in viscosity may not cause significant changes in the reynolds number. Thus, the average viscosity can be input by the user without further measuring the viscosity.

According to another embodiment of the invention, temperature measurements may be used to detect deviations in flow meter parameters. The inlet temperature and the outlet temperature remain relatively close to each other as the process fluid flows through the flow meter 100. Similarly, flow tube 101 and flow tube 102 are maintained at substantially the same temperature. According to an embodiment of the invention, the flow meter 100 includes two or more temperature sensors, such as RTDs 240. Although FIG. 2 shows only six RTDs, it should be understood that in other embodiments, the flow meter 100 may include more or less than six RTD sensors 240. The RTD sensor 240 may monitor the temperature of the flow tubes 101, 102. The coating 310 can, for example, impede fluid flow through the flow tubes 101, 102. Thus, coating 310 can also cause an abnormal change in the temperature gradient from the inlet to the outlet of a given flow tube in 101 or 102. In addition, coating 310 can cause a temperature gradient from flow tube 101 to flow tube 102. Clogging also affects temperature gradients because there is effectively little or no fluid traveling through the flow meter 100.

Thus, according to embodiments of the present invention, deviations in flow meter parameters may be detected based on temperature gradients. More specifically, in accordance with an embodiment of the present invention, the bias may be determined by tracking changes in temperature gradients obtained by more than one temperature sensor, such as RTD sensor 240. According to one embodiment, the temperature gradient is measured from the inlet of the flow meter 100 to the outlet of the flow meter 100. According to another embodiment of the invention, a temperature gradient is measured from one flow tube 101 of the flow meter 100 to another flow tube 102 of the flow meter 100. According to an embodiment of the present invention, the coating layer 310 may be detected if the temperature gradient exceeds a threshold temperature gradient. According to one embodiment, the temperature gradient threshold comprises a predetermined value. According to another embodiment, the temperature gradient threshold is determined by a user or operator.

In certain embodiments, the flow meter 100 may include a temperature gradient even when there is no deviation. Thus, according to an embodiment of the present invention, a deviation can be detected from a change in an already existing temperature gradient.

The above description provides various methods for detecting flow meter parameter deviations of the flow meter 100. According to embodiments of the invention, the deviation of the flow meter parameter may be used to make a diagnosis that may be indicative of a coating. Each method includes different advantages, and the particular method used may depend on the environment or available equipment. Some methods allow for detecting deviations in parameters when there are no deviations in the flow measurements. Additionally, more than one or all of the above methods may be employed in a single flow meter system. Thus, meter electronics 20 can compare the deviation detection obtained using one method with the results obtained using another method.

The detailed description of the embodiments presented above is not an exhaustive description of all embodiments contemplated by the inventors to fall within the scope of the invention. Indeed, those skilled in the art will recognize that certain elements of the above-described embodiments may be variously combined or subtracted to form further embodiments, and that such further embodiments fall within the scope and teachings of the present invention. It will be apparent to those skilled in the art that the above-described embodiments may be combined in whole or in part to form further embodiments within the scope and teachings of the invention.

Thus, while specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other flow meters and not just the embodiments described above and shown in the figures. Therefore, the scope of the invention should be determined by the appended claims.

Claims (22)

1. A method for detecting a deviation in a flow meter parameter, comprising the steps of:

measuring a differential pressure across at least a portion of the flow meter;

determining an expected pressure differential based on the known fixed fluid viscosity;

comparing the measured pressure differential to the expected pressure differential; and

if the difference between the measured differential pressure and the expected differential pressure exceeds a threshold limit, a deviation in a flow meter parameter is detected.

2. The method of claim 1, further comprising the step of measuring a differential pressure across the flow meter.

3. The method of claim 1, wherein the expected pressure differential is obtained by a pre-prepared pressure differential-flow curve for a known fixed fluid viscosity.

4. The method of claim 1, further comprising the step of storing the expected differential pressure within meter electronics.

5. The method of claim 1, wherein the threshold limit comprises a predetermined value.

6. The method of claim 1, wherein the flow meter comprises a coriolis flow meter.

7. The method of claim 1, wherein the deviation in the flow meter parameter indicates the presence of a coating in the flow meter.

8. A method for detecting a deviation in a flow meter parameter, comprising the steps of:

measuring a differential pressure across the flow meter;

calculating an expected fluid flow based on the pressure differential; and

the measured fluid flow rate is compared to the calculated fluid flow rate and a deviation in a flowmeter parameter is detected if a difference between the measured fluid flow rate and the calculated fluid flow rate exceeds a threshold limit.

9. The method of claim 8, wherein the step of calculating the expected fluid flow comprises the step of characterizing the flow meter as an orifice flow meter.

10. The method of claim 9, further comprising the step of determining a flow meter flow coefficient.

11. The method of claim 9, further comprising the step of storing the expected fluid flow within meter electronics.

12. The method of claim 8, wherein the threshold limit comprises a predetermined value.

13. The method of claim 8, wherein the flow meter comprises a coriolis flow meter.

14. The method of claim 8, wherein the deviation in the flow meter parameter indicates the presence of a coating in the flow meter.

15. A method for detecting a deviation in a flow meter parameter, comprising the steps of:

measuring a differential pressure across at least a portion of the flow meter;

calculating a friction coefficient based on the measured flow rate and the measured differential pressure; and

the calculated coefficient of friction is compared to an expected coefficient of friction based on the measured flow and a deviation in the flow meter parameter is detected if the difference between the calculated coefficient of friction and the expected coefficient of friction exceeds a threshold limit.

16. The method of claim 15, wherein the step of calculating the coefficient of friction comprises using the formula:

wherein the content of the first and second substances,

Δ P ═ pressure drop

L is the length of the pipe between the pressure tapping pipes

Coefficient of friction

Mean fluid velocity

Rho ═ fluid density

D-pipe diameter.

17. The method of claim 15, wherein the expected coefficient of friction is obtained from a previous measurement.

18. The method of claim 15, wherein the differential pressure is measured across the flow meter.

19. The method of claim 15, wherein the expected friction coefficient is calculated based on a reynolds number used to measure flow.

20. The method of claim 15, further comprising the step of storing the expected coefficient of friction within meter electronics.

21. The method of claim 15, wherein the flow meter comprises a coriolis flow meter.

22. The method of claim 15, wherein the deviation in the flow meter parameter indicates the presence of a coating in the flow meter.