Flow Meter Differential Pressure Monitoring

Abstract

Apparatus and associated systems, methods and computer program products relate to monitoring the performance of an operating gas meter by automatic and substantially continuous differential pressure (dP) measurement. Measured dP may be compared against a baseline dP characteristic to determine if the measured dP exceeds a threshold value above a baseline dP characteristic. If the threshold is exceeded, then the system may generate a signal to request repair or replacement of the meter. After installation, some embodiments collect dP data over time and/or over a range of flow rates to automatically learn a baseline dP characteristic under installation conditions. A system may switch from a default baseline dP characteristic to a learned baseline dP characteristic. Some embodiments may further correct volume or flow rate signals for line pressure and/or temperature. Further embodiments provide a passive apparatus to protect a dP sensor against transients in line pressure and/or differential pressure.

1 .- 16 . (canceled) 
   
   
       17 . A processor-implemented method to adaptively learn a baseline differential pressure characteristic of a meter in an installation, the method comprising:
 (a) automatically measuring differential pressure (dP) across a rotary-type fluid flow meter over a period of time;   (b) for each dP measurement, determining a flow rate through the meter;   (c) over the period of time, automatically generating at least one baseline dP characteristic based on the measured differential pressure and determined flow rate information; and   (d) storing the at least one baseline dP characteristic in an electronic data store device for subsequent retrieval and comparison to a subsequent dP measurement.   
   
   
       18 . The method of  claim 17 , further comprising:
 (e) monitoring the performance of the meter over the period of time by comparing the measured dP information to a threshold differential pressure that is greater than an initial baseline dP characteristic at the determined flow rate.   
   
   
       19 . The method of  claim 18 , further comprising:
 (f) measuring differential pressure across the meter;   (g) for each dP measurement in step (f), determining a flow rate through the meter;   (h) comparing the measured dP information to a threshold differential pressure that is greater than the generated baseline dP characteristic at the determined flow rate; and   (i) monitoring the performance of the meter based on the comparison in (h).   
   
   
       20 . The method of  claim 17 , wherein the threshold differential pressure comprises a differential pressure that is based on a selected ratio of the baseline dP characteristic at the determined flow rate, wherein the selected ratio is between about 1.1 and 5.0. 
   
   
       21 . The method of  claim 20 , wherein the selected ratio is about 1.5. 
   
   
       22 . The method of  claim 17 , wherein the threshold differential pressure comprises a differential pressure that is based on a function of one or more measured variables selected from the group consisting of: flow rate, line pressure, and line temperature. 
   
   
       23 . The method of  claim 17 , wherein generating at least one baseline dP characteristic comprises generating two or more baseline dP characteristics, each baseline dP characteristic being associated with a different combination of line pressure and line temperature. 
   
   
       24 . A computer program product tangibly embodied in an information carrier and containing instructions that, when executed, cause a processor to perform operations to automatically learn a baseline dP characteristic for a meter installed to measure a gas being transported in a gas line, the operations comprising:
 selecting a predetermined baseline dP characteristic for a gas meter of a rotary type;   automatically determining a differential pressure across the meter at each of a plurality of measured flow rates measured over a period of time;   determining at each measured flow rate whether any of the determined differential pressures exceeds the selected baseline dP characteristic by more than a threshold value; and   during the period of time, storing the determined differential pressure at each of the plurality of measured flow rates in an electronic data storage device to define a second baseline dP characteristic.   
   
   
       25 . The computer program product of  claim 24 , further comprising determining that sufficient differential pressure data points have been determined according to a set of acceptance criteria. 
   
   
       26 . The computer program product of  claim 24 , further comprising determining at each of a second plurality of measured flow rates whether a differential pressure measurement exceeds the second baseline dP characteristic by more than a second threshold value. 
   
   
       27 . The computer program product of  claim 24 , wherein the selected predetermined performance characteristic comprises a plurality of pairs of differential pressure and flow rate measurements. 
   
   
       28 . The computer program product of  claim 24 , wherein the selected predetermined performance characteristic comprises information determined in a meter shop or factory. 
   
   
       29 . The computer program product of  claim 24 , wherein the second baseline dP characteristic comprises information determined upon installing the meter in a distribution system. 
   
   
       30 . The computer program product of  claim 24 , further comprising substantially simultaneously measuring the flow rate of gas through the meter and the differential pressure of gas at an inlet and an outlet of the meter. 
   
   
       31 . An apparatus to limit fluid pressure levels applied to ports configured to sense a differential pressure, the apparatus comprising:
 a first fluid port connectable to a first input port of a differential pressure sensor;   a second fluid port connectable to a second input port of the differential pressure sensor;   a first fluid pathway to provide substantially uninterrupted fluid communication between the first fluid port and a third fluid port that is connectable to be in fluid communication with a fluid line, the first fluid pathway comprising a first flow restrictor portion to substantially attenuate transient pressure levels from the third fluid port to the first fluid port;   a second fluid pathway to provide substantially uninterrupted fluid communication between the second fluid port and a fourth fluid port that is connectable to be in fluid communication with the fluid line, the second fluid pathway comprising a second flow restrictor portion to substantially attenuate transient pressure levels from the fourth fluid port to the second fluid port; and   a pressure relief element that actuates to open a fluid communication pathway between the first fluid port and the second fluid port in response to a differential pressure between the first and second fluid ports exceeding a threshold value.   
   
   
       32 . The apparatus of  claim 31 , wherein the threshold value is about 0.5 pounds per square inch. 
   
   
       33 . The apparatus of  claim 31 , wherein the first and second flow restrictor portions substantially limit fluid flow through each of the first and second fluid pathways, respectively, to less than about 0.05 liters per minute. 
   
   
       34 . The apparatus of  claim 31 , wherein the pressure relief element comprises a one-way check valve. 
   
   
       35 . The apparatus of  claim 31 , wherein the pressure relief element comprises two opposing one-way valves. 
   
   
       36 . The apparatus of  claim 31 , wherein the pressure relief element comprises a spring operable to close the fluid communication pathway between the first fluid port and the second fluid port when the differential pressure between the first and second fluid ports does not substantially exceed a threshold value. 
   
   
       37 . The apparatus of  claim 31 , wherein the pressure relief element is operable to actuate by opening a fluid communication pathway to allow fluid to flow from the first fluid port to the second fluid port in response to a pressure at the first fluid port exceeding a pressure at the second fluid port by the threshold value. 
   
   
       38 . The apparatus of  claim 37 , wherein the pressure relief element is operable to actuate by opening a fluid communication pathway to allow fluid to flow from the second fluid port to the first fluid port in response to a pressure at the first fluid port exceeding a pressure at the second fluid port by a second threshold value. 
   
   
       39 . The apparatus of  claim 31 , further comprising the differential pressure sensor with the first input port connected to the first fluid port and the second input port connected to the second fluid port. 
   
   
       40 . The apparatus of  claim 31 , wherein the first and second restrictor portions each comprises a pin hole through which fluid may be communicated through the first and second fluid pathways, respectively. 
   
   
       41 . The apparatus of  claim 31 , wherein the first and second restrictor portions each comprises a sintered type metal flow restrictor through which fluid may be communicated through the first and second fluid pathways, respectively. 
   
   
       42 . A method to substantially compensate for an offset signal from a differential pressure transducer in a fluid flow measurement system, the method comprising:
 (a) in an unattended fluid flow measurement system, measuring an offset value in a differential pressure measurement signal generated by a differential pressure (dP) sensor configured to measure differential pressure across a fluid flow element, the measurement being made upon determining that a flow rate through the fluid flow element is measured to be substantially below a threshold flow rate that is substantially close to zero;   (b) storing the determined offset value in an electronic data store for subsequent retrieval during at least a portion of a predetermined time period after determining the offset value; and   (c) retrieving and using the determined offset value to substantially remove an offset from a measured differential pressure signal generated by the dP sensor.   
   
   
       43 . The method of clam  42 , further comprising repeating step (a) upon the end of the predetermined time period. 
   
   
       44 . The method of clam  42 , further comprising repeating step (a) in response to a predetermined temperature change. 
   
   
       45 . The method of  claim 42 , wherein determining that a flow rate through the fluid flow element is measured to be substantially below a threshold flow rate that is substantially close to zero comprises measuring the fluid flow rate at least two times.