GB2189323A

GB2189323A - Fluid flow meter

Info

Publication number: GB2189323A
Application number: GB08609402A
Authority: GB
Inventors: John William Shadrach; Peter Smallwood
Original assignee: Smith Meters Ltd
Current assignee: Smith Meters Ltd
Priority date: 1986-04-17
Filing date: 1986-04-17
Publication date: 1987-10-21
Anticipated expiration: 2006-04-17
Also published as: GB2189323B; GB8609402D0

Abstract

A gas meter 11 has a tangent arm 14 which rotates in response to gas flow. Transducer 16 supplies electrical signals related to rotation of the arm to a silicon chip device 17 which has a non-volatile memory. Data relating the rate of rotation of tangent arm to the gas flow which causes it are stored in the memory. Logic reading circuits receive the electrical signals and derive from the memory the corresponding flow value. The data stored are derived by comparing each meter's performance with a standard meter. Thus each meter has an individual data bank. No other calibration, for instance adjustment of mechanical parts, is required. A respective temperature,21, pressure sensor is provided to allow correction of flow values for temperature, pressure variations. <IMAGE>

Description

SPECIFICATION Fluid flow meters This invention relates to fluid flow meters of the kind in which a mechanical movement caused by the flow is used to measure the flow. Such meters tend to vary in their performance and require calibration before they can be used.

The invention provides a fluid flow meter ofthe kind in which a mechanical movement caused bythe flow is used tomeasure the flow having a calibration device comprising an electronic memory in which is stored data relating the mechanical movements to flow values measured forthatspecific meter, and meansforderiving,fromthememory,theflowvalue corresponding to a sensed mechanical movement.

Since each meter has an individual memory containing its own flow characteristics no other calibration, and particularly no adjustment ofthe flow characteristic, is required.

The invention also extends to a method of caibrating a fluid flow meter comprising testing the meter at different flows, measuring the flows on a standard reference number, and feeding into an electronic memory data relating the meter's mechanical movementto measured flows.

The calibration device may include means for computing the volumetric flow from the derived flow values, and for displaying and/or relaying the computed value. There may be included a temperature sensor and the calibration device may make a correction fortemperature variations.

A specific embodiment of the invention is shown in the accompanying diagrammatic drawing of a gas meter in side section.

The meter (11) is of the kind having a pair of measuring compartments in which flexible diaphragms move backandforth as gas is alternately admitted and exhausted from the compartments through valves. The back and forth movements are transmitted into oscillations of flag rods (12), which oscillations are taken through a crank assembly (13) to rotate a common tangent arm (14).Ashaft (15) driven bythetangentarm (14)to open and close the valves (not shown) in a timed cycle of action. The rotations ofthe tangent arm (14) are a measure ofthe gasflowthroughthe meter, but the exact measure varies from meter to meter because of small variations in diaphragm performance, valve timing, etc.A calibration of each meter is, therefore, necessary. Previously, it has been necessary to carry out time consuming mechanical calibration adjustments to each individual meter, for instance altering the valve timing, the gearing, the tangent arm radius, to alter the meter performance so that the meter performs within a prescribed tolerance range.

As shown in the diagram, the new meter has a transducer (16), mounted adjacent the path ofthe tangent arm (14) and which produces an electrical signal each time the arm passes it. The transducer may, for instance, be a reed switch sensing the presence of a magnet carried by the tangent arm or a capacitance device. A silicon chip (17) (shown at greater than actual size forthe purpose of clarity) receives these signals, derives from them a measure ofthe gas consumption (as described in more detail hereinafter) and displays the computation on an electrical display device (18). The display device may be a liquid crystal display. Electronic signals representing the computation may also be relayed over output line (19)to a remote reading means. A replaceable battery (20) powers the electronic circuits.

The silicon chip device (17) has a non-volatile memory in which is stored a record of the actual performance ofthe particular meter in which it is installed, i.e. a record of the volumetric gas flow measured by another, standard, meter and the rates of rotation ofthe tangent arm which accompanied these gas flows. In orderto compute the actual rate offlow, therefore, the chip device compares the incoming signals from the transducer (16) with its memory, determines the flow rate represented by the signals, and uses this to add to a measured volumestorerepresentingthetotal gasvolume passed through the meter. It is the measured volume store which supplies signals to the display and to the remote reading means.A temperature sensor (21 ) located in the gas stream provides a signal to the silicon chip device (17) so that a correction for temperature variations can be made to the computed flow rate.

To calibrate the meter, instead of mechanical adjustments, the meter is subjected to a test in which different gas flows are passed through it, the actual flow being measured by a standard, particularly accurate, meter. The recordings of the actual flow rates and the tangent arm rotations associated with them are fed into the non-volatile memory of the chip.

The particularly accurate meter may be a bell prover, i.e. a cylindrical holder in which a plunger works to expel air, the linear movement ofthe plunger being an accurate measure of the volume of air passing. The meter undertest is connected to receive airflow from the holder, the outlet from the meter being through an orifice which limits the flow.

Output line (19) from the meter is relayed to test control equipment.

Avolume of gas is displaced from the holder through the meter, at a flow rate selected bythe choice of orifice size. The movement of the holder is then determined for an integral numberof revolutions of the tangent arm. Hence the volume represented by one revolution can befound and the calibration factor determined. The test is repeated for other flow rates and the resultantfactors stored on the silicon chip. The process is fully automatic, the test equipment providing the signals to feed the silicon chip memory. No other calibration is necessary. The performance of the meterthereafter will be substantially equal to that of the standard meter, any variations being due to change of the meter characteristics with time.

A correction for alteration of meter performance with pressure variation may also be incorporated, using a pressure transducer in the gas stream.

Claims

1. Afluid flow meter of the kind in which a mechanical movement caused by the flow is used to measuretheflow, having a calibration device comprising an electronic memory in which is stored data relating mechanical movementtoflowvalue, the data being that individually measured forthe meter, and reading means for reading from the memory the stored fiow value corresponding to a sensed mechanical movement.

2. Ameterasclaimed in claim 1, wherein the electronic memory is a silicon chip device.

3. Ameterasclaimed in claim 1 or claim 2, wherein the reading means includes logic means for deriving from theflowvalues a measure of the volume ofthe fluid flow and wherein there is means for displaying the computed volume.

4. A meter as claimed in anyofclaims 1 to3, having also a temperature sensor providing a temperature signal to the reading means which includes means for adjusting the flow values for temperature variations.

5. A meter as claimed in any of claims 1 to 4, having also a pressure sensor providing a pressure signal to the reading means which includes means for adjusting the flow values for pressure variations.

6. A gas meter substantially as described hereinbefore with reference to the accompanying drawing.

7. A method of calibrating a fluid flow meter comprising passing a fluid through the meter, measuring the fluid flow rates on a standard reference meter and feeding into an electronic memory ofthe meter data relating the meter's response to the fluid flowto the measured flow rates.

8. A method of calibrating a fluid flow meter as claimed in claim 7, wherein the meter is run at two or more flow rates, data relating to each flow rate being fed into the memory.

9. A method of calibrating a gas meter substantially as described hereinbefore with referenceto the accompanying drawing.