GB2204955A - Temperature compensation - Google Patents

Abstract

A temperature compensation device (14) is intended for mounting with its back plate (26) in contact with an outside wall of a gas meter without intrusion into the gas meter. A temperature sensor (28) is mounted in close proximity to the back plate to achieve a temperature close to that of the flowing gas. Logic circuits (21) receive electrical measurement signals from the meter, correct them for temperature variations, and display the corrected measurement at (23). An ambient temperature sensor may provide data to the logic circuits in order for a more accurate temperature measurement to be made. The device is powered by a replaceable dry battery (19) so as to be wholly self-contained. It may be attached to a gas meter which produces an electric pulse for each volume of gas used or to a mechanical gas meter if the mechanical counter thereof is read electrically. <IMAGE>

Description

TEMPERATURE COMPENSATION.

This invention relates to temperature compensation devices particularly for use with meters for gaseous fluids which measure volumetric flow, The invention provides a temperature compensation device for use with a gas meter which comprises a housing having a back plate adapted to be mounted adjacent nt one wall of the meter, a temperature sensor in said housing mounted on said back plate, electrical logic circuits in said housing connected to receive electrical output signals from the meter and from said temperature sensor, and adapted to produce therefrom a temperature corrected version of the meter volumetric output signal.

The temperature compensation device may have a display means for showing the corrected measurement. There may also be electrical battery means in the housing for powering the logic circuits. The battery means may also supply power to the index of a meter on which the compensation device is mounted whereby to produce the electrical signal representing the metered measurement in its uncompensated form.

The logic circuits may include means for increasing the accuracy of the sensed temperature signal by extrapolating from data including arrbient temperature and/or flow rate.

The invention also extends to a gas meter having a temperature compensation device as set out above. The gas meter may produce its measurement signal in either mechanical form translated into an electrical signal or may produce it directly in electrical form, e.g.

a series of pulses. The gas meter may derive its electrical energy from a battery powering the compensation device.

A specific embodiment of the invention is shown in the accompanying drawings, in which:- Figure 1 is a side view of a volumetric gas meter having a temperature compensation device, and Figure 2 is a section through the temperature compensation device of Figure 1, shown on a larger scale.

The gas meter (11) is of a kind which intrinsically measures volume, without reference to temperature variations. The meter has a pair of chambers in which flexible diaphragms work back and forth, the measured gas being alternately admitted and exhausted from the chambers. The rate at which the diaphragms work is a measure of the rate at which gas passes through. The meter includes an index (12) containing a mechanical counter which counts the reciprocations of the diaphragms and display means which shows the running total of the volume of gas which has passed.

It is known that the volume of a given mass of a gas varies with variation of temperature. The total volume shown by index (12) is not therefore a true indication of the amount of gas which has passed through the meter, if the temperature of the gas has varied from a selected calibration temperature.

A temperature compensation device (14) is therefore added to the meter (11), to compensate the volume indication of index (12) continuously as the gas temperature varies. The device (14) comprises a housing (15), a back plate (26) of which is closely secured to the lower part of the meter by means of a location hook (16) which fits over a lip (17) of the meter and flexible tapes (18) which pass around the circumference of the meter.

Within the device as seen in Figure 2 there is mounted an electrical dry battery (19) which can be removed and replaced through an opening (20). The battery powers a printed circuit (21) which carries out the compensation operation and causes a corrected running volume measurement to be displayed on a liquid crystal display (23).

Information is supplied to the printed circuit (21) for use in the compensation operation as follows: (A) the uncompensated reading from index (12) is set up in an electrical form and transmitted on ccnnection line (25). The electrical form may be derived by electrically "reading" the mechanical index, e.g. by electrical coding devices such as are described in U.K. Patent No.

1213125. Alternatively, the electrical form may be derived by causing the diaphragm movements to produce electrical pulses, the pulses being counted on the printed circuit board. In either case, the electrical signals are powered from a battery (19).

(B) a temperature measurement signal from a temperature sensing device (28) is taken on line (29) to the printed circuit board. The sensing device is mounted on a good heat conductor, in this case a phosphor bronze mounting clip (30) for the battery (19). Since the clip is mounted on back plate (26) which is closely adjacent the gas meter wall, it attains a temperature which is close to the temperature of the flowing gas. The sensing device produces a variable output current which is a measure of the sensed temperature. The sensing operation may be by means of a temperature-variable semi-conductor, thermistor or a thermocouple.

Although the temperature sensed is close to that of the flowing gas, there is some difference, and for greater accuracy a closer approximation may be derived by a logic circuit on the printed circuit board. This may, for instance, have means for sensing ambient temperature, so that a gradient from ambient to the temperature at the sensor (28) can be obtained and then extrapolated to estimate a more correct gas temperature. Another factor adversely affecting the temperature sensed by sensor (28) is higher gas flow rates, since at slower gas flow rates the back plate (26) has mcre time to reach a closer approximation to the gas temperature. The printed circuit board already receives information related to the flow rate and may therefore use this to apply another correction factor to the sensed temperature measurement.

It will be noted that the temperature compensation device (14) dces not require any openings made into the meter, but is simply attached to the outside wall of the meter with electrical connections to the index.

Thus the sealing problem inherent in any opening into the meter is avoided.

Although the invention is described in relation to a diaphragm type gas meter, it will be appreciated that it can be applied to any gas meter which measures volume without relation to temperature variations.

Claims (16)

CLAIMS:

1. A temperature compensation device for use with a gas meter, which comprises a housing having a back plate adapted to be mounted adjacent one wall of the meter, a temperature sensor in said housing mounted adjacent said back plate, electrical logic circuits in said housing connected to receive electrical output signals from the meter and from said temperature sensor and adapted to produce therefrom a temperaturecorrected version of the meter volumetric output signal.

2. A temperature compensation device as claimed in claim 1, wherein said temperature sensor is located wholly within said housing.

3. A temperature compensation device as claimed in claim 1 or claim 2, wherein there is display means for showing the corrected measurement.

4. A temperature compensation device as claimed in any of claims 1 to 3, including means for mounting an electrical battery and for allowing a battery to be changed.

5. A temperature compensation device as claimed in any of claims 1 to 3, wherein said temperature sensor is mounted on a good heat conductor secured to or integral with said back plate.

6. A temperature compensation device as claimed in claim 5, wherein said good heat conductor is a rr;etal mounting clip for mounting an electrical battery.

7. A temperature compensation device as claimed in any of claims 1 to 6, wherein said temperature sensor is a temperature-variable semiconductor or a thermistor, or a thermocouple.

8. A temperature compensation device as claimed in any of claims 1 to 7, wherein said logic circuits comprise a printed circuit adapted to be powered by a dry battery.

9. A temperature compensation device as claimed in any of claims 1 to 8, wherein said logic circuits are also adapted to increase the accuracy of the signal from the temperature sensor by extrapolating from other data.

10. A temperature compensation device as claimed in claim 9, comprising also an ambient temperature sensor for providing a signal forming part of said other data.

11. A temperature compensation device as claimed in any of claims 1 to 10, wherein said logic circuits are adapted to apply a correction factor for temperature sensor inaccuracy at higher flow rates.

12. A temperature ccmpensation device substantially as described hereinbefore with reference to the accompanying drawings.

13. A gas meter having a temperature compensation device as claimed in any of claims 1 to 12.

14. A gas meter as claimed in claim 13, adapted to produce or reproduce its metered measurement signal in electrical form for transmission to the temperature compensation device.

15. A gas meter as claimed in claim 13 or claim 14, wherein said compensation device is mounted with its back plate in close juxtaposition with an exterior wall of the gas meter, but has no extensions into the body of the gas meter.

16. A gas meter having a temperature compensation device substantially as described hereinbefore with reference to the accompanying drawings.