GB2123557A - Flow meter measurement techniques - Google Patents

Abstract

A flow meter includes an electrical switching arrangement (3, 4) capable of attaining different electrical states in response to motion of a flow driven element (1). By counting the occurence of these states the rotation rate of the element (1) is counted and the flow rate determined. A sampling controller (5) tests periodically for a test time d and with a period T, for an attained state in the switching arrangment. When the test for the attained state is successful in times within a period of P min, defined by the minimum period of the attained state when in use, the controller confirms the attained state. By monitoring the sequence of confirmed states which appear at the output (C) of the controller (5) the flow consumption can be monitored and both power consumption and susceptibility to noise interference can be reduced. <IMAGE>

Description

SPECIFICATION Flow meter measuring techniques This invention relates to flow meters and more especially, although not exclusively to remote utilization thereof.

Flow meters may be employed to measure volume flow or rate of flow of a substance past a defined point. Volume measurement is particularly useful with regard to measuring consumption of the substance, for example gas. In relation to gas meters, it is desirable to both monitor and measure consumption remotely from the meter, thereby avoiding consumer involvement.

Consequently mechanical indication of consumption must be translated into a format suitable for relaying from a remote meter. Clearly, an electrical format is suitable and simple counting of revolutions of a flow driven rotation element by means of a transducer activated by the element revolution is adequate. Many arrangements of transducer may be utilized and our copending application PQ 54019 discloses a system in a flow meter to both monitor flow and register tampering with the meter. However, it is desirable to utilize arrangements whereby electrical energy use is limited, that is to say a low power arrangement of transducers is employed.

Unfortunately, at low power operating levels and remote location of the counting means for the transducer arrangement, large electrical noise signals can be picked up resulting in spurious and hence inaccurate counting.

It is an object of this invention to provide a sampling technique for flow meters allowing reduction in electrical power consumption and noise sensitivity.

According to one aspect of the invention there if provided a flow meter arrangement comprising an electrical switching arrangement being capable, in response to motion of a flow driven element, of attaining any of a number of electrical states, the meter arrangement further comprising a sampling controller arranged to test, periodically for a test time d and with a period T, for an attained state in said switching arrangement, the controller confirming said attained state when the test for said attained state is successful n times within a period min defined by a minimum period of said attained state when in use.

In a preferred embodiment the switching arrangement includes reed switches arranged to respond to a magnet disposed on a flow driven rotation element and n has a value of four.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example only, to the accompanying drawings in which: Figure 1 illustrates a switching arrangement and sampling controller.

Figure 2 illustrates a test sequence for the sampling controller.

Figure 3 illustrates the sampling controller.

Referring to Figure 1, a flow driven element 1 is caused to rotate as a consequence of flow through a flow meter arrangement of which the element forms a part. Clearly other types of flow driven elements may be used. Translation of the mechanical rotation into an electrical format is achieved by attaching a magnet 2 to the element such that the annular passage of the magnet periodically closes a reed switch 3 disposed adjacent the element. In use, the maximum flow level through the flow arrangement will cause the reed switch to be closed for a minimum period Mien' the period will clearly be increased if flow levels are reduced from the maximum.

If the reed switch is linked in series to a resistor 4 and electrical power applied across the series linked components, reed switch 3 and resistor 4, the voltage at a point A linking the two components will reflect whether the reed switch is closed or not, hence translating the mechanical rotation into an electrical format. The electrical switching arrangement comprising the two components can be monitored and the voltage at point A will reflect the two states that are attainable by the reed switch. By counting the occurrence of these states, the number of rotations of the element can be counted and related to flow through the flow arrangement.

A sampling controller 5 included in the flow meter arrangement applies the electrical power across the series linked components, reed switch 3 and resistor 4, and an input B of the controller is connected to point A. The quantity of electrical power applied to the above linked components can be reduced by utilizing lower power levels.

However, a point is reached in this reduction, at which electrical noise picked up by the flow meter arrangement begins to produce spurious counting of the occurrence of the states in the switching arrangement.

The power level applied to the series linked components can be increased to a level where spurious counting does not occur. If the application of power is restricted to a time w and applied periodically with a period T, as illustrated in Figure 2(a), the quantity of power used is reduced. During the time w when power is applied, the state of the switching arrangement, and hence the reed switch can be tested by checking that the voltage appearing at input B of the controller is above a predetermined threshold level. Furthermore, by restricting the time d of this test to be significantly less than time w as illustrated in Figure 2(b), noise picked up by the flow arrangement must coincide with time d and have a magnitude greater than the input B predetermined level. Therefore sensitivity to noise is reduced allowing a reduction in the power level applied to the series linked components.Clearly the periodicity of the test will be substantially the value of T.

As a further precaution, by ensuring that the period T for applying power to the series linked components 3 and 4 is less than half the minimum closure period Pmjn for reed switch 3, at least two consecutive tests will produce a voltage at input B of the controller that is above a predetermined level if the switch is closed. The number of such tests n within the period Pmjn can be altered by variation of the period T relative to the period Pmjn.

Furthermore, the controller can be arranged to only confirm the state of the electrical arrangement if n consecutive tests occur, for example n may have a value of 4 and this example is illustrated in Figure 2. It will be apparent that when successful tests occur a different threshold level for input B may be selected in order to examine for a different state of the electrical arrangement which may have a differing period Pmjn. By monitoring the sequence of confirmed states which appear at an output C of the controller, flow consumption can be monitored and both power consumption and susceptability to noise interference can be reduced.

An example of a controller capable of performing the above functions is illustrated in Figure 3. The controller 5 is connected to the linked components 4 and 3 and a point A linking the two components is connected to input B of the controller, as also shown in Figure 1. The controller comprises a power suppiy 6, which is activated by pulses from an output m of a clock 7, and supplies power to the components 4 and 3.

The pulses from clock output m prpduce the power pulses illustrated in Figure 2(a) having a period T and width w.

Input B of the controller is relayed through an input amplifier 1 firstly to an AND gate 8, and secondly through an inverter 9 connected to a further AND gate 10. The two AND gates 8 and 10 also receive pulses from an output N of the clock 7, which pulses are synchronised to those from output m and are illustrated in Figure 2(b). These pulses have a period T and width d, which pulses occur when the power supply is activated.

Consequently AND gate 8 tests for a predetermined voltage level at controller input B, and AND gate 10 tests for a zero voltage level at controller input D. If a voltage occurs at input B, AND gate 8 is enabled and pulses from the clock pass through to a counter 12, which counts the pulses and emits an output pulse when 4 pulses are received. This counter is reset whenever AND gate 10 is enabled and a clock pulse passes therethrough. The pulse from counter 1 2 is relayed to an input R of bistable element 13 which alters the state of output C of the controller. If the voltage at controller input B is zero AND gate 8 is closed and AND gate 10 is enabled. Consequently pulses from clock 7 pass through to another counter 14, which counts pulses and emits an output pulse when 4 pulses are received.This counter is reset whenever AND gate 8 is enabled and a clock pulse passes therethrough. The pulse from counter 14 is also relayed to an input S of the element 13, which alters the state of output C of the controller to a state different to that when input R of the element 1 3 has received a pulse.

In this way the controller output C has one of two states, which is achieved only when 4 similar consecutive input values are received at the controller input B. Values of n can be altered by changing the counters 12 and 14 and pulse period and widths produced by clock 7 can be changed by alteration of the clock. Many other configuration of controller can be chosen and their construction will be straightforward to those skilled in the art.

It will be apparent that differing value of d, w, n, T and Pmjn may be utilized to produce the object of the invention and the transducers used are not limited to reed switches, for example optical switching may be utilized.

It will be understood that the embodiment illustrated shows an application of the invention in one form only for the purposes of illustration. In practice the invention may be applied to many different configuration, utilizing other forms of transducer operated switching arrangements, the detailed embodiments being straightforward for those skilled in the art to implement.

Claims (7)

1. A flow meter arrangement comprising an electrical switching arrangement being capable, in response to a flow driven element, of attaining any of a number of electrical states, the meter arrangement further comprising a sampling controller arranged to test, periodically for a test time d and with a period T, for an attained state in said switching arrangement, the controller confirming said attained state when the test for said attained state is successful n times within a period Pmjn defined by a minimum period of said attained state when in use.

2. A flow meter arrangement according to Claim 1, wherein the electrical switching arrangement is energised periodically for a time w with a period substantially equal to T and the sampling controller tests during the time w.

3. A flow meter arrangement according to Claim 2, wherein the time d has a value less than the time w.

4. A flow meter arrangement according to any one of Claims 1, 2 or 3, wherein the flow driven element is a rotation element.

5. A flow meter arrangement according to any preceding claim, wherein the electrical switching arrangement includes at least one reed switch arranged to respond to at least one magnet provided on said flow driven element and the sampling controller tests the electrical state of said at least one reed switch.

6. A flow meter arrangement according to any one of claims 1 to 4, wherein the electrical switching arrangement includes at least one optically activated switch arranged to be activated by said element and the sampling controller tests the electrical state of said at least one optically activated switch.

7. A flow meter arrangement substantially as herein described with reference to and as illustrated in the accompanying drawings.