GB2050626A

GB2050626A - Liquid Flow-rate Measurement

Info

Publication number: GB2050626A
Application number: GB8015999A
Authority: GB
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA; SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1979-05-15
Filing date: 1980-05-14
Publication date: 1981-01-07
Also published as: FR2456940A1; DE3018601A1; FR2456940B1

Abstract

The flow-rate of a liquid into or out of a container 1 such as an oil reservoir of an engine is measured by detecting the instants at which the surface of the liquid is detected at a predetermined series of fixed levels N1, N2,....Nn e.g. by a series of switches 7 actuated by a floating magnet 9, and the time between the surface passing adjacent predetermined levels is measured. The time value is divided into the value of the internal volume of the container 1 between the said two levels in order to give the required flow rate. <IMAGE>

Description

SPECIFICATION Liquid-flow Measurement This invention relates to a device for measuring liquid-flow as a result of which the volume of a liquid contained in a reservoir or other enclosure varies. The device is applicable especially for the measurement of leakage oil-flow of an engine.

Up to the present time no device exists which is capable of effecting a direct measurement of the leakage flow of oil in an engine. Previously proposed sensors only effect a measurement of the oil level in the oil reservoir of an engine. In order to know the leakage flow it is thus necessary to derive as a function of time the measurement of the oil level; this operation is imprecise and sensitive because of the small variation in the electrical signal generated by the sensor.

Furthermore, from French Patent Application No. 2,354,551, a method is known according to which a leakage flow of excess proportions is detected in a lubricating installation of a machine by collecting the oil losses in an enclosure, by emptying this enclosure into the lubrication circuit as soon as the oil level in the space reaches a predetermined level, by measuring the time passing between two successive emptying operations of the enclosure, by comparing this time with a reference value and operating an alarm as soon as the said time is less than this reference value.

According to the present invention there is provided a device for measuring the flow of liquid to or from an enclosure comprising means for measuring the liquid level within the enclosure and arranged to generate discrete, different, analogue signals related to the said level at a number of predetermined levels (N1 to Nn) means for measuring the time elapsed (to) between successive said discrete signals and means for processing a representative signal A V0 to corresponding to the passage of the liquid level through two predetermined adjacent said levels, A V0 being the volume of the interior of the enclosure between the said two adjacent predetermined levels.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagram in vertical section of a liquid enclosure provided with a device embodying the invention; Figure 2 is a graph of voltage as a function of time of the output signal of a liquid-level detector incorporated in the embodiment of Figure 1; and Figure 3 is a block diagram of the circuit for operating on the output signal of the liquid-level detector of Figure 2.

The device shown in Figure 1 comprises, disposed in an oil reservoir or other enclosure 1 of an engine, a first conductor 2 of low electrical resistance and connected to a reference potential source (earth) 3, a second conductor 4 constituted by a string of equal value seriesconnected resistors 5, this conductor 4 being connected between a stabilised voltage source 6 and the reference potential 3. Normally open contact sets 7, each set being operable by a magnetic field serve to connect each resistor at the terminal 5a to a fourth conductor 8 of low electrical resistance and a float 9 carrying a magnetic field source 9a such as a permanent magnet is sufficient to close a said contact set 7 lying at the same level as the float 9.

The contact sets 7 are distributed over a series of fixed levels N1, N2,... Nn at a predetermined spacing so that each part of the internal volume of the reservoir 1 has between two adjacent levels Ni-i, N, a constant value åVO.

When the reservoir 1 is filled, the float 9 rises and closes the contacts 7 adjacent which it lies.

Progressively as the leakage losses empty the reservoir 1 of its oil, the float 9 descends and successively places in contact between the conductor 8 and one of the terminals 5a through one of the contact sets 7 at the level of which the float 9 lies at any given instant. The conductor 8 is thus at the potential of this terminal 5a. This potential is measured by a voltmeter 10 connected across the conductors 2 and 8. The signal 11 delivered at the output terminal 1 Oa of the voltmeter 10 is shown in Figure 2.The amplitude of this signal is a function of the level of the closed contact set 7 and therefore of the level of the float 9; this signal is processed to provide a display on an analogue or digital indicator (not shown) indicates the level of oil in the reservoir 1, and therefore the volume of oil remaining within the reservoir.

The signal 11 is processed by a circuit shown in Figure 3 so as to obtain the flow value of the oil loss.

The circuit of Figure 3 comprises a differentiating circuit 12 receiving the signal 11 and emitting a calibrated pulse 1 3 at each step or vertical trace 1 a of the signal 11, in the positive or negative sense according to the direction of oil flow. The circuit also comprises a counter 14 for counting the pulses of a clock pulse generator 1 5.

This counter is reset to zero by one of the trailing or leading edges of each pulse 13.

The circuit has a memory 1 6 for storing the output signal (t) of the counter 14 and transmits information to to a processing circuit 17, on the appearance of each pulse 13.

The processing circuit 1 7 generates, starting from signal to a signal f(AVo) to analogue to - to A display device 18 responds to the signal f(AV0) to to indicate the flow value of the oil loss.

The apparatus hereinbefore described serves to replace the derivation as a function of time of a signal representing the liquid level in the enclosure by an integration in time of this signal, the latter operation being much simpler than those previously proposed.

Claims

1. A device for measuring the flow of liquid to or from an enclosure comprising means for measuring the liquid level within the enclosure and arranged to generate discrete, different, analogue signals related to the said level at a number of predetermined levels (N, to Nn) means for measuring the time elapsed (to) between successive said discrete signals and means for processing a representative signal Avo to corresponding to the passage of the liquid level through two predetermined adjacent said levels, åVO being the volume of the interior of the enclosure between the said two adjacent predetermined levels.

2. A device according to claim 1, wherein the liquid level measuring means comprises a float carrying magnetic field generating means, a series of contact sets operable by the magnetic field of which each set corresponds to one of the predetermined levels and is disposed at that level, an electrical conductor, voltage source means of different values, each contact set being -associated with one of the voltage source means and the said conductor, and means for measuring the voltage of the said conductor.

3. A device according to claim 1 or claim 2, wherein the elapsed time measuring means comprises a differentiating circuit serving to process the signals received from the level measuring means and a clock pulse generator for measuring the time elapsed between two consecutive pulses supplied by the differentiating circuit.

4. An oil circuit incorporating a reservoir with a measuring device according to any one of claims 1 to 3.