GB2177510A

GB2177510A - Detecting the presence or absence of a liquid

Info

Publication number: GB2177510A
Application number: GB08615817A
Authority: GB
Inventors: Geoffrey Glasgow
Original assignee: PARTRIDGE WILSON AND Co L
Current assignee: PARTRIDGE WILSON AND Co L
Priority date: 1985-07-01
Filing date: 1986-06-27
Publication date: 1987-01-21
Also published as: GB8615817D0

Abstract

An ultrasonic signal is passed through a pipe D in a liquid (e.g. beer) dispensing system to determine the presence or absence of liquid within the pipe according to the attenuation of the soundwaves. The attenuation level of the received ultrasonic signal is compared (at F) with a predetermined reference level, and if the attenuation is low a "no liquid" indication (at K) is provided.This indication signal can be used to shut down the pump in the dispensing system or to shut a valve to prevent drainage of the system. The indication signal may be temporarily delayed (at H) in order to obviate spurious operation of the "No liquid" detector to prevent it tripping when a gas or foam pocket passes through the ultrasonic beam. <IMAGE>

Description

SPECIFICATION Apparatus for detecting the presence or absence of a liquid This invention relates to apparatus for detecting the presence or absence of a liquid in a passageway. For example, the apparatus is suitable for detecting the presence or absence of liquid in a feed pipe of a liquid dispenser.

The present invention finds useful application in a beer dispenser Hitherto, the first indication that beer is about to run out is the appearance of foam or gas at the beer dispenser tap, at which point the supply pipe has been emptied and the whole dispenser system effectively drained. Re-establishing the beer in the dispenser pipes free of gas pockets or foam can result in the wastage of an appreciable quantity of beer.

According to the present invention, apparatus for detecting the presence or absence of a liquid within a passageway comprises an ultrasonic transmitter at one side of the passageway, means for energising the transmitter, an ultrasonic receiver at an opposite side of the passageway, and means responsive to an output from the receiver for producing a first indication if there is liquid in the passageway between the transmitter and the receiver and a second indication if liquid is absent in the passageway between the transmitter and the receiver.

The present invention will now be described, by way of example only, with reference to the accompanying drawing which is a schematic diagram of apparatus for detecting the presence or absence of liquid in a passageway in a beer dispensing system.

The purpose of the apparatus to be described is to detect the presence or absence of a liquid within a pipe in a dispensing system. Although the invention is particularly described with reference to a beer dispensing system it is to be understood that it may be applied also to systems for dispensing other liquids. A particular feature of the apparatus to be described is its ability to differentiate between a homogeneous liquid and a mixture containing a large volume of gas, i.e. foam.

Referring now to the drawing there is shown a section of pipe D which forms part of a liquid dis pensing system. The liquid being dispensed passes through the pipe. A region of the pipe D1 is formed with a reduced wall thickness, or a waisted section. In the pipe section D1 an ultrasonic trans mitter C is positioned on one side of the pipe adja cent to the pipe wall and diametrically opposite there is located an ultrasonic receiver E also adja cent to the pipe wall. The transmitter and receiver are located in close contact with the wall of the pipe D, so as to prevent the interposition of a sound absorbing layer of air.

The ultrasonic transmitter C is driven by the out put of an amplifier B which in turn receives an in put signal from an oscillator A. The frequency of operation of the oscillator is set at a convenient frequency, for example about 400 KHz.

The output of the ultrasonic receiver E is passed to a level detector F and filter G. In the embodiment being described the level detector and filter form a composite circuit. The output of the ultrasonic receiver E is an alternating signal at the transmitter frequency. The level detector F basically comprises an envelope detector which is combined with a filter G to ensure peak sensitivity to the selected ultrasonic DC output which is either high or low determined by the attenuation level of the ultrasonic signal in passing between the transmitter C and the receiver E through the pipe D and its contents.

The DC output of level detector F is connected through a time delay circuit H to control energisation of an output relay J, indicator K or a solenoid valve (not shown). The contacts of relay J may be used to operate the solenoid valve or to control operation of a pump (not shown). The pump forms part of the liquid dispensing system and, in operation, provides a head of liquid in a dispensing system incorporating the pipe D. The solenoid valve is preferably connected to prevent drainage of the dispensing system and, in particular, to prevent the entry of gas into the system.

Indicator means K may be provided to give a visual indication to an operator that the liquid detector apparatus has sensed an absence of liquid in the delivery pipe D and has closed the solenoid valve or shut-down the pump. This visual indication will then be taken to indicate the need to either replenish the reservoir of liquid supplying the dispensing system, or to connect the system to a fresh source, i.e. a full barrel.

The purpose of the time delay means H is to prevent spurious operation of the system due to an isolated gas pocket or pocket of foam passing along the delivery pipe D. The time delay means comprises a resistor/capacitor charging circuit, in which the capacitor is arranged to be charged from the DC output produced by the level detector F.

Charging current is supplied via a resistor so that the values of the resistance and capacitance of these two components set a known charging time constant. A switching transistor is connected in parallel with the capacitor between the charging line and earth. The base of this transistor is also connected with the output from the level detector F, and its polarity is chosen so that the transistor will be switched into conduction by a low level output appearing on its base terminal, and switched into non-conduction by a high level output at its base terminal. Therefore, in operation of the time delay means, a high level output from the level detector F will switch this transistor into a non-conducting state and will commence charging of the time delay capacitor.Alternatively, a low level output from the level detector F will cease charging the capacitor and will switch the said transistor into conduction, the effect of which is to discharge the capacitor to earth.

The resistor/capacitor charging circuit is connected between the level detector F output and an input of a comparator circuit. A second input of this comparator circuit is connected with a thresh old voltage setting means which provides a reference switching level for the comparator. Thus, when the charging circuit voltage exceeds this reference level the comparator is switched into a first state, and when the charging circuit voltage lies below the reference level the comparator occupies a second state. The output relay J, connected to control operation of a pump or solenoid valve, is arranged to operate the pump or open the valve when the comparator output is in its second state, and to shut down the pump or close the valve when the comparator output occupies its first state.

A visual indicator, if provided, is arranged to display a "no liquid" indication when the comparator output is in its first state, and otherwise to be extinguished. As shown in the accompanying drawing a power supply P is connected to provide voltage supplies to the described circuits.

In operation of the above described apparatus, ultrasonic pressure waves are generated by the transmitter C and pass through the adjacent wall of the pipe D, thence through the fluid contained within the pipe and through the opposite wall of the pipe into the receiver E. The receiver E converts these ultrasonic pressure waves back into an electrical signal the amplitude of which is determined by the amount of attenuation experienced by the pressure waves in passing through pipe D and through the fluid contained in the pipe. Attenuation of the pressure waves is least when the pipe is filled with liquid, and is most when the pipe contains air or foam. Thus, the output of the level detector F is at its lowest when the pipe is filled with liquid, and is at its highest when there is no liquid or only foam in the pipe.

If the output of level detector F remains high, i.e.

indicating an absence of liquid in the pipe, then the output relay J operates to shut down the pump or close the solenoid valve, and the indicator means K provides an appropriate indication.

However, if the output of level detector F experiences a transient change of state due to the passage of a gas or foam pocket past the ultrasonic transmitter and receiver, then the time delay means H operates to prevent spurious shutdown by the output relay J. It does this as follows; Initially, with liquid in the pipe D, the output of level detector F is low and the resistor/capacitor charging circuit is discharged. Upon the level detector output going high the resistor/capacitor circuit begins charging but, assuming the comparator reference level has been suitably set, this change of status is not immediately propagated to the output circuits. If within the time period of the charging circuit, i.e. that is before the voltage on the charging circuit capacitor reaches the comparator reference level, the level detector output returns to a low level then the transistor in parallel with the capacitor is switched to a conducting state and the capacitor is immediately dicharged. The output of the time delay means H is, therefore, prevented from changing state until the output of the level detector F has resided at a high "low liquid" level for longer than the time constant of the charging circuit. This time constant may be adjusted by varying the reference level of the comparator in order to provide a degree of adjustment to compensate for the particular characteristics of individual dispensing systems.

Claims

1. Apparatus for detecting the presence or absence of a liquid within a passageway comprising an ultrasonic transmitter at one side of the passageway, means for energising the transmitter, an ultrasonic receiver at an opposite side of the passageway, and means responsive to a output from the receiver for producing a first indication if there is liquid in the passageway between the transmitter and the receiver and a second indication if liquid is absent in the passageway between the transmitter and the receiver.

2. Apparatus as claimed in claim 1 wherein the means responsive to the output from the ultrasonic receiver comprises an output level detector responsive to the amplitude level of the receiver output.

3. Apparatus as claimed in claim 2 wherein the output level detector includes means for setting an amplitude threshold level in order to differentiate between a first receiver output level corresponding to a presence of liquid and a second receiver output level corresponding to an absence of liquid.

4. Apparatus as claimed in any one of claims 13 wherein the second indication is utilised to suspend operation of a pump connected to supply liquid via the said passageway.

5. Apparatus as claimed in any one of claims 13 wherein the second indication is utilised to operate a solenoid valve to shut-off a supply of liquid via the said passageway.

6. Apparatus as claimed in any preceding claim wherein the means responsive to the output of the receiver incudes time delay means to delay propagation of a second indication relative to the progapation of a first indication.

7. Apparatus as claimed in claim 6 wherein the period of said time delay is sufficient to obviate an indication that liquid is absent due to temporary presence of a gas bubble in the passageway between the ultrasonic transmitter and receiver.

8. Apparatus as claimed in claim 6 or 7 wherein the time delay means comprise a resistor capacitor charging circuit.

9. Apparatus as claimed in claim 9 wherein the said resistor/capacitor charging circuit is connected to a input of a comparator circuit for comparison with a reference level.

10. Apparatus as claimed in claim 9 wherein the reference level of said comparator circuit is adjustable whereby to determine the period of the delay.

11. Apparatus for detecting the presence or absence of a liquid within a passageway substantially as described with reference to the accompanying drawings.