GB2177523A - A system for dispensing a liquid - Google Patents

Abstract

A system for dispensing a liquid e.g. beer comprises a plurality of controllable dispensing outlets (5); a pump (3) for pumping liquid to the outlets; a motor (11) for driving the pump; and a control circuit for controlling the motor. The control circuit comprises monitoring means (6) for monitoring the pressure of liquid fed from the pump and electronic means (8, 9), connected with the monitoring means, for regulating the motor for maintaining the pressure substantially constant. Circuitry is also provided for determining when the supply of liquid is exhausted and for stopping the motor thereupon. Exhaustion is capable of being distinguished from a full flow condition. <IMAGE>

Description

SPECIFICATION A system for dispensing a liquid It is desirable, in the beer dispensing trade, to be able to distribute beer from the cellar pump at a constant pressure, regardless of the number of dispense valves opened and therefore regardless ofthe quantity offlowthrough the pump, within the capacity of the pump, any pump having a maximum flow rate at a given pressure.

A centrifugal pump driven by a series wound, brush commutator motor is very common in the trade. The pump's natural characteristic isto produce falling output pressure as flow increases, art a given motorspeed. In orderto produce constant pressure, so thatthe flow rate at any one tap orvalve is unaffected by the opening or closing oftaps on otherlinesfromthesamepump,thespeed ofthe motor needs to be varied over a wide range up to the motor's maximum speed, so that the speed is increased to meetgreaterflowand maintain the delivery pressure.

A series wound motor's speed is easily control led by altering the supplied voltage (the average or r.m.s.

voltage). Different pumps require different voltages suppliedtothemotorto produce the same pressure/ flow condition, this being dependent on pump design and efficiency.Acontrol circuitto maintain a constant pressure at the pump needs then to be able to monitor the delivered pressure and does not need to be able to detect flow. However, in orderthatthe pump does completely stop when all the line valves are closed, the control circuit must removetheapp- lied voltage when the pressure rises higherthan that required.

As a centrifugal pump is capable of being driven at slow speed without increasing the outlet pressure, it is important that the circuit is arranged to ensure that the pump cannot continueto run after all the delivery valves are closed. If a solitary outlet valve were to be closed very slowly, a natural response of a constant pressurecontrollerwould betoslowlyreducethe motor speed, with a riskthat itwill not stop altoge- therwhen all flow ceases. The solution tothisand other problems are solved in a following example of the present invention.

It is also necessary that, in the event that the container supplying the pump empties, the pump is shut down to prevent the destruction of seals in the pump which arise from running dry.

According to the present invention from one aspect, there is provided a system for dispensing a liquid, comprising a plurality of controllable dispensing outlets; a pump for pumping liquid to the outlets; a motorfor driving the pump; and a control circuit for controlling the motor, the circuitcomprising monitoring means, for monitoring the pressure of liquid fed from the pump; and electronic means, connected with the monitoring means, for regulating the motor for maintaining the said pressuresubstantiallycon- stant.

According to the present invention from another aspect, there is provided a circuit for detecting when a pump driven by a motor is no longer pumping liquid from a container, the circuit comprising: meansfor monitoring the pressureoffluidfedfrom the pump; and means for de-energising the motor and, in response thereto, using an output from the monitoring meanstodeterminewhetherthemonito- red pressurefallsordoes notfall in response to such de-energisation,the motor being re-energised if the monitored pressure falls and being keptdeenergised ifthe monitored pressure does not fall.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa schematic diagram of an example of a system according tothe invention; and Figure 2 is a diagram of a pressure transducer of a control circuit of the system.

Inthefollowing example, the speed of a beerpump motor is controlled by an electroniccircuitthatvaries the applied voltage in response to alterations in a signal voltage that is derived from a pressure trans- ducer compared with a signal voltage that represents a desired outlet pressure for the beer at dispense valves. The elec.tronics switches the motor on as the pressure falls in responseto opening of a valve, con trolsthespeedto maintain the pressure regardless of flow rate and switches the motor offwhen the pressure rises above the desired pressure in responseto all dispense valves being closed.

Referring first to Figure 1, reference numeral 1 des ignates a beer supply containerfrom which beer may be pumped via a pipeline 2 by a pump 3to a plurality of beer pipelines 4, each terminating in a respective dispense valve 5. In the pipeline 2 and downstream of the pump 3 is a pressure transducer 6 whose construction will be described below, there being anon- return valve7 between the pump3andthetransdu- cer6. The transducer 6 produces on a line 8a signal voltage (or current orfrequency) proportional to the actual pressure in the pipeline 2, this signal being fed to an input pin ofa phase control circuit 9.Phase con trolcircuit9isa readily availableTDA2085Atype integrated circuit (IC) to phase control the conduction of a Triac 10 via an output pin connected to the gate of Triac 10. The Triac 10 is connected between an A.C.

supply and a motor 11 which drives the pump 3, the Triaccarrying the main load currentforthe motor 11.

Reference numeral 12 denotes a power on indicator lamp. Also connected to the power supplyvia a fuse 13 is a voltage regulator 14whose output is connected to a rotary potentiometer 15forsetting thede- livery pressure and to the transducer 6 as a constant voltage supplytherefore. The potentiometer 15 applies a delivery pressure setting input to another input pin of phase control IC 9. Another output pin of phase control lC9providesasignal proportionaltothe phase angle of the state of conduction of Triac 10, which signal is applied to a comparatorcircuit 16and (via a starting detector circuit 17)to: the input of a circuit 18for modifying the setting input to phase control IC 9; the input of an oscillator circuit 20 for controlling oscillation ofthesetting input; andtothe start/reset input of a timer 21. The output of comparator circuit 16 is connected via a memory network 22 to an input an AND gate 23.The output of timer 21 is connected to a latch 24 having one output connec ted to another input pin of phase control circuit 9 and anotheroutput connected to an enabling inputofan AND gate 25, whose output is connected for resetting latch 24when it is a "1" state. The other output of latch 24 is also connected to an "end of enable" detection circuit 26 whose output is connected to a "no beer" indicator lamp 27 and (via a "pulse end" detection circuit 28) to the other input of gate 23, whose output is also connected for resetting latch 24when it is in a "1" state. Reference numeral 29 denotes a manual reset push-button for the latch 24.

The outputfrom transducer 6 as a signal proportional to actual delivery pressure is also connected bothtoadelaycircuit30(providing,forexample,a few seconds delay) and to an input of a comparator circuit 31 whose other input is connected to the output of delay circuit 30. The output of comparator circuit31 is connected to the other input of AND gate 25.

A preferred design of pressure transducer 6 to produce a signal voltage proportional to actual pressure is shown in Figure 2 and consists essentially of a chamber 32 through which the beer flows as it leaves the pump 3.The extreme ends ofthe chamber32are threaded at 33 to enable the connections to the pump 3 and the beer lines 4. A convoluted diaphragm 34 covers an aperture in one side ofthe chamber. The diaphragm is constructed of a rubber material of a non-toxic nature as it is in contact with the beer on one side. The rubber material is reinforced by a woven fabric encased by the rubber material. The entire convoluted diaphragm has a rolling action and is available, as a moulded component, underthetrade names "Rolafram" and "Bellofram".

The convoluted diaphragm is sandwiched be tween the body35 ofthechamber32 and a clamp ring 36 secured with four bolts or screws (not shown in Figure 2), which forms the cylinder surface forthe diaphragm and also locates centrally a tube 37 seamlesslyformed in a steel material. A piston 38 sli des in the tube and is shaped to suittheconvoluted diaphragm. The design ensures that the convolution radius is maintained reasonably equal all the way round.

A component 39 centralises two other parts to the tube. The first, a variable resistor or potentiometer 40 with a sliding action, is mounted and secured with two bolts 41 screwed into the clamp ring 36.

The extreme end ofthe moving part of the potentiometer is maintained in contact with the piston byan internal spring (not shown in Figure 2). Alternativelyto a variable resistor, a variable capacitor or in ductor a strain gauge orvarying optical signal could be used.

The potentiometer is manufactured by COLVERN as an LM10.

The second part located bythe component 39 is a spring 42 to oppose the movement ofthe diaphragm and piston, which move together, and is also located in the piston.

In Figure 2, reference 43 denotes the electrical con nectionsfrom the potentiometer 40.

When a constantvoltagefrom regulatorl4isapp- lied across the ends of'ih e ofthe potentiometer, the voltage measured from the wiper or moving contact ofthe potentiometer varies as the diaphragm and piston move, acted on by beer pressure in the chamber, against the spring. The absolute travel of the piston is constrained to the designed limits ofthe rolling diaphragm by, atone end, a shoulder in the clamp ring 36 and, atthe other, by the piston contacting the fixed partofthe potentiometer40.

The pressure range of the transducer could be selected by changing the spring 42.

Diaphragms offlat rubber sheets have been used as alternatives to the convoluted diaphragm, with a different piston design, but these have produced very limited movementforthe potentiometer and have been subjectto failure due to continuous stretching and contracting in use. However, such a design my be suitable for other applications of the invention.

The phase control IC 9 is used to control the conduction of Triac 10. The action of phase control is a common method of being able to control the voltage applied to a load in an A.C. circuit. The phase control IC has (as mentioned) an output pin to drive the gate of Triac 10, and also two input pins suchthatthe angle of phase control is dependent on the difference between the two signal voltages applied to these pins. Namely, one input pin receives a signal dependent on the desired pressure that has been set and the other input pin receives a signal dependent on the actual pressure as detected by the transducer 6, thetheTriac being controlled so that the actual pressure is maintained substantially constant.When the two inputs are nearly equal,the phase angle ofthe Triac 10 is linearly controlled. If there one input pin isat a much higher voltage than the other, then the phase angle issuchthattheTriac 10 is in full conduction and the motor 11 receives the full supply voltage.

Conversely, if the same input pin is taken to a much lower voltage than the other, then the Triac 10 switches off, electrically isolating the motor 11 from the supply.

The phase control IC 9 and a suitable Triac 10 are ideal for controlling the motor 11,which is a series wound motor. Similar results could be obtained using an electrical network replacing the IC. The IC has a number of otherfeatures which are also used to the full in the design ofthis constant pressure pump controller, as will be set out later.

When the pump 3 and its associated control system are installed, the delivery pressure must be set to suit the particular installation (to suit various requirements as regards height two be pumped, lengths of lines, etc.), and this is the purpose ofthe potentiometer 15. The latter may be of the rotary type for selecting the desired output pressure, and may be calibrated with pressure settings. The potentiometer 15 is connected across the same constantvoltage supply as the transducer 6 for the provision of the two inputsignalsforthe phase control IC9.

The phase control IC 9 requires external components (resistors, capacitors etc.) to create the stability and response characteristic of the changing phase angle to changes in the two inputs. The stability components are included in a stability circuit 19 and are chosen so that the system cannot become unstable and uncontrollably oscillate but respond reasonably fast to pressure changes. Also, there is the oscillator circuit 20, which is a simple oscillator circuit with a slow oscillation rate which is initiated when the phase control IC 9 starts to power the motor 11. The oscillator output is added to the signal from the potentiometer 15 (selecting the desired pressure) to the phase control IC which then varies in a controlled fashion.The resulting pressure variation is small compared with the actual pressure setting and produces no noticeable effect at a dispense valve when open. When the valve is closed, even very slowly, this pressure variation ensures that periodicallythe pressure rises above the actual desired pressure and can stop the motor. To ensure thatthe system cannot hunt or oscillate about the desired pressure setting when it should be off, a further feature is incorporated.

As mentioned, the other output pin ofthe phase control IC 9 produces a signal voltage proportional to the phase angle, and when the phase angle is reduced to nearly switch off, a feedback loop from this pin via circuit 18 causes the voltage from the selected pressure potentiometer 15 to be modified so that it represents a lower set pressure. The result is a clean switch off, as the motor 11 nearly stopping caused the set pressure to suddenly be less than the existing pressure. The line pressure now has to fall belowthis new artificial setting before re-start. On re-start, the pressure reference voltage is restored to its previous value.

If a dispense valve is closed normally, then these features are not noticeable in operation as the line pressure rises abruptly as the dispense valve closes and this rise will be sufficient to cause the Triac 10 to be switched off.

When the motor 11 is stopped, the signal proportional to phase angle causes the oscillator circuit 20 to stop varying the desired pressure signal and remains thus until the motor re-starts on falling pressure.

When the beersupply container 1 empties,thefollowing sequence of events occurs.

The inlet pipeline section to the pump 3 empties, the chamber of the pump wholly or partially empties into the outlet pipeline section and the outlet pressure falls as the pump is incapable of pressurising the outlet pipeline section with air or gas (the container may be pressurised with carbon dioxide). The control circuitry, on monitoring the sudden pressure drop, causes the Triac phase angle to go to maximum thus applying the full supply voltage to the motor 11. This then runs at maximum speed. The motor 11 would also run at maximum speed at"Full Flow", i.e. with all dispense valves open, and it is necessary to distinguish between the conditions "Full Flow" and "No Beer". This is done (as will be explained below) bytemporarilystopping orslowing down the pump motor, the difference between "Full Flow" and "No Beer" being recognisable by pressure measurement.If "Full I Flow" exists before the motor stops, the pressure in the pipeline 2 must fall further immediately itstarts to stop. If, however, the supply container 1 has previously emptied, then, when the motor 1 starts to stopthe line pressure remains unaltered.

The operation of the control circuitry is as follows.

Normally, when the actual pressure detected by transducer 6 exceeds the set pressure, the conducting phase angle of Triac 10is reduced, eventually to totally switch the pump 3 off. When the actual pressure is less than the set pressure, the phase control circuit9 increasesthe phase angle,to startorac- celerate the motor 11. Stability network 19 controls the speed of response and stability ofthe changing phase angle. The phase control circuit 9 outputs a signal which is proportional to the actual phase angle and indicates to starting detector circuit 17 when no conduction is occuring (pump stopped or stopping).

In this condition, the detector 17 outputs a signal to three circuits as follows. Circuit 18 modifies the set pressure signal to represent a lower pressure so that the actual pressure detected by the transducer 6 now hastofall belowthis pressure before conduction will commence. The signal from the detector 17 also inhibits, or holds in a stopped condition, oscillator 20.

When the pressure falls below the modified set pres- sure and conduction commences, the modification or shift is removed and the oscillator 20 starts. The oscillator 20 causes small, low frequency variations ofthe set input signal. The third circuit affected by the detector 17 is the timer 21. Thetimer 21 is is held ready whilstthe pump is not powered. When the detector 17 senses the start of the pump, the timer 21 runs (for about40-45 seconds) but is re-setifthe conduction ceases. At the end ofthe time period, the timer 21 sets latch 24. One of the timer period, the timer 21 sets latch 24. One of the outputs of latch 24 is an in hibitsignaltostopconductionofTriac10viacircuit9 and thereby stop the pump 3.The latch 24 also gener atesan"enable"signal of approximately 4 seconds duration. The enable signal is used in two ways.

The actual pressure signal from the transducer 6 is also fed to thetwo inputs of comparator 31 with a delayviadelay30 (orshortmemory) on oneofthem.

The network 30/31 produces a logic signal of one of two states (one representing a falling pressure condition, the other a steady or rising pressure condition) which is applied to AND gate 25. When the inhibit from the latch 24 removes the power via the phase control circuit 9 and Triac 10, the motor immediately slows. If a pressure falling signal is generated by the comparator 31 at anytime whilstthe "enable"signal exists, the AND gate 25 outputs a re-set to the latch 24 that then enables conduction to re-commence. This will, if a good flow exists, happen very quickly and before the motor 11 has stopped.

If the pressure remains steady or (though unlikely) rises whilst the enable signal exists, the AND gate 25 will not cause the latch 24to reset and the motor 11 will stop altogether.

After the "enable" terminates, further pressure falls will have no effect.

The other use ofthe enable signal from latch 24 is made as it ends. On the one hand, the "No Beer" indicator 27 is lit via circuit 26 and, on the other hand, also a pulse from circuit 28 is generated to feed AND gate 23. Thesignal proportional to phase angle from the phase control circuit 9 is used by comparator 16 to detect the full conduction state and thereby a logic signal isproducedthatisfedtomemorynetwork22 that has the capacity to rememberthatfull conduc tion eyisted, fora minimum period slightly longer than the "enable" (typically 6 seconds). If full conduction did exist when the inhibit from the latch 24 occurred, then AND gate 23 has no effect when the "end of enable" pulse occurs. If, however, the state of less than full conduction had existed, the memory signal andthe"end of enable" pulse cause gate 23to output a second re-set signal for the latch 24.

Athirdsource of re-setforthe latch 24 isfromthe manually operated push button 29.

The net resu It of this is to ensure that the control circuit does not continue to run when it should not and further notto falsely detect "No Beer".

Claims (11)

1. A system for dispensing a liquid, comprising a plurality of controllable dispensing outlets; a pump for pumping liquid to the outlets; a motorfordriving the pump; and a control circuitforcontrollingthe motor,the circuit comprising monitoring means,for monitoring the pressure of liquid fed from the pump; and electronic means, connected with the monitoring means,forregulating the motorfor maintaining the said pressure substantially constant.

2. Asystem according to Claim 1, wherein the said monitoring means comprises transducer means including a potentiometer providing an output dependent on the pressure of liquid fed from the pump.

3. Asystem according to Claim 1 or2,wherein the said electronic means comprises control means connected with the said monitoring means for regulating current fed to the said motor in dependence upon the pressure of liquid fed from the pump.

4. Asystem according to Claim 3, wherein the said control means comprises a circuit connected for controlling the conduction of switch means whose degree of conduction is controllable, the motor being energised via the switch means.

5. A system according to Claim 4, wherein the switch means comprises a Triac.

6. A system according to Claim 4 or 5, wherein the circuit connected for controlling the conduction ofthe switch means comprises a circuit having an input which receives a first signal, dependent on a desired pressure value, and an input which receives a second signal, dependent on the pressure of liquid fed from the pump.

7. A system according to Claim 6, wherein there is provided a potentiometer for providing the said first signal.

8. Asystem according to anypreceding claim, further including means for de-energising the motor and, in response thereto, using an outputfrom the monitoring means to determinewhetherthe monitored pressure falls or remains substantially constant in response to such de-energisation, the motor being re-energised if the monitored pressure falls and being keptde-energised if the monitored pressure does notfall.

9. A system according to Claim 8, including comparison means, for comparing the monitored pressure substantially atthe instant of de-energisation of the motor with the monitored pressure after a predetermined period oftime to determinewhetherthe monitored pressure falls or does not fall.

10. A circuit for detecting when a pump driven by a motor is no longer pumping liquid from a con tainer,thecircuitcomprising: means for monitoring the pressure offluid fed from the pump; and means for de-energising the motor and, in response thereto, using an outputfromthe monitoring meanstodeter- mine whetherthe monitored pressure falls or does notfall in response to such de-energisation,the motor being re-energised if the monitored pressure falls and being kept de-energised ifthe monitored pressure does not fall.

11. A system for dispensing a liquid, substanti ally as herein described with reference to the ac- companying drawings.