GB2157850A - Devices for dispensing measured quantities of liquid - Google Patents

Abstract

A liquid, such as beer, is supplied by pump 3 via duct 1 of constant cross-sectional area to a solenoid outlet valve 5. The duct 1 has a first thermistor A followed in the direction of flow by an electrical heater H, and thermistors B and C. Operating a push button 8 causes a controller 7 to open the valve 5 and energise the heater H. The flow of liquid through the duct 1 is then heated by the heater H until the heat is sensed by the thermistor B and then by the thermistor C. When this happens the controller switches off the heater H and the drop in temperature is sensed by the thermistor B and then by the thermistor C. The controller 7 can calculate from the volume of liquid dispensed from known volume of the duct 1 between the thermistors B and C and the time taken for change in liquid temperature to be sensed. The heating and cooling sequence is repeated until the total volume to be dispensed has been sensed; then the controller closes the valve 5. The thermistor A enables thermistors B and C to sense changes in temperature regardless of the initial temperature of the liquid leaving the pump 3. <IMAGE>

Description

SPECIFICATION Devices for dispensing measured quantities of liquid Metering devices for dispensing measured quantities of liquid are generally of one of two different types.-The first type operates on a positive displacement principle and these devices generally dispense a predetermined volume of liquid upon the movement of a piston from one end of a cylinder to the other or the displacement of a flexible membrane from one side of a chamber to the other. The other type operates upon a flow principle and generally speaking the velocity of flow of liquid through a duct of known cross-sectional area is measured by causing a liquid flow to rotate a rotor in the duct and then computing the volume from the number of revolutions made by the rotor.

In general, metering devices of the positive displacement type give more consistently accurate results and they are generally called for by the Authorities involved in public houses for measuring the volumes of beer and other beverages which are dispensed.

Devices of the positive displacement type do, however, have the disadvantage that they are somewhat cumbersome and difficult to clean and also that any one metering device will, at each operation, only dispense a particular predetermined volume of liquid and to enable this volume to be altered, other than by very small amounts for adjustment pruposes, it is necessary to replace the cylinder or other chamber and the piston or membrane which is movable within it.

Thus in effect to alter substantially the volume of liquid dispensed, the whole metering device must be replaced.

The aim of the present invention is to provide a device for dispensing measured quantities of liquid which operates with a constant flow of liquid through a duct, but measures this flow volumetrically and thus provides a more accurate determination of the volume of liquid dispensed than is generally possible with the type of metering device in which the velocity of flow is measured by means of a rotor.

According to the present invention, a device for dispensing measured quantities of liquid, such as beer, comprises a duct of constant cross-sectional area through which, in operation, the liquid flows, three temperature sensors which are spaced apart along the duct and which emit electrical signals upon changes of temperature occurring in the liquid in the duct, the duct having a predetermined volume between the second and third temperature sensors considered in the direction of flow of the liquid through the duct, an electrical heater for heating the liquid as it flows through the duct between the first, upstream sensor and the second sensor, an electrically controlled outlet valve downstream of the third, downstream sensor and an electronic controller, which is electrically connected to the sensors, the heater and the outlet valve and which includes a timing device and computing means, the controller, when set in operation, opening the valve and performing the following operations in sequence: (a) the heater is switched on; (b) a first time interval between the switching on of the heater and the second sensor indicating a rise in temperature of the liquid above that at the first sensor is measured; (c) a second time interval between the second sensor indicating the rise of temperature and the third sensor indicating the rise in temperature is measured and, when the third sensor indicates the rise in temperature, the heater is switched off; (d) a third time interval between the switching off of the heater and the second sensor indicating a fall in temperature of the liquid to that at the first sensor is measured; and, (e) a fourth time interval between the second sensor indicating the fall in temperature and the third sensor indicating the fall of temperature is measured; whereby the predetermined volume of liquid flows through the duct in each of the second and fourth time intervals, and volumes equal to the predetermined volume multiplied by the ratio of the first time interval to the second time interval and the predetermined volume multiplied by the ratio of the third time interval to the fourth time interval flow through the duct in the first and third time intervals respectively, and the controller then repeats the sequence of operations and calculates the total of the volumes of flow through the duct in all the time intervals and then shuts the valve when a required final total volume of liquid has flowed through the duct.

With this device, the switching on and off of the heater produces sudden temperature changes in the flow of liquid through the duct and the points at which the changes take place, either upwards or downwards as the heater is switched on or is switched off act as markers in the liquid flow so that in effect a number of predetermined volumes of the liquid are dispensed and the accuracy of the device may be made similar to that of a metering device of the positive displacement type.

It will be seen that the total volume dispensed consists of a number of the predetermined volumes within the duct between the second and third temperature sensors and also a number of other volumes which may themselves vary. The magnitude of these other volumes will depend upon the exact rate of heating effected by the heater and the exact rate of cooling of the liquid after the heater has been switched off, both of which are dependent upon the thermal inertia of the heater, and also on the response time of the second temperature sensor.However, if, say, the heater heats up the liquid more rapidly, then less liquid will have flowed through the duct during the heating time, but this will be compensated for by a reduction in the first time interval and a consequent reduction in the ratio of the first time interval to the second time interval which will give rise to a corresponding reduction in the volume flowing in the first time inteval as calculated by the controller. Changes in the rate of cooling of the liquid will be compensated for in the same way.Thus, the mesurement of the total volume dispensed by measuring the total number of predetermined volumes, that is the volume between the second and third temperature sensors, dispensed and the number of further volumes dispensed between the switching on and off of the heater and the registration of the consequent change in temperature by the second temperature sensor enables the computing means in the controller to calculate very precisely the total volume of liquid dispensed. What is more, where this is necessary, the computing means in the controller can be arranged to shut the valve only a part of the way through either one of the second or fourth time intervals so that during the last sequence of operations, only a part of the full predetermined volume of liquid is dispensed and the valve is closed part of the way through either the second or the fourth time interval.In this way a very exact volume of liquid can be dispensed.

What is important to ensure that exactly the predetermined volumes of liquid are dispensed in each of the full second and fourth time intervals is that the response time of the second and third temperature sensors should be the same as each other.

The first temperature sensor is necessary to allow for variations in the temperature of the liquid entering the duct so that the second and third temperature sensors sense the differential between the temperature of the liquid flowing past them and of the temperture of the liquid flowing past the first sensor. Thus the second and the third sensors detect upward or downward movements of the temperature of the liquid which are brought about solely by the switching on or off of the heater and are not sensitive to variations in the temperature of the liquid brought about by variations in the temperature of the initial supply of the liquid.

Preferably all of the temperature sensors are thermistors and the computing means in the controller is preferably a micro-processor although it may alternatively be a hard wired logic circuit.

Variations in the volume of liquid dispensed can easily be achieved by adjusting the microprocessor or the logic circuitry to close the valve upon a different total of the volumes of the flow through the duct being calculated.

An example of a liquid dispensing device in accordance with the invention is illustrated highly diagramatically in the accompanying drawings in which: Figure 1 is a diagram of the duct with the heater and sensors; and Figure 2 is a diagram of the device as a whole.

The device comprises a housing 1 having a duct 1 a extending throught it. The duct is of constant cross-sectional area and has an inlet connected by a pipe 2 to a pump 3 for supplying the liquid to be dispensed. Of course, if the liquid to be dispensed is already under pressure, the pump 3 is not necessary. The duct in the housing 1 has an outlet connected by a pipe 4 through a solenoid valve 5 to a dispensing outlet 6, which in this example is a beer dispensing nozzle at a bar. The duct 1 a has at its upstream end a first thermistor A, followed by an electrical heater H, a second thermistor B and a third thermistor C. The three thermistors A, B and C and the heater H are all connected to an electronic controller 7 which includes a microprocessor with a timing device or counter and also a circuit for energising the heater H and a circuit for energising the solenoid valve 5. The device is set in operation by closing a push button switch 8.

The operation of this example of the device in accordance with the invention is shown by a simplified flow chart as follows:-

Start (push button) t S/V open + H'on + Dwell count start (1) (T8 > TA).(TC=TA)=Start flow count + stop dwell count. (2) (TByTA).(TC > TA)=Stop flow count + H'off' + + start dwell count. (3) (TB=TA).(TC > TA)=Start flow count + stop dwell count (4) (TB=TA).(TC=TA)=Stop flow count + H'on' + + start dwell count

step (1) to step (2) = one unit volume step (2) to step (3) 3 ) = Q x unit volume (where Q = dwell count next flow count step (3) to step (4) = one unit volume step (4) to step (1) = y x unit volume (where y = dwell count next flow count In this flow chart TA, TB and TC are the temperatures at the three sensors A, B and C respectively.

The controller will continue to compute this loop of instructions and accumulate the total liquid output between the various steps until such time as the number of unit volumes and fractions or multiples thereof equal the required total volume to be dispensed. When this happens, the controller closes the solenoid valve and resets itself ready to dispense another metered volume of liquid.

In this particular example, the unit volume between the temperature sensors B and C is 1 ml and accordingly to dispense a half pint measure of beer, a number of cycles of the sequence of operations is necessary to provide a total volume of 284.1 5ml. A dispensing speed of up to half a pint in five seconds is envisaged.

In view of the rapidity of the repetition of the cycle of operations of the device which is necessary to produce this dispensing speed, it is most desirable to keep the thermal inertia of the heater to a minimum. This can be done in various ways. One is by direct electrode heating of the beer or other liquid, which relies on the conductivity of the liquid to bring about the heating. Residual heat is therefore contained within the electrode probes. A second way, which is more practical is by the use of metal plating, which is electrically heated, on the inside of a small bore non-conductive tube. Other electrical heating elements may be used such as a carbon loaded porous ceramic material which has an inherently large surface area with a small physical volume and a low thermal mass.

The controller preferably also includes an additional resetting timer which monitors the switching of the thermistor B and the thermistor C to ensure that a minimum flow rate through the dispensing device is achieved and if it is not achieved, which when beer is being dispensed suggests either that the supply has run out or that the system has become blocked with carbon dioxide, the dispensing device ceases to operate.

Claims (4)

1. A device for dispensing measured quantities of liquid, for example beer, the device comprising a duct of constant cross-sectional area through which, in operation, the liquid flows, three temperature sensors which are spaced apart aiong the duct and which produce electrical responses upon changes of temperature occurring in the liquid in the duct, the duct having a predetermined volume between the second and third temperature sensors considered in the direction of flow of the liquid through the duct, an electrical heater for heating the liquid as it flows through the duct between the first, upstream sensor and the second sensor, an electrically controlled outlet valve downstream of the third, downstream sensor and an electronic controller, which is electrically connected to the sensors, the heater and the outlet valve and which includes a timing device and computing means, the controller, when set in operation, opening the valve and performing the following operations in sequence: (a) the heater is switched on; (b) a first time interval between the switching on of the heater and the second sensor indicating a rise in temperature of the liquid above that at the first sensor is measured; (c) a second time interval between the second sensor indicating the rise of temperature and the third sensor indicating the rise in temperature is measured and, when the third sensor indicates the rise in temperature, the heater is switched off; (d) a third time interval between the switching off of the heater and the second sensor indicating a fall in temperature of the liquid to that at the first sensor is measured; and, (e) a fourth time interval between the second sensor indicating the fall in temperature and the third sensor indicating the fall of temperature is measured; whereby the predetermine volume of liquid flows through the duct in each of the second and fourth time intervals, and volumes equal to the predetermined volume multiplied by the ratio of the first time interval to the second time interval and the predetermined volume multiplied by the ratio of the third time interval to the fourth time interval flow through the duct in the first and third time intervals respectively, and the controller then repeats the sequence of operations and calculates the total of the volumes of flow through the duct in all the time intervals and then shuts the valve when a required final total volume of liquid has flowed through the duct.

2. A device according to Claim 1, in which the temperature sensors are thermistors.

3. A device according to Claim 1 or Claim 2, in which the computing means in the controller is a micro-processor.

4. A device according to Claim 1, substantially as described with reference to the accompanying drawings.