GB2033582A - Liquid metering method and device - Google Patents

Abstract

A device for automatically metering liquid includes a container 10 for holding liquid F to be metered and having a liquid discharge control valve 12. The upper end of the container is closed by a cover 15 having an inlet pipe 21 for pressure compensation, in which inlet pipe there is a nozzle-like opening 20 of a given cross-section in whose flow range an NTC resistor system 30 of an anemometer circuit. The output of the anemometer circuit is a voltage proportional to the airflow rate through the inlet pipe 21, the voltage being fed to an input of an analog voltage/frequency converter 50 which supplies an a.c. voltage (or a pulse train) at a frequency proportional to said voltage. The frequency of the output of the converter is compared with a preset comparison count value in a counter 60. The count value counted by the counter 60 is proportional to the volume of air which has flowed into the container during pressure compensation, and an output of the counter is fed to a circuit 80 controlling the discharge valve 12 in the liquid discharge pipe 11. <IMAGE>

Description

SPECIFICATION Liquid metering method and device The present invention relates to a method and to a metering device for the automatic metering of quantities of liquid, with a container for receiving the liquid to be metered having a liquid discharge pipe at the bottom and which is equipped with a discharge valve.

Except in the case of packaged products beverage dispensing machines require liquid volume metering means. Very varied constructions of metering devices are known. The best known and most frequently encountered method comprises directly measuring the liquids. In the case of an appropriate discharge pressure metering vessels, metering pumps and metering diaphragms connected in the flow to be measured are used. Thus, the measuring devices are in direct contact with the liquids to be metered. Virtually all liquids for beverage dispensing machines easily spoil. Thus, the metering devices and also the storage containers must be cooled and must also be cleaned at regular intervals. Maintenance can only be carried out by trained personnel and costs are correspondingly high.

In addition metering devices are known which operate with an indirect measuring method. In this case the vacuum formed as a result of the liquid discharge is measured by a metering diaphragm.

This measuring method presupposes a mechanical construction having a stable dispensing vessel or a pressure chamber, together with a diaphragm, whose cavity content is equal to or larger than the quantity of liquid to be dispensed. Thus, this diaphragm can only be regulated in a given volume ratio. Mechanical changes are required in the case of larger quantities. In addition the diaphragm must be very light in order to keep the vacuum low, which in turn means waiting times for lowering the diaphragm between the individual dispensing operations. Avery accurately operating aircutoffvalve is also required and once again trained personnel are required for maintenance purposes.

Furthermore a method and an apparatus for metering quantities of liquid are known which, with the aid of a known NTC anemometer measures the after-flowing air in a container from which the liquid is metered by means of an electrical discharge valve.

In this known measuring method there is a conversion into a proportional analogous direct current and with this the feeding of a low-loss capacitor of known size with a voltage rise which is linearly proportional to the outflowing quantity of liquid.

However, in practice this method leads to a measuring accuracy which is well below that of the hitherto known methods for known reasons, such as capacitor losses, loading by the following evaluation circuit, measurement on the capacitor charging curve, too low variation possibilities in the quantity and the like.

The problem of the present invention is therefore to obviate the problem of having to pay trained personnel when charging dispensing machines, to reduce the cleaning problem to a minimum and to provide a maintenance-free metering device which can be electronically set to virtually random quantities, whereby through electronic pre-selection both programming and release are not bound to a specific dispensing unit and whereby a higher degree of measuring precision is obtained.

According to the invention this problem is solved by a metering device, wherein the container has an upper cover provided with an inlet pipe for pressure compensation, in the inlet pipe is arranged a nozzlelike opening with a given cross-section in whose flow range is arranged an NTC resistor system of a per se known anemometer circuit at whose output is available a voltage which is proportional to the flow rate and consequently to the air flow rate, said voltage being supplied to the input of an analog voltage/frequency converter which supplies an a.c.

voltage or an impulse sequence with a frequency proportional to said voltage, said frequency being supplied to a counting circuit for comparison with a comparison count value preset by means of a setting device, whereby the count value counted by the counting circuit is proportional to the quantity of air which has flowed in during pressure compensation, and wherein the output of the counting circuit is applied to a control circuit for the discharge valve constructed as an electrical control valve.

According to an embodiment of the invention the NTC resistor system comprises two NTC resistors which in per se known manner are connected via connecting lines to a bridge circuit with seriesconnected amplifier within the anemometer circuit, an output line of the amplifier which carries the voltage proportional to the air flow rate is connected to the input of a voltage-controlled oscillator and the control input of a gate connected in the output of the latter oscillator within the said analog voltage/ frequency converter from whose output leads an output line carrying the voltage with the indicated frequency which is connected to the input of a counter within the counting circuit, which also comprises a comparator to whose one input is supplied the count value of the counter and to whose other input is supplied a comparison count value from a register settable by a setting device via an input line and whose output carrying the signal for the comparison result is connected via an output line with the control circuit for the discharge valve.

According to a further feature of the invention the counting circuit is constructed as a ring counter with a predetermined number of stages, which on reaching a given count value supplies via the output line a signal for blocking the discharge valve and the said frequency can be preset by means of a setting device in the analog voltage/frequency converter for modifying the quantity to be metered.

According to the method of the invention for metering quantities of liquids the discharge valve of the container receiving the liquid to be metered is controlled by means of an anemometer with an NTC resistor system for measuring the flow rate of the air during pressure compensation at a nozzle-like opening of known cross-section in per se known manner, by means of a series-connected analog voltage/ frequency converter for producing a frequency prop ortional to the air flow rate during pressure compensation, by means of a digital counting circuit for counting the oscillations or pulses corresponding to the volume of air passing through during pressure compensation and a control circuit series-connected with the said counting circuit.

As a result of the construction of the device according to the invention it is possible to measure the airflowing through the air intake in the form of its wind velocity per unit of time. The wind velocity is converted into a corresponding electrical signal, for example by means of an NTC anemometer. Compared with the hitherto known measuring methods the present method converts the voltage supplied by the NTC anemometer via an analog - digital converter into a frequency which can then be evaluated in a counter. By preprogramming the counter or by comparison the measurement can be terminated at any predetermined value. As the losses in digital technology are negligible cocmpared with those encountered with capacitors the measuring precision is essentially only dependent on the selected frequency (pulses/quantity).

Furthermore through presetting specific values e.g. in the counter the present measuring method makes it possible to take account of the heat capacity of the NTC resistor combination and which for example in the case of capacitor measuring could lead to errors if account was not taken thereof in the evaluation circuit, which in turn would greatly limit the measuring range. In addition this method also makes it possible to carry out further evaluation using digital technology.

This greatly simplifies the setting of quantities, the setting of the measuring precision and subsequent servicing. In addition the setting or the subsequent changing of quantities is greatly simplified by the present invention because, through the evaluation via pulse/quantity, a number or code can be fed in from which it is possible to directly calculate the quantity. Thus, with only a single dispensing unit and a corresponding electronic control system, such as run-off control, step-by-step switch, shift register, store or the like or operation from the outside it is possible to directly and successively dispense different predetermined quantities.

The invention will be described in greater detail hereinafter relative to a non-limitative embodiment and with reference to the attached drawings, wherein show: Figure 1 a diagrammatic view of a container with a liquid to be metered, in conjunction with the metering device according to the invention.

Figure 2 a block circuit diagram of a preferred embodiment of the metering device according to the invention.

The metering device comprises a container 10 which receives the liquid Fto be metered and which is open at the top and has preferably at the bottom, a discharge pipe 11, carrying a discharge valve 12 which can be constructed as an electromagnetic control valve.

In the upper container cover 15 is provided an intake connection 21 with a nozzle-like opening 20 through which can flow the air in the direction of arrow X for pressure compensation in the space above the liquid F in the container 10.

The cross-section of opening 20 is predetermined and with normal operation only requires a low flow speed for pressure compensation purposes.

The nozzle-shaped opening 2C with its precisely defined cross-section makes it possible to measure the quantity of air which flows following the outflow of liquid from the container 10 during pressure compensation in the form of the flow rate which occurs or to determine the air throughput on the basis of the predetermined opening cross-section.

This is achieved by means of an anemometer circuit 40 functioning as a measuring sensor operating with an NTC resistor system 30 and which supplies a voltage U1 proportional to the flow rate and consequently to the air throughput. The electronic device will be described in greater detail hereinafter. Disturbing or interfering influences resulting from changes in the atmospheric humidity and atmospheric pressure are of no consequence for the use of the metering device according to the invention. The metering device is essentially to be used in beverage dispensing machines.

The per se known NTC resistor system 30 is placed in the nozzle-like opening 20 in the air flow zone and by means of the series-connected electronic devices serves to control the discharge valve 12. For a more detailed description of the air flow measurement by means of NTC anemometers reference is made to "Technischen Informationen fur die Industrie", TI 159, pages 5 to 9, Valvo G.m.b.H.

Anemometers are known and their operation is based on the fact that the cooling of an electrically heated NTC resistor in a gaseous or liquid medium is a function of the heat capacity, temperature and flow rate of the medium. After eliminating the influence of the temperature of the flow medium to be measured and the calibration of the device the voltage or current change at the NTC resister system 30 can be used as the sole measuring quantity for the flow rate and consequently for determining the air volume which flows in during pressure compensation.

The anemometer circuit 40 is connected with an analog voltagelfrequency converter 50 and the latter is connected to a counting circuit 60, which is in turn connected to a control circuit 80. The output of control circuit 80 is connected to the not shown operating winding of discharge valve 12.

Figure 2 shows in greater detail the electronic devices for controlling discharge valve 12.

Anemometer circuit 40 is connected to two NTC resistors 31, 32 in the NTC resistor system 30 which is located in the vicinity of nozzle-like opening 20.

The NTC resistors 31,32 arranged in known manner in a bridge circuit 41 via connecting lines 33,34,35, 36 are exposed to the air flowing through opening 20 during pressure compensation. NTC resistor 32 represents the actual sensor for the air flow, whilst NTC resistor 31 is encapsulated in wind-tight manner, as indicated by dotted lines and serves to compensate the influence of temperature in the bridge circuit. A series-connected amplifier 42 supplies a voltage U1 proportional to the air flow rate.

Suitable miniaturised NTC resistors sealed in glass are for example marketed by VALVO G.m.b.H. under type designation 2322627 11472. Further details of these NTC resistors can be obtained from the above-mentioned information sheet of VALVO G.m.b.H.

The voltage U1 proportional to the air flow rate and consequently to the air throughput obtained from anemometer circuit 40 is available at an output line 43. According to the invention this voltage is supplied to the analog voltage/frequency converter 50 which at its output delivers to an output line 53 an a.c. voltage with a frequency f1 which is proportional to voltage U1 and consequently to the air flow rate and airthroughput. This a.c. voltage can be sinusoidal or rectangular. In the latter case the signal on line 53 would for example be an impulse sequence with the repetition frequency f1. The Expert is aware of an adequately large number of possibilities for the realisation of a voltage-controlled oscillator 51 which represents the core of the analog voltage/frequency converter 50.A gate 52, whose control input is also subject to the action of voltage U1 is located at the output of the voltage-controlled oscillator 51. Gate 52 ensures that the output signal of the voltagecontrolled oscillator 51 is blocked as soon as the voltage U1 and consequently the air flow rate has reached a zero value, i.e. when the pressure compensation on changing the liquid volume F in container 10 has stopped.

As the cross-section of the nozzle-shaped opening 20 is known the possibility is obtained with the knowledge of the air flow rate which occurs and the duration of the pressure compensation process of determining the volume of air passed through and consequently the quantity of liquid A F discharged at discharge valve 12 because they are both equal.

According to the invention by counting the oscillations of the a.c. voltage with frequency f1 a count value is obtained which is proportional to the volume of air which has passed through and conse quentlythe liquid quantity A Fdischarged at discharge valve 12. For this purpose the counting circuit 60 contains a digital counter 61, which is constructed in per se known manner and which counts the oscillations of frequency f1, which can vary during a pressure compensation process in accordance with the flow rate at 20.

The counter 61 can be constructed in the most varied ways. In the most simple case it counts up to a count value predetermined by fixed wiring with a not shown AND gate, which is thereby connected through and delivers a voltage for controlling discharge valve 12 which is constructed as an electrical control valve.

However, in the present embodiment counter 61 is connected to a comparator 63, whose other input is connected to a register 62 with a preset comparison count value. An output line 64 for the comparison result then always carries an output signal if the digital count value in register 62 and in counter61 coincide. It is obvious that counter 61 is reset after the signal appears on output line 64. In the present embodiment of the invention a setting device 70 is provided for presetting the count value in register 62. The connection between register 62 and setting device 70 is formed by an input line 71 which is constructed as a bus as a function of the number of different bits required with bit-parallel feed-in. The setting device 70 can be a keying system, a rotary switch, a fixed-wired combination of logic voltage values or any other reversing switch or a read-only store.

In the case for example of using the object of the invention for metering beverages in a beverages dispensing machine, where the volume of liquid to be dispensed is constant it is merely necessary to have a plug-in, fixed-wired logic circuit for determining the comparison count value. In this case it would be possible for example to economise on register 62 and to connect the logic circuit directly with comparator 63 for feeding in the comparison count value.

It is possible to connect a further counter 66 for counting the metering processes to the output of comparator 63. Counter 66 is shown by dotted lines in Figure 2. Counter 66 is always advanced when a signal for controlling the discharge valve 12 appears on output line 64. It is consequently possible to count the number of individual metered quantities of liquid dispensed and to indicate them with suitable means.

Control circuit 80 is in practice a power amplifier for supplying the magnet winding (not shown of discharge valve 20).

In the simplest case the preprogrammable counter 61 can be replaced by a ring counter comprising a predetermined number of stages, which in a given logic state in a particular stage delivers a signal for the control of discharge valve 12 to the output line 64 and thereby blocks the same. During the next dispensing process the ring counter would count on until the same logic state was again reached at the same stage in order to block discharge valve 12.

Obviously the dispensing of the metered quantity of liquid is initiated with conventional means, which are not shown here, i.e. for example by opening discharge valve 12, controlled by a coin insertion device with valuation contact or a simple pushbutton. The control of the valve opening can form part of an automatic run-off control, for example with a step-by-step switch.

Thus, the metering device according to the invention does not operate with sensing or scanning in the liquid flow and instead the determination of the metered quantity takes place in digital form and consequently this device is substantially free from maintenance and very reliable on dissociation from the actual dispensing unit.

The digital comparison circuit with comparison value feed-in can be preset to virtually any quantities to be metered. A metering device with a high measuring precision is obtained on finding that the anemometer and analog voltage/frequency converter circuit undergo no fluctuations in their transmission and conversion characteristics, whereby in particular the influence of temperature and operating voltage changes is eliminated by suitable circuit measures.

As the anemometer sensor (NTC resistor system) together with the intake pipe for the pressure compensation is not in contact with the liquid to be metered and the volume of the particular container does not influence the metering process it is possible to effortlessly replace the liquid to be metered, as well as the container used. As a result it is possible to subsequently incorporate the metering device according to the invention. The pre-requisite is that the associated intake pipe with its accurately defined nozzle-like opening and a discharge valve, constructed as an electrical control valve, controllable by the metering device can be fitted.

The counters for determining the metered quantity can be constructed either as forwards-only or reversible counters, the important point being that a particular counter state brings about the blocking of the discharge valve.

In addition to the possibility of changing the comparison count value in digital form on a setting device on changing the metering quantity it is possible according to another embodiment to so preset the frequency f1 at the output of the analog voltage/frequency converter by means of an additional setting device, such as for example a potentiometer for delivering a fixed bias voltage to a voltage-controlled oscillator that the ratio of the supplied pulse count or oscillation frequency to the quantity of air flowing through is modified. As a result it is possible with an unchanged comparison count value or counter state (in the ring counter) to change the quantity to be metered for releasing the blocking of the discharge valve. This possibility is particularly advantageous if a simple counter circuit without digital setting device is used.

The heat capacity of the NTC resistor system 30 which in the case of the hitherto known measuring circuits functioning with RC systems and analog voltages caused an error which could only be compensated by a certain expenditure and a limitation of the measuring range is taken into account with the metering device according to the invention by presetting a particular count value in the counter and essentially leads to no disturbing limitation of the measuring range.

The setting device 70 for fixing the quantity of liquid to be metered can also be designed for successively dispensing different quantities. It can for example be constructed as a run-off control with a step-by-step switch or as a selector switch operable from the outside. The metering device according to the invention is therefore also suitable for beverages filling machines. The above-described electronic counter mechanism for counting the dispensing processes can then be used for counting the filled units.

The invention is not limited to the embodiments of the metering device described and presented hereinbefore and various modifications can be made thereto without passing beyond the scope of the invention.

Claims (8)

1. A metering device for the automatic metering of quantities of liquid, with a container for receiving the liquid to be metered having a liquid discharge pipe at the bottom and which is equipped with a discharge valve, wherein the container has an upper cover provided with an inlet pipe for pressure compensation, in the inlet pipe is arranged a nozzlelike opening with a given cross-section in whose flow range is arranged an NTC resistor system of a per se known anemometer circuit at whose output is available a voltage which is proportional to the flow rate and consequently to the air flow rate, said voltage being supplied to the input of an analog voltage/frequency converter which supplies an a.c.

voltage or an impulse sequence with a frequency proportional to said voltage, said frequency being supplied to a counting circuit for comparison with a comparison count value preset by means of a setting device, whereby the count value counted by the counting circuit is proportional to the quantity of air which has flowed in during pressure compensation, and wherein the output of the counting circuit is applied to a control circuit for the discharge valve construction as an electrical control valve.

2. A metering device according to Claim 1, wherein the NTC resistor system comprises two NTC resistors which in per se known manner are connected via connecting lines to a bridge circuit with series-connected amplifier within the anemometer circuit, an output line of the amplifier which carries the voltage proportional to the air flow rate is connected to the input of a voltage-controlled oscillator and the control input of a gate connected in the output of the latter oscillator within the said analog voltage/frequency converter from whose output leads an output line carrying the voltage with the indicated frequency which is connected to the input of a counter within the counting circuit, which also comprises a comparator to whose one input is supplied the count value of the counter and to whose other input is supplied a comparison count value from a register settable by a setting device via an input line and whose output carrying the signal for the comparison result is connected via an output line with the control circuit for the discharge valve.

3. A metering device according to Claim 2, wherein a counter for the number of metering processes is connected to the output line of the comparator.

4. A metering device according to Claim 1, wherein the counting circuit is constructed as a ring counter with a predetermined number of stages which on reaching a predetermined count value supplies a signal for blocking the discharge valve by means of the output line.

5. A metering device according to Claim 1, wherein the frequency can be preset by means of a setting device in the analog voltage/frequency converterforthe purpose of modifying the metering quantity.

6. A method for the automatic metering of liquid quantities using a metering device according to Claims 1 to 6, wherein the discharge valve of the container receiving the liquid to be metered is controlled by means of an anemometer with an NTC resistor system for measuring the flow rate of the air during pressure compensation at a nozzle-like opening of known cross-section in per se known manner, by means of a series-connected analog voltage/ frequency converter for producing a frequency proportional to the air flow rate during pressure compensation, by means of a digital counting circuit for counting the oscillations or pulses corresponding to the volume of air passing through during pressure compensation and a control circuit series-connected with the said counting circuit.

7. A metering device substantially as described hereinbefore with reference to the drawings and in particular Claims 1 to 5.

8. A method for the automatic metering of liquid quantities substantially as described hereinbefore with reference to the drawings and in particular Claim 6.