Patent Publication Number: US-2022228893-A1

Title: Flow detection circuit

Description:
TECHNICAL FIELD 
     The various aspects and embodiments thereof relate to a circuit and device for detection of a flow through a duct as part of a system for dispensing beverages, using a capacitive sensor. 
     BACKGROUND 
     U.S. Pat. No. 6,545,488B2 discloses a system for capacitive flow measurement through a duct in a large transportation system. Two electrodes are helically wound around the duct and a signal is applied to the electrodes. Upon change of flow through the duct, a frequency of a signal in a detection circuit varies. The detection is transformed to a voltage signal, which is used for further processing. 
     SUMMARY 
     When using variation of capacitance for changing an oscillating frequency, use of an inductance is highly preferred. Inductances are bulky and relatively expensive circuit components. Furthermore, for further conversion of frequency changes to a voltage signal, a significant amount of circuitry is required. It is preferred to provide a more efficient arrangement for detecting flow through the duct of a beverage dispensing system. 
     A first aspect provides a circuit for detecting a flow through a duct of a tap for dispensing beverages. The circuit comprises an alternating signal source having a signal terminal arranged to provide an alternating signal to a capacitive element comprising two electrodes provided at opposite sides of the duct along at least part of the length of the duct and a detection circuit. The detection circuit is arranged to be connected to the capacitive element and arranged to detect a signal amplitude value from the capacitive element at a sensing terminal comprised by the detection circuit, the detection circuit being arranged to provide a detection signal at a detection terminal comprised by the detection circuit based on the signal amplitude value at a detection terminal comprised by the detection circuit. The flow detection circuit also comprises a processing circuit arranged to receive the detection signal, determine whether the detection signal satisfies a pre-determined criterion; and provide a flow signal if the pre-determined criterion is met. 
     This system works with one frequency throughout the circuit, thus reducing complexity. Furthermore, it may be implemented in the analogue domain, in the digital domain or partially in the analogue domain and partially in the digital domain without departing from the scope of this aspect. 
     In an implementation, the alternating signal source has a signal terminal arranged to be connected to a first capacitor electrode provided along at least part of a length of the duct and the detection circuit is arranged to be connected to a second capacitor electrode provided along at least part of a length of the duct for receiving an electrode signal. 
     A further implementation further comprises an adding circuit for summing the detection signal and a reference control signal for providing a controlled detection signal, wherein the processing circuit is further arranged to provide a reference control signal based on the controlled detection signal. 
     The skilled person will understand that a subtractor also falls within the definition of an adder. With this implementation, large variation in the amplitude of the signal at the second electrode may be controlled within boundaries such that detection of flow and characteristics of the flow may be more convenient. 
     In another implementation, the detection circuit comprises a peak detection circuit and the detection signal is based on the output of the peak detection signal. Whereas other types of circuit may be used for determining an amplitude value, like multipliers, a peak detector is preferred for determining amplitude. 
     In yet another embodiment, the detection circuit is arranged to detect fluctuations of charge on the second electrode and to provide a voltage signal based on the detected fluctuations. Whereas the circuit may be implemented as current based, voltage based circuitry is preferred. 
     A second aspect provides a casing for housing a duct for a beverage dispensing tap. The casing comprises an elongate bore having a proximal opening and a distal opening for housing and guiding the duct, a first electrode provided over at least part of the length of the bore and a second electrode provided over at least part of the length of the bore. In this casing, the first electrode is arranged to be connected to the signal terminal of a circuit according to any of the preceding claims; and the second electrode is arranged to be connected to the sensing terminal of a circuit according to the first aspect. Such casing comprises the electrodes preferred for operation of the circuit according to the first aspect, providing an advantageous arrangement for housing a duct for dispensing beer—or another beverage—and detection flow of the beer. 
     In an embodiment, the casing comprises a first shell and a second shell, the first shell comprising a first elongate recess and the second shell comprising a second elongate recess such that when the first shell and the second shell are joined for forming the case, the first recess and the second recess provide at least part of the duct. This casing is advantageous for use of a disposable duct, which may be conveniently inserted and removed from the bore. Furthermore, if the casing is provided by means of two halves, electrodes and circuitry may all be provided on one and the same shell part. 
     A third aspect provides a dispensing device for dispensing a beverage. The device comprises the casing according to the second aspect, the circuit according to the first aspect. In this device, the first electrode is connected to the signal terminal; and the second electrode is connected to the sensing terminal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various aspects and implementations thereof will now be elucidated in conjunction with drawings. In the drawings: 
         FIG. 1 : shows a beverage dispensing system; and 
         FIG. 2 : shows a flow detection circuit; 
         FIG. 3 : shows another flow detection circuit; and 
         FIG. 4 : shows an electrical circuit equivalent of the other flow detection circuit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a beer dispensing system  100  as an implementation of a dispensing device for dispensing beverages. The beer dispensing system  100  comprises a duct  120  for providing or forming a channel for beer to flow from a reservoir like a keg or a large tank (not shown) to a dispense valve  122 . The valve  122  can be an integral part of the duct, or the  120  duct can be coupled to the valve  122 . The duct  120  is or at least comprises preferably a flexible and more preferably a resilient tube comprising an organic polymer, like PVC, silicon, polyethylene, other, or a combination thereof. 
     The duct  120  is provided in and extends through a bore  114  in a casing  112  that constitutes a stand for a dispense tap  116 . The dispense tap  116  comprises a tap handle  118  for operating the dispense valve  122 . Within the casing  112 , a first electrode  132  and a second electrode  134  are provided. The first electrode  132  and the second electrode  134  are provided such that they are located at opposite sides of the duct  120  for at least a part of the length of the duct  120 . 
     Such constellation may be achieved by providing the first electrode  132  and the second electrode  134  in the casing, at opposite sides at the inner wall of the bore  114  and substantially parallel to the length of the bore  114  and the duct  112 . In this constellation, the electrodes are provided opposite to one another over their full lengths. Alternatively, the electrodes are provided in any other way such that they are provided at opposite sides at least for one or more parts of the length of the bore  114 . 
     The beer dispensing system further comprises a flow detection circuit  200  for detecting whether beer is drawn from the reservoir using the beer dispensing system  100 . The flow detection circuit  200  is connected to the first electrode  132  and the second electrode  134 . 
     The casing may be provided by means of two shells to facilitate removal and insertion of the duct  120 . This is particularly advantageous if the duct  120  is a disposable duct. In such embodiment, the first electrode  132  and the second electrode  134  are preferably provided on the same shell part, together with a flow detection circuit  200 . The duct  120  may be embedded in a first shell having a recess as part of the bore  114 . 
     Subsequently, a second shell is joined with the first shell for forming the casing  112 . Alternatively, the duct  120  is led through the bore  114  with a closed bore, i.e. with the two halves joined, or, if the casing  112  mainly comprises a single unit through which the bore is provided. The duct  120  may be inserted in the bore  114  from above or below, in the constellation shows by  FIG. 1 . The bore  114  may be provided inside a massive casing  112  or as a tube or pipe, either rigid or flexible, in a hollow casing  112 . The shape and dimension of the cross-section of the bore  114  may vary or be substantially the same over the length of the bore  114 . 
     The duct  120  is preferably provided inside the bore  114  such that it does not contacts the first electrode  132  and the second electrode  134 . Whereas the duct  120  is preferably provided as a flexible dispensing line predominantly comprising an organic polymer that is electrically insulating, liquid and water condensation in particular, may provide a conductive path. Therefore, the duct  120  is provided at a distance from the first electrode  132  and the second electrode  134 . Alternatively or additionally, the first electrode  132  and the second electrode  134  are provided with an insulating film, at least at a side facing the inner space of the bore  114 . 
     The bore  114  may be provided as a rigid guide for the duct  120  or as a flexible guide. In the latter case, the bore  114  may be provided comprising a flexible tubing inside which tubing the duct  120  may be provided. 
       FIG. 2  shows the flow detection circuit  200  in further detail.  FIG. 2  shows functional components preferred for implementing the flow detection circuit  200 . The flow detection circuit  200  comprises a signal generator  202  for providing an alternating signal, as a voltage source or a current source. Preferably, the signal generator  202  generates a sine wave, preferably at a frequency between 1.5 kHz and 3 kHz, more preferably between 2 kHz and 2.5 kHz and most preferably at 2.3 kHz. It is noted that depending on the values of the various components, other values of the frequency may be selected, between 1 kHz and 4 kHz, between 5 kHz and 10 1  kHz, between 10 1  kHz at 5·10 1 -kHz or above, even up to 102 kHz and up. 
     In another implementation, the signal generator generates another wave form, including at least one of a triangular signal, a block wave, a saw tooth signal, other, or a combination thereof. The frequency of the signal is preferably set, though it may be variable. 
     The generated signal is applied to the first electrode  132 . The signal may optionally be provided via a buffer, decoupling capacitor, a resistor, another type of impedance or a combination thereof. Together with the second electrode  134 , the first electrode  132  constitutes a capacitor  204 . Variations of charge on the first electrode  132  due to the alternating signal applied will result in variations of charge on the second electrode  134 —as is the basic principle of a capacitance like the capacitor  204 . 
     The fluctuations in charge on the second electrode  134  result in an alternating current at the second electrode  134 . The amount of the fluctuation depends on characteristics of the medium between the first electrode  132  and the second electrode  134 . Such characteristics include, but are not limited to, distance between the electrode, permittivity of the medium or media between the electrodes and other characteristics of the medium or media. 
     The alternating current is provided to an amplifier and preferably to a trans impedance amplifier  206  for converting the alternating current to an alternating voltage. The alternating voltage has the same frequency as the signal provided by the signal generator  202 . The amplified voltage signal is provided to a band stop filter or notch filter  208  which has a centre frequency substantial equal to a frequency of mains voltage supply. For the majority of the world this is 50 Hz, for some regions including the Americas this is 60 Hz. At some locations, other frequencies may apply. Alternatively or additionally, for reducing influence of the mains power grid, the casing  112  may be provided with shielding for reducing electromagnetic interference on the flow detection circuitry. 
     The alternating signal is subsequently provided to a bandpass filter  210 . The bandpass filter  210  has a centre frequency substantially equal to the frequency of the signal provided by the signal generator  202 . The bandpass filter  210  may be provided comprising capacitances and inductances as to define slopes and centre frequency independently. However, as inductances may be bulky and relatively expensive, use of a multiple feedback bandpass filter (MFB filter) is preferred. 
     The signal thus filtered is provided to a rectifier  212 . The rectifier  212  is in this implementation a half-bridge rectifier. Alternatively, the rectifier  212  may be implemented as a full bridge rectifier. However, the input signal is a data signal of which only the top output level of the rectified signal is relevant, for which reason not the full signal is required to be rectified—as opposed to a power signal. 
     The rectified signal is provided to a level detection circuit  214  for detecting a peak level of the rectified signal. Of the filtered and rectified signal, the peak level is determined and the level detection circuit and the output of the peak detector  214  is provided to an amplifier  216 . 
     The amplified signal at the output of the amplifier is provided to a feedback control loop. The feedback control loop comprises an adder  218  —which may with minor design modifications also be implemented as a subtractor—and a control circuit  220 . The control circuit  220  is preferably implemented as a PID control circuit  220 —a proportional—integral —derivative controller. 
     The PID control circuit  220  is preferably provided as part of a microcontroller  240 . Hence, the output of the adder  218  is sampled and digitised prior to being provided to the PID control circuit  220 . The output of the PID control circuit  220  is initially digital and converted to the analogue domain prior to being provided to the adder  218 . 
     A reason for providing the feedback control loop is that depending on the container in which beer is dispensed into, such as a glass or a jug, the variations in the signals may vary significantly in magnitude. The feed control loop ensures the analogue output of the circuit as provided to the microcontroller is provided in the proper range, for example between 0 and 5 Volt, between 0 and 3.3 Volt, between 0 and 2.5 Volt or another range. 
     The digitised signal provided to the PID control circuit  220  is also provided to a central control circuit  242 . The central control circuit  242  is part of the microprocessor  240  of which the functionality may be programmed or already available upon manufacturing. The central control circuit evaluates the digitised output signal of the adder  218 —the controlled signal—to one or more pre-determined values. These values may be stored in a storage module  244 , either provided separately or as part of the microcontroller  240 . 
     The values may also be adjusted based on ambient temperature. To that purpose, the microcontroller  240  is connected to a temperature sensor  250 . 
     If the controlled signal is above or below a particular pre-determined value, it may be determined that beer is dispensed from the beer dispensing system  100 . It has been determined that as beer is being dispensed from the beer dispensing system  100 , the level of the alternating current at a terminal of the second electrode varies. This variation of the amplitude of the received capacitor current depends on a type of container used—glass, jug, pitcher or bucket—and how the container is being held—by the full hand or by the tips of a few fingers only. 
     Hence, as the controlled signal is at a particular value, it may firstly be detected that beer is being drafted and in a container in particular, such as a pitcher, a jug or a glass. Second, it may be established in what type of container—pitcher, glass, jug—beer is being drafted. Third, it may be established how the container is being held. Fourth, as detection is based on the duct  120  being present in the bore  114 , between the first electrode  132  and the second electrode  134 , it may be detected whether the duct  120  is present at all. 
     Based on the determinations, further data processing may be executed. A proper beer is being drafted by fully opening the valve  122  of the tap  116 , commonly executed by swivelling the tap handle  118  by e.g. about ninety degrees. This means that the dispense valve is either open or closed; the flow is either maximal or zero. If the period in time of drafting may be determined based on processing of the controlled signal (or another signal in the chain) is multiplied by the maximum flow, the amount of beer drafted may be calculated. In this way, a pre-warning may be issued in case a keg or other reservoir is almost empty. 
     The microcontroller  240  also comprises an actuator circuit  246  which may be programmed or already available upon manufacturing. The actuator circuit is arranged to control an actuator outside the microcontroller  240 , like the light emitting diode  260 . The light emitting diode  260  may provide a lighting functionality for lighting the casing  112  or part thereof. Alternatively or additionally, other light sources, a display screen for showing text, video or still images, an audio source or other peripheral devices may be controlled. 
     With the type of container determined, the type of container may be shown on a screen close to the dispensing system  100 . And if it is determined how the container is being held, feedback may be provided to a person using the dispensing system  100 . For example, if it is preferred a glass is being held by the tips of fingers rather than the full hand, the user may be informed to take corrective action if it is determined the glass is being held by the full hand. 
     Another action may be taken by a remotely located actuator. To that purpose, the flow detection circuit comprises a communication module  248  connected to the central control circuit  242 —or another part of the microcontroller  240 . Instructions to remotely located actuators may be provided to the communication module  248 , which transfers the instructions using a protocol like IEEE 802.11, popularly known as WiFi, Zigbee, Bluetooth, LoRa, an LTE protocol, other, or a combination thereof. Alternatively or additionally, data may be received via the communication module  248 , for example for programming the microcontroller  240 . 
     The dispensing system  100  thus provided is preferably used for dispensing beer, but it may also be used for dispensing other beverages like cider, alcopops or soft drinks. 
     The filters used in the flow detection circuit  200  are preferably active filters, which may be implemented using commercially available operational amplifiers. 
     In the embodiments discussed above, the first electrode  132  and the second electrode  134  are provide at either side of the bore  114 —or the duct  112 , for that matter—and the first electrode  132  is connected to the signal generator  202  and the second electrode  134  is connected to the signal detection circuit right of the capacitive element the capacitor  204  embodies. In another embodiment, the capacitor  204  is provided in a capacitive divider, in series with or parallel to a further capacitive element having a substantially fixed capacity value. 
     As the capacity value of the capacitor  204  changes upon beer being drawn through the duct  112  and amplitude of a signal provided by the signal generator changes, depending on the configuration, a change of current through or voltage over the capacitor  204  and/or through/over the further capacitor may change. This change may be detected and used to determine whether a liquid flowing through the duct is dispensed in a container. In case the capacitors are connected in parallel, a change in current is to be detected and in case the capacitors are connected in series, a change in voltage is to be detected. It is noted that this relates to the amplitude of the signal, rather than the actual value. 
       FIG. 3  shows a sensing arrangement  300  as another implementation of a sensing setup according to the aspects discussed above for use in, for example, the beer dispensing system  100 .  FIG. 3  shows the sensing arrangement  300  comprising beer conduit module  302  and a sensing module  304 . The beer conduit module  302  comprises a beer conduit  312  connected at a distal end to a beer keg  306  arranged to hold beer—or another dispensable liquid—and connected at a proximal end to a tap like the dispense tap  116  as shown by  FIG. 1 . 
     Around the beer conduit  312 , a transmitter electrode  314 , a first receiving electrode  316  and an optional second receiving electrode  318  are provided. Between the transmitter electrode  314  and the first receiving electrode  316 , an optional first shielding electrode  320  is provided and between the first receiving electrode  316  and the second receiving electrode  318 , an optional second shielding electrode  322  is provided. The electrodes are preferably not provided in direct contact with the beer conduit, but this may be the case in another implementation. 
     The electrodes preferably fully surround the beer conduit  312 . In an implementation in which the casing  112  ( FIG. 1 ) is provided having two or more shell parts, the electrodes may be constituted as comprising multiple electrode parts, wherein each part is comprises by a shell part of the casing  112 . With the casing  112  assembled, the electrode parts of each electrode are in conductive contact with one another—but not with parts of other electrodes. In another implementation, not all shell parts comprise parts of each electrode, in which case each electrode may not fully surround the beer conduit  312 . 
     Preferably, the shielding electrodes, if present, are—measured along the length of the beer conduit  312 —preferably shorter than the transmitter electrode  312 , the first receiving electrode  316  and the second receiving electrode  318 . The shielding electrodes are connected to ground level or to the zero reference of the signal source V 1 . 
     The sensing module  304  comprises a signal source V 1 , a first reference capacitor C 1  and a second reference capacitor C 2 . The reference capacitors may be provided external to a housing in which most of the flow detection circuit  200  may be embedded and in particular external to the microcontroller  240  or any other digital circuitry of the flow detection circuit  200 . The signal source V 1  is substantially the same, similar or at least equivalent to the signal generator  202  of  FIG. 1 , unless indicated otherwise. 
     The signal source V 1  is at a first terminal connected to ground or a zero reference and at a second terminal connected to the transmitter electrode  314  and a first terminal of the second reference capacitor C 2 . Between a second terminal of the second reference capacitor C 2  and a first terminal of a first reference capacitor C 1 , a reference voltage terminal is provided, with a reference voltage. A second terminal of the first reference capacitor C 1  is connected to ground level or the zero reference terminal of the signal source V 1 . Further components may be provided between the first reference capacitor C 1  and the second reference capacitor C 2  for providing a first reference voltage at a terminal of the first reference capacitor C 1  not connected to the signal source C 1  and a second reference voltage at a terminal of the second reference capacitor C 2  not connected to ground. 
     The sensing module  304  comprises a first signal comparator  342  and a second signal comparator  344 . The signal comparators are arranged to compare analogue input signals and to provide an output signal in response to the comparing operation. The signal comparators may be implemented using analogue operational amplifier circuits. Alternatively or additionally, the comparing of signals may be executed in a digital domain. To that end, the signal comparators may comprise analogue to digital converters. 
     The comparing by the signal comparators may take place instantaneously, in a continuous time domain. Alternatively or additionally, the comparing may take place in an amplitude domain, comparing amplitudes of the reference voltage and a voltage as sensed by means of the first receiving electrode  316  and the second receiving electrode  318 . Such comparing in the amplitude domain may takes place continuously or at regular intervals, for example every fifth, tenth or twentieth of a second to every one or two seconds. 
     A first signal comparator  342  is connected to the first receiving electrode  316  and the reference voltage terminal. A second signal comparator  344  is connected to the second receiving electrode  318  and the reference voltage terminal. In this configuration, the first signal comparator  342  compares voltages on the first signal electrode to  316  the reference voltage and the second signal comparator  344  compares voltage on the second signal electrode  318  to the reference voltage. 
     The comparators provide an output signal based on a difference between the input voltages. Further signal processing, prior to comparing, after comparing or both, may take place, in a way as discussed in conjunction with  FIG. 2 , otherwise, or a combination thereof. The output signals of the comparators as detection signals may subsequently be provided to a processing unit like the microcontroller  240 . In the processing unit, both or one of the detection signals are evaluated to one or more pre-determined criteria; if one, some or all of the pre-determined criteria are met, the flow signal may be provided, indicating detection of a flow through the dispensing line or duct  120 . 
       FIG. 3  shows a parasitic capacitance C 6  from the beer conduit  302  to ground to model a connection between the beer conduit  302  and ground via a person drawing a beer. Furthermore, a keg parasitic capacitance C 7  is drawn to model a capacitance from the beer conduit  302  to ground via the beer keg  306  and the beer conduit  302 . 
       FIG. 4  shows an equivalent circuit diagram  400  of the configuration depicted by  FIG. 3 .  FIG. 4  shows the first reference capacitor C 1  and the second reference capacitor C 2 .  FIG. 4  also shows a first receiving terminal Rx 1  providing an input to the first comparator  342  and a second receiving terminal Rx 2  providing an input to the second comparator  344 . The transmitting electrode  314  is modelled as a transmitting capacitance C 3 , the first receiving electrode  316  is modelled as a first receiving capacitance C 4  and the second receiving electrode  318  is modelled as a second receiving capacitance C 5 . 
     The beer conduit  312  is modelled as a chain of resistances; a first conduit resistance R 1  between the transmitting electrode  314  and the first receiving electrode  316  and a second conduit resistance R 2  between the first receiving electrode  316  and the second receiving electrode. The proximal end of the beer conduit  312  up to the dispense tap  116  is modelled as a third conduit resistance R 3  and the dispense tap  116  itself is modelled as a tap resistance R 5 . The distal end of the beer conduit  312  between the transmitting electrode  314  and the keg  306  is modelled as a fourth conduit resistance R 4  and the resistance over the keg to keg parasitic capacitance C 7  is modelled as a keg resistance R 6 . 
     During a dispensing operation of the beer dispensing system  100 , while dispensing beer, at least one of the modelled conduit resistances and the transmitting electrode  314  and the receiving electrodes changes. As a result, the voltages at the first receiving terminal Rx 1  and the second receiving terminal Rx 2  change. With the values of first reference capacitance C 1  and the second reference capacitance C 2  being substantially constant, the reference voltage is substantially constant. 
     Variation of at least one value of capacitances and/or resistances at one side of the bridge and no substantial change at the other side of the capacitive bridge circuit allows the first comparator  342  and the second comparator  344  to determine the change in the value of at least one of the modelled conduit resistances and the transmitting electrode  314  and the receiving electrodes by determining differences between the reference voltage and the voltages at the first receiving terminal Rx 1  and the second receiving terminal Rx 2 . 
     It is noted that the second sensing electrode  318  and the second comparator  344  are optional, yet preferred for increasing accuracy of determining a flow through the beer conduit  312  and optionally the amount of the flow. 
     In the description above for  FIG. 3  and  FIG. 4 , it is noted that certain elements may be connected to a zero references or a ground terminal. A ground terminal is defined as a terminal having a fixed voltage level—usually zero—relative to the ground. A zero reference level is a voltage level of one terminal of a voltage supply or another particular terminal in a circuit. In the implementations discussed above, this terminal is the lower terminal of voltage source V 1  as depicted by  FIG. 3 . The zero reference is not always the same as the voltage level of the ground terminal (the ground level), as the zero reference may float relative to the ground level. The zero reference is only equal to the ground level if the zero reference terminal is connected to ground—like the protected ground of a wall socket or similar or equivalent. 
     Referring to  FIG. 3 , the shielding electrodes are connected to the same level as the zero reference of V 1 , as is the terminal of the first reference capacitance C 1  opposite to the reference terminal. These nodes may be connected to ground, but this does not have to be the case. The parasitic keg capacitance C 7  is at the terminal opposite to the distal end of the beer conduit  312  to ground. The latter is the case, as the beer keg  306  is commonly placed in a beer cellar and/or refrigerator, away from the beer dispensing system  100 , which does not provide a feasible option for connecting the zero reference to the environment of the beer keg  306 . 
     In another implementation, the signal provided on the first receiving electrode  316  and the second receiving electrode  318  is not compared to a voltage of the capacitive divider constituted by C 1  an C 2 , but fed to the circuit depicted by  FIG. 2 , with the signal on the receiving electrodes being provides to the trans impedance amplifier  206 . Alternatively, an equivalent circuit may be provided, with or without the appropriate filters, in analogue or digital form. In such embodiment, the first reference capacitance C 1  and the second reference capacitance C 2  may be omitted. Additionally or alternative, the first comparator  342  and the second comparator  344  may be omitted. 
     Likewise, the electrodes depicted by  FIG. 1  may also form part of a capacitive bridge circuit as depicted by  FIG. 3  and  FIG. 4 . 
     In summary, the aspects relate to a dispensing system for a beverage comprising in a tap system a bore for housing a duct. Along the bore, close to or on the duct, at least two electrodes are provided such that at least at some locations along the duct, the two electrodes are provided opposite to one another with the duct in between, thus constituting a capacitor. An oscillating signal, preferably have a sine waveform, is provided to one electrode and a signal is read out from the other electrode. As a beverage is drawn through the duct into a container, capacitance of the capacitor changes. The flowing beverage may have different characteristics, but capacitance may also change as the beverage in the duct is in conducting contact with a container that may be in contact with an ground contact. The change of capacitance results in a change of the amplitude of a detection circuit connected to the second electrode. 
     In the description above, it will be understood that when an element such as layer, region or substrate is referred to as being “on” or “onto” another element, the element is either directly on the other element, or intervening elements may also be present. Also, it will be understood that the values given in the description above, are given by way of example and that other values may be possible and/or may be strived for. 
     Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components. 
     It is to be noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting examples. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The word ‘comprising’ does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. 
     A person skilled in the art will readily appreciate that various parameters and values thereof disclosed in the description may be modified and that various embodiments disclosed and/or claimed may be combined without departing from the scope of the invention. 
     It is stipulated that the reference signs in the claims do not limit the scope of the claims, but are merely inserted to enhance the legibility of the claims.