Technical Field

The present disclosure relates to the field of automatic dispensers. In particular, a sensor unit configured to detect operation events of an automatic dispenser and a system comprising the sensor unit and the automatic dispenser are presented. A method for detecting operation events of an automatic dispenser and a computer program product are presented also.

Background

In recent years, there has been a rise in the number of new infections incurred inside hospitals. Especially patients are affected by this phenomenon. The main cause for these new infections is suspected to be an incorrect or improper use of hand hygiene products, such as fluid disinfectants, also due to the rising workload of the

employees of the hospitals.

A suitable countermeasure could be a comprehensive electronic recording of the usage of hand hygiene products. However, until now, such an approach is not easily possible for some kinds of dispensers. For example, the monitoring of an automatic dispenser already attached to a wall of a patient room is technically difficult as the monitoring function has to be retrofitted.

Conventional sensor units monitor the operation of an automatic dispenser based on measurements of a weight of a disinfectant fluid acting on the sensor or based on a movement of a pumping arm of the dispenser. An example of a sensor unit of the latter type is given in WO 2018/053627 Al, wherein an actuation of the dispenser is measured by a vibration sensor. Another example is presented in US 2011/0121974 Al, wherein a movement or vibration of the dispenser is associated with an actuation of the dispenser.

It has been found that the use of vibration sensors to monitor dispenser operation can lead to erroneous measurements. Such erroneous measurements can, for example, occur as a result of shocks acting on the dispenser from the outside. Summary

There is a need for a sensor unit that can be used with automatic dispensers for reliably detecting operation events of said dispensers.

According to one aspect, a sensor unit configured to detect operation events of an automatic dispenser is provided. The sensor unit comprises a detection unit configured to detect a change in an operating voltage of the dispenser and a controller. The controller is configured to analyse the voltage change for a

predetermined characteristic and, based on the analysis, assign the voltage change to an operation event of the dispenser. The controller is further configured to create a dataset indicative of the operation event.

The sensor unit may be an independent assembly that can handled separately from the automatic dispenser. As such, the sensor unit may be usable with different kinds of automatic dispensers. The sensor unit may be configured to be connected to the automatic dispenser during its initial installation process, or may be retrofitted to an already installed dispenser. In other variants, the sensor unit may be integrated into the automatic dispenser at a manufacturing site.

The detection unit may be configured to measure the operating voltage of the dispenser. The detection unit may further be configured to create a digital signal representative of said voltage. The operating voltage may be continuously measured by the detection unit, or the detection unit may measure the operating voltage at pre-defined points in time. Alternatively or additionally, the detection unit may comprise a comparing unit configured to compare the measured operating voltage to a pre-defined threshold and to trigger the detection unit to create the digital voltage signal if the operating voltage is above the threshold. The predetermined characteristic may comprise at least one of the following: an initial voltage before the voltage change, an end voltage after the voltage change, a voltage offset between an initial voltage and an end voltage, an amplitude of the voltage change (i.e., the voltage change "as such"), an indication whether the voltage change is a voltage decrease or increase (i.e., a "direction" of the voltage change), a duration of the voltage change, and a rate of the voltage change.

In some variants, the end voltage may be defined as the voltage that would be measured as the initial voltage of an immediately following dispensing operation. In such or other variants, any voltage recovery processes may not yet be fully completed when the end voltage is measured. In some variants, the amplitude of the voltage change may be defined as the largest difference between the initial voltage and any other voltage value measured temporally after the initial voltage and before the end voltage.

The controller may be configured to assign the voltage change to the operation event based on a comparison of the predetermined characteristic with at least one detection threshold associated with the predetermined characteristic. In some variants, the detection threshold may be defined so as to take into account one or more of the following effects upon detection of operation events: a (possibly changing) charging level of a power source of the dispenser, a (possibly variable) recovery time of the power source of the dispenser between dispensing events, a specific characteristic of the power source of the dispenser, environmental influences (temperature, humidity, air pressure), defects of the dispensing mechanism and software defects.

The controller may be configured to create an indication dependent on a result of the comparison. The indication may, for example, indicate that the comparison of the predetermined characteristic with the at least one detection threshold associated with the predetermined characteristic yields a negative result. A negative result may be a voltage change above a maximum detection threshold and/or below a minimum detection threshold. The indication may comprise at least one of a value of the voltage change violating the detection threshold, a value of the detection threshold, a predetermined characteristic of the voltage change, an associated operation event, and a time stamp. The indication may be included in the data set.

The controller may be configured to modify the at least one detection threshold based on one or multiple detected voltage changes that have previously been assigned to an operation event. As an example, the controller may modify the detection threshold by comparing the voltage changes assigned to the same operation event during successive voltage measurements and identify a specific trend in the measurements. If, for example, the measurements successively get closer to the threshold, the threshold may be moved farther away so as to maintain a certain safety margin. Additionally, or in the alternative, if the measurements successively move farther away from the threshold, the threshold may be moved closer to the measurements. Multiple operation event types may be defined for categorizing operation events, wherein each operation event type is associated with at least one detection threshold. Different operation event types may be associated with different detection thresholds. The controller may be configured to assign the operation event to a particular operation event type based on the at least one predetermined

characteristic and the at least one detection threshold associated with this operation event type.

The operation event type may comprise at least one of the following event types: an activation of the dispenser, a start of a dispensing event, a recovery process of the dispenser after a dispensing event, a recovery time of the power supply of the dispenser after actuation, a replacement of the dispenser, an opening of a cover of the dispenser, and a change in the power supply of the dispenser.

The controller may be configured to include one or more of the following items of information in the data set: an operation event type, a time stamp, a voltage offset between an initial voltage and an end voltage of the voltage change, an amplitude of the voltage change, a duration of the voltage change, an indication as discussed above, and a battery level of the dispenser in the data set.

The sensor unit may further comprise a data interface configured to output the dataset (e.g., to a portable storage device or to a remote processing unit). The data interface may be configured to output the data set wirelessly or via a wired connection. A wireless data output may for example be performed via Bluetooth, Wireless LAN (WLAN), ZigBee, Radio Frequency Identification (RFID) or Near Field Communication (NFC). A wire-based data output may for example be performed via a data cable or a portable storage device.

The sensor unit may further comprise a detection interface configured to connect the sensor unit to a power source of the dispenser. The sensor unit may be connected to the power source of the dispenser remotely or locally. When connected locally, the sensor unit may be located in a housing of the dispenser. In this case, the detection interface may comprise wires, a connection clip and/or an inductive and/or capacitive element. When connected locally, the detection interface may comprise one of a male and a female plug directly coupled to a plug of the opposite type at the side of the dispenser. When connected remotely, the sensor unit may be located outside a housing of the dispenser (e.g., using a wired connection between the sensor unit and the power source of the dispenser). The detection interface may be electrically connected to the detection unit of the sensor unit, in order to enable the detection unit to detect a voltage change.

Power may be supplied to the sensor unit from a power source of the dispenser. In this case, the detection interface may be configured to source power from the power source of the dispenser to the sensor unit. Additionally, or in the alternative, the sensor unit may comprise a power source configured to supply power to the sensor unit. The power source may comprise one or both of a rechargeable battery and a solar cell module.

The sensor unit may further comprise a signaling unit configured to signal to a user an operation event and/or additional information. The signaling unit may comprise at least one of an optoelectronic module and an acoustic exciter.

According to a further aspect, a system is provided comprising the sensor unit presented herein and an automatic dispenser to which the sensor unit is coupled so as to be configured to detect a change in an operating voltage of the dispenser.

The automatic dispenser may be a fluid dispenser, such as a dispenser for fluid disinfectants. The automatic dispenser may be configured to be wall-mounted. The dispenser may be a dispenser that detects the presence of a user (e.g., by using an infrared sensor) and, based on said detection, automatically dispenses a fluid, for example using a motor-operated pumping mechanism. The dispenser may comprise a power source, for example batteries or a solar cell module, for providing electrical power to the pumping mechanism. The power source may be accessible by a user for replacement and/or reparation purposes.

The dispenser may be a disinfectant dispenser, a soap dispenser, a hand care dispenser or a cleaning agent dispenser. The dispenser may be configured to dispense a fluid substance or a non-fluid substance or article.

According to a further aspect, a method for detecting operation events of an automatic dispenser is provided. The method comprises detecting a change in an operating voltage of the dispenser and analysing the voltage change for a

predetermined characteristic. The method further comprises assigning the voltage change to an operation event of the dispenser based on the analysis, and creating a dataset associated with the operation. The method may be performed by the sensor unit presented herein. As such, the method may comprise one or more further steps as described above and below.

The method may further comprise starting the detection of a voltage change in response to the detection of a predefined criterion. The predefined criterion may be at least one of a lapse of time interval and a result of a comparison of the voltage change with a threshold.

According to a still further aspect a computer program product is provided comprising program code portions for performing the steps of the method presented herein when the computer program product is executed on one or more processors.

Brief Description of the Drawings

Further details, advantages and aspects of the present disclosure will become apparent from the following description of embodiments taken in conjunction with the drawings, wherein:

Fig. 1A shows a perspective front view of an embodiment of a sensor unit connected to an automatic dispenser;

Fig. IB shows a perspective rear view of the sensor unit of Fig. 1A with an opened housing;

Fig. 2A shows a perspective rear view of the sensor unit of Fig. 1 connected to a power source of the automatic dispenser according to a first connection method;

Fig. 2B shows a perspective side view of a second embodiment of a sensor unit connected to a power source of an automatic dispenser according to a second connection method;

Fig. 3 shows an exemplary time dependency of an operating voltage of an automatic dispenser;

Fig. 4 shows the time dependency of Fig. 3 with several exemplary detection thresholds; Fig. 5 shows the determination of exemplary event parameter values for the time dependency of Fig. 3;

Fig. 6 shows an exemplary dataset created by a controller of the sensor unit and being indicative of operation event types; and

Fig. 7 shows a flow diagram of an exemplary method performed by a sensor unit for detecting operation events of a dispenser.

Detailed Description

In the following description, exemplary embodiments of a sensor unit configured to detect operation events of an automatic dispenser, a system comprising the sensor unit and the dispenser, as well as a method for detecting operation events of an automatic dispenser will be explained with reference to the drawings. The same reference numerals will be used to denote the same or similar structural features.

Fig. 1A shows a perspective front view of a first embodiment of a sensor unit 10. The sensor unit 10 comprises a housing 12, a power source 14, a signaling unit 16 and a detection interface 18. The sensor unit 10 is connected to an automatic dispenser 20. The dispenser 20 is configured to detect the presence of a user and dispense, based on the detection, a fluid, such as a disinfectant, by using a motor-operated pumping mechanism (not shown). In the embodiment depicted in Fig. 1A, the sensor unit 10 and the dispenser 20 are mounted to a wall 22.

The power source 14 is optional and comprises a solar cell module. The solar cell module 14 is configured to supply power to the sensor unit 10. Alternatively, or in addition, the power source 14 may comprise a battery pack. The battery pack may be rechargeable and may be connected to the solar cell module. In a still further variant, the sensor unit 10 sources power from the dispenser 20.

The signaling unit 16 comprises an optoelectronic module, e.g., a Light Emitting Display (LED) or a Liquid Crystal Display (LCD), configured to provide optical information to a user. Alternatively or additionally, the signaling unit 16 may comprise an acoustic exciter (e.g., a speaker) configured to provide acoustic information to a user. Fig. IB shows a perspective rear view of the sensor unit 10, wherein the rear part of the housing 12 has been removed. A detection unit 24, a controller 26, a data interface 28 and a portion of the detection interface 18 are arranged inside the housing 12.

In this embodiment, the detection unit 24 comprises an optional voltage converter 24A, a comparator 24B and an analog-to-digital-converter (ADC) 24C. The voltage converter 24A is electrically connected to the detection interface 18 and configured to convert a higher input voltage to a lower output voltage or vice versa. The comparator 24B is configured to send a signal (e.g., a wake-up signal or an activation signal) to the ADC 24C when an input voltage of the comparator 24B exceeds a voltage threshold. The ADC 24C is configured to measure a voltage, e.g., received from the voltage converter 24A or from the detection interface 18 directly. The ADC 24C is further configured to convert the measured voltage into a digital signal representative of the voltage change and to transmit the digital signal to the controller 26.

The controller 26 is configured to receive and process the digital signal from the detection unit 24 and to create one or more data sets. The controller 26 may for example be a microcontroller (pC), a field programmable gate array (FPGA) or a system on a chip (SoC). The controller 26 may be coupled to a memory (not shown) of the sensor unit 10 for storing the datasets.

The controller 26 is configured to analyze changes in the digital signal received from the ADC 24C for a predetermined characteristic, to assign the signal change to an operation event of the dispenser based on the analysis, and to create a dataset indicative of the operation event. The operation of the controller 26 will be described in more detail with reference to Figs. 3 to 5 below.

The data interface 28 is configured to output datasets created by the controller 26 for processing by a remote processing unit (not shown). The processing unit may for example be comprised by a data hub of a hand hygiene compliance system of a hospital. The hand hygiene compliance system may be configured to monitor the usage of disinfectants throughout a hospital. In the embodiment of Fig. IB, the data interface 28 is configured to transmit the datasets in a wireless manner, e.g., via WLAN. In an alternative embodiment, the datasets may be transmitted by the data interface 28 (e.g., via a Universal Serial Bus (USB) port) to a portable storage device coupled to the sensor unit 10. The storage device (not shown) may then be connected to the processing unit in order to transmit the data sets stored on the storage device to the processing unit.

The detection interface 18 is configured to connect the sensor unit 10, and in particular the detection unit 24, to a power source of the dispenser 20, either directly (e.g., locally) or indirectly (e.g., remotely). Solutions for connecting the sensor unit 10 to the dispenser 20 via the detection interface 18 will now be described with reference to Figs. 2A and 2B.

Figs. 2A and 2B show different variants of electrically connecting the sensor unit 10, 110 to the dispenser 20. Fig. 2A shows a first embodiment, wherein the sensor unit 10 is located remotely from the dispenser 20 (see Fig. 1A) and electrically connected to a power source 21 of the dispenser 20 via wires 30A, 30B. Fig. 2B shows a second embodiment, wherein a sensor unit 110 is located in a housing of the dispenser 20 and electrically connected to the power source 21 via male and female connectors 118A, 118B.

The power source 21 is depicted in Figs. 2A and 2B to comprise batteries 21A. It is to be understood that the power source 21 may comprise a variety of other elements, such as a transformer coupled to an external power source, such as a wall socket.

By electrically connecting the sensor unit 10 to the power source 21, the detection unit 24 (e.g., the ADC 24C) is able to measure a voltage of the power source 21, which in the following will be referred to as "operating voltage of the dispenser". In the embodiment depicted in Fig. 2A, the detection interface 18 is electrically connected to wires 30A, 30B and connection clips 31A, 31B. The connection clips 31A and 3 IB are respectively electrically connected to a positive and a negative terminal of the power source 21. The wires 30A and 30B are likewise electrically connected to the clips 31A and 31B, respectively. In the embodiment depicted in Fig. 2A, the detection interface 18 comprises quick exchange plugs 30C and 30D configured to electrically connect the sensor unit 10 to the wires 30A and 30B. The quick exchange plugs 30C and 30D enable a quick exchange of the sensor unit 10 and/or the dispenser 20 without the need of disconnecting the wires 30A, 30B from the clips 31 A, 31B.

The detection interface 18 illustrated in Fig. 2A provides an easy way for connecting the sensor unit 10 to the dispenser 20. Moreover, the sensor unit 10 can be connected to already installed dispensers 20, i.e., may be retrofitted thereto. Hence, the usage of automatic dispensers initially not equipped with voltage sensing capabilities can be monitored in an easy way by retrofitting them with the sensor unit 10 as described above.

In the embodiment depicted in Fig. 2B, the sensor unit 110 is co-located with and electrically connected to a power source 21 of a dispenser 20 via a detection interface 118. In this embodiment, the sensor unit 110 does not comprise a power source 14 and a signaling unit 16. The detection interface 118 comprises a male plug 118A on the side of the sensor unit 110 and a female plug 118B on the side of the dispenser 20. In this embodiment, the sensor unit 110 can be fully inserted into a recess 33 of the power source 21. Furthermore, electrical power can be directly provided from the power source 21 to the sensor unit 110 via the detection interface 118. Thus, the overall size of the sensor unit 110 can be reduced as no additional power source of the sensor unit 110 is needed.

In the scenario illustrated in Fig. 2B, the sensor unit 10, 110 may be connected to the dispenser 20 by a manufacturer of the dispenser 20. In other words, newly manufactured dispensers may already be equipped with a sensor module 10, 110.

Fig. 3 shows an embodiment of a time dependency 34 of an operating voltage of an automatic dispenser 20. The operating voltage is measured by the detection unit 24 and analyzed by the controller 26 for a predetermined characteristic. In the embodiment of Fig. 3, six exemplary types of voltage changes 36A to 36F with specific predetermined characteristics are marked and will be explained in detail in the following.

The first voltage change type 36A comprises besides one of multiple regularly appearing power drops an additional larger power drop. Thus, an exemplary predetermined characteristic of the voltage change 36A would be a voltage change rate (i.e., the first temporal derivative of the operating voltage) changing its sign twice within a short period of time, with an end voltage being smaller than an initial voltage.

The second voltage change type 36B comprises a sudden and significant drop of the operating voltage. Thus, an exemplary characteristic of the voltage change 36B would be a voltage decrease having a large amplitude over a certain period of time. During the detection of the third voltage change type 36C, the operating voltage continuously increases. An exemplary characteristic of the voltage change 36C would therefore be a voltage increase (i.e., an overall positive sign of a voltage change rate).

The fourth voltage change type 36D comprises an almost instantaneous jump of the operating voltage to a specific value. Thus, an exemplary characteristic of the fourth voltage change type 36D would be the amount of the voltage increase (i.e., its amplitude).

During the detection of the fifth voltage change type 36E, the operating voltage slightly increases. Hence, an exemplary characteristic of the voltage change 36E would be a minimal voltage offset between an initial voltage and an end voltage during a longer period of time.

The sixth voltage change type 36F is a brief voltage drop. Therefore, an exemplary characteristic would be a change rate of the operating voltage changing its sign twice during a short period of time.

Each predetermined characteristic can be defined by a value of the voltage change (i.e., a voltage amplitude) and an associated time duration. As an example, during detection of voltage change 36B, the operating voltage drops during 50 ms by 500 mV. As a further example, during detection of voltage change 36D, the operating voltage increases by 100 mV during 200 ms.

For the measured time dependency of the operating voltage, at least one detection threshold can be predefined. The at least one detection threshold may be modified during operation of the dispenser 20.

Fig. 4 shows two exemplary types of detection thresholds for the time dependency 34 illustrated in Fig. 3. In Fig. 3, a first detection threshold 40 and a second detection threshold 42 are depicted. The first detection threshold 40 (depicted in Fig. 4 by a dotted line) defines a first limit for evaluating the measured operating voltage further. An operation voltage change that remains above the first detection threshold 40 would not be considered to comprise an operation event. The second detection threshold 42 (depicted in Fig. 4 by a solid line) defines a second limit for detecting a specific operation event of the dispenser 20. An operating voltage falling below the second detection threshold 42 would not be assigned to an actuation event of the dispenser 20.

The detection thresholds may be defined to take into account one or more of the

5 following circumstances that may have an influence on properly detecting an

operation event: a possibly changing charging level of a power source of the dispenser 20, a recovery time of the power source of the dispenser 20 between dispensing events, a specific characteristic of the power source of the dispenser 20 (e.g., to cover different dispenser types), changing environmental influences

ίq (temperature, humidity, air pressure), defects of the dispensing mechanism and

software defects. A software defect may for example be determined upon detecting a substantially continuous actuation of the dispenser 20, e.g., 60 actuations per minute over a time period of 10 minutes. Such a detected behavior of the dispenser 20 is not plausible and may thus be associated with a software defect (e.g., of the firmware) of the dispenser 20.

If the predetermined characteristic of a detected voltage change satisfies the detection thresholds 40, 42 (i.e., falls below the detection threshold 40 but remains above the detection threshold 42), the controller 26 assigns the voltage change to an operation event. The assignment is based on the insight that the power produced by the power source 21 of the dispenser 20 is directly related to the operating voltage of the power source 21 by the formula AW=AU*Q, wherein defines the electrical charge of the power source. In other words, a change in the operating voltage All of the power source 21 is to be understood as an amount of energy AW sourced from the power source 21 to perform operation events of the dispenser (e.g., for actuation of an electrically-operated pump).

With reference again to Fig. 3, the exemplary voltage change types 36A to 36F are assigned to specific operation events of the dispenser as follows.

30

The predetermined characteristic of the voltage change 36A is caused by an operation event of the dispenser which is short in time and only requires a minimum amount of energy. A typical example of such kind of operation event would be the activation of a sensor of the dispenser 20, e.g., an infrared sensor that detects the

35 presence of a user's hands and will lead to a dispensing event. Thus, the voltage change 36A is indicative an activation of the dispenser, but will as such not be considered further since it remains above the threshold 40. The characteristic voltage change 36B is caused by an operation event consuming a significant amount of energy, such as the start of an electric motor of the dispenser 20. The voltage change 36B satisfies the detection thresholds 40, 42 (i.e., falls below the detection threshold 40 but remains above the detection threshold 42). Hence, the controller 26 assigns the voltage change 36B to the start of a dispensing event on the time axis.

The voltage change 36C is caused by an operation event lasting a longer time span, but requiring a fewer amount of energy than the start of an electric motor of the dispenser 20. Typically, these conditions are fulfilled during an actual pumping event, that is the electric motor repeatedly moving a pumping piston or other mechanical member of the dispenser 20. Therefore, the controller 26 assigns the voltage change 36C to a dispensing event over a certain time span that started with detection of voltage change 36B.

During the voltage change 36D, the electric motor consumes fewer energy over a shorter time span than during the voltage change 36C. This voltage characteristic may occur when the actual dispensing event is finished and the pumping mechanism returns to its initial position. Therefore, the controller 26 assigns the voltage change 36D to a recovery process of the dispenser 20 after a dispensing event. Start of voltage change 36D may mark the end of the time span that started with detection of voltage change 36B.

The time behaviour of the voltage change 36E is associated with an operation event during which the electric motor of the dispenser 20 is switched off and consumes no further energy. This is typically the case during a recovery step of the power source 21 after a dispensing event. Hence, the controller 26 assigns the voltage change 36E to a recovery time of the power source 21 of the dispenser 20 after actuation. Thus, the controller 26 assigns the voltage change 36F the end of a dispensing event.

Besides the regularly appearing voltage peaks 36F, no further change is measured after voltage change 36E. This behaviour indicates that the power source 21 of the automatic dispenser 20 is not loaded at all.

It is to be understood that the voltage changes 36A to 36F depicted in Fig. 3, their predetermined characteristics as well as the associated operation events assigned thereto are purely explanatory and should in no way restrict the scope of the present disclosure. The controller 26 is configured to modify, or adjust, one or both of detection thresholds 40, 42 based on multiple detected voltage changes that have previously been assigned to operation events. This adjustment is exemplarily shown for detection threshold 42 in Fig. 4.

According to one implementation, a table storing pre-set detection thresholds 40, 42 is stored in a memory of the sensor unit 10, 110. The pre-set minimum and/or maximum voltage values may be updated continuously as will now be described in more detail. Additionally, each specific voltage change 36 assigned to an operation event is stored as a data set in the memory. The controller 26 is configured to compare the voltage change 36 assigned to a specific operation event (e.g., the voltage change 36B assigned to the start of a dispensing event) in the current voltage measurement with a voltage change 36 assigned to the same specific operation event in former voltage measurements, (i.e., the voltage change assigned to the start of a dispensing event in multiple previous measurements). Based on the comparison, the controller 26 calculates a trend for the measured voltage values of the specific operation event (e.g., the start of a dispensing event). For example, if a trend for the voltage decrease of voltage change 36B shows a tendency to get substantially continuously closer to the detection threshold 42 during several voltage measurements, the controller 26 adjusts the detection threshold 42 in the direction of arrow 43 towards the adjusted detection threshold 44, representing a lower minimum value of the operating voltage. As another example, the controller 26 adjusts the detection threshold 40 to a higher minimum value for performing voltage measurements if the trend for the power drop of voltage change 36B shows a tendency to move continuously farther away from the detection threshold 40 during several voltage measurements.

It is to be understood that the adjusted detection threshold 44 is taken in

consideration when assigning the voltage changes to operation events. For example, the adjusted detection threshold 44 may replace the detection threshold 42. That is, the predetermined characteristic of a voltage change is then compared to the detection thresholds 40 and 44.

As the detection thresholds 40, 42 may constantly be adjusted, the sensor unit 10, 110 can be used with a variety of different dispensers and/or on a variety of different locations. For example, the charging level of a dispenser's power source may vary among different dispensers. Moreover, different dispensers may be equipped with different power sources, e.g., different kinds of batteries showing different electrochemical behaviours. As a further example, the environmental conditions, such as temperature, humidity and air pressure may vary between different locations of the sensor unit. However, as the detection thresholds 40, 42 are constantly adjusted based on former measurements, these disturbing effects to the measurement can be quickly recognized and covered by the detection thresholds 40, 42.

In one variation, the controller 26 is configured to create an indication of a

comparison of a predetermined characteristic of a particular voltage change with at least one of the detection thresholds 40, 42. For example, a predetermined characteristic (e.g., amplitude of voltage change 36B) may satisfy detection threshold 40 but violate detection threshold 42. The indication may be stored in a memory of the sensor unit 10 (e.g., in a data set). The indication may for example mark an operation event that has violated a detection threshold. The indication may be associated, for example in a data set, with the voltage level of the violated detection threshold, the voltage value by which the detection threshold was violated and a timestamp. Alternatively, or additionally, the controller 26 may adjust the violated detection threshold 40, 42 after the indication has been created.

On the other hand, keeping the detection thresholds 40, 42 unchanged is

advantageous in a case in which the sensor unit 10, 110 is always operated with the same dispenser 20 and on the same location. In this case, it can be assumed that for example the environmental conditions and the electrochemical behaviour of the power source of the dispenser only vary slightly. Hence, the pre-set detection thresholds 40, 42 already cover these disturbances and constantly adjusting the detection thresholds 40, 42 would provide no further measurement accuracy.

Additionally, as the detection unit 24 is already precisely calibrated, it is very likely that a voltage measurement violating the detection thresholds 40, 42 should in fact be considered as an error, rather than adjusting the detection thresholds 40, 42 based on this measurement.

The controller 26 is further configured to define multiple operation event types for categorizing operation events. Each operation event type is associated with at least one detection threshold 40, 42. For example, an operation event having

predetermined characteristics that satisfy both detection thresholds 40, 42 is assigned to the operation event type "actuation". As a further example, an operation event violating the detection threshold 42 is assigned to the operation event type "error". A specific operation event type may be characterized by specific event parameters, such as a time stamp of the event, a time duration of the event and/or a voltage change (e.g., an amplitude) of the event. Exemplary values of event parameters for the operation event "actuation" as discussed above, i.e., an operation event having predetermined characteristics that satisfy both detection thresholds 40, 42, are shown in Fig. 5.

In Fig. 5, the operation event "actuation" comprises the voltage changes 36B to 36D of Fig. 3. A parameter denoted t_start in Fig. 5 represents the beginning of the operation event "actuation", in particular the beginning of the voltage change 36B. The parameter t_start is the point in time where the representation of the time dependency 34 falls below the first detection threshold 40. At point in time t_start, the detected voltage exceeds a threshold amplitude A_thresh that equals the value of the first detection threshold 40.

The start of the actual pumping event (i.e., the start of voltage change 36C) is denoted by t_peak. This is the point in time where the representation of the time dependency 34 increases after the sudden drop during the voltage change 36B. At t_peak, the sign of the derivative of the representation of the time dependency 34 changes from negative to positive. Additionally, or in the alternative, the point in time t_peak may be derived as by the global minimum of the representation of the time dependency 34. Said global minimum may be also calculated using the first temporal derivative of the representation of the time dependency 34 (either numerically or analytically).

Knowing t_peak, the amplitude A_peak of the operating voltage at the start of the actual pumping event may be determined. For example, A_peak be read out from a memory in which the representation of the time dependency 34 is stored (e.g., in the form of tuples [measured voltage; time]) by looking up the measured voltage at the point in time corresponding to t_peak.

The point in time t_end represents the end of the operation event type "actuation" and is the point in time where the representation of the time dependency 34 rises above the first detection threshold 40 again, i.e., above the value A_thresh. The time duration of the operation event "actuation" is given by the difference between t_start and t_end. Likewise, the voltage change (i.e., the amplitude) of the operation event type "actuation" is given by the difference between A_thresh and A_peak. Furthermore, t_peak may be used as a time stamp of the operation event

"actuation". It is to be understood that the depicted event parameters (time duration, voltage change and time stamp) are purely explanatory and are in no way considered to restrict the present disclosure.

After the controller 26 has identified an operation event of a particular operation event type, the controller 26 creates a dataset. Fig. 6 shows an exemplary table 37 with four exemplary data sets 37A to 37D created by the controller 26 and being indicative of different operation event types.

As can be seen from Fig. 6, the table 37 indicates for each dataset 37A to 37D (i.e., for each detected operation event) a consecutively assigned operation event type number, a time stamp, a category of the operation event type, an initial voltage of the operation event, a voltage change (amplitude) during the detection of the operation event, a duration of the operation event type, a voltage offset between initial and end voltage of the operation event type, a battery level of the dispenser and an indication whether the voltage change assigned to the operation event type violates a detection threshold. The time stamp, the amplitude during the detection of the operation event type and the duration of the operation event type may be calculated as described in conjunction with Fig. 5 above.

Fig. 6 shows that operation events 1 and 2 comprise a voltage decrease (amplitude) of about 500 mV that satisfies both detection thresholds 40, 42. Therefore, the operation events 1 and 2 are both assigned to the operation event type "Actuation".

Operation event 3 shows a voltage decrease of 50 mV, a time duration of 120 ms and no offset. This operation event is assigned to an operation event type

"Maintenance", indicative, for example, of the opening of a cover of the dispenser 20.

The voltage decrease of event number 4 is 2000 mV, lasts 2100 ms and also shows a large offset of 500 mV. These characteristics are unusual for a normal operating dispenser. Since the detection threshold 42 has been violated, this operation event is assigned to the operation event type "Error".

The table 37 may be stored in a storage medium (not shown) of the sensor unit 10, 110. Such an approach permits comparing different data sets 37A to D with one another. This comparison has already been described above with regard to adjusting the detection thresholds 40, 42. Alternatively or additionally, the table 37 may be transmitted to a processing unit via the data interface 28, as also described above. Therefore, the usage of an automatic dispenser 20 equipped with the sensor unit 10, 110 can be monitored by a central health care monitoring system.

Fig. 7 shows a flow diagram 100 of an exemplary method performed by a sensor unit 10, 110 connected to a power source 21 of an automatic dispenser 20 for detecting operation events of the dispenser 20.

At the beginning, the sensor unit 10, 110 is waken up from a sleep mode (step SI) in order to perform a measurement of an operating voltage of the dispenser 20. For example, the controller 26 may be configured to send a wake-up signal at predefined points in time to the detection unit 24 (e.g., in fixed time intervals). Alternatively or additionally, the comparator 24B may be configured to trigger a wake-up signal to the ADC 24C if a predefined threshold of the operating voltage is trespassed.

In step S2, the detection unit 24 changes to a measurement mode for measuring the operating voltage of the power source 21 of the dispenser 20.

The actual measurement of the operating voltage starts in step S3, wherein the ADC 24C measures the operating voltage of the power source 21, creates a digital signal representative of the operating voltage and transmits the signal to the controller 26.

In step S4, the controller 26 analyses the signal received from the ADC 24C for a change of a voltage signal. If no voltage signal change is detected in step S4, the sensor unit 10, 110 returns to the sleep mode. In the case of a detected voltage signal change, the controller 26 analyses in step S5 the voltage change for a predetermined characteristic as described with reference to Figs. 3 and 4 above.

The controller 26 then selectively assigns the detected signal change to an operation event of the dispenser 20 in step S6 and creates in table 37 a new dataset indicative of the operation event in step S7 (see Fig. 6).

As described with reference to Fig. 4, the controller 26 stores the signal

characteristics (e.g., the predetermined characteristic and a trend change rate for operation events) on a storage medium of the sensor unit 10, 110 in step S8. The controller 26 may adjust the pre-set detection thresholds based on one or more (including the last) voltage measurements (step S91) or creates an error indication if the voltage change assigned to an operation event violates the pre-set detection thresholds (step S92). The sensor unit 10, 110 then returns to the sleep mode.

Analysing the operation of an automatic dispenser 20 based on its operating voltage provides for a high accuracy. Even a slight voltage change is precisely detectable by voltage sensors, therefore enabling a very exact analysis of the operation of the dispenser 20. Moreover, voltage sensors are widely available at low costs. Thus, the production costs of a sensor unit 10, 110 as described herein are low.

Additionally, automatic dispensers 20 are often mounted to walls and are thus subject to external shocks. For example in a hospital very often patient beds or heavy medical equipment is passing close to the wall-mounted dispenser 20, creating strong vibrations. If the operation of such a dispenser 20 is analysed based on mechanical parameters, e.g., the movement of a pumping arm or the vibration of an motor-operated pumping mechanism, the measurement of these parameters will be negatively influenced by the external vibrations. However, the operating voltage of the power source 21 of the dispenser 20 is not affected by external vibrations.

While exemplary realisations of a sensor unit and a system comprising the same have been described, it will be understood that the sensor unit and the system can be modified in many ways. Therefore, the present disclosure is only limited by the claims appended hereto.