PORTABLE NEGATIVE PRESSURE DEVICE

Abstract

A portable negative pressure wound therapy device adapted to be carried by a user, comprising an electrically actuated suction pump for draining wound fluids from a patient, at least one microelectronic controller, at least one electronic memory and a housing for containing the electrical and/or electronic components. The device further comprises at least one microelectronic impact sensor, wherein the impact sensor is adapted to detect an impact acting on the device.

Claims

1. A portable negative pressure wound therapy device adapted to be carried by a user, comprising: a housing that contains electrical and/or electronic components; an electrically actuated suction pump to drain wound fluids from a patient; at least one microelectronic controller; and at least one electronic memory; wherein the portable negative pressure wound therapy device further comprises at least one microelectronic impact sensor, and the at least one microelectronic impact sensor is adapted to detect an impact acting on the portable negative pressure wound therapy device.

2. The portable negative pressure wound therapy device according to claim 1, wherein the at least one microelectronic impact sensor is one or more selected from a group of linear acceleration sensors, gyration sensors, humidity sensors, temperature sensors, magnetic field sensors and atmospheric air pressure sensor.

3. The portable negative pressure wound therapy device according to claim 2, further comprising at least one linear acceleration sensor.

4. The portable negative pressure wound therapy device according to claim 1, wherein the portable negative pressure wound therapy device is adapted to record impact sensor data on the at least one electronic memory, the impact sensor data being based on the detected impact.

5. The portable negative pressure wound therapy device according to claim 4, wherein the portable negative pressure wound therapy device is adapted to record an impact if the impact is above a predetermined threshold level.

6. The portable negative pressure wound therapy device according to claim 5, wherein the predetermined threshold level for linear acceleration is an acceleration value selected from a range of 3 g to 100 g.

7. The portable negative pressure wound therapy device according to claim 1, further comprising: a linear acceleration sensor capable of detecting acceleration in the three axis of space; and a gyration sensor capable of detecting gyration in the three axis of gyration, wherein the linear acceleration sensor and the gyration sensor are components of a single microelectronic inertial measurement unit (IMU) integrated in a chip.

8. The portable negative pressure wound therapy device according to claim 1, wherein the at least one microelectronic impact sensor comprises a separate power supply, and the separate power supply is independent of a power supply supplying the electrically actuated suction pump and the microelectronic controller.

9. The Pportable negative pressure wound therapy device according to claim 1, further comprising a separate electronic memory, wherein the separate electronic memory is adapted to record impact sensor data and the separate electronic memory operates independent of the electronic memory used by the controller to store operating instructions.

10. The portable negative pressure wound therapy device according to claim 1, further comprising a real time clock, whereby the portable negative pressure wound therapy device is adapted to record a time of an impact detected by the at least one microelectronic impact sensor.

11. The portable negative pressure wound therapy device according to claim 1, wherein the at least one microelectronic impact sensor comprises a sleep-to-wakeup function, the sleep-to-wakeup function including: a sleep phase correlating with a lower sampling rate, the sleep phase being active when the portable negative pressure wound therapy device is switched off; a wake phase correlating with a higher sampling rate, the wake phase being active when the portable negative pressure wound therapy device is switched on; and a sleep-to-wake transition if the impact detected by the at least one microelectronic impact sensor is above a predetermined threshold level, the sleep-to-wake transition operates independent of whether the portable negative pressure wound therapy device is switched on or off.

12. The portable negative pressure wound therapy device according to claim 11, wherein the sampling rate during the sleep phase is between 1 Hz and 50 Hz and wherein the sampling rate during the wake phase is between 500 Hz and 2000 Hz.

13. The portable negative pressure wound therapy device according to claim 1, further comprising a remote interface to transmit impact sensor data to a remote device.

14. A method to record an impact condition to which a negative pressure therapy device was exposed, comprising: setting, using a controller, at least a first predetermined impact threshold; detecting, using an act sensor, an impact to which the negative pressure therapy device was exposed and, recording, using the controller, the impact if the impact detected by the impact sensor is above the first predetermined threshold.

15. The method according to claim 14, wherein the detected mpact includes at least one of linear acceleration and rotation.

16. The method of claim 14, further comprising: setting, using the controller, a second predetermined impact threshold, the second predetermined impact threshold being higher than the first predetermined impact threshold; and if the impact detected by the impact sensor is above the second predetermined impact threshold, then at least one of: (i) alarming a user, and (ii) locking the negative pressure wound therapy device.

17. The portable negative pressure wound therapy device according to claim 8, wherein the separate power supply is one of a battery or a capacitor.

18. The portable negative pressure wound therapy device according to claim 13, wherein the remote interface to transmit impact sensor data includes the interne.

19. The portable negative pressure wound therapy device according to claim 9, wherein the separate electronic memory is flash memory.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Further characteristics, details, and advantages of the invention result from the appended patent claims and from the drawings and the following description of preferred embodiments of the invention. The drawings show:

[0084] FIG. 1A schematic drawing of a simple negative pressure wound therapy device including the negative pressure bandage applied to a wound of a patient.

[0085] FIGS. 2a to e Different views of a typical portable negative pressure wound therapy device to generate a vacuum for medical applications.

[0086] FIG. 3A schematic drawing of the piping system and of the electronic components of a negative pressure wound therapy device according to a preferred embodiment of the present invention.

[0087] FIG. 4A schematic drawing of the structure of the electronic control system and of the electric components of a portable negative pressure wound therapy device according to a preferred embodiment of the invention.

[0088] FIG. 5A schematic drawing of the structure of a stand-alone impact sensor module according to a preferred embodiment of the invention.

[0089] FIG. 6 Example of a warning message displayed to the user of a portable negative pressure wound therapy device according to a preferred embodiment of the invention.

[0090] FIGS. 7a to c Acceleration detected during a drop impact test, to which a portable negative pressure wound therapy device according to a preferred embodiment of the invention was subjected. Acceleration values are given as g-forces.

[0091] 7a Impact on bottom front face

[0092] 7b Impact on side face

[0093] 7c Orientation of the x-axis and the y-axis

[0094] FIGS. 8a to f Acceleration forces detected during different acceleration impacts, to which a portable negative pressure wound therapy device according to a preferred embodiment of the invention was subjected. From the output of the three linear acceleration channels the magnitude M.sub.a was calculated (FIG. 8a, b, d, e, f). Rotation magnitude M.sub. was calculated (FIG. 8c) from the gyration sensor recordings made during the same drop experiment also shown in example 8a. The charts show the values for the magnitudes M.sub.a and M.sub. in relative units.

[0095] 8a Acceleration signals recorded during a drop from 1.0 m

[0096] 8b Acceleration signals recorded during a sitting to a chair movement of a test user

[0097] 8c Angular velocity signals recorded during the same drop from 1.0 m as in impact 8a

[0098] 8d Indication of the incidents occurring during the experiment of example 8a

[0099] 8e Acceleration signals recorded while a test user was walking down a stair carrying the portable negative pressure wound therapy device

[0100] 8f Acceleration signals recorded while the portable negative pressure wound therapy device was flipped to the front face

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0101] A simple negative pressure wound therapy device 1, which is in fluid communication with a wound 2 of a patient to be treated is shown in FIG. 1 schematically. The therapy device 1 comprises a container 3 for collecting the fluids (such as blood, instillation fluids and the like) that are sucked from the wound 2. Wound therapy devices of this type are known in the prior art. The container (or canister) 3 is typically made of a solid material, such as a plastic material. It is usually a disposable article designed for single use. Conveniently, the container 3 can be detachably mounted to the housing part 4 of the device, which contains the electrical components of the apparatus. The container 3 can be evacuated by the electrically actuated suction pump 5. A connection (not shown) is provided for a suction line 6 that leads to the wound such that vacuum communication can be established between the suction pump 5, the container 3, and the suction line 6 that leads to the wound. A filter or air/liquid-separator 7 located within the fluid-pathway between the container 3 and the suction pump 5 is used to prevent exudate from being sucked into the pump 5. A negative pressure wound therapy device typically comprises additional components such as a control system for controlling activity of the pump and means for interacting with the user, such as a touch-screen display or control buttons. These components are not shown in FIG. 1.

[0102] In some embodiments, the portable negative pressure wound therapy device does not have a container for receiving the drained body fluids. Instead, the body fluids can be contained, for example, in the dressing. This is achieved by providing absorbent layers (not shown in FIG. 1). Such negative pressure wound therapy devices, which do not make use of a separate solid exudate canister are typically used for treating less exudating wounds, for example surgical wounds.

[0103] FIGS. 2a to e show a typical example of a portable device 1 for the provision of the vacuum for medical applications. The device 1 comprises a first housing part 4 in which a vacuum-producing device in the form of an air suction pump as well as the electrical components for the device are accommodated, including batteries or preferably rechargeable batteries. A recharging connection for the batteries is designated by reference symbol 8. Moreover, the device 1 comprises a second housing part in the form of a container 3 for receiving body fluids, in particular, for receiving wound exudates suctioned away from a wound. Preferably, the entire second housing part is constituted as a disposable single-use item. In its upper region, a connection gland 9 for a suction tube is provided that can, for example, lead to a wound dressing sealing the wound when the device 1 is used in the vacuum therapy of wounds and there it may, for example, communicate with the wound space through a port to apply and maintain a vacuum to the wound space and to suction away wound exudates into the container. For this purpose, the container 3 communicates with the suction pump 5.

[0104] It can also be seen from FIG. 2 d on the side 10 of the second housing part 3 facing the body, a grip recess 11 is formed in the shape of an opening extending right through the second housing part 3. In this way, the device 1, or only its second housing part 3, can be gripped and handled with one hand.

[0105] In the preferred embodiment shown, a manually operable element 12 is provided in this grip recess 11 on the upper side of the device 1, for example, in the form of a pushbutton that acts on locking and back-gripping means (not shown). In the joined condition of the two housing parts 3 and 4, the locking or back-gripping means are in a locked condition holding the two housing parts 3, 4 together by positive action. Only upon operation of the operating element 12, the lock is released so that the housing parts 3, 4 can be separated from each other.

[0106] FIG. 3 shows the nature of the piping system and of the electronic components of a negative pressure wound therapy device according to a preferred embodiment of the invention. According to this preferred embodiment, the device comprises an inventive microelectronic impact sensor, wherein the impact sensor is adapted to detect an acceleration impact acting on the device. Apart from the inventive feature, the device is similar to negative pressure wound therapy device of the type exemplified in FIG. 2.

[0107] In contrast to the very basic system shown in FIG. 1, the device of FIG. 3 includes additional components (known from the art) such as the air rinsing pathway of the fluid system. Based on FIG. 3 one embodiment of the inventive device is explained. FIG. 3 shows the previously described or a similar device for providing a vacuum for medical applications in a purely schematic representation, wherein relevant reference symbols are used for the corresponding components. However, FIG. 3 shows only the components that are relevant for the following description. FIG. 3 depicts a schematically indicated wound to be treated with a vacuum with a vacuum-tight wound dressing 13, to which the suction tube 6 emanating from the container 3 leads. From the container 3, a further tube section 14 leads outwardly through the already mentioned filter 7. If the container 3 or the first housing part 4 is put into its operating position on the first or basic housing part 4 of the device 1, the tube section 14 is connected to a further tube section 15 within the first housing part 4 that leads to the intake side of the suction pump 5. When the suction pump 5 operates, a vacuum is applied to the container 3 and to the suction tube 6 via tube sections 14, 15.

[0108] Moreover, a pressure sensor 17 for measuring the pressure is provided in the tube section 15 between container 3 and suction pump 5. Its signals are sent to an electronic control unit, collectively identified by reference symbol 18, which performs open-loop and closed-loop control of the device 1 in total. The electronic control unit 18 comprises a microelectronic controller and at least one electronic memory. Also shown is the charging connection 8 for rechargeable batteries that are located in a compartment 19 and a connection 20 for a schematically indicated power supply unit 21. Reference symbol 22 indicates a display unit, preferably having a capacitive switch membrane (touchscreen). A user may control operation of the device via said touchscreen. The electrical connection to the electronic control unit 18 is indicated via electrical lines 23. The suction pump 5 is controlled by the electronic control unit 18 in which, by means of the signals of the pressure sensor 17, a pressure and vacuum closed-loop control is implemented with known open-loop and closed-loop control mechanisms (setpoint/actual value control mechanisms), so that the pressure value corresponding to the currently selected program is controlled in the tube section 15.

[0109] Also shown is an additional rinsing or aeration tube 24 that, only shown by way of example, leads through the container 3 and just like the suction tube 6 leads to the wound dressing 13. When the container 3 is attached in its intended assembly position on the first housing part 4, this rinsing tube 24 communicates with a tube section 25 provided in the first housing part 4 in which an electromagnetically operated valve 26 is provided that can be actuated by the electronic control unit 18 and connects the tube section 25 with the atmospheric air when it is open, so that an air current toward the wound via the rinsing tube 24 can be generated.

[0110] The device 1 and its electronic control unit 18 also feature a data interface 27, preferably a USB interface, by means of which the electronic control unit 18 or its method of operation can be programmed. In addition, device 1 comprises a speaker 28 which is connected to the control unit 18. The speaker can be used to generate acoustic alarm signals.

[0111] According to the invention, the portable negative pressure wound therapy device further comprises an impact sensor 29, which is capable of communicating with electronic control unit 18. As explained above, the electronic control unit 18 comprises a microcontroller. The impact sensor 29 is one or more selected from the group of linear acceleration sensors, gyration sensors, humidity sensors, temperature sensors, magnetic field sensors and atmospheric air pressure sensor. Preferably, the impact sensor 29 is a linear acceleration sensor, optionally in combination with a gyration sensor and/or a magnetic field sensor.

[0112] It is possible, that the impact sensor 29 communicates directly, by means of an interface, with the electronic control unit 18. In this embodiment (herein called an integrated impact sensor), the impact sensor 29 is an integrated component of the control system 18 of the device. Also, the impact sensor data are processed by the electronic control unit 18 and the sensor raw data and/or the processed data storage is controlled by the electronic control unit 18. The integrated impact sensor 29 is usually (but not necessarily) provided with electric energy by the main power supply system of the device.

[0113] More preferably, the impact sensor 29 is a component of a stand-alone impact sensor module. A stand-alone impact sensor module is explained in more detail in FIG. 5 below.

[0114] Interaction of the impact sensor 29 with the control unit 18 is also shown in FIG. 4 below.

[0115] The impact sensor 29 can conveniently be mounted to the same main board, on which electronic control unit 18 is sitting.

[0116] Proceeding to FIG. 4, communication of the control unit with peripheral components is shown schematically. One peripheral component communicating with the controller is the integrated impact sensor (termed accelerometer in FIG. 4). Instead of an integrated impact sensor a stand-alone impact sensor module can be used likewise.

[0117] The control unit includes elements/functions such as the microelectronic controller (microcontroller), a protection circuit for the power supply, a fuel gauge for the power supply, a charging circuit for the power supply, power converter circuits, a speaker controller and switching circuits for controlling the suction pump and the electromagnetic valve.

[0118] The peripheral electric/electronic components include a source of electric energy, preferably a rechargeable battery, the suction pump, preferably a membrane pump and at least one electronic memory typically including both ROM and RAM chips. In up-to date devices, the peripheral electric/electronic components may additionally include, for example, a vacuum valve for a rinsing fluid pathway (as exemplified in FIG. 3), interfaces such as a USB connector, electric connectors, such as a connector for the battery charger, a light sensor, a pressure sensor for sensing the pressure within the closed fluid-system of the device, a speaker for signalling warnings to the user, one or more LEDs for signalling warnings and/or status information to the user, a display, preferably a touchscreen display for interacting with the user, a backlight for the display, buttons, such as an on/off button. More advanced peripheral components such as a wireless interface for communication of the control unit with a remote computer may optionally be present.

[0119] The control unit is the central instance for controlling and monitoring function of the device.

[0120] According to the invention the peripheral components include an impact sensor, which may be an integrated impact sensor or preferably a stand-alone impact sensor module, each of which communicate with the microcontroller via an interface. The microcontroller receives impact sensor data. If an integrated impact sensor is used, the microcontroller receives the sensor raw data, for example acceleration data or temperature data. The raw data are processed as explained in detail above. If a stand-alone impact sensor module is used, the microcontroller receives the processed data and may, for example, display warnings to the user or lock the device.

[0121] The stand-alone impact sensor module shown in FIG. 5 comprises at least one impact sensor and a further microelectronic controller (in the following called impact sensor module controller, in FIG. 5 the impact sensor module controller is shortly termed Controller) cooperating with the impact sensor. The impact sensor module controller functions independent of the microelectronic controller of the control unit. The module further comprises a data interface, such as a RS232 interface, a memory, such as a flash memory and a real-time clock. The sensor, the interface, the memory and the real-time clock are in direct electronic communication with the impact sensor module controller. A separate battery or accumulator supplies electric energy to the components of the module thus making the module independent of the charging status of the main battery of the device. According to a particularly preferred embodiment of the invention, the module comprises at least one linear acceleration sensor, capable of detecting crash impacts. In practice, the sensor capable of detecting crashes should comprise at least an integrated linear acceleration sensor chip capable of detecting acceleration in the three axis of space (a.sub.x, a.sub.y, a.sub.z). A particular advantage of using a stand-alone impact sensor module is, that the module can function independently of the working status of the device. The stand-alone impact sensor module can be active even if the device is switched off, as described in connection with the preferred embodiments herein. Thus, the stand-alone impact sensor module may perpetually report detrimental impacts that were acting on the device, for example also during storage of the device or during transport of the device.

[0122] FIG. 6 shows an example of a warning message that is signalled to the user by means of a LCD-display. The alarm message informs the user that an impact was acting on the device and furthermore that the device is locked. Unlocking of the device can only be accomplished by a service technician authorised by the supplier/manufacturer. Before unlocking the device the service technician will perform a careful inspection of the device, optionally in combination with a prophylactically exchange of components, which are typically prone to deficiency after an impact of the type reported by the impact sensor. Hereby the service technician can also utilise information about the strength of the impact, which is stored in the memory of the device.

EXAMPLE 1

[0123] FIGS. 7a and b show examples of unprocessed acceleration sensor data (g-forces) recorded from an linear acceleration sensor mounted to the main board of a portable negative pressure wound therapy device (VivanoTec negative pressure unit from Paul Hartmann AG, Germany). The data corresponding to FIG. 7 a were received while the device was subjected to a drop test. During the test, the device was dropped to a hard surface (metal plate) from a height of 0.4 m above ground. In this experiment, as detected by a high speed camera running at 2000 fps, the device crashed to the bottom front face.

[0124] FIG. 7b shows another experiment, where the device crashed to the side face. The acceleration values corresponding to the g-forces along the two axes x and y (see FIG. 7c) are displayed in the diagram. Each of the x- and y-axis sensors detected maximum acceleration values of more than 120 g in both tests. The g-force peak occurs in less than 1 ms. The resolution of the sensor was set to 1000 Hz. Therefore, the actual acceleration peak values could have been even higher. Peaks may escape detection, if occurring in a time interval much smaller than the timely resolution of the sensor. Drops of the type described in these examples (according to FIGS. 7a and b) do not leave any visible damages to the device in most cases. However, the acceleration occurring during the drop can potentially impose stress to internal mechanical or electronic components, which may lead to a malfunction during future therapy cycles. It is a significant advantage of the invention that the impact sensor is capable of warning a user of the device of any sleeping malfunction that may wake up during later usage of the device. Therefore, a portable negative pressure wound therapy device according to the invention is more reliable and safer.

EXAMPLE 2

[0125] FIG. 8 a shows examples of processed impact sensor data recorded by means of an inertial sensor module mounted to the main board of a portable negative pressure wound therapy device (VivanoTec negative pressure unit from Paul Hartmann AG, Germany). For the experiments the IMU motion sensor LSM9DSO (iNEMO inertial module) from ST Microelectronics, United Kingdom was used. This inertial module device has three acceleration channels, three angular rate channels and three magnetic field channels. Data from the magnetic field channels were not recorded.

[0126] The data corresponding to FIG. 8 a were received while the device was subjected to a drop test. During the test the device was dropped to a soft ground (rubber plate) from a height of 1.0 m above ground. A maximum magnitude M.sub.a value >11 (relative units) was observed. A drop of this kind usually does not leave any visible damages to the device. However, the acceleration occurring during the drop can potentially impose stress to internal mechanical or electronic components, such as electric contacts or tube connections, which may lead to a malfunction during future therapy cycles.

[0127] The data corresponding to FIG. 8b were received while the same VivanoTec device was carried on the body of a moving test user. During the recording the user was changing his position from an upright (standing) position to sitting down to a chair. The movement of the test user generated acceleration signals detected by the impact sensor. A maximum magnitude M.sub.a value of about 4 (relative units) was observed. However, such comparatively low acceleration forces will not cause any detrimental stress to the device. An impact of such kind must not cause any warning signals to the user.

[0128] The diagrams show the magnitude M.sub.a calculated from the recorded outputs of the three linear acceleration sensors included in a MEMS motion sensor (H3LIS331 DL from ST Sensor Technology, United Kingdom). M.sub.a was calculated as a relative value using the formula

M.sub.a={square root over ((a.sub.x.sup.2+a.sub.y.sup.2+a.sub.z.sup.2))}

wherein the values (a.sub.x, a.sub.y; a.sub.z) correspond to the output of the sensor channels measuring linear acceleration along the three space axis (x; y; z).

[0129] Suitable predetermined impact thresholds, for example impact thresholds for acceleration, can be set by repeatedly performing experiments of the type described in this example. The impact thresholds for acceleration will have to be determined for each type of device, because they depend on device specific parameters like stability, weight, material and shape of the device. The data displayed in this example indicate, that an adequate threshold will have to be above the non-detrimental impact (device carried by user while changing his position from standing to sitting, whereby a maximum magnitude M.sub.a value of 4 relative units was observed) and below the potentially detrimental impact (dropping the device from a height of 1 m to ground, whereby a maximum magnitude M.sub.a value of about 11 relative units was observed). In order to set adequate thresholds, a series of experiments of the type described in this example will have to be carried out.

[0130] FIG. 8c shows the magnitude M.sub. reflecting the overall gyration forces that the device was exposed to during the same experiment (drop to a soft ground) already described under FIG. 8a. A maximum magnitude M.sub. value of >42 (relative units) was observed. A comparison of FIG. 8a with FIG. 8c shows that the peak of acceleration magnitude M.sub.a coincides with the peak of gyration magnitude M.sub.. This indicates that the crash entails both strong linear acceleration and strong rotation forces, which occur simultaneously.

[0131] FIG. 8d again shows the graph of FIG. 8a providing additional information about the incidents occurring during curve progression. The free fall phase of the experiment, during which gravity approaches towards zero (therefore minimising magnitude M.sub.a, if the device is dropped vertically) is indicated by a first circle. The free fall ends with the impact to the ground leading to the acceleration peak. After the drop, the height of the fall can be estimated, using the recorded acceleration values and a standard function analysis algorithm. The algorithm is adapted to detect the begin of the free fall (t.sub.ff; first downward turning point of the acceleration function) and the begin of the impact (t.sub.im, first upward turning point of the acceleration function). The height of the fall can then be calculated using the formula

s(height)=g(gravity)(t.sub.imt.sub.ff).sup.2

[0132] For the estimation of the height of the fall the air resistance is disregarded. In the case shown in FIGS. 8a/d the time span of the free fall (taken from the diagram) is about 0,33 s leading to an estimated drop height of 1.07 m [9.81 m/s.sup.2(0.33 s).sup.2=1.07 m], which is a good approximation to the actual value of 1.00 m.

[0133] FIG. 8 e shows the magnitude M.sub., which was recorded while the device was carried on the body of a moving test user, who went down a stair. All observed peaks of magnitude M.sub. are below 3.5 (relative units) and thus remain in a similar range as the peaks observed in the experiment shown in FIG. 8b. Comparatively higher values (as compared to the walking down the stairs) of magnitude M.sub. (more than 6) were detected, when the device was flipped over to the face side (FIG. 8f). However, the relative magnitude M.sub. values related to the flip are still far below the relative magnitude M.sub. values caused by a drop as described in accordance with FIG. 8a (more than 11).The VivanoTec device used for the experiments described in this example 2 would not suffer any detrimental effects after a flip.

[0134] The experiments shown in connection with this example 2 demonstrate, that an acceleration threshold, for example a threshold of 8 relative units for the exemplified case, can conveniently be determined by subjecting the device to a series of movement and crash conditions, which are non-detrimental or detrimental for the device, respectively. Exceeding of the threshold can serve as trigger, for example, to record impact sensor data on a memory, to provoke a warning message, to lock the device, to send a message to a remote server (if a remote interface is present) or to increase sampling rate of the sensor. It is also possible to use several (for example two or three) different thresholds resulting in different activities, if the threshold is exceeded. On preferred example is to use a lower threshold, for example 2 relative units to activate the sleep-to-wakeup function and to use a comparatively higher threshold, for example 8 relative units to display a warning message and/or lock the device. Examples for threshold dependent activities are described more in detail in the description of specific preferred embodiments above.