Field of the Invention

The present invention relates to a sensor unit for activation based on the presence of a voltage in a cable.

Background of the Invention

Electrical devices are frequently used both in industry and households. The functioning of these devices can be quite crucial for an enterprise or household. The electrical devices could e.g. be monitoring systems for monitoring important elements in a produc- tion plant or heating or cooling systems where a temperature has to be maintained to avoid damaging goods.

Therefore it is of great importance to ensure that power supply to these devices is maintained.

Object of the Invention

It is an object of the present invention to solve the above-mentioned problem.

Description of the Invention

The object is obtained by a sensor unit for activation based on the presence of a voltage in a cable comprising at least two conductors for conducting current characterised in, that said sensor unit comprises

• at least two voltage sensors for measuring a voltage difference at the surface of said cable,

· attachment means for attaching said sensor unit and thereby said voltage sensors at different positions around said cable surface, • detection means for detecting an electrical field by detecting a voltage difference measured by said voltage sensors,

• a communication device for communicating a wireless signal based on the presence of an electrical field.

Thereby the unit can easily be mounted externally on existent cables for communicating to external devices whether there is supply voltage in the cable. E.g. the unit will communicate disablement of supply voltage or changes in supply voltage to external devices.

In an embodiment said communication device comprises activation means for activating said communication device, based on the presence of an electrical field.

The communication device is only activated when necessary, and thereby a sensor unit using very little power or having a long battery life is obtained.

In an embodiment the sensor unit comprises three voltage sensors and said attachment means is for attaching said three voltage sensors at different positions around said cable surface.

Thereby it is ensured that no matter how the sensors are positioned around the cable, a different voltage will be detected by at least two of the voltage sensors.

In an embodiment said attachment means is a clip-on device to be attached on said ca- ble and wherein said detection means, communication device and activation means are integrated in said device.

Thereby the entire unit can simply be clipped onto a cable. The unit is easy and fast to mount and does not require technicians, and by mounting of the unit around the cable it is not necessary to remove isolation from the conductors. No external antennas or power source are required. In an embodiment detection means for detecting an electrical field comprises means for detecting the presence of an electrical field. Hence the presence of an electrical field indicates that a voltage is present at the cable conductors. In an embodiment detection means for detecting an electrical field comprise means for detecting the level of an electrical field. Thereby an electrical field getting stronger or weaker indicates that a voltage is getting stronger or weaker, respectively, in the conductors of the cable. In an embodiment the communication device is a communication unit for communicating via a telephone network. Thereby an already established communication network is used, and existing phones and phone centrals are used as alert devices. The use of mobile phone networks could be an advantage since mobile phones are carried by users always and therefore an alert will reach the user of the phone very fast. In an al- ternative embodiment a private network is used.

In an embodiment the activation of a communication device is performed by establishing electrical supply connection between a power supply and said communication device.

Thereby a very simple method of activating a device is used, and furthermore it is ensured that power is not used by the device before the connection is established.

In an embodiment said sensor unit comprises a visual indicator such as a light indicator indicating when an electrical field is detected.

Thereby, as backup, the user can very easily establish whether a voltage is present in the conductors. Furthermore, indicators could be used to indicate whether the unit is connected to a wireless communication network. embodiment the sensor unit comprises a positioning element, such as a GPS. Thereby an alert message can include a GPS position for indicating the position of the unit transmitting the message. This could be particularly useful, if numerous units are present or if the unit is part of a stolen item. In an embodiment the sensor unit comprises a visual indicator such as a light indicator indicating when the power in the power supply, e.g. a battery, is below a predefined threshold.

Thereby the user can easily identify whether power is present in the unit. Furthermore, the unit can be adapted to communicate whether power is lacking/the battery needs to be replaced.

Description of the Drawing

Figure 1 illustrates the principle of a sensor unit according to the present invention per se as well as mounted on a cable, figure 2 illustrates the elements in the housing of a sensor unit according to the present invention, figure 3 is a flow diagram illustrating the operation of a sensor unit according to the present invention, figure 4 illustrates a detailed embodiment of the principle in a sensor unit having two voltage sensors, figure 5 illustrates a detailed embodiment of the principle in a sensor unit having three voltage sensors, figure 6 illustrates the elements in a voltage sensor surface, figure 7 illustrates the sensor surface being divided in sub elements, figure 8 illustrates an embodiment of the measurement circuit in a sensor comprising three voltage sensors.

Detailed Description of the Invention

Figure 1 illustrates an embodiment of a sensor unit 101 according to the present inven- tion per se as well as mounted on a cable 103 having a number of conductors 109. The sensor unit 101 comprises a housing 105 including its components, and furthermore the unit comprises a clip-on device enabling the housing to be mounted around a cable 103. The clip-on device could e.g. be an arm 107 with a spring-like connection to the housing 105 thereby squeezing the cable 103 between the arm 107 and housing 105 when mounted on the cable 103. Alternatively the housing could be mounted to the cable by alternative fastening means such as glue, hose clamps or the like. It is advantageous to be able to clip the housing onto a cable, whereby both mounting and removing or replacing is a fast and simple process. The figure furthermore illustrates a sensor unit 101 mounted on a cable 103 having a number of conductors 109 for conducting current. In this example five conductors are present representing a three-phase cable including conductors for ground and for zero.

Figure 2 illustrates the elements in the housing 201 of a sensor unit according to the present invention. The unit comprises an electro field measurement unit 201, a micro- processor 203, a relay 205, a battery 207 and a GSM module 209. The electro field measurement unit 201 is for detecting the presence of an electrical field at the cable, and it is electronically connected to the microprocessor 203. The microprocessor 203 is further electronically connected to the relay 205 and the GSM module 209. The GSM module is further connected to a battery supply 207 via the relay 205. The mi- croprocessor 203 is programmed to control the sensor unit and detects via the electro field measurement unit 201 when a supply voltage (no electro field) is no longer present in the cable. When no supply voltage is present the microprocessor (203) enables power supply to the GSM module 209 using the relay 205 for establishing connection between the battery 207 and the GSM module 297. When activated the GSM module is programmed to transmit an alert message via the GSM network In an embodiment the housing is made from plastic material and encapsulates the components in a water tight manner. Thereby the unit can be used in humid areas.

The unit could furthermore comprise a power level detector connected to the battery for measuring the battery power level and thereby for indicating the need for battery replacement or a recharge, e.g. via the GSM module or via a LED mounted in the housing. The unit could furthermore include LED's for indicating e.g. lack or presence of voltage in the cable or for indicating the power level in the battery.

Figure 3 is a flow diagram illustrating the operation of a sensor unit according to one embodiment of the present invention. The electro field measurement unit constantly transmits a signal to the microprocessor, and initially in 301 the microprocessor listens to this signal from the electro field measurement unit. If a signal is present 303 the listening 301 is continued. As soon as no electrical field is detected the constant signal is disabled. In 303 the microprocessor continues to 305.

In 305 the signal is disabled and the microprocessor listens for a time period, e.g. 3 seconds, to confirm that the signal transmitted from the electro field measurement unit is actually disabled. In 307 the process restarts at 301, if the signal is detected 306. Otherwise 308 the process continues to step 309. In 309 the microprocessor enables the relay to establish power supply between the battery and the GSM module. Then in 311 the microprocessor transmits a signal to the GSM module and based on this the GSM module transmits a GSM alert message via GSM to a predefined receiver, e.g. a mobile phone. Having transmitted the alert message the microprocessor disables the relay in 313 to remove power supply between the battery and the GSM module, this could e.g. be performed, once it has been confirmed that a GSM message has been transmitted.

The above process could in one embodiment be performed a predefined number of times, e.g. with an interval of 10 minutes. The advantage of this periodic repetition is that it is ensured that the predefined receiver of the GSM alert reacts to the warning, and it also indicates to the receiver if power is missing for a longer period of time. As a next step the microprocessor could wait for a longer period, e.g. 12 hours, and then restart the complete process described above to further ensure that the predefined receiver of the GSM alert reacts to the warning. In another embodiment the communication could be performed via a server, which handles the communication on to whom should react to the warning. Thereby the sensor unit only needs to make one alert and from there the server will make sure the alert reaches its final destination. This solution enhances battery life of the sensor unit. As soon as the electro field measurement unit once more detects an electrical field the constant signal is enabled, and the microprocessor enables the relay to establish power supply between the battery and the GSM module. The microprocessor then transmits a signal to the GSM module and based on this signal the GSM module transmits a GSM power on alert message via GSM to the predefined receiver. Having transmitted the alert message the microprocessor disables the relay to remove power supply between the battery and the GSM module, whereby the GSM module is shut down.

The microprocessor could be programmed with a sleep mode whereby any other functionality is disabled while listening to the constant signal from the electro field meas- urement unit. Both the sleep mode as well as the relay ensures that a minimum of power is used when listening. Only if a change occurs all elements are enabled reducing the amount of power used and thereby increasing the battery life.

Figure 4 illustrates a detailed embodiment of the principle in a sensor unit having two voltage sensors 402, 403. In this example a cable 401 comprising three conductors is illustrated, where the three conductors represent respectively Neutral (N), Live (L) and Earth (E). The sensor unit is mounted around the cable 401 and comprises two voltage sensors 402 and 403. In this embodiment, where only two voltage sensors are used and if measurements are being performed on a cable comprising solely two conductors e.g. a Neutral and Live conductor, it is necessary to ensure that the two voltage sensors 402, 403 are positioned relative to the conductors where one conductor is closer to a specific conductor than another voltage sensor, this is to avoid a medium measurement by each voltage sensor. In an embodiment such a position could be ensured by an indicator on the sensor unit, indicating when valid position is obtained, this indicator could e.g. be a light indicator.

Figure 5 illustrates a detailed embodiment of the principle in a sensor unit mounted on a cable 501, wherein the voltage sensor has three voltage sensors 502, 503, 504. In this embodiment it is not possible to position the voltage sensors 502, 503, 504 relative to the conductors whereby the same medium measurement is made by each voltage sensor. There will always be a voltage difference between at least two of the voltage sensor measurements.

Figure 6 illustrates the elements in a voltage sensor which is illustrated relative to a cable 601. The voltage sensor comprises a polyamide layer 602, a copper foil layer 603 being connected ground on an amplifier circuit for screening from external noise and a copper foil being the actual voltage sensor surface for measuring electrical field from the cable 601. The two layers of copper foil 603, 604 could in one embodiment have a thickness of 0.035 mm mounted on each side of the polyamide foil by gluing. In an embodiment the polyamide foil has a thickness of 0.05 mm.

Figure 7 illustrates the voltage sensor surface being divided in sub surfaces 701, 702, 703. The middle sub surface 702 is for measuring the electrical field, whereas the outer sub surfaces 701, 703 are both connected to ground on an amplifier circuit for screening from external noise.

Figure 8 illustrates an embodiment of the measurement circuit in a sensor unit compris- ing three voltage sensor surfaces. The circuit comprises three elements being a filter 804, a CPU 808 and a communication element 812 for wireless communication, e.g. a GSM module. The filter 804 receives voltage signal representing measured voltage 801, 802, 803 measured by each of three voltage sensors. These signals are filtered by removing frequencies below 5 Hz and above 500 Hz. The filter element further com- prises an analogue switching circuit and an amplifier for pairing and measuring the differences between all measured voltages 801 and 802, 801 and 803, 802 and 803. By measuring these paired differences the influence of external noise is reduced significant- The CPU 808 is programmed to control the filter element by transmitting signal 805 to turn the analogue circuit in the filter element on and off. The signal 806 is transmitted to select the pair of measured voltages to be used for measurement. Finally the filter transmits a signal 807 to the CPU 808 representing the voltage difference between the selected pair of measured voltages.

The CPU 808 is further programmed to control the GSM module 812 by transmitting signal 809 to turn the GSM module 812 on and off. The signal 810 is messages to be transmitted by the GSM module 812 such as alarm, log and status messages for transmittal via the GSM module 812 such as to a central server for distributing this to specific recipients. Finally the signal 811 from GSM module 812 to CPU 808 is conformation messages indicated that messages transmitted from GSM module to a recipient has been received.

In the following an embodiment of the measuring sequence performed by the measurement circuit is described:

The electrical field is measured periodically via the voltage sensors in the sensor unit. The interval between measurements can be set manually with shorter or longer intervals, influencing battery life.

The analogue amplifier circuit is only turned on when measurements are performed, thereby a longer battery life is obtained.

The electrical field is measured based on voltage difference sensed between pairs of voltage sensors in a sequence, e.g. first sensor 1 and 2, then sensor 1 and 3 and finally sensor 2 and 3.

A mean value is determined based on the three measurements where the highest measurement is given double weight.

The mean value is normalised to a value between 0 and 999.

The normalised value is compared to a threshold value.

If the sensor unit has not already sent a power off alert and if the normalised mean value is below the threshold value, then a power off alert is sent via the GSM module. If an alert is sent, then a new threshold value is determined based on the normalised mean value multiplied by 4.

8. If the sensor unit has not already sent a power on alert and if the normalised mean value is above the threshold value, then a power on alert is sent via the GSM module. If an alert is sent, then a new threshold value is determined based on the mean value divided by 4.

9. When a new threshold value is calculated, it can only be between predefined minimum and maximum values, e.g. between 50 and 300.

10. The GSM module is only turned on when communicating.

11. If no connection is obtained between the GSM module and a recipient, then a periodic re-transmittal is performed.

Examples of values could be that in the start-up phase a minimum threshold value is set to 50, if a normalised value is measured to 800, then a power on alert is sent via the GSM module and a new threshold value is determined to 200. If a normalised value is measured below 200, then a power of alert is sent via the GSM module and if later a even lower value is measured then a power of alert is sent again.

The unit could furthermore be set up to transmit alert messages to multiple predefined receivers. Furthermore, the time periods of 3 minutes and 12 hours respectively could also be set differently by the user depending on the specific purpose of the unit.

The user could in an embodiment also register/deregister to the sensor unit alert database by calling it.

The unit could furthermore transmit an alert to the receiver when the power level of the battery is below a predefined threshold level, e.g. below 25%.

In the present example the sensor unit detects the presence of an electrical field around the cable and based on that, one or more warnings are transmitted to one or more mobile phones. Thereby indicating that power to a device is missing. The unit could alternatively or as a supplement to the warning also control an emergency generator. Thereby power to the device is immediately re-established. This communication be- tween the sensor unit and the emergency power supply could be obtained by transmitting a digital signal to the generator, e.g. from a communication element in the sensor unit. The sensor unit could furthermore include a memory device for logging activity for periods, e.g. to enable subsequent failure analysis. The sensor unit could include a USB port for use along with e.g. a USB stick to read out any data stored in the included memory device. The sensor unit could furthermore include a GPS module to indicate the position of an electrical device where power is failing.

The sensor unit has a lot of different applications. It can e.g. be used in the fishing industry to prevent batteries on ships from going flat, if land power fails when the ship is docked. The unit could also be used for warning in case of power failure of pumps keeping basements free from water.

The sensor unit could furthermore be used in aquaculture in connection with failures on diffuser blowers for oxygen in holding systems or water coolers.

The sensor unit could furthermore be used in the insurance industry, e.g. in connection with power failures in summer homes preventing water damage as a result of frozen pipes due to no power and therefore no heat. The sensor unit could furthermore be used in agriculture, e.g. in connection with ventilation power failures or unauthorised start-up of sludge pumps.

In a specific embodiment the sensor unit could comprise an input port, e.g. for receiving a digital signal. This port could be connected to other devices such as a PLC's or alert units. The unit could then receive information from these other devices, such as external alerts, which also could be transmitted via the GSM module in the sensor unit to the mobile unit. Furthermore, the sensor unit could be adapted to receive an acknowledgement signal from a mobile device having received an alert. Such acknowledgement could be part of a log file stored in the sensor unit. For saving battery power the sensor unit could shut down after receiving the acknowledgement.