Wireless sensor system

[0001] This is a U.S. National Stage of International Application No. PCT/DE02/03732 filed on 1 Oct., 2002.

[0002] This patent application claims priority of German patent application no. 101 50 128.5 filed 11 Oct. 2001.

[0003] The invention relates to a sensor system which is not connected by wire (“wire-free”), to a monitoring system based on this sensor system, and to two uses of the sensor system.

[0004] Until now, environmental changes have mainly been detected by sensors which pass on state information via wire lines, and are at the same time supplied with electrical power via these wire lines. The wiring, which is often complex and thus costly, is problematic in this case.

[0005] Battery-operated sensors are likewise known, which pass on the corresponding measured values by radio. However, these have the disadvantage that the batteries must be serviced. Particularly where there are a large number of devices to be monitored, the batteries cause logistic problems for servicing, as well as high costs.

[0006] DE 198 26 513 A1 discloses an automation system for control of a processing apparatus having a radio sensor which is used to reduce the installation complexity. For this purpose, it has a radio sensor which can be operated by means of a solar cell, possibly in conjunction with an energy store.

[0007] One object of the present invention is to provide an improved capability for power-saving status checking, which can be implemented such that it can be installed easily.

[0008] This and other objects are attained in accordance with one aspect of the present invention directed to a sensor system having at least one voltage generator for conversion of non-electrical energy to electrical energy, for example a solar cell, an inductive element or a piezoelement. There is therefore no need for a battery to operate it. The voltage generator is followed by at least one energy store, for example a rechargeable battery or a capacitor. The energy store is connected to at least one voltage converter, which converts the stored energy to an output signal which is suitable for operation of a processor controller. For example, the voltage converter could cut off voltage peaks which would damage the processor controller. In addition, at least one sensor is provided which detects the desired state, for example a light intensity sensor, a contact sensor or a position sensor. Furthermore, at least one transmitter is provided for wire-free transmission of transmission messages, in particular in the form of radio signals. The transmission messages can be produced by means of the processor controller and contain at least one measured value from the at least one sensor. However, they may also contain two or more measured values, for example from two or more sensors.

[0009] The sensor system also contains a timer circuit, which can be triggered as a function of a state value, for example of a voltage level, of the at least one energy store, and which activates the sensor system in order to transmit at least one transmission message after a time interval which is determined by it.

[0010] In accordance with an embodiment of the invention, the time interval may, for example, either be fixed and predetermined by the design of the timer circuit or may be redefined variably on each activation by the processor circuit. For this purpose, in particular, the state of charge of the energy store may be checked and included in the definition of the transmission frequency per unit time, in order to allow the sensor to be operated for periods which are as long as possible. After its activation, the energy should typically be sufficient to operate the running timer circuit even if the external energy supply then fails, for example if it becomes cloudy and a solar cell is being used.

[0011] It is particularly advantageous if the sensor can also be operated as a voltage generator, because this allows the number of components to be reduced, and thus the susceptibility to faults.

[0012] It is advantageous for at least one voltage generator to be a solar cell, because this allows for an energy supply which operates throughout the year. The solar cell is particularly advantageous for illumination measurement because, in this case, it can be used as a voltage generator and as an illumination sensor at the same time.

[0013] It is also advantageous for at least one voltage generator to be a piezoelectric transducer and/or an inductive converter, because this provides a low-cost energy source. Particularly in the case of position finding, for example for doors, windows and the like, it is advantageous for this voltage generator to be used as a sensor for position finding at the same time. It is advantageous in order to achieve a long operating life for a solar cell also to be provided as a voltage generator.

[0014] In order to achieve a long time interval and/or to provide two or more activation cycles even when the energy supply is low or has failed, it is advantageous for the timer circuit to have semiconductor modules based on ULP (“Ultra Low Power”) technology.

[0015] In order to identify the sensor, particularly when two or more sensors and/or sensor systems are used at the same time, it is advantageous for the transmission message also to contain at least one identification code.

[0016] Furthermore, the above-mentioned object is achieved by a monitoring system which contains at least one sensor system as described above, as well as at least one receiving and evaluation system. The sensor system typically passes information on by means of the transmission message without the use of wires, for example by radio, to a receiving and evaluation system which is connected to the electrical mains system. The receiving and evaluation system is, for example, an illumination controller, or it contains display elements, bus systems and/or actuators (louvre control etc.). The receiving and evaluation system may advantageously monitor two or more sensor systems.

[0017] The above-mentioned object is also achieved by the use of the sensor system and/or of the monitoring system for position finding, for example for windows, doors or other moving devices in buildings. This use is becoming increasingly important for reasons related to safety, energy saving and in order to increase the convenience in both commercial premises and in the field of private dwellings. In this case, it is advantageous if the sensor can also be used as a voltage generator, particularly if it contains an inductive or piezoelectric element. Other elements, for example electrostrictive or magnetostrictive elements, are also generally feasible.

[0018] The above-mentioned object is also achieved by the use of the sensor system and/or of the monitoring system for illumination signaling, with the voltage generator and the sensor in particular at least partially including the same solar cell; the solar cell is then used as a combined voltage generator and illumination sensor. The illumination intensity at workstations, in commercial premises, in private households, on public roads, in public squares, and in installations etc. is being controlled to an increasing extent as a function of the daylight incidence, in order on the one hand to achieve optimum lighting quality and in order on the other hand to save energy. The discovery makes it possible, for example, to switch on the illumination in the outdoor area or in buildings.

[0019] The sensor system and the monitoring system will be explained schematically in more detail in the following exemplary embodiments.

[0023] FIG. 1 shows a block diagram of a sensor system S for position finding.

[0024] The wire-free sensor system S passes on information by radio to actuators, bus systems or display elements, which are typically connected to the electrical mains system. The power for operation of the sensor system S together with the associated radio transmitter 5 is supplied from the ambient lighting and/or from the mechanical movement of the devices to be monitored, so that there is no need for a battery to operate it.

[0025] A voltage generator 1 in the form of a solar cell 11 (in general: a photovoltaic element) produces an electrical voltage when light falls on it. This is designed such that a voltage of about two volts is emitted even when the illumination intensities are low. For cost reasons, the solar cell 11 is preferably chosen to be sufficiently small that the processor controller 4 cannot be operated directly from it continuously. This is possible, for example, when a low frequency is used for how often the sensor system S transmits its signal. This greatly reduces the energy which is required, for example, for operation in one day. In order nevertheless to obtain as much power as possible, an energy store 2, preferably a low-loss capacitor of high capacitance or an electrochemical storage cell, is first of all charged with electrical energy to supplement the solar cell. The design in conjunction with the solar cell 11 is in this case chosen such that it is reliably possible to bridge even extremely dark phases, such as those which may occur in winter.

[0026] Furthermore, this exemplary embodiment additionally makes use of one or more energy converters 2 which convert the movement energy (thick arrow) of the device to be monitored (for example pressing of door catches, opening or closing of windows or doors) to electrical energy for feeding the sensor system S. Piezoelectric transducers 12, inductive converters 13 and, as a special case of them, a so-called Wiegand element may be used, in particular, for this purpose (see www.hta-be.bfh.ch/˜felser/stadium).

[0027] When the voltage of the energy store 2 reaches a sufficient level, then a timer circuit 6 is activated which now activates the entire sensor system S with the processor controller 4 and the transmitter 5 at sensible intervals. The time interval is either predetermined and is fixed by the design of the timer circuit 6 or is redefined by the processor controller 4 on each activation. For this purpose, in particular, the state of charge of the energy store 2 can be checked and can be included in the definition of the transmission frequency per unit time, in order to allow the sensor system S to be operated for periods which are as long as possible during dark phases. A voltage converter 3 provides the approximately constant voltage, which is required for operation of the processor controller 4 and advantageously of the transmitter 5 as well, during each of the short operating phases.

[0028] On each activation, the state of the device being monitored is measured at that time by means of a sensor 7. The measurement may, for example, produce binary information (door open or closed, etc.) or else one or more analog measured values (opening angle of the window etc.). The result is coded together with an identification number for the sensor system S into a radio transmission message, which is transmitted from the radio-frequency transmitter 5 via the connected antenna 51. The radio transmission message may have redundancies included, in order to improve the transmission reliability. Other types of wire-free transmission may also be used instead of radio transmission, for example IR light.

[0029] It is likewise preferable to provide a storage circuit 21 which can carry out energy management without the timer 6.

[0030] The processor 4, which can be a microprocessor, regulates the transmission of information according to the energy management of storage circuit 21 or timer 6 and the information load to be transmitted.

[0031] The timer circuit 6 is advantageously designed for an extremely low power demand, since it operates continuously as a single component. Either an analog or a digital timer circuit 6 may be used.

[0032] All sensors 7 which can be checked by the processor, for example via an A/D converter module, may be used as position sensors 71. For binary position finding, these are preferably reed contacts, which respond to a magnetic field from a permanent magnet which is connected to the moving part. Inductive or rotation angle sensors, for example, are suitable for analog position finding purposes.

[0033] The transmitter 5 preferably essentially comprises a transmission stage with a radio-frequency oscillator which can start to oscillate very quickly. It preferably operates with an SAW resonator as the frequency-determining component. The transmitter 5 is designed for a very low current consumption and operates with a comparatively wide bandwidth, in order to keep the transmission duration short. The wide bandwidth allows very short transmission times, and thus low energy consumption.

[0034] FIG. 2 shows a block diagram of the associated receiving and evaluation system R.

[0035] The receiving system comprises a radio-frequency receiver 8 and a processor-based signal processing unit 9. It receives the messages which are transmitted from the sensor, and are temporarily stored and processed.

[0036] The radio signal from the sensor system is typically received via the antennas 81 by all of the associated radio-frequency receivers 8 located in that vicinity, and are evaluated with processor assistance. After evaluation, only the receiver systems which have been addressed react and, via a suitable coupling 10, such as a bus system result in an action from the alarm transmitter, drive and actuator (for example heating valves when a window is open) or feed the measurement data to a bus system, for example a PLC bus, for further storage and processing.

[0037] Error-tolerant transmission methods are preferably used for data transmission, particularly those with forward error correction or block-oriented redundancy methods. An option for data encryption is advantageous. It is advantageous to transmit the data in a very short time in order to provide protection against collisions when two or more sensors are located in the reception area of receiving electronics. A position indicating value, an identification number and, possibly, further data such as the time etc. are transmitted, by way of example.

[0038] The data is transmitted at fixed or variable time intervals even without any movement of the devices being monitored, but data transmission can also be triggered in each case by a state change of these devices.

[0039] FIG. 3 shows a block diagram of an illumination sensor system.

[0040] The illumination intensity at workstations, in commercial premises, in private households, on public roads, in public squares, and in installations etc. is being controlled to an increasing extent as a function of the daylight incidence, in order on the one hand to achieve optimum illumination quality and in order on the other hand to save energy.

[0041] In contrast to the sensor system shown in FIG. 1, there is no mechanically activated voltage generator 12, 13 in this case. In fact, the solar cell 11 is used exclusively as a voltage generator 1 and sensor 7. Whenever it is activated, the illumination intensity is measured at that time via the solar cell 11. The result is coded together with the identification number of the sensor 11 into a radio message, which is transmitted by the radio frequency transmitter 5 via the connected antenna 51. The radio message may have redundancies included, in order to improve the transmission reliability.

[0042] The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which includes every combination of any features which are stated in the claims, even if this combination of features is not explicitly stated in the claims.