Humidity sensor

Abstract

The invention relates to a humidity sensor comprising: a first electrode having a first surface material; a second electrode having a second surface material that is different from the first surface material such that an electrical voltage is generated when the first surface material and the second surface material come into contact with a humid medium; a voltage-increasing device for increasing the electrical voltage; an energy storage device for storing the electrical energy provided by the two electrodes; and a transmitter unit for wirelessly transmitting information, wherein the energy storage device is arranged downstream of the voltage-increasing device in the signal direction so that, in a sensor state of the humidity sensor, an electrical supply energy for a control device for providing a sensor signal is present at an output of the energy storage device, and one of the electrodes is shaped as a coil which is electrically connected to a capacitor in order to form a resonant circuit so that, in a test state of the humidity sensor, the resonant circuit can be excited by an external high-frequency signal in order to generate the electrical supply energy for the control device in order to provide a test signal.

Description

[0001] Humidity sensor

[0002] The invention relates to a humidity sensor with a first electrode having a first surface material and with a second electrode having a second surface material different from the first surface material, so that an electrical voltage is generated upon contact of the first surface material and the second surface material with a moist medium, with a voltage increasing device for increasing the electrical voltage, with an energy storage device for storing electrical energy provided by at least one of the two electrodes and with a transmitter unit for the wireless transmission of information.

[0003] DE 10 2018 006 950 A1 discloses a humidity sensor with a first electrode and a second electrode, which have different metallic surface materials. Upon contact with moisture or a liquid, they generate an electrical voltage that is applied to an energy storage device for storing electrical energy. The energy storage device has an electrical capacitor that, after charging, feeds a voltage booster that increases the electrical voltage to such an extent that a supply voltage for operating a transmitter device for wirelessly transmitting information, for example, location or identification data, can be transmitted to an evaluation device.A disadvantage of the known humidity sensor is that the potential difference between the two electrodes must be relatively large to charge the energy storage device. Furthermore, the energy storage device must have a capacitor with a relatively high capacitance to provide the necessary operating energy for the energy storage device. Furthermore, the humidity sensor cannot be tested after installation.

[0004] The object of the present invention is therefore to further develop a humidity sensor in such a way that the effectiveness and in particular the operational reliability is increased in a simple manner.

[0005] To achieve this object, the invention in conjunction with the preamble of patent claim 1 is characterized in that the energy storage device is arranged downstream of the voltage boosting device in the signal direction, so that in a sensor state of the humidity sensor, an electrical supply energy for a control device for providing a sensor signal is present at an output of the energy storage device, that one of the electrodes is shaped as a coil which is electrically connected to a capacitor to form a resonant circuit, so that in a test state of the humidity sensor, the resonant circuit can be excited by an external high-frequency signal to generate the electrical supply energy for the control device for providing a test signal.

[0006] According to the invention, an energy storage device is arranged upstream of a voltage booster device in the signal direction. This means that when the humidity sensor is operated in a humid environment (sensor state), the potential difference across the two electrodes is first increased to a voltage level by means of the voltage booster device, so that the downstream energy storage device can be charged with an increased electrical voltage. Due to the increased voltage applied to the energy storage device, electrical power for a downstream control device can be supplied more quickly or using the energy storage device with a lower capacity.The invention further enables the localization or identification of the humidity sensor not only in a humid environment (sensor state), but also in a non-humid environment (test state). For this purpose, one of the electrodes is shaped as an electrical coil (inductance) which is connected to an electrical capacitor to form a resonant circuit. The resonant circuit can be excited by an external high-frequency signal, so that electrical energy is provided to power the control device. The control device generates a test signal for locating the humidity sensor or for testing the humidity sensor without the humidity sensor having to be arranged in a humid environment. Thus, a functional test of the humidity sensor can be carried out in any state of the humidity sensor, whether in a humid environment or not.

[0007] According to a preferred embodiment of the invention, the voltage booster device has an operating point control. This ensures that the energy storage device is always charged with a power adjustment. This advantageously allows for a shortened charging time or the use of smaller electrodes for the same charging time.

[0008] According to a further development of the invention, the voltage boosting device is designed such that a voltage increase is present at an output of the voltage boosting device to a minimum voltage value of 3 V. A relatively high voltage is therefore present at the input of the energy storage device, so that the capacity of the energy storage device (capacitor) can be made smaller for the same charging power. This can advantageously save costs.

[0009] According to a further development of the invention, the voltage booster is designed such that a voltage boost occurs at a minimum input voltage of 200 mV, in particular 300 mV, preferably 350 mV. The voltage booster is preferably designed as a charge pump with operating point control. Advantageously, the electrodes only need to supply a comparatively small potential difference. This ensures a faster response of the humidity sensor and a larger measuring range.

[0010] According to a further development of the invention, the resonant circuit is connected to a charging device for providing the electrical input voltage for the voltage booster circuit from a resonant signal of the resonant circuit. Preferably, the charging device comprises a charging capacitor that is gradually charged to the point where it provides the electrical supply voltage for the voltage booster. The charging device is arranged between the resonant circuit and the voltage booster. The existing components of the humidity sensor in the sensor state, namely the voltage booster, the energy storage device, and the control device, can be used to transmit the test signal.

[0011] According to a further development of the invention, the electrode designed as a coil is spiral-shaped and arranged on a flat support. The spiral-shaped coil surrounds or frames the other electrode, which is also arranged flatly on the support. Advantageously, the spiral-shaped electrode serves as an RFID antenna, which is tuned to the preferably high-frequency external electromagnetic alternating field in such a way that, together with the capacitor of the resonant circuit, the resonance signal is generated, wherein the resonance frequency depends solely on the inductance of the coil and the capacitance of the capacitor. The coil of the resonant circuit serves, on the one hand, to supply the resonant circuit with electrical energy and, on the other hand, as part of the resonant circuit for providing the resonance signal.

[0012] According to a further development of the invention, the control device comprises a microcontroller and a transmitter unit. The microcontroller stores information data from the humidity sensor, for example, an identifier, in a memory. The transmitter device can, for example, comprise a radio antenna, by means of which the test or sensor signal is transmitted to an external evaluation device.

[0013] An embodiment of the invention is explained in more detail below with reference to the drawings

[0014] The drawings show:

[0015] Fig. 1 is a block diagram of a humidity sensor according to the invention and

[0016] Fig. 2 is a plan view of a first electrode and a second electrode of the humidity sensor.

[0017] A humidity sensor 1 can be used to detect humidity. For this purpose, the humidity sensor must be located in a humid medium. It is then in a sensing state. If the humidity sensor 1 is located in a dry medium, it is in a non-sensing state, or test state, as explained later.

[0018] The humidity sensor 1 has a first electrode 2 with a first surface material 3 and a second electrode 4 with a second surface material 5. The first surface material 3 and the second surface material 5 are made of different materials, preferably different metal materials. For example, the first surface material 3 can be made of gold, copper, or nickel. For example, the second surface material 5 can be made of zinc. If the humidity sensor 1 is in a sensor state, i.e., the first electrode 2 and the second electrode 4 are located in a moist medium 6, for example, a liquid, an electrical tap voltage can be tapped at terminals of the first electrode 2 and the second electrode 4, which serves as an electrical input voltage Ui for a voltage booster 7.

[0019] The voltage booster device 7 is preferably designed as a charge pump, which, in the manner of a DC-DC converter, provides a boost voltage II2 (output voltage) on the output side from the tap voltage Ui (input voltage). The charge pump 7 can preferably have several capacitors and diodes.

[0020] An energy storage device 8 is arranged downstream of the voltage booster 7 in the signal direction S. The output signal U2 of the voltage booster 7 forms an input signal of the energy storage device 8. The energy storage device 8 is used to charge electrical energy sufficient to power a control device 9 arranged downstream in the signal direction S. In the present exemplary embodiment, the energy storage device 8 comprises a capacitor that is charged to a supply voltage USP. The supply voltage USP can, for example, have a minimum voltage value of 3 V.

[0021] Preferably, the charge pump 7 has an operating point control, so that the voltage booster 7 for charging the energy storage device 8 is always in a power adjustment mode. This allows the charging time of the capacitor of the energy storage device 8 to be reduced or the charging time to be shortened.

[0022] The voltage boost of the voltage booster 7 is so large that, in order to provide the booster voltage U2 at the output of approximately 3 V, the tap voltage U1 and thus the input voltage U1 of the voltage booster 7 can have a minimum voltage value of 100 mV, in particular 200 mV or 300 mV, preferably at least 350 mV. Advantageously, the first electrode 2 and / or the second electrode 4 each need only have a small potential in the sensor state.

[0023] The control device 9 has a microcontroller 10 and a transmitting unit 11, by means of which a sensor signal 12 can be transmitted wirelessly to an external evaluation device 13 when the humidity sensor 1 is in the sensor state. For this purpose, the evaluation device 13 has a receiving unit 14. For example, the identifier of the humidity sensor 1 is transmitted as the sensor signal 12. The evaluation device 13 contains means for identifying the humidity sensor 1 from the sensor signal 12, so that the humidity sensor 1 can be identified as a humidity-detecting humidity sensor 1. For example, the humidity sensor 1 can serve as a leak sensor for detecting a leak, for example, in a pipeline. Humidity detection occurs when a minimum voltage value of 200 mV is present at the two electrodes 2 and 4 and a current of, for example, 100 μA flows, which is sufficient to control the voltage booster device 7.The voltage booster device 7 can, for example, charge a 200 pF capacitor of the energy storage device 8 in a time between one and five minutes, so that the microcontroller 10 of the control device 9 can then be started to generate the sensor signal 12 containing the identification of the humidity sensor 1. The sensor signal 12 is transmitted wirelessly by radio from the transmitter unit 11 to a receiver unit 14 of the external evaluation device 13.

[0024] To enable localization of the humidity sensor 1 or testing of the same in a non-humidity state or test state of the humidity sensor 1, one of the electrodes, here the first electrode 2 in the exemplary embodiment, is designed as a coil. A capacitor 15 is connected in parallel to the coil 2, so that the coil 2 and the capacitor 15 form a parallel resonant circuit 16.

[0025] As can be seen from Figure 2, the first electrode 2 is spiral-shaped and is arranged flatly on a carrier 17. In the center or inside of the coil 2, the second electrode 4 is arranged flatly on the same carrier 17, which is designed as an electrode carrier. The second electrode 2 can be rectangular—as shown in Figure 2—or oval-shaped or circular.

[0026] In the present embodiment, the first electrode 2 has a first surface material 3 made of gold. The second electrode 4 has a zinc material as its second surface material 5.

[0027] The electrode carrier 17 can consist of a rigid or flexible plastic material.

[0028] The spiral coil electrode 2 thus surrounds the second electrode 4, with both electrodes 2, 4 extending in a common plane.

[0029] The resonant circuit 16 is connected to a charging device 18 for providing the input voltage U1 of the voltage boosting device 7. Output terminals of the charging device 18 form input terminals of the voltage boosting device 7. In the test state or in the non-humidity state of the humidity sensor 1, the potential at the first electrode 2 and the second electrode 4 is zero, so that the connection of the second electrode 4 (zinc electrode) to the negative input terminal of the voltage boosting device 7 has no influence on the input voltage U 1 hThe input voltage U1 of the voltage booster 7 is generated solely by exciting the resonant circuit 16. For this purpose, the electrode coil 2 serves as an RFID antenna, which is fed by an external high-frequency signal 19 from a high-frequency source 20. The high-frequency source 20 is configured such that a high-frequency alternating electromagnetic field is generated as the high-frequency signal 19, to which the electrode coil 2 is exposed.

[0030] The resonant circuit 16 is connected to a charging device 18 for providing the input voltage Ui of the voltage boosting device 7. In the present embodiment, the charging device 18 has a diode 21, a resistor 22 and a charging capacitor 23 which is connected to the input terminals of the voltage boosting device 7.

[0031] The resonance signal (voltage signal U R ) is charged to 200 mV by means of the charging device 18, which is available as input voltage Ui for the voltage boosting circuit 7

[0032] If the capacitor 15 of the resonant circuit 16 has a capacitance of 100 nF, for example, the charging capacitor 23 has a capacitance of 50 pF. The resistor 22 can have a value of 10 kΩ. The diode 21 is connected between a terminal of the charging capacitor 23 and the capacitor 15 in such a way that the charging capacitor 23 is charged in one direction, for example to 200 mV. The input voltage U1 thus generated at the input of the voltage booster 7 is sufficient to activate the voltage booster 7, so that after subsequent charging of the energy storage device 8, the microcontroller 10 of the control device 9 can be activated to transmit the identification of the humidity sensor 1 as a test signal 24 via the radio interface from the transmitting unit 11 of the control device 9 to the receiving unit 14 of the evaluation device 13. This means that even in non-moist conditions orTest condition of humidity sensor 1 allows localization or testing of humidity sensor 1.

[0033] The electrode coil 2 can have a number of turns in the range between two and 50. If the electrode coil 2 has, for example, 10 turns, the resonant frequency in the present embodiment is 200 kHz. This depends on the desired resonant frequency. The sensor signal 12 and test signal 24 transmitted by the transmitter unit 11 can be in a MHz range, for example, in the range of 868 MHz.

[0034] The humidity sensor 1 is in the sensing state when the electrodes 2, 4 are in a liquid, such as water. It is also in the sensing state when the two electrodes 2, 4 are in contact with a moisture-binding medium, such as a moisture-sensitive fleece (fleece with a LiCl coating or other hygroscopic coating).

Claims

Patent claims 1. Humidity sensor comprising a first electrode (2) having a first surface material (3) and a second electrode (4) having a second surface material (5) different from the first surface material (3), such that an electrical voltage (U1) is generated when the first surface material (3) and the second surface material (5) come into contact with a moist medium (6), comprising a voltage boosting device (7) for increasing the electrical voltage (U1), an energy storage device (8) for storing electrical energy stored by at least one of the two electrodes (2, 4), and a transmitter unit (11) for wireless transmission of information, characterized in that - that the energy storage device (8) is downstream of the voltage boosting device (7) in the signal direction (S), so that in a sensor state of the humidity sensor (1) an electrical supply energy (U) is available at an output of the energy storage device (8). SP ) for a control device (9) to provide a sensor signal (12), - that one of the electrodes (2, 4) is shaped as a coil which is electrically connected to a capacitor (15) to form a resonant circuit (16), so that in a test state of the humidity sensor (1) the resonant circuit (16) can be excited by an external high-frequency signal (19) to generate the electrical supply energy (U) SP ) for the control unit (9) to provide a test signal (24). Humidity sensor according to claim 1, characterized in that the voltage boosting device (7) has an operating point control such that the voltage boosting device (7) is in a power-adjusting mode. Humidity sensor according to claim 1 or 2, characterized in that the voltage boosting device (7) is configured such that a minimum voltage value of 3 V is present at an output of the voltage boosting device (7). Humidity sensor according to any one of claims 1 to 3, characterized in that the voltage boosting device (7) is configured such that the voltage boosting occurs at a minimum input voltage at the input of the voltage boosting device (7) of 100 mV, in particular 300 mV, preferably at least 350 mV.Humidity sensor according to one of claims 1 to 4, characterized in that the resonant resonant circuit (16) is connected to a charging device (18) for providing the input voltage (U1) of the voltage boosting device (7) from a resonant signal (U. R ) of the resonant circuit (16). Humidity sensor according to claim 5, characterized in that the charging device (18) has a charging capacitor (23) which is connected to the input of the voltage boosting device (7) and which has a higher capacitance than the capacitor (15) of the resonant circuit (16). Humidity sensor according to any one of claims 1 to 6, characterized in that the resonant circuit (16) is designed as a parallel resonant circuit (16). Humidity sensor according to any one of claims 1 to 7, characterized in that one electrode (2) of the resonant circuit (16), designed as a coil, is arranged spirally around the other electrode (4) on a carrier (17). Humidity sensor according to any one of claims 1 to 8, characterized in that the electrode (2), designed as a coil, has a number of turns in a range between 2 and 50 turns. Humidity sensor according to any one of claims 1 to 9, characterized in that the control unit (9) comprises a microcontroller (10) and the transmitter unit (11) for wireless transmission of the sensor signal (12) and / or the test signal (24) to an external evaluation unit (13).

Images