JP2014010011A - Humidity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity sensor capable of detecting a sensor characteristic failure caused by the time-degradation of a moisture sensitive film without heater heating.SOLUTION: First and second variable capacities C1 and C2 included in a sensor element 10 and first and second capacities Ct1 and Ct2 included in an abnormality detection element 20 are combined to perform humidity detection. Thus, humidity detection is carried out by three systems, i.e., the system of the first and second variable capacities C1 and C2, the system of the first variable capacity C1 and the second capacity Ct2, and the system of the second variable capacity C2 and the first capacity Ct1. Sensor characteristics change between the case of time-degradation of a moisture sensitive film and the case of no time-degradation. Thus, the result of the humidity detection by the three systems takes a value deviated from that of the case of time-degradation of the moisture sensitive film, and a sensor characteristic failure is detected based on this.

Description

  The present invention relates to a humidity sensor that detects humidity based on a change in capacitance formed by a dielectric film in accordance with humidity.

  Conventionally, in Patent Document 1, an acceleration sensor has been proposed as a physical quantity sensor having a capacitive sensor element provided with a variable capacitance that changes a capacitance value in accordance with a change in a physical quantity to be detected. This acceleration sensor has a mode in which the sticking failure between the movable electrode and the fixed electrode for constituting the variable capacitance provided in the capacitive sensor element, that is, the mode in which the state where the movable electrode and the fixed electrode are in contact with each other continues to cause an output abnormality It is possible to detect. Specifically, in the acceleration sensor, the movable electrode and the fixed electrode are basically separated from each other, and therefore, when a sticking failure occurs, an output completely different from that in the normal state is generated. For this reason, a sticking defect can be detected.

  On the other hand, Patent Document 2 proposes a capacitive humidity sensor that includes a reference element in addition to a sensing element and detects an abnormality by comparing the reference element and the sensing element. In this humidity sensor, the reference element is heated by a heater to remove the adhering water and refresh it, thereby correcting the fluctuation amount due to the deterioration of the moisture sensitive film over time.

Japanese Patent No. 4207154 JP2011-94979A

  However, in the acceleration sensor in which the movable electrode and the fixed electrode are spaced apart as in Patent Document 1, the sticking failure can be detected. However, in the humidity sensor that detects humidity by changing the capacitance of the moisture sensitive film, An abnormality due to deterioration of the moisture sensitive film over time cannot be detected. In other words, since the sticking failure is completely different from the normal output, the abnormality can be easily detected. However, sensor output failure such as that the output humidity is represented by a value different from the actual humidity, just as the output fluctuates slightly compared to normal when the moisture sensitive film deteriorates over time. In the case, no abnormality can be detected.

  In the humidity sensor of Patent Document 2, the amount of fluctuation is corrected by refreshing by heating the heater, but it is difficult to detect a minute humidity change (change less than 1 to several% RH) due to heater heat generation. . That is, since the humidity is detected by the relative humidity, a deviation occurs in the detected humidity due to the temperature change, and it becomes difficult to detect a minute humidity change. Moreover, since power consumption due to heater heating occurs, power consumption increases. Furthermore, since the heater cannot be heated in an atmosphere where a flammable gas exists, there also arises a problem that it cannot be applied to a humidity sensor that detects the humidity of such an atmosphere.

  An object of this invention is to provide the humidity sensor which can detect the sensor characteristic defect by the time-dependent deterioration of a moisture sensitive film | membrane, without performing a heater heating in view of the said point.

  In order to achieve the above object, according to the first aspect of the present invention, a periodic carrier wave (PW1, PW2) composed of a moisture sensitive film whose dielectric constant is changed according to humidity and having an opposite phase to each other is applied. In addition to the sensor element (10) constituting the first system, the first variable capacitor (C1) and the second variable capacitor (C2) are connected, and the first variable capacitor and the second variable capacitor are connected in series. Having an abnormality detection capacitor (Ct1, Ct2) composed of a dielectric film connected in parallel to one of the first variable capacitor and the second variable capacitor. The abnormality detection capacitor and the first variable capacitor And an abnormality detecting element (20) constituting a system different from the first system connected in series by a variable capacitor on the opposite side to the one connected in parallel to the abnormality detecting capacitor of the second variable capacitors. ing.

  The differential between the first variable capacitor and the second variable capacitor and between the abnormality detection capacitor and the first variable capacitor and the second variable capacitor connected in series to the abnormality detection capacitor. A conversion circuit (30) that converts a voltage into a capacitance, a signal processing circuit (40) that processes a signal output from the conversion circuit and generates a sensor output, and the first system and the first system are different in the application of a carrier wave. And a control circuit (50) for controlling which one of the systems is applied, and the first system and the system different from the first system constitute a first variable capacitor and a second variable capacitor. The first variable capacitor, the second variable capacitor, and the anomaly detection so that the sensor output characteristics with respect to humidity change with the same inclination before deterioration with time, and the sensor output characteristics with respect to humidity change with different inclination after deterioration with time. It is characterized by the capacity being set

  Using the humidity sensor configured as described above, humidity detection is performed by combining the first and second variable capacitors included in the sensor element and the abnormality detection capacitor included in the abnormality detection element. Thereby, humidity detection by a system different from the first system and the first system can be performed. The sensor characteristics change depending on whether the moisture sensitive film has not deteriorated over time or not. Therefore, the results of humidity detection in each system show that the moisture sensitive film has deteriorated over time. It becomes a value deviated from the case where it does not exist. Therefore, by comparing the results of humidity detection in each system, it is possible to detect an abnormality that deviates from the case where the moisture sensitive film has not deteriorated with time, that is, a sensor characteristic defect. As a result, it is possible to accurately detect a sensor characteristic defect due to deterioration of the moisture sensitive film over time without heating the heater.

  In the invention according to claim 2, the abnormality detection element includes a first capacitor (Ct1) connected in parallel to the first variable capacitor and a second capacitor (Ct2) connected in parallel to the second variable capacitor. As a system different from the first system, a second system composed of a first capacitor and a second variable capacitor and a third system composed of a first variable capacitor and a second capacitor are provided. It is characterized by being.

  As described above, if the three systems are provided, the absolute value of the fluctuation amount of the sensor characteristic accompanying the deterioration of the moisture sensitive film with time can be obtained. Therefore, abnormality detection may be performed based on the absolute value of the fluctuation amount, and if this is fed back and corrected, fluctuation due to deterioration with time of the moisture sensitive film can be canceled, and the moisture sensitive film changes with time. However, accurate humidity can be detected.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

It is the block diagram which showed the circuit structure of the humidity sensor concerning 1st Embodiment of this invention. 3 is a circuit diagram schematically showing circuit configurations of a sensor element 10 and an abnormality detection element 20. FIG. It is the figure which showed an example of the characteristic of the humidity with respect to the sensor output before deterioration with time of a moisture sensitive film and after deterioration with time. It is the block diagram which showed the circuit structure of the humidity sensor concerning 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
A first embodiment of the present invention will be described. First, the configuration of a capacitive humidity sensor according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the humidity sensor includes a sensor element 10, an abnormality detection element 20, a CV conversion circuit 30, a signal processing circuit 40, and a control circuit 50.

  The sensor element 10 includes a first variable capacitor C1 and a second variable capacitor C2 formed by a moisture sensitive film. The moisture sensitive film is composed of a dielectric film that changes its capacity based on the amount of moisture adhering to the humidity. The variable capacitors C1 and C2 are configured by providing fixed electrodes on both front and back surfaces of the moisture sensitive film. The first variable capacitor C1 and the second variable capacitor C2 are connected in series by connecting one of the fixed electrodes to each other, and the other fixed electrode is inverted with each other via the switches 11 and 12. A rectangular wave voltage signal (carrier wave) PW1, PW2 can be applied. During normal humidity detection, the switches 11 and 12 are turned on, so that the potential between the first variable capacitor C1 and the second variable capacitor C2 is a differential capacitor (hereinafter referred to as a differential capacitor) that represents a minute capacitance change caused by a humidity change. , The capacitance difference ΔC) is input to the CV conversion circuit 30.

  The first variable capacity C1 and the second variable capacity C2 are not the same capacity but are unbalanced capacity, and the change in capacity according to the humidity is set to change between the first variable capacity C1 and the second variable capacity C2. Yes. Regarding the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor C2, the sensor output is saturated if it is output as it is, so that the offset correction is performed so that the capacitance difference ΔC becomes 0 at a specific humidity. It is.

  The abnormality detection element 20 includes a first capacitor Ct1 connected in parallel to the first variable capacitor C1 and a second capacitor Ct2 connected in parallel to the second variable capacitor C2. The first capacitor Ct1 and the second capacitor Ct2 are equivalent to an abnormality detection capacitor, are not moisture-sensitive films, but are formed of dielectric films, and each of the capacitors Ct1 and Ct2 is provided with fixed electrodes on both front and back surfaces of the dielectric film. It is configured. The first capacitor Ct1 and the second capacitor Ct2 are also connected in series by connecting one of the fixed electrodes to each other, and the other fixed electrode is periodically switched to each other via the switches 13 and 14. Square wave voltage signals (carrier waves) PW1 and PW2 can be applied. Further, the first variable capacitor C1 and the second variable capacitor C2 in the sensor element 10 and the first capacitor Ct1 and the second capacitor Ct2 in the abnormality detection element 20 are connected. For this reason, when an abnormality is detected, potentials between various combinations of capacitors can be input to the CV conversion circuit 30 as the capacitance difference ΔC based on the on / off operation of the switches 11 to 14.

  The first capacitor Ct1 and the second capacitor Ct2 have the same capacity as the first variable capacitor C1 and the second variable capacitor C2, respectively, in a specific humidity environment, for example, at 50% RH. The first capacitor Ct1 and the second capacitor Ct2 are used to perform offset correction of the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor C2 and to form the first variable capacitor C1 and the second variable capacitor C2. It is used to detect an abnormality (sensor characteristic failure) based on the deterioration of the wet film over time.

  Specifically, the first capacitor Ct1 and the second capacitor Ct2 include the offset correction capacitors ΔCt1 and ΔCt2 for performing the offset correction, and the abnormality detection capacitors Ct1 ′ and Ct2 ′. include. Therefore, when the circuit configuration of the sensor element 10 and the abnormality detection element 20 is schematically shown, a circuit diagram as shown in FIG. 2 is obtained. Accordingly, the capacitance difference ΔC at the specific humidity between the first variable capacitor C1 and the second variable capacitor C2 is set to 0 by the offset correction capacitors ΔCt1 and ΔCt2. Further, the first capacity Ct1 and the second capacity Ct2 are set to the same capacity as the first variable capacity C1 and the second variable capacity C2, respectively, under a specific humidity environment by the abnormality detection capacity Ct1 ′ and Ct2 ′. Yes.

  The offset correction capacitors ΔCt1 and ΔCt2 included in the first capacitor Ct1 and the second capacitor Ct2 are adjusted in advance based on the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor C2. In addition, as described above, the first variable capacitor C1 and the second variable capacitor C2 and the first capacitor Ct1 and the second capacitor Ct2 are connected. This is called connection point A.

  The CV conversion circuit 30 converts the change in the differential capacitance composed of any combination of the first and second variable capacitors C1 and C2 and the first and second capacitors Ct1 and Ct2 into a voltage and takes it out. The configuration includes an operational amplifier 31, a capacitor 32, and a switch 33.

  An inverting input terminal of the operational amplifier 31 is connected to the connection point A, and a capacitor 32 and a switch 33 are connected in parallel between the inverting input terminal and the output terminal. The switch 33 is driven by a switch control signal from the control circuit 50, and the non-inverting input terminal of the operational amplifier 31 has a voltage Vdd / 2 that is half of the voltage Vdd used as the voltage signals PW1 and PW2. (Ie, midpoint voltage) is input.

  The signal processing circuit 40 includes a sample and hold circuit, an SCF (switched capacitor filter) circuit, an amplifier circuit, and the like. The sample hold circuit is driven based on a control signal from the control circuit 50, samples the output of the CV conversion circuit 30, and holds it for a certain period. The SCF circuit removes noise from the output voltage of the sample and hold circuit and extracts only a component in a predetermined frequency band. The amplifier circuit is a circuit that amplifies the signal after noise removal by the SCF circuit at a predetermined amplification factor, and the signal amplified by the amplifier circuit is generated as a sensor output. The amplification factor in the amplifier circuit is adjusted so that the relationship between the sensor output and humidity matches the desired sensor characteristics, and the first and second variable capacitors C1 and C2 and the first and second capacitors Ct1, Individual amplification factors can be set according to the capacity selected from Ct2.

  The control circuit 50 outputs voltage signals PW1, PW2, a switch control signal indicating the switching timing of the switches 11 to 14, a control signal indicating the switching timing of the switch 33, and a control signal to the sample hold circuit and the amplifier circuit. Specifically, the control circuit 50 applies the voltage signal PW1 to either the first variable capacitor C1 or the first capacitor Ct1, or applies the voltage signal PW2 to the second variable capacitor C2 or the second capacitor Ct2. Control what to do. Further, the control circuit 50 controls on / off of the switch 33 in accordance with the period of the voltage signals PW1, PW2, and controls the sampling timing of the sample hold circuit. Further, the control circuit 50 is configured to indicate, by a control signal, whether it is normal humidity detection or abnormality detection for the amplifier circuit in the signal processing circuit 40.

  For example, a sensor output or a control signal from the control circuit 5 is input to a microcomputer provided outside, and humidity detection or abnormality detection is performed based on the sensor output by the microcomputer.

  In the humidity sensor configured as described above, as an initial setting, offset correction and amplification factor adjustment are performed so that the relationship between humidity (% RH) and sensor output becomes a desired relationship. doing.

  First, the offset correction capacitors ΔC1 and ΔC2 included in the first capacitor Ct1 and the second capacitor Ct2 and the amplification in the amplifier circuit so that the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor becomes 0 at a specific humidity. The rate is set. Thereby, the switches 11 and 12 are turned on, the switches 13 and 14 are turned off, and the sensor characteristics when the sensor output is generated based on the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor are the desired characteristics. It becomes. This is the reference characteristic of the sensor characteristic.

  In addition, reference humidity detection can be performed using the first variable capacitor C1 and the second capacitor Ct2 for abnormality detection. Then, the amplification factor is adjusted so that the characteristic indicated by the relationship between the reference humidity and the sensor output in this case matches the sensor characteristic when the first and second variable capacitors C1 and C2 are used. Similarly, reference humidity detection can be performed using the second variable capacitor C2 and the first capacitor Ct1 for abnormality detection. Then, the amplification factor is adjusted so that the characteristic indicated by the relationship between the reference humidity and the sensor output in this case matches the sensor characteristic when the first and second variable capacitors C1 and C2 are used.

  If such a setting is performed, if the moisture-sensitive film has not deteriorated with time, the system of the first variable capacitor C1 and the second variable capacitor C2 (first system), the first variable capacitor C1, and the second capacitor Ct2 Alternatively, the same sensor output represents the same humidity regardless of the system (second system or third system) of the second variable capacitor C2 and the first capacitor Ct1.

  Next, the operation of the humidity sensor after completion of the initial setting will be described separately for normal humidity detection and abnormality detection. For example, if the humidity sensor is used for mounting on a vehicle, the normal humidity detection is performed during a period in which the ignition switch is turned on. Humidity detection may always be performed during this period, but the humidity does not change abruptly, so in order to reduce power consumption, wakeup is performed every predetermined period and humidity is detected during other periods. You may make it be in a state. The abnormality detection may be performed at any time as long as the power supply to the humidity sensor can be turned on. For example, the abnormality detection is performed at the time of initial check performed at the same time as the ignition switch is turned on.

  During normal humidity detection, the switches 11 and 12 are turned on and the switches 13 and 14 are turned off based on the switch control signal from the control circuit 50. Therefore, the voltage signals PW1, PW2 are applied to the first variable capacitor C1 and the second variable capacitor C2 via the switches 11, 12. Then, a control signal for controlling on / off of the switch 33 and a control signal to the sample hold circuit are output from the control circuit 50 in accordance with the cycle of the voltage signals PW1 and PW2. As a result, a sensor output corresponding to the capacitance difference ΔC between the first variable capacitor C1 and the second variable capacitor C2 is generated from the signal processing circuit 40, and the microcomputer stores the sensor output and humidity stored in advance. Humidity can be detected based on the relationship.

  Note that the ON / OFF timing of the switch 33 and the control of the sample hold circuit at the time of humidity detection are the same as those at the time of acceleration detection disclosed in Patent Document 1.

  When detecting an abnormality, the switches 11 and 12 are turned on and the switches 13 and 14 are turned off as in the case of normal humidity detection to perform the same operation as in the humidity detection, and the abnormality detection element 20 is used to perform the above operation. An operation similar to that at the time of humidity detection is performed for abnormality detection. In the case of the present embodiment, for abnormality detection, the switches 11 and 14 are turned on and the switches 12 and 13 are turned off to perform the same operation as the above humidity detection, and the switches 11 and 14 are turned off and the switches 12 and 13 are turned on. It is turned on and performs the same operation as when the humidity is detected. That is, abnormality detection is performed by measuring humidity by combining the first and second variable capacitors C1 and C2 with the first and second capacitors Ct1 and Ct2. The order of the combination at this time is arbitrary, but here, an example thereof will be described.

  First, similarly to the normal humidity detection, the switches 11 and 12 are turned on and the switches 13 and 14 are turned off to detect the humidity using the first and second variable capacitors C1 and C2. Since the humidity at this time is a value detected using the first and second variable capacitors C1 and C2, the moisture sensitive films constituting the first and second variable capacitors C1 and C2 are deteriorated over time. In this case, the sensor characteristic variation due to the deterioration with time is included.

  Subsequently, the switches 11 and 14 are turned on and the switches 12 and 13 are turned off, so that the humidity is detected using the first variable capacitor C1 and the second capacitor Ct2. The humidity at this time is a value detected using the first variable capacitor C1 and the second capacitor Ct2. Since the second capacitor Ct2 is composed of a dielectric film that is not a moisture sensitive film and hardly deteriorates with time, when the moisture sensitive film constituting the first variable capacitor C1 deteriorates with time, The humidity includes sensor characteristic fluctuations due to deterioration over time.

  Further, the switches 11 and 14 are turned off and the switches 12 and 13 are turned on, whereby humidity detection is performed using the second variable capacitor C2 and the first capacitor Ct1. The humidity at this time is a value detected using the second variable capacitor C2 and the second capacitor Ct1. Since the first capacitor Ct1 is made of a dielectric film that is not a moisture sensitive film and hardly deteriorates with time, when the moisture sensitive film constituting the second variable capacitor C2 deteriorates with time, The humidity includes sensor characteristic fluctuations due to deterioration over time.

  Thus, humidity detection is performed by combining the first and second variable capacitors C1 and C2 included in the sensor element 10 with the first and second capacitors Ct1 and Ct2 included in the abnormality detection element 20. Thus, humidity detection can be performed by the three systems of the first and second variable capacitors C1 and C2, the first variable capacitor C1 and the second capacitor Ct2, and the second variable capacitor C2 and the first capacitor Ct1. .

  The sensor characteristics change depending on whether the moisture sensitive film is not deteriorated with time or when the moisture sensitive film is deteriorated with time. Therefore, the humidity detection results of the above three systems indicate that the moisture sensitive film deteriorates with time. The value deviates from the case where it is not. Therefore, by comparing the humidity detection results of the three systems, it is possible to detect an abnormality that deviates from the case where the moisture sensitive film has not deteriorated over time. For example, when the moisture sensitive film deteriorates with time, the characteristics of each system deviate from the reference characteristics of the sensor characteristics as shown in FIG.

  For example, as shown in FIG. 3, when the humidity is detected using the first and second variable capacitors C1 and C2, the sensor output appears as a higher value than the reference characteristic even at the same humidity (( 1)). When the humidity is detected using the first variable capacitor C1 and the second capacitor Ct2, the sensor output appears as a higher value than the reference characteristic even if the humidity is the same ((2) in the figure). When humidity detection is performed using the second variable capacitor C2 and the first capacitor Ct1, even if the humidity is the same as the reference characteristic, the sensor output appears as a lower value ((3) in the figure).

  Therefore, when the moisture-sensitive film has deteriorated over time, the humidity detected based on the sensor output in each system has a different value, which is caused by the deterioration with time based on the difference in humidity. Abnormality of the humidity sensor can be detected. For example, if the humidity difference between the systems exceeds a predetermined threshold, it is detected that an abnormality of the humidity sensor due to deterioration with time has occurred. As a result, it is possible to accurately detect a sensor characteristic failure due to deterioration of the moisture sensitive film over time.

  As described above, according to the humidity sensor of the present embodiment, it is possible to detect a sensor characteristic failure due to deterioration with time of the moisture sensitive film without performing heater heating. Such abnormality detection is performed based on the humidity of each system under the same situation, and can only be performed at a specific humidity. Therefore, abnormality detection can be performed at any humidity regardless of whether the humidity is a specific humidity. Therefore, it is possible to detect an abnormality even if it is not necessary to provide a system for detecting an accurate humidity as a reference. In addition, since heater heating is not performed, an increase in power consumption can be suppressed, and a humidity sensor can be applied even in an atmosphere where flammable gas exists. In addition, since a minute humidity change due to heater heating does not occur, it becomes possible to detect humidity more accurately.

  Here, the sensor characteristics failure is detected by comparing the humidity obtained from the sensor output when the voltage signals PW1 and PW2 are applied to the first system to the third system, respectively, but the sensor output itself is compared. By doing so, a sensor characteristic defect may be detected.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, the characteristics of each system are not adjusted by adjusting the amplification factor of the amplifier circuit as in the first embodiment, but are performed by an external storage device. In other respects, the present embodiment is the same as the first embodiment, and therefore only different parts from the first embodiment will be described.

  As shown in FIG. 4, the sensor output output from the signal processing circuit 40 is transmitted to the external storage device 60. The external storage device 60 stores initial values of the characteristics of each system or correction values necessary for matching the characteristics of each system in accordance with the initial values. For this reason, in the present embodiment, the sensor output is corrected to the value obtained by combining the characteristics of each system based on the stored initial value or correction value in the external storage device 60. The humidity is detected by the microcomputer based on the sensor output after correction by the external storage device 60.

  In this way, even if the external storage device 60 stores the initial values of the characteristics of each system or the correction values necessary for matching the characteristics of each system according to the initial values, As in the first embodiment, it is possible to detect an abnormality of the humidity sensor due to the deterioration of the moisture sensitive film over time.

(Other embodiments)
In the embodiment described above, humidity detection is performed by three systems: the first and second variable capacitors C1 and C2, the first variable capacitor C1 and the second capacitor Ct2, and the second variable capacitor C2 and the first capacitor Ct1. And the abnormality due to the deterioration of the humidity sensor with time was detected. However, this is merely an example. In addition to the system of the first and second variable capacitors C1 and C2, the system of the first variable capacitor C1 and the second capacitor Ct2 or the second variable capacitor C2 and the first variable capacitor If there is at least two systems of any one of the capacitors Ct1, abnormality detection can be performed. That is, when the moisture sensitive film deteriorates with time, in addition to the systems of the first and second variable capacitors C1 and C2, there is a system in which the slope of the sensor characteristic (the slope of the sensor output with respect to humidity) differs from that of the system. If there is at least one, abnormality detection can be performed.

  However, if three systems are provided, the absolute value of the fluctuation amount of the sensor characteristic accompanying the time-dependent deterioration of the moisture sensitive film can be obtained. That is, the humidity obtained when using the system of the first and second variable capacitors C1 and C2 includes a value including deterioration with time of the moisture sensitive film constituting the first and second variable capacitors C1 and C2. Become. Further, the humidity obtained when the system of the first variable capacitor C1 and the second capacitor Ct2 is used has a value including deterioration with time of the moisture sensitive film constituting the first variable capacitor C1. Further, the humidity obtained when the system of the second variable capacitor C2 and the first capacitor Ct1 is used has a value including deterioration with time of the moisture sensitive film constituting the second variable capacitor C2. Therefore, it is possible to derive three functional expressions including two variables in the three systems, with the time-dependent deterioration of the moisture sensitive films constituting the first and second variable capacitors C1 and C2 as variables. For this reason, two variables can be obtained by solving the functional equation, and this is an error in the sensor output corresponding to the deterioration with time of the moisture-sensitive film constituting the first and second variable capacitors C1 and C2, that is, the humidity. It becomes an error. By feeding back this error, for example, by correcting the amplification factor and the correction amount in the external storage device 60, it is possible to cancel fluctuations due to deterioration of the moisture sensitive film over time, and accurate even if the moisture sensitive film changes over time. It becomes possible to detect humidity.

  It should be noted that the humidity error associated with the time-dependent change of the moisture sensitive film is similar to that of any humidity. For this reason, if the detected error is fed back and corrected, fluctuations due to deterioration of the moisture sensitive film over time can be canceled at any humidity, and accurate even if the moisture sensitive film changes over time. It becomes possible to detect humidity.

  Moreover, although the said embodiment demonstrated the structure provided with the external storage device 60 and the microcomputer which is not illustrated in the exterior of the humidity sensor, these may be provided in the humidity sensor.

  Further, in the above embodiment, when a sensor characteristic defect is detected, a signal indicating that the sensor characteristic defect has been detected is sent to a notifying means (not shown) so that the notification means notifies that the sensor characteristic defect has been detected. You can also.

DESCRIPTION OF SYMBOLS 10 Sensor element 11-14 Switch 20 Abnormality detection element 30 CV conversion circuit 40 Signal processing circuit 50 Control circuit 60 External storage device C1 1st variable capacity C2 2nd variable capacity Ct1 1st capacity Ct2 2nd capacity

Claims (7)

A first variable capacitor (C1) and a second variable capacitor (C2) that are composed of a moisture sensitive film that changes the dielectric constant according to humidity and to which periodic carrier waves (PW1, PW2) having opposite phases are applied. A sensor element (10) constituting a first system by connecting the first variable capacitor and the second variable capacitor in series;
An abnormality detection capacitor (Ct1, Ct2) configured by a dielectric film connected in parallel to one of the first variable capacitor and the second variable capacitor, the abnormality detection capacitor and the first variable An abnormality detection element (20) constituting a system different from the first system connected in series by a capacitor and a variable capacitor on the opposite side of the second variable capacitor connected in parallel with the abnormality detection capacitor; ,
Difference between the first variable capacitor and the second variable capacitor, or between the abnormality detection capacitor and one of the first variable capacitor and the second variable capacitor connected in series to the abnormality detection capacitor. A conversion circuit (30) for converting dynamic capacity to voltage;
A signal processing circuit (40) for processing a signal output from the conversion circuit to generate a sensor output;
A control circuit (50) for controlling whether the carrier wave is applied to the first system or a system different from the first system, and humidity is detected based on the sensor output Configured as
The first system and the system different from the first system are such that the sensor output characteristics with respect to humidity have the same inclination before the moisture-sensitive film constituting the first variable capacitor and the second variable capacitor deteriorates with time. The humidity is characterized in that the first variable capacitor, the second variable capacitor, and the abnormality detection capacitor are set so that the characteristic of the sensor output with respect to humidity changes with a different slope after the deterioration with time. Sensor.   The abnormality detection element includes a first capacitor (Ct1) connected in parallel to the first variable capacitor and a second capacitor (Ct2) connected in parallel to the second variable capacitor, As a system different from the system, the system has a second system composed of the first capacitor and the second variable capacitor, and a third system composed of the first variable capacitor and the second capacitor. The humidity sensor according to claim 1.   The signal processing circuit includes an amplifier circuit, and before the deterioration with time, the characteristics of the sensor output with respect to humidity in the first system, the second system, and the third system are matched. The amplification factor is set for each of the first system, the second system, and the third system, and the carrier wave is applied to each of the first system, the second system, and the third system when an abnormality is detected. The humidity sensor according to claim 2, wherein a sensor characteristic failure is detected by comparing the sensor output at the time of detection or the humidity obtained from the sensor output.   When the abnormality is detected, the amplifier circuit feeds back a sensor output when the carrier wave is applied to each of the first system, the second system, and the third system or an error in humidity obtained from the sensor output. The humidity sensor according to claim 3, wherein the amplification factor is corrected.   A sensor output in each of the first system, the second system, and the third system or a humidity correction amount obtained from the sensor output is stored in a storage device (60). A sensor by correcting the sensor output when the carrier wave is applied to each of the second system and the third system or the humidity obtained from the sensor output with the correction amount stored in the storage device and comparing the sensor output The humidity sensor according to claim 2, wherein a characteristic defect is detected.   When the abnormality is detected, the storage device feeds back a sensor output when the carrier wave is applied to each of the first system, the second system, and the third system or an error in humidity obtained from the sensor output. The humidity sensor according to claim 5, wherein the correction amount stored in is corrected.   The humidity sensor according to any one of claims 3 to 6, wherein when the sensor characteristic defect is detected, the notification unit is instructed to notify that the sensor characteristic defect has been detected. .

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