JPH0543330U - Condensation detection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In a dew condensation detection circuit that uses a humidity sensor whose resistance value rapidly increases in high humidity conditions, the accuracy of the dew condensation state and the humidity range to be detected against variations in the resistance value of the humidity sensor. To improve. A humidity sensor 3 is connected between the inverting input terminal 2a of the differential amplifier 2 and a reference potential, and a feedback resistor 4 is connected between the output terminal 2c of the differential amplifier 2 and the inverting input terminal 2a. A predetermined bias voltage 7 is supplied to the non-inverting input terminal 2b of the differential amplifier 2.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement in a dew condensation detection circuit of an electronic device equipped with a rotary head such as a VTR or DAT.

[0002]

[Prior Art]

 In VTR, DAT, etc., a magnetic tape is run while keeping contact with the rotary head and various running mechanisms to record and reproduce image signals and audio signals. Therefore, if moisture adheres to the inside of the device due to condensation, the frictional resistance between the magnetic tape and the running mechanism increases, and as a result, the tape speed becomes unstable, or the tape winds around the rotating head and stops. There are cases.

In order to prevent the occurrence of such a phenomenon, for example, a humidity sensor of a conductive material-polymer composite type is mounted inside an electronic device, and when a dew condensation phenomenon occurs inside the device, the device is automatically forcibly stopped. Controlling to the state.

FIG. 4 is a circuit configuration diagram of a conventional condensation detection circuit. The conventional dew condensation detection circuit 101 supplies a sensor output voltage 104 obtained by dividing the power supply voltage VCC by a series circuit of a resistor 102 and a humidity sensor 103 to a non-inverting input terminal 105a of a differential amplifier 105, A bias voltage 108 obtained by dividing the voltage VCC by a series circuit of a resistor 106 and a resistor 107 is supplied to an inverting input terminal 105b of a differential amplifier 105.

The output voltage 109 of the dew condensation detection circuit 101 shown in FIG. 4 is supplied to a voltage determination circuit and a logic circuit not shown. When the output voltage 109 exceeds a preset threshold voltage, the voltage determination circuit and the logic circuit determine that it is in a dew condensation state and perform necessary control such as controlling the device to a forced stop state.

[0006]

[Problems to be solved by the device]

 FIG. 5 is a graph showing the relative humidity-resistance value characteristics of the dew condensation sensor. The horizontal axis shows the relative humidity on a linear scale, and the vertical axis shows the resistance value on a logarithmic scale. As shown in this figure, the humidity sensor 103 has a characteristic that the resistance value rapidly increases in a high humidity state. However, in contrast to the standard characteristic shown by the solid line TYP, the characteristic variation as shown by the dotted line MAX and the dotted line MIN. Is big.

Since the conventional dew condensation detection circuit 101 has a configuration in which the output voltage 104 of the humidity sensor 103 is amplified by the fixed gain amplifier 105 and the output voltage 109 is taken out, the resistance value change of the humidity sensor 103 is gentle. In a region where the humidity is low, the change in the output voltage 109 with respect to a predetermined amount of change in humidity is gentle. Therefore, when the output voltage 109 is compared with a predetermined threshold voltage to determine whether or not the dew condensation state is present, the dew condensation detection humidity greatly varies due to the characteristic variation of the humidity sensor 103.

FIG. 6 is a graph showing a relative humidity-output voltage characteristic of the conventional dew condensation detecting circuit. FIG. 6 shows a circuit designed so that the output voltage 109 of the dew condensation detection circuit 101 becomes 2.5 V when the humidity sensor 103 having the standard characteristics is placed in an atmosphere with a humidity of 96% (resistance value is about 50 KΩ). The characteristic is shown, where the horizontal axis is the relative humidity and the vertical axis is the output voltage 109. The characteristic TYP shown by the solid line is the characteristic when the humidity sensor 103 of the standard characteristic is used, and the characteristic MAX, MIN shown by the dotted line is the characteristic when the humidity sensor 103 having the maximum and minimum resistance values is used.

Considering the resistance variation shown in FIG. 5, the dew condensation detection humidity range is 87.5% to 98.5%. For this reason, depending on the characteristics of the humidity sensor 103 used, even in a humidity atmosphere where dew condensation does not occur, the dew condensation state is determined, and the operation of the device is stopped.

Further, since the conventional dew condensation detection circuit 101 obtains the sensor output voltage 104 by dividing the voltage of the resistor 102 and the humidity sensor 103, the sensor output voltage 104 changes sharply in the vicinity of the humidity to be detected. .. Therefore, the bias voltage setting by the resistors 106 and 107 becomes delicate, and it is difficult to adjust the bias voltage to obtain the desired output voltage 109.

Further, when the humidity is close to 100%, the resistance value of the humidity sensor 103 becomes extremely large, so that the power supply voltage VCC is almost applied to the humidity sensor 103. Therefore, when the power supply voltage VCC is higher than the maximum applied voltage of the humidity sensor 103, the humidity sensor 103 may be broken in a high humidity state.

The present invention has been made to solve such a problem, and its purpose is to improve the accuracy of the humidity range for detecting dew condensation by using a humidity sensor having large characteristic fluctuation and to easily set the detection output voltage. In addition, it is to realize a dew condensation detecting circuit with a simple configuration, in which an overvoltage is not applied to the humidity sensor.

[0013]

[Means for Solving the Problems]

 In order to solve the above problems, the dew condensation detecting circuit according to claim 1 includes a humidity sensor having a characteristic that the resistance value rapidly increases in a high humidity state, between the inverting input terminal of the differential amplifier and the reference potential. It is characterized in that a feedback resistor is connected between the output terminal and the inverting input terminal of the differential amplifier and a predetermined bias voltage is supplied to the non-inverting input terminal of the differential amplifier.

The value of the feedback resistor is preferably set to be substantially equal to the resistance value of the humidity sensor at the humidity to be detected.

Further, the bias potential is preferably set so that the voltage applied to the humidity sensor is lower than the application allowable voltage of the humidity sensor.

[0016]

In the dew condensation detection circuit according to claim 1, the differential amplifier gain is determined based on the ratio of the resistance value of the humidity sensor and the resistance value of the feedback resistor. Therefore, when the resistance value of the humidity sensor is low. Has a large detection gain, and the gain of the differential amplifier decreases in a high humidity state where the resistance value of the humidity sensor rapidly increases. Therefore, the output voltage changes sharply on the low humidity side where the resistance value changes slowly, and the humidity range for detecting dew condensation can be narrowed. Therefore, it is possible to provide a dew condensation detecting circuit with high detection accuracy.

Further, by setting the resistance value of the humidity sensor and the feedback resistance value at the humidity to be detected to be substantially equal to each other, the change in the output voltage in the vicinity of the humidity for detecting dew condensation becomes gentle, so the output voltage is set. It becomes easy to set the bias voltage for this purpose.

Since the potential of the inverting input terminal of the differential amplifier to which one end of the humidity sensor is connected becomes equal to the bias voltage regardless of the resistance value of the humidity sensor, the reference voltage supplied to the other end of the humidity sensor. If the difference between the bias voltage and the bias voltage is set below the breakdown voltage of the humidity sensor, no overvoltage will be applied to the humidity sensor.

[0019]

【Example】

 An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit configuration diagram of a dew condensation detecting circuit according to the present invention. The dew condensation detection circuit 1 connects the humidity sensor 3 between the inverting input terminal 2a of the differential amplifier 2 and the reference potential (ground potential), and also connects the humidity sensor 3 between the output terminal 2c of the differential amplifier 2 and the inverting input terminal 2a. The feedback resistor 4 is connected to.

The value of the feedback resistor 4 is substantially the same as or equal to the resistance value of the humidity sensor 3 at the humidity to be detected (for example, the resistance value of the humidity sensor 3 at the humidity to be detected). Is 50 KΩ, the value of the feedback resistor 3 is set to several tens KΩ).

A bias voltage 7 obtained by dividing the VCC power supply voltage by a series circuit of a resistor 5 and a resistor 6 is supplied to the non-inverting input terminal 2b of the differential amplifier 2. The bias voltage 7 is set lower than the allowable voltage applied to the humidity sensor 3.

When the resistance value of the humidity sensor 3 having the standard characteristic at the humidity to be detected and the resistance value of the return resistor 4 are set to the same value, a voltage value twice the bias voltage 7 is shown. Do not set it to a voltage judgment circuit or threshold voltage of logic.

Next, the operation of the dew condensation detecting circuit 1 according to the present invention will be described. Since the differential amplifier 2 operates so as not to generate a potential difference between the input terminals 2a and 2b, the voltage applied to the humidity sensor 3 is the value of the bias voltage 7 regardless of the change in the resistance value of the humidity sensor 3. Becomes

The output voltage 8 is a voltage obtained by multiplying the ratio of the feedback resistance 4 and the resistance value of the humidity sensor 3 by the bias voltage 7. Therefore, in the low humidity region where the resistance value of the humidity sensor 3 is small, The gain decreases as the gain increases, the humidity increases, and the resistance value of the humidity sensor 3 increases.

When the resistance value of the humidity sensor 3 at the humidity to be detected and the resistance value of the feedback resistor 4 are set to the same value, the gain of the dew condensation detection circuit 1 is 2 (at the humidity to be detected). 6 dB), and when the resistance value of the humidity sensor 3 further increases, the gain decreases toward 1 (0 dB). Therefore, in the conventional circuit configuration, the output voltage changes rapidly, and the output voltage changes gradually in the high humidity region where it is difficult to adjust the threshold value. Therefore, the characteristic adjustment of the condensation detection circuit 1 is easy. Becomes

FIG. 2 is a graph showing an output voltage characteristic of the dew condensation detecting circuit according to the present invention. The horizontal axis represents the relative humidity and the vertical axis represents the output voltage 8. The characteristic TYP shown by the solid line is the output characteristic of the humidity sensor 3 having the standard characteristic shown in FIG. 5, and the respective characteristics MIN and MAX shown by the dotted lines are the output characteristic of the humidity sensor 3 having minimum and maximum resistance values.

In a circuit configured to obtain an output voltage 8 of 2.5 V when the humidity sensor 3 having the standard characteristics is placed in an atmosphere having a humidity of 96% (resistance value of about 50 KΩ), variations in characteristics of the humidity sensor 3 occur. As a result, the humidity detection range is 92.5% to 98.5%, and the shift to the low humidity side is small compared to the conventional circuit configuration.

FIG. 3 is a circuit configuration diagram of another condensation detecting circuit according to the present invention. The dew condensation detecting circuit 11 is configured such that one end of the humidity sensor 3 is connected to a VCC power source and the output voltage 18 becomes higher as the humidity becomes higher. In the circuit configuration shown in FIG. 3, since the voltage difference between the VCC power supply voltage and the bias voltage 7 is applied to the humidity sensor 3, the difference voltage is set to be lower than the allowable application voltage of the humidity sensor 3. There is.

[0029]

[Effect of the device]

 As described above, the dew condensation detection circuit according to the present invention is configured to determine the gain of the differential amplifier based on the ratio between the resistance value of the humidity sensor and the resistance value of the return resistance. When it is low, the detection gain is large, and in high humidity where the resistance value of the humidity sensor increases rapidly, the gain of the differential amplifier decreases. For this reason, the output voltage changes sharply on the low humidity side where the resistance value changes slowly, and the humidity range for detecting dew condensation can be narrowed. Therefore, it is possible to provide a dew condensation detecting circuit with high detection accuracy.

Further, by setting the resistance value of the humidity sensor and the feedback resistance value at the humidity to be detected to be substantially equal to each other, the change in the output voltage in the vicinity of the humidity for detecting dew condensation becomes gentle, so the output voltage is set. It becomes easy to set the bias voltage for this purpose.

Since the potential of the inverting input terminal of the differential amplifier to which one end of the humidity sensor is connected becomes equal to the bias voltage regardless of the resistance value of the humidity sensor, the reference voltage supplied to the other end of the humidity sensor. If the difference between the bias voltage and the bias voltage is set below the withstand voltage of the humidity sensor, overvoltage will not be applied to the humidity sensor, and overvoltage breakdown of the humidity sensor can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a condensation detection circuit according to the present invention.

FIG. 2 is a graph showing the output voltage characteristic of the condensation detection circuit according to the present invention.

FIG. 3 is a circuit configuration diagram of another condensation detection circuit according to the present invention.

FIG. 4 is a circuit configuration diagram of a conventional condensation detection circuit.

FIG. 5 is a graph showing a relative humidity-resistance value characteristic of a dew condensation sensor.

FIG. 6 is a graph showing relative humidity-output voltage characteristics of a conventional condensation detection circuit.

[Explanation of symbols]

1, 11 ... Condensation detection circuit, 2 ... Differential amplifier, 2a ... Inversion input terminal, 2b ... Non-inversion input terminal, 2c ... Output terminal, 3
... humidity sensor, 4 ... feedback resistance, 5, 6 ... resistor for dividing voltage for generating bias voltage, 7 ... bias voltage, 8,
18 ... Output voltage of dew condensation detection circuit.

Claims (3)

[Scope of utility model registration request] 1. A dew condensation detecting circuit using a humidity sensor having a characteristic that a resistance value rapidly increases in a high humidity state, wherein the humidity sensor is provided between an inverting input terminal of a differential amplifier and a reference potential. In addition to the connection, a feedback resistor is connected between the output terminal of the differential amplifier and the inverting input terminal, and a predetermined bias voltage is supplied to the non-inverting input terminal of the differential amplifier. Condensation detection circuit. 2. The dew condensation detection circuit according to claim 1, wherein a value of the feedback resistor is set to be substantially equal to a resistance value of the humidity sensor at a humidity to be detected. 3. The dew condensation detection circuit according to claim 1, wherein the bias potential is set so that a voltage applied to the humidity sensor is lower than an application allowable voltage of the humidity sensor.