Humidity detection device and image forming apparatus
A humidity detection device includes a humidity sensor, a resistor connected to one-side of the humidity sensor, a first switching part connected to the resistor; a diode connected to the first switching part; a second switching part connected to the other-side of the humidity sensor, a potential difference generating part connected to the second switching part, a power supply supplying a voltage, and a control part applying the voltage as an alternating voltage to the humidity sensor by controlling the first switching part and the second switching part. The control part applies a current to the diode, the resistor and the humidity sensor in a first direction by connecting the second switching part to the ground, and applies the current to the resistor and the humidity sensor in a second direction, which is an opposite direction from the first direction, by connecting the first switching part to the ground.
1. A humidity detection device, comprising:
a humidity sensor that detects a humidity; having at least a first side and a second side to be connected,
a resistor having a first side and second side, the first side being directly connected to the second side of the humidity sensor;
a first switching part that switches between an ON state and an OFF state, and is directly connected to the second side of the resistor;
a diode that is directly connected to the first switching part;
a second switching part that switches between an ON state and an OFF state, and is directly connected to the first side of the humidity sensor;
a potential difference generating part that is connected to the second switching part;
a power supply that supplies a voltage, and
a control part that applies the voltage from the power supply as an alternating voltage to the humidity sensor by controlling the first switching part and the second switching part, wherein
the control part
applies a current to the diode, the resistor and the humidity sensor in a first direction by connecting the second switching part to the ground, and
applies the current to the resistor and the humidity sensor in a second direction, which is an opposite direction from the first direction, by connecting the first switching part to the ground.
2. The humidity detection device according to claim 1 , wherein
the control part,
based on a forward voltage of the diode when a current is applied to the diode, the resistor and the humidity sensor in the first direction, calculates a first impedance of the humidity sensor, and identifies a first humidity from the calculated first impedance, and,
based on a voltage obtained between the resistor and the humidity sensor when a current is applied to the resistor and the humidity sensor in the second direction, calculates a second impedance of the humidity sensor, and identifies a second humidity from the calculated second impedance.
3. The humidity detection device according to claim 2 , wherein
the control part selects one of the first humidity and the second humidity as a humidity detected by the humidity sensor.
4. The humidity detection device according to claim 3 , wherein
the control part
selects the second humidity as the humidity detected by the humidity sensor when the voltage obtained between the resistor and the humidity sensor is equal to or greater than a predetermined threshold, and
selects the first humidity as the humidity detected by the humidity sensor when the voltage obtained between the resistor and the humidity sensor is less than the predetermined threshold.
5. The humidity detection device according to claim 3 , wherein
the control part
selects the second humidity as the humidity detected by the humidity sensor when the second humidity is equal to or greater than a predetermined threshold, and
selects the first humidity as the humidity detected by the humidity sensor when the second humidity is less than the predetermined threshold.
6. The humidity detection device according to claim 3 , wherein
the control part selects the second humidity as the humidity detected by the humidity sensor when the second impedance is less than or equal to a predetermined threshold, and
selects the first humidity as the humidity detected by the humidity sensor when the second impedance is greater than the predetermined threshold.
7. The humidity detection device according to claim 2 , further comprising:
a storage part that stores a reverse saturation current, which is calculated in an environment of a region where detection accuracy based on resistance divided voltage is high,
wherein when an impedance of the humidity sensor is higher than a predetermined impedance, the control part corrects a forward voltage of the diode using the reverse saturation current stored in the storage part.
8. The humidity detection device according to claim 7 , further comprising:
a temperature sensor that detects a temperature (T), wherein
the storage part further stores the forward voltage (VF) of the diode, an emission coefficient (n) of the diode, and the Boltzmann coefficient (k), and
the control part
calculates a current value (I) flowing through either the humidity sensor or the resistor,
calculates the reverse saturation current (TO) according to the following Eq. (1):
I 0= I ÷exp( VF÷nkT ) (1),
where T means an absolute temperature, and
stores the calculated reverse saturation current in the storage part.
9. The humidity detection device according to claim 8 , wherein
the region where the detection accuracy based on the resistance divided voltage is high is a region where a temperature of the region is 15 degrees Celsius.
10. The humidity detection device according to claim 1 , wherein
the potential difference generating part equalizes
a magnitude of a current that is applied to the humidity sensor in the first direction and
a magnitude of a current that is applied to the humidity sensor in the second direction.
11. The humidity detection device according to claim 10 , wherein
the potential difference generating part is a digital-to-analog converter.
12. The humidity detection device according to claim 10 , wherein
the potential difference generating part is configured with
a resistor that is different from the resistor and
a diode that is different from the diode.
13. The humidity detection device according to claim 1 , wherein
when a current is applied to the resistor and the humidity sensor in the second direction, the potential difference generating part generates a voltage drop corresponding to a forward voltage of the diode, and applies the voltage to the voltage from the power supply before a voltage from the power supply is applied to the humidity sensor.
14. The humidity detection device according to claim 1 , wherein
the first switching part is a bipolar transistor,
the potential difference generating part is a resistor that is different from the resistor, and
a current flowing through the other resistor is a base current of the bipolar transistor.
15. The humidity detection device according to claim 1 , further comprising:
a temperature sensor that detects an ambient temperature of the humidity sensor.
16. An image forming apparatus, comprising
the humidity detection device according to claim 1 .
17. A humidity detection device, comprising:
a humidity sensor that detects a humidity; having at least two sides to be connected,
a resistor that is connected to one-side of the humidity sensor;
a first switching part that switches between an ON state and an OFF state, and is connected to the resistor;
a diode that is connected to the first switching part;
a second switching part that switches between an ON state and an OFF state, and is connected to the other-side of the humidity sensor;
a potential difference generating part that is connected to the second switching part;
a power supply that supplies a voltage, and
a control part that applies the voltage from the power supply as an alternating voltage to the humidity sensor by controlling the first switching part and the second switching part, wherein
the control part
applies a current to the diode, the resistor and the humidity sensor in a first direction by connecting the second switching part to the ground, and
applies the current to the resistor and the humidity sensor in a second direction, which is an opposite direction from the first direction, by connecting the first switching part to the ground,
the control part,
based on a forward voltage of the diode when a current is applied to the diode, the resistor and the humidity sensor in the first direction, calculates a first impedance of the humidity sensor, and identifies a first humidity from the calculated first impedance, and,
based on a voltage obtained between the resistor and the humidity sensor when a current is applied to the resistor and the humidity sensor in the second direction, calculates a second impedance of the humidity sensor, and identifies a second humidity from the calculated second impedance,
the control part, when the first impedance is less than or equal to a predetermined impedance,
calculates a current value of a current flowing through the resistor, and
calculates a characteristic of a forward voltage of the diode from the calculated current value, and,
the control part, when the first impedance is greater than the predetermined impedance,
calculates a current value of a current flowing through the humidity sensor from the calculated characteristic, and
calculates the first impedance and the second impedance.