JP3119386B2 - measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity measuring apparatus for measuring humidity by using a humidity sensor whose resistance changes according to humidity.

[0002]

2. Description of the Related Art In recent years, in order to more precisely control the operation of an apparatus, there has been a growing demand for improving and expanding the measurement accuracy and the measurement range for detecting the relative humidity of the operating environment.
For example, in the above-described electrophotographic apparatus, the lower limit of the conventional low humidity side of about 20% may be reduced to 1% in order to further improve the quality of an output image.
There is a demand for about 0%.

In order to satisfy this requirement, a humidity sensor whose resistance value changes according to the humidity and a capacitor are connected in series, a DC voltage is applied to both ends of the humidity sensor and the capacitor, and the voltage of the capacitor reaches a predetermined value. There is proposed an apparatus for calculating the time and sensor characteristics by a linear approximation formula.

[0004]

However, particularly when the range of the low humidity side is to be expanded, the resistance value of the humidity sensor increases, and the charging time increases, which causes a problem. For example, when the temperature becomes about 25 ° C. and about 10%, the resistance value of the humidity sensor becomes 10 GΩ or more, and a charging time of about 300 ms is required even if the capacitance value of the charging capacitor is reduced to about 30 PF. If the charging time is extended to this level, the humidity sensor will no longer be equivalent to a DC voltage being applied effectively, and the humidity sensor will rapidly deteriorate due to bias of internal ions. Becomes

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a resistance element whose resistance value changes according to humidity,
And a capacitor connected in series with the resistance element.
DC voltage and AC voltage
A voltage applying means for applying a flowing voltage;
Detecting means for detecting that the pressure has reached a predetermined voltage;
The time since the voltage application means started applying DC voltage is counted.
Counting means for counting and applying the voltage when not measuring
Means for applying an AC voltage,
A DC voltage is applied to the stage, and the detecting means reaches a predetermined voltage.
When the counting means detects that
Control means for determining humidity based on the
The detection means can detect multiple predetermined voltages
A predetermined voltage of a value corresponding to the count value of the counting means.
A pressure-switching measuring device is provided.

Further, a resistance whose resistance value changes in accordance with humidity is used.
Element and a capacitor connected in series to the resistance element
And the resistance element and the capacitor connected in series
Voltage applying means for applying a DC voltage and an AC voltage to the
Detecting that the voltage of the capacitor has reached a predetermined voltage
The detecting means and the voltage applying means start applying a DC voltage.
Counting means to count the time since
To apply an AC voltage to the voltage applying means,
Causes the voltage applying means to apply a DC voltage, and
The counter when detecting that the stage has reached a predetermined voltage.
Control to judge humidity based on count value
Means for detecting the voltage of the capacitor.
Amplifying means for amplifying at an arbitrary amplification degree;
Means that performs detection with an amplification degree corresponding to the count value
Provide a setting device.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a measuring apparatus according to an embodiment of the present invention. 2 shows a timing chart, and FIG. 4 shows output characteristics of the humidity sensor used in the present invention.

1 is a microcomputer and 2 is a humidity sensor. The humidity sensor 2 is, for example, a polymer type ceramic sensor or the like, and its resistance value changes according to temperature and humidity as shown in FIG.

Reference numerals 3 and 4 denote electronic switches, and the open drain terminals of the output ports of one microcomputer may be used as they are. FIG. 2 is a control timing chart of the electronic switches 3 and 4.

As shown in FIG. 2, the control timing of the electronic switches 3 and 4 at the time of non-measurement is such that an AC charge of a predetermined frequency is applied to the sensor to reduce the distribution of ions inside the humidity sensor 2 generated at the time of measurement. Switching control is performed so as to be applied to both ends. One of the humidity sensors 2 is fixed at a voltage E, and the other end of the humidity sensor 2 is set at 0 at a predetermined frequency f.
[V] and 2E [V] are applied. Although it depends on the type of the sensor element to be used, the numerical value is controlled at about E = 1 [V] and f = 1 [kHz].

At the time of measurement, the electronic switch 3 is turned on and the electric charge of the capacitor C1 is discharged, and the electronic switches 3 and 4 are both turned off, and the voltage E is applied to the series circuit of the humidity sensor 2 and the capacitor C1. Then, charging of the capacitor C1 is started. In the present embodiment, the condition where the sensor resistance value is the highest in the measurement range as a humidity measurement device, that is, even in the resistance value in the generally lowest humidity environment, is within 10 times the maximum cycle of the AC application use range of the sensor element. Since the detection voltage is set to a voltage at which charging is performed in a time period, the application of a stable AC voltage that is started immediately thereafter quickly alleviates the internal ion distribution, and greatly reduces the life of the element. For example, in the case of a polymer-type humidity sensor generally used for consumer and industrial purposes, the resistance value becomes about 1 GΩ at a temperature of 15 ° C. and a humidity of about 5%. When the detection voltage is about 0.8 V, the measurement is completed in about 50 ms. The maximum cycle of AC application of the sensor element is 10ms
And the time during which a unidirectional electric field is continuously applied at the time of measurement is 100 ms, which is 10 times the maximum cycle of the AC application.
If it is about, by applying a stable AC voltage to the sensor before and after the measurement, the internal ions and electrons
The polarization can be sufficiently relaxed, the deterioration of the element life can be avoided, and a low humidity of 20% or less can be measured.

When the time Ts from the start of charging to the arrival at the threshold value V3 is detected, the sensor resistance Rs can be calculated by the following equation.

[0014]

[Outside 1]

The sensor resistance Rs measured as described above
Therefore, the relative humidity H is obtained as follows.

The output curve of the sensor is linearly approximated by dividing it into five regions for each temperature as shown in FIG. The flow up to obtaining the relative humidity will be described with reference to the flowchart shown in FIG.

A linear approximation region is selected from the sensor resistance Rs and the ambient temperature T measured by a temperature sensor (not shown) provided in the vicinity of the humidity sensor 2, and a CPU
Are obtained from the look-up table stored in step S3.

From Rs, T, Cn, Dn, En, Fn to A
N (T) and BN (T) are obtained.

The obtained AN (T) and BN (T)
Yields the relative humidity H.

As described above, by applying an AC voltage at the time of non-measurement, continuous application of a unidirectional electric field can be relaxed up to about 10 times the maximum period of use of the AC application. In addition to the sudden increase in the value, the charging speed drops rapidly due to the effects of the parallel resistance of the capacitor including the substrate pattern, leakage current, etc., and in the worst case, the charging does not proceed even to more than 1/2 of the applied voltage. In a low humidity environment, if the sensor resistance value exceeds 1 GΩ, the measurement does not end within the time allowed for continuous application of the electric field, causing irreversible damage to the sensor element. There is a risk that it will. Therefore, when there is such a fear, the threshold voltage may be set to about 1/5 of the applied voltage as shown in FIG.

Further, as shown in FIG. 7, two comparators 5 and 6 having different threshold levels are provided, and the time until the comparator 5 having the higher threshold level detects the threshold is counted. When the counter 7 counts for more than the time allowed for the continuous application of the electric field before the voltage of the capacitor C1 reaches the threshold value, the low threshold level is set. , The time until the comparator 6 detects the threshold value is counted to measure the humidity. The proper use of the comparator is executed by software in the microcomputer.

As shown in FIG. 8, it is also possible to perform measurement by switching the threshold value of the comparator according to the output signal from the microprocessor.

The voltages E and 2E in FIG. 1 can be obtained by dividing the reference voltages E and 2E from Vcc by a precision resistor as shown in FIG.

In the configuration shown in FIG. 1, the voltage dividing resistor must be reduced in order to prevent a measurement error from increasing during high-humidity measurement. As a result, the power efficiency is reduced, and the measurement environment itself is reduced due to the Joule heat of the resistor. May be disturbed.

To prevent this, the reference voltages E and 2E may be supplied via the voltage followers 11 and 12 as shown in FIG.

It is to be noted that the humidity data obtained by the above-described method can be properly judged, and an average value of a predetermined number of data can be taken, so that stable humidity measurement can be performed.
FIG. 11 shows a flowchart for that purpose.

First, the register in the microcomputer 1 is initialized (step S21), and the calculated humidity data Hn is input (step S22). Then, the maximum value Hmax and the minimum value Hmi of the stored humidity data.
n is compared with the input humidity data Hn (step S23). In step S23, the humidity data Hn is (Hmi
When it is larger than (n−α) and smaller than (Hmax + β), the humidity data is updated (α and β are constants).
If the humidity data Hn is out of the range in step S23, the process proceeds to step S22. That is, if the deviation is significantly larger than the appropriate range, the data is not updated. When updating the humidity data, the register R ₀ ~R _K-1 by moving the respective contents into the register R ₁ to R _K (step S24), and inputs the humidity data Hn in register R ₀ (step S25).

If the content of the register R _K-1 is still 0, the process proceeds to step S22, otherwise, the process proceeds to the next (step S26). In step S26, R _K-1 ≠ 0
In the case of ( ₁₎ , the minimum value Hmin and the maximum value Hmax of the registers R _{0 to} R _K−1 are obtained, and the average value of the humidity data is obtained by the following equation (step S27).

[0029]

[Outside 2]

Then, the contents of the average value output register are set to Hn.
(Step S28), and the process proceeds to step S22.

By updating the average value in this way,
Stable humidity measurement becomes possible.

As a result, a wide range of humidity can be measured with high accuracy. Further, since the accuracy of the sensor peripheral circuit can be reduced, the circuit can be simplified and the cost can be reduced accordingly. Further, deterioration and unstable operation of the sensor can be completely eliminated. Further, erroneous measurement data due to the influence of electrostatic noise or the like can be completely removed.

Next, another embodiment of the present invention will be described.

Reference numeral 101 denotes a humidity sensor element whose electric conductivity changes according to a change in relative humidity. Usually, the electric conductivity increases as the humidity increases. One side of the humidity sensor 101 is connected to a constant voltage source of 1V. 102 is a charging capacitor; 103 is a comparator for checking whether the voltage of the charging capacitor 102 is higher or lower than a predetermined value;
04 is a comparison voltage generator, 105 is a switch element for applying 2V at a predetermined timing to the opposite side of the humidity sensor 101 to which 1V is applied, 106 is a switch element for applying 0V, and 107 is a switch element for applying 0V. A counter circuit 108 for measuring the charging time is a controller for controlling the system, and is composed of a board on which a so-called one-chip microcomputer is mounted. Reference numeral 112 denotes an impedance converter constituted by an operational amplifier, which lowers the impedance of the charging voltage of the charging capacitor 102 and transmits the voltage to the next stage. 1
Reference numeral 12 denotes an amplifying circuit also constituted by an operational amplifier,
4 and 113 determine the degree of amplification.

The operation of the above configuration will be described. At the time of non-measurement, the controller 108 turns on the switch elements 105 and 106 alternately at a frequency of about 1 KHz (see FIG. 13). As a result, 2 V and 0 V are alternately applied to the terminal of the sensor 101 on the side opposite to the side to which 1 V is applied, and an AC voltage of ± 1 V is eventually applied to both ends of the sensor 101.

At the time of measurement, the controller 108 does not perform this operation at the timing when the switch element 105 is turned on, and simultaneously invalidates the clear signal to the counter circuit 107 and validates the start signal. As a result, the series circuit of the charging capacitor 102 and the humidity sensor 101 enters the charging operation with the power supply at 1 V, and the counter circuit 107 starts the counting operation by the internal clock.

The charged voltage is supplied to the impedance converter 1
01, amplified to a predetermined amplification factor by the amplifier 102,
The comparator 103 detects that a predetermined voltage value is reached.

When the amplified voltage exceeds a predetermined voltage value, the output of the comparator 103 goes high, and a stop signal for the counter 107 is generated. When the controller 108 detects this stop signal, it takes in the counter value, that is, the time required to reach a predetermined charging voltage. Thereafter, the resistance value of the humidity sensor 101 is determined based on this value, and the relative humidity is determined based on the resistance value and the temperature value measured by another block.

According to this configuration, even if the humidity sensor 101 has a high resistance of about several tens GΩ and the charging speed is reduced,
Since the state of charge is detected in an enlarged manner, the time required to reach a predetermined value can be shortened, and element deterioration due to continuous application of a unidirectional voltage to the sensor element can be avoided. In addition, when calculating the sensor resistance with respect to the measured charging time, it is necessary to calculate in consideration of the influence of amplification.

In the above-described embodiment, it is necessary to set the amplification factor so that the measurement is completed within a predetermined time when the sensor element reaches several tens GΩ at low humidity. Therefore, when the resistance value of the sensor element decreases to several tens of kilohms at high humidity, the time required to reach a predetermined charging voltage is shortened by several digits or more. A counter circuit using a clock is required. An embodiment taking this point into consideration will be described with reference to FIGS. 14, 15, and 16. FIG. The feature of this embodiment resides in that the amplification factor of the amplifier circuit is appropriately switched so that the voltage charged within a predetermined time is within a predetermined range.

In FIG. 14, block 120 is cpu1.
16 is an amplifier circuit whose amplification factor can be switched by a control signal from the control circuit 16. The operation procedure will be described with reference to the timing chart of FIG. 15 and the flowchart of FIG. First, at the time of non-measurement, a pulse wave of ± 1 V is stably applied to both ends of the humidity sensor 101. And at the time of measurement, 2V
Side and ground side are separated from the circuit. cpu11
6, the same control signal as in the previous measurement is output, and the same amplification factor as in the previous measurement is set (step S31). After a predetermined time (time during which no element deterioration occurs due to continuous application of a unidirectional electric field), the A / D conversion circuit 11
5, a timing signal is output (step S32), and the amplified value of the voltage charged in the capacitor is sampled and held, A / D converted, and the cpu 116 captures the converted value (step S33). If this value is within the predetermined range (step S34), the cpu 116 takes the amplification value and the charging time into consideration from the amplification value of the charging voltage at this time, and
01 is calculated, and the humidity is calculated based on the calculated resistance value (step S37). On the other hand, when the amplification value of the charging voltage is not within the predetermined range (step S34), for example, when the charging voltage is low, the control value from cpu 116 is switched (step S35), and the amplification is increased and the measurement is performed again. However, in order to supply a stable AC electric field to the humidity sensor 101, when measuring again, an appropriate time before starting the measurement,
An AC pulse is applied (step S36). This makes it possible to measure the resistance value of the humidity sensor 101 without requiring excessive accuracy for each component such as A / D conversion, and a humidity measuring device capable of measuring a wide range from low humidity to high humidity. Can be provided at low cost.

In the above-described embodiment, the sensor resistance is determined by appropriately switching the amplification factor to amplify the voltage charged within a certain time to a value within a certain range. The charging time may be set as short as possible so as to reduce the burden as much as possible, and the charging time may be optimized (minimized) for the measurement.

As shown in the flowchart of FIG. 17, first, the charging time is set to a minimum value (for example, 10 μS) (step S38), and the amplification degree is optimized in the same procedure as in FIG. If the sensor resistance is high and the voltage does not reach the predetermined voltage even when the amplification degree is maximized, the charging time is set long (for example, 10 ms) (step S38), and the amplification degree is optimized by the same procedure.

As described above, since the charging operation can be temporally and voltage-expanded and observed, the application time of the electric field applied to the sensor element can be suppressed to a predetermined value or less, and several tens G
It is possible to realize a humidity measuring device capable of measuring a high resistance such as Ω in a short time and measuring a low humidity region such as 5 to 20%.

Next, another embodiment will be described.

First, the circuit of the embodiment shown in FIG. 18 will be described. Reference numerals 201 to 211 are analog switches, which apply a rectangular wave signal to the humidity sensor 223, connect the humidity sensor 223 to the D / A converter 222,
The humidity sensor 223 is connected to the capacitors 211 and 212, and the comparison reference power supplies 229 and 230 are connected to the minus input terminal of the comparator 217.

Reference numerals 213 to 216 denote 2-input AND gates.
The switching timing of the analog switches 206, 208, 209, 211 is controlled. Reference numerals 221, 229, and 230 are reference power supplies, which have a fixed voltage. Reference numeral 222 denotes a D / A converter for a variable power supply used when measuring the resistance of the humidity sensor, and a control signal is sent to a signal line 245 by the control unit 220 to switch digital data. Counting unit 219
Thus, the calculation result can be calculated by the calculation unit 218 based on the count result. Reference numerals 224 to 228 denote inverter circuits, which are elements that invert the input signal and output the inverted signal. The above components are connected as follows in the first embodiment.

The capacitors 211, 2 having one terminal grounded
12 are connected to analog switches 201 and 20 respectively.
2 and connected to one end of the analog switches 201 and 202
The other end is connected to a signal line 231, and through the signal line 231, a + signal input terminal of the comparator 217, a signal input terminal of the analog switch 203 whose other end is grounded, and one signal input terminal of the analog switch 207. It is connected. One of the signal input terminals of the analog switches 204 and 205 is connected to the +
Connected to terminal. The other signal input terminals of the reference power supplies 28 and 29 are both connected to one signal input terminal of the comparator 217 through a signal line 240.

The other signal input terminal of the analog switch 208 whose one signal input terminal is grounded is
The analog switch 21 is connected to one signal input terminal of the analog switches 207 and 206 and one terminal of the humidity sensor 223, and similarly has one signal input terminal grounded.
1 is a signal input terminal of one of the analog switches 209 and 210 and the other is a signal input terminal of the humidity sensor 2.
23 is connected to another terminal. The other signal input terminals of the analog switches 206 and 209 are both connected to the signal line 2.
Power supply 221 whose negative terminal is grounded through 48
And the other signal input terminal of the analog switch 210 is connected through a signal line 246 to the D / A converter 2.
22 analog signal output terminals. The control terminal of the analog switch 201 is connected to a control signal output terminal of the control unit 220 through a signal line 237.
The input of the inverter 224 is connected to the signal line 237, and the output is connected to the signal line 236. Then, the signal line 236 is connected to the control terminal of the analog switch 202. Similarly, the control terminal of the analog switch 205 is connected to the control signal output terminal of the control unit 220 through the signal line 235. The input of the inverter 225 is the signal line 23
5, the output is connected to the signal line 234. And
The signal line 234 is connected to the control terminal of the analog switch 204. The control terminals of the analog switches 207 and 210 are both connected to the output terminal of the inverter 228 through the signal line 233.

Analog switches 206, 208, 20
The control terminals 9 and 211 each have a 2-input AN.
D gates 213, 214, 215, and 216 are connected to the output terminals of the D gates 213, 214, 215, and 216.
One of the input terminals of 4, 215, and 216 is connected to the control signal output terminal of the control unit 220 through the signal line 32. The other signal input terminals of the AND gates 213 and 214 are both connected to a control signal output terminal of the control unit 220 through a signal line 254. Similarly, the other signal input terminals of the AND gates 215 and 216 are connected to the control unit 220 through a signal line 255.
Is connected to the control signal output terminal of The signal line 32 is also connected to the control terminal of the analog switch 203 and the input terminal of the inverter 226. 226, 22
7, 228 are three inverters configured as a kind of delay element, and the signal output terminal of the inverter 226 is
The signal input terminal of the inverter 227 is connected to the signal input terminal of the inverter 227, and the signal output terminal of the inverter 227 is connected to the signal input terminal of the inverter 228. The signal output terminal of the comparator 217 is connected to the signal input terminal of the counting section 219 through the signal line 241. The digital signal input terminal of the D / A converter 222 is connected to the digital control signal output terminal of the control unit 220. The control unit 220 and the count unit 219 are connected by a bidirectional signal line 244.

The counting section 219 outputs operation information to the operation section 218 through the signal line 243. The arithmetic unit 218 is connected to a control signal output terminal of the control unit 220 through a signal line 242. The signal line 232 is connected to a control signal input terminal of the counting section 219.

Next, the operation will be described. FIG. 21 is an operation timing chart.

At the time of non-humidity measurement, the control unit 220
At the same time, an H signal is output to the signal line 232 and the AND gates 213 to 216 are activated.
The analog switch 203 is turned on to fix the potential of the signal line 231 to the ground level. In this state, when H is output to 254 and L is output to 255, the analog switches 206 and 211 are turned on, and the analog switches 20 and 211 are turned on.
9, 208 are turned off. Similarly, 254 is L, 255
Is output to the analog switches 206 and 2
11 is turned off, and the analog switches 209 and 208 are turned off.
Is turned on. And since the signal line 233 also becomes L,
The analog switches 207 and 210 are off.
In this state, the humidity sensor 223 is connected to the power supply 22 as shown in FIG.
A rectangular wave with a duty of 50% and an amplitude twice the voltage of 1 is applied. Usually this frequency is 50HZ ~ 100KH
It is about Z. Next, the procedure for measuring the humidity will be described.
When the controller 220 is in the non-humidity measurement state, the D / A converter 2
Standard setting voltage digital data is set to the digital input terminal 22. At the same time, H is output to the signal line 237, the analog switch 201 is turned on, the analog switch 202 is turned off, and a capacitor C2 optimal for measuring the middle humidity region is connected to the signal line 31. At that time, the capacitor C2 is 4700 PF
The capacity of the value of about. The capacitor C1 has a capacity suitable for low humidity measurement, for example, a capacity of about 47 PF.

At the same time, H is output to the signal line 235, and the analog switch 205 is turned on.
04 is turned off, and a comparison reference power supply 230 optimal for measuring the medium resistance region is connected to the signal line 240 in advance. At that time, the reference power supply 230 is set to a voltage of about 0.1 V in advance for the purpose. This value is a value that can ignore the effect of the voltage-dependent stray capacitance of an analog switch or the like in order to obtain sufficient accuracy. Power supply 229
Is set to a voltage of about 0.3 V which can take a noise margin when noise becomes a problem.

Next, the measurement procedure under these conditions will be described.
The control unit 220 outputs L to the measurement signal line 232. As a result, all of the AND gates 213 to 216 are turned off, and the output thereof becomes L. And analog switch 2
06, 208, 209 and 211 are all in the OFF state. At the same time, the analog switch 203 is turned off, and the signal line 231 enters a floating state.

At the next timing, the inverter 22
6 and 228, the signal line 233 becomes H, the analog switches 207 and 210 are turned on, and the D / A converter 222
Starts the charging of the capacitor C2 through the humidity sensor 223.

The control unit 220 resets the counting unit 219 in advance by adding H to the signal line 244 immediately before outputting L to the signal line 232.

At the moment when the signal line 232 becomes L, the counting section 219 detects the L level on the signal line 232 and starts counting (the counting section 219 naturally includes a time base).

When the potential of the signal line 231 reaches the set potential of 0.1 V of the power supply 230, the output of the comparator 217 is inverted from L to H. When the counting section 219 detects the inversion timing, it stops counting. The value is output on a signal line 243. The calculation unit 218 calculates the capacitance of the charging capacitor used, the set potential D of the comparison reference power supply,
The set analog output voltage value of the / A converter 222 and the measurement environment temperature measured in advance are read from the control unit 220 through the signal line 242, and the data on the signal line 243 are calculated based on the above conditions, and the relative humidity, Operates to determine absolute humidity. At the same time as the signal line 241 becomes H,
The control unit 220 sets the signal line 232 to H, and the operation at the time of non-humidity measurement is performed again.

When the count value of the count section 219 does not reach a certain level, the control section 220 outputs a signal line 244.
Then, the information is received from the counting section 219, and the operation returns to the operation at the time of non-humidity measurement, and the re-humidity measurement is performed after a relaxation time of 10 sec or more.

At that time, L is set to the signal line 237, and the above humidity measurement is repeated by connecting the capacitor C1 to the signal line 231. The measurement is usually performed several times under the same temperature condition, and the data is averaged by the arithmetic unit 218. Also in this case, a method of once returning to the operation at the time of non-humidity measurement while the measurement is being performed, and taking a relaxation time of 10 sec or more, and then performing the measurement again.

At this time, if the variation between the data becomes a certain value or more, the signal line 220 is switched to the 0.3 V power supply 229 by adding L to the signal line 235, and the measurement is performed again.

When the count value of the counting section 219 reaches a certain level or more, the control section 220 sets the signal line 2
At 44, the information is received from the counting unit 219, and the operation returns to the operation at the time of non-humidity measurement, and the measurement is performed again after a relaxation time of 10 seconds or more.

At this time, the digital information on the signal line 245 is changed, the analog output value of the D / A converter 222 is increased, and control is performed so that the charging time can be shortened, and the above humidity measurement is repeated.

By using analog switches for the switches in the circuit, bidirectional signal control can be performed on a one-chip IC, and the above control can be realized.

Note that the resistance value of the humidity sensor is as follows: R = TS / (C · 1 log (1 / (1-Vref / VA)
D) Where, R: resistance value of humidity sensor C: capacitance of 11 or 12 Vref: set potential of comparison reference voltage source of 29 or 30, VAD: analog output voltage of D / A converter of 22: TS: C From 0 V to Vref. The calculating unit 220 has the conversion map of the resistance value of R and the relative humidity of FIG.
It is possible to easily determine the relative humidity.

However, in this embodiment, Vref and
Since VAD is variable, it is also possible to measure Vref and VAD by varying Vref and VAD at the start of charging without discharging the capacitance.

FIG. 19 shows another circuit.

Circuits 260 to 264 are added to the circuit of FIG. Reference numeral 260 denotes an analog switch whose control terminal is connected to the signal line 262 and connected to the control terminal of the control unit 220, and one of its signal input terminals is the signal line 2
31, the other signal input terminal is connected to one terminal of the reference resistor 261, and the other signal terminal of the reference resistor 261 is connected to the signal line 246. In addition, the signal line 262
Is connected to the input terminal of the inverter 263, and the output terminal is connected to one signal input terminal of the two-input AND gate 264. The AND gate 264 is inserted as a gate circuit in the signal line 232 of the first embodiment. Specifically, in the first embodiment, the signal line 232 is separated from the control terminal of the analog switch 203, and the signal line 232 is
Is connected to the other input gate terminal of the AND gate 264, and the output terminal of the AND gate 264 is connected to the control terminal of the analog switch 203.

Next, the operation will be described. The basic operation is
Since L is output to the normal signal line 262, this is exactly the same as FIG. It is assumed that all the initial settings for measuring the actual humidity have been completed.

In a low humidity state, the resistance of the sensor is increased (to about 1 GΩ). It is necessary to reduce the capacitance of the capacitors C1 and C2, so that the input / output capacitance of the analog switch, the input capacitance and the stray capacitance of the comparator are required. Is affected. At that time, the reference resistance 61 is used to measure an accurate capacitance value. That is, in the operating state at the time of non-humidity measurement,
The control unit 220 outputs H to the signal line 262, turns on the analog switch 260, and turns off the analog switch 203. In this state, the analog switches 207, 21
Since 0 is off, the analog signal output voltage of the D / A converter 222 starts to charge the capacitors 211 and 212 through the reference resistor 261 and the analog switch 260. The control unit 220 adds H to the signal line 244 immediately before outputting H to the signal line 262, and resets the counting unit 219 in advance.

At the moment when the signal line 262 becomes H, the counting unit 219 detects the L level on the signal line 262 and starts counting (the counting means 219 naturally includes a time base).

The potential of the signal line 231 is changed to the power sources 229 and 230
, The output of the comparator 217 inverts from L to H. When the counting unit 219 detects the inversion timing, it stops counting and outputs the count value on the signal line 243. The calculation unit 218 calculates the capacity of the charging capacitor used, the set potential of the comparison reference power source,
An analog output voltage value set by the D / A converter 222,
The reference resistance value of the resistor 261 and the measurement environment temperature measured in advance are read from the control unit 220 through the signal line 242, and the measurement time data on the signal line 243 is calculated under the above conditions, and the execution capacity on the signal line 231 is calculated. Is calculated.

After that, the control section 220 sets the signal line 262 to L, and moves to the normal measurement routine. Then, the capacity value read by the calculation unit is used as reference capacity data for the humidity calculation in the subsequent measurement. Since this operation may change due to environmental changes, in the worst case, it is possible to always execute the above-described capacitance calculation process before measurement, and to determine the capacitance of the capacitors C1 and C2. It is preferable to perform the above operation not only at the time of switching, but also at the time of changing setting data of the D / A converter 222, and also at the time of switching the comparison reference power supplies 229 and 230.

FIG. 20 shows an embodiment. In order to improve the reliability of the operation of the circuit, the arithmetic unit 218 is an external CPU,
Except for the capacitors 211 and 212, the precision resistor 261 and the humidity sensor 223, all are configured as a one-chip IC. More specifically, the capacitors 211 and 212, the precision resistor 261 and the humidity sensor 223 are formed on the same ceramic substrate to form an HIC. Then, the control lines 242 and 243 are drawn out, and signal processing is performed by the CPU of the host.

As described above, it is possible to realize a low-cost humidity measurement circuit that can be easily integrated into an IC. In addition, the conventional method cannot determine the humidity with high accuracy due to low humidity, but by using this method, it is possible to easily measure the humidity with high accuracy. Further, there is no need to worry that a DC component is applied by an AC signal applied to the humidity sensor by the inversion voltage applying means, and the reliability of the humidity sensor is improved.

Next, another embodiment will be described. FIG.
FIG. 2 is a circuit diagram of the measuring device of the embodiment. 301 is a counter, 302 is a central processing unit (CPU), 303 is a humidity sensor, 305 is an oscillator for inputting a clock signal of the counter of the counter 301, and a standard resistor 3
44 is 100 MΩ. FIG. 23 illustrates the measurement data.

The resistance value of the humidity sensor when the capacitor 321 indicates the rated value, the resistance value of the humidity sensor when the rated value of the capacitor 321 changes, and an error thereof.

FIG. 24 is a timing chart at the time of measurement. As shown in the timing chart, an AC voltage is applied to point b in FIG. The calibration mode signal “H” is output from the CPU 302 to the transistor 313. At the same time, a count start signal is also output to the counter 301. As a result, the transistor 313 is turned “OFF”, the capacitor 321 starts charging, and the voltage V shown in FIG.
When the potential becomes the same as ref, a signal of “H” is output from the comparator 331 (a voltage divided by resistance is applied to point c so that a voltage equal to Vref is applied). Input to the terminal.

Then, the measured value is sent to the CPU 302, and the time (t) until the charged voltage of the capacitor 321 reaches Vref inside the CPU 302 is measured.

Here, the resistance value of the standard resistor has a certain linear function r (t) = αt (r
Is the measured resistance value α is a constant).

However, this measurement data is stored in the condenser 3
The change in the rated value of 21 causes an error shown in FIG. Compare the measured data with the theoretical data,
If the error of t is Δt, and the slope of α ′ is α ′, α ′ = γ
/ (T-Δt) (γ is a constant). Next, when the calibration mode signal from the CPU is set to “L”, the transistor 31
3 becomes “ON”, and an AC voltage is applied to the humidity sensor 303 and the capacitor 321.

Thereafter, the same measurement as described above is performed to determine the time until the charging of the capacitor 321 is completed. The resistance value of the humidity sensor 303 can be expressed as a linear function based on the obtained t and α ′. If the resistance value of the humidity sensor is R, R = α′t. The actual humidity is calculated by a function F (R
(T)). These calculations are processed inside the CPU 302 to measure the actual humidity. Therefore, even when the rated value of the capacitor 321 changes, the data measured from the standard resistance is calibrated to the resistance value of the humidity sensor, so that a highly accurate humidity value can be measured at low cost.

Next, another embodiment will be described with reference to FIG.

Reference numeral 301 denotes a counter, 302 denotes a central processing unit (CPU), 303 denotes a humidity sensor, 304 denotes a pulse generator, 305 denotes an oscillator for inputting a clock signal of the counter of the counter 301, and 306 denotes an analog switch IC. is there.

The standard resistors 341, 342, and 343 are 10 MΩ, 100 MΩ, and 1 GΩ, respectively.

The CPU 302 sends a 2-bit signal to the analog switch IC 306 to determine the resistance to be measured. ("00" is a humidity sensor of 3; "01" is a resistance 341; "10" and "11" are a resistance 342;
343)

When a pulse generation command is output from the CPU 302 to the pulse generator 304, the transistor 311,
An AC voltage is applied to point b via 312. At the same time, the voltage is applied to the standard resistor 341 and the capacitor 321.

The CPU 302 outputs a signal for stopping pulse generation and a start signal to the counter. Then, when the capacitor 321 starts charging and becomes the same potential as Vref, an “H” signal is output from the comparator 331 (at point c, a voltage corresponding to Vref is input by resistance division). Stop. Then, the measured value is sent to the CPU 302 and CP
The discharge voltage of the capacitor 321 is Vr inside U302.
The time (t) to reach ef is measured. This measurement is repeated three times.

Here, the resistance value of the humidity sensor and the actual humidity value are given by a linear function R1 (t) = γt + δ (R1 is a standard resistance value γ, δ) with the time t shown in FIG.
Is a constant).

From this data, an error from the theoretical data can be obtained in the same manner as in the above-described embodiment.

Thereafter, the same measurement is performed on the humidity sensor 303 to determine the charging time t of the capacitor 321. The resistance value R of the humidity sensor 303 is R = α't + β
(Α ′ and β are constants). And the actual humidity is R
It is obtained by a certain function F (R (t)) using (t) as a variable. These calculations are processed inside the CPU 302 to measure the actual humidity. Therefore, even when the rated value of the capacitor 321 changes, the data measured from the three standard resistors is calibrated to the resistance value of the humidity sensor, so that more accurate humidity can be measured.

For example, in the case of a copying machine using an electrophotographic system, for example, the above-mentioned humidity measuring circuit is provided inside, and a switch for putting the copying machine itself into a service mode for maintenance is provided on an operation panel of the copying machine. The switch is provided with a humidity sensor calibration mode switch. The serviceman activates this humidity sensor calibration mode at the time of maintenance to display the calibration value for the humidity sensor at that time, and if the calibration value is larger than a certain reference value, the deterioration of each element will progress. Is recognized, and at that time the serviceman exchanges. With these operations, high image quality can be stabilized.

In the conventional method, in order to obtain a higher accuracy of the resistance value of the humidity sensor and the actual humidity, a high-precision condenser has been relied on. However, the capacitor has a characteristic that its rated value is easily changed by the external temperature, humidity and applied voltage, so that there is a disadvantage that the accuracy of the measured value is not improved for the cost.

However, by correcting the calibration value which can be obtained when measuring the standard resistance to the measurement value of the humidity sensor, it has become possible to detect a more accurate measurement value at low cost. .

As a result, if an image forming apparatus using an electrophotographic system, that is, a so-called copying machine is taken as an example, it has become possible to cope with high image quality in recent years at a low cost.

[0097]

According to the present invention as described above, according to the present invention, containing
Humidity can be measured satisfactorily while preventing deterioration of
It works.

[Brief description of the drawings]

FIG. 1 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart in the measuring device of FIG.

FIG. 3 is a timing chart in the measuring device of FIG. 1;

FIG. 4 is a characteristic diagram of a humidity sensor.

FIG. 5 is a diagram obtained by linearly approximating the characteristics of a humidity sensor.

FIG. 6 is a flowchart of a humidity calculation.

FIG. 7 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 8 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 9 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 10 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 11 is a flowchart for calculating an average humidity value.

FIG. 12 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 13 is a timing chart in the measuring device of FIG.

FIG. 14 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 15 is a timing chart in the measuring device of FIG. 14;

FIG. 16 is a flowchart of a humidity calculation.

FIG. 17 is a flowchart of calculating humidity.

FIG. 18 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 19 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 20 is a diagram illustrating an example of mounting the circuit of the embodiment.

FIG. 21 is a timing chart in the measuring device of FIG. 18;

FIG. 22 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

FIG. 23 illustrates measurement data.

FIG. 24 is a timing chart in the measuring device of FIG. 22.

FIG. 25 is a block diagram of a measuring apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 microcomputer 2 humidity sensor 4 switch 5 comparator 7 counter C1 capacitor E voltage source 2E voltage source

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-63723 (JP, A) JP-A-56-112672 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/00-27/24

Claims (2)

(57) [Claims] 1. A resistance element whose resistance value changes according to humidity.
And a capacitor connected in series with the resistance element, and a capacitor connected directly to the resistance element and the capacitor connected in series.
Voltage applying means for applying a flowing voltage and an AC voltage, and detecting that the voltage of the capacitor has reached a predetermined voltage.
Detecting means, and the time from when the voltage applying means starts applying a DC voltage.
Counting means for counting, and when not measuring, applying an AC voltage to the voltage applying means,
During measurement, a DC voltage is applied to the voltage applying means, and
Before the detecting means detects that a predetermined voltage has been reached.
Judgment of humidity based on the count value by the counting means
Control means for detecting a plurality of predetermined voltages.
A predetermined voltage of a value corresponding to the count value of the counting means.
A measuring device characterized by switching to pressure . 2. A resistance element whose resistance value changes according to humidity.
And a capacitor connected in series with the resistance element, and a capacitor connected directly to the resistance element and the capacitor connected in series.
Voltage applying means for applying a flowing voltage and an AC voltage, and detecting that the voltage of the capacitor has reached a predetermined voltage.
Detecting means, and the time from when the voltage applying means starts applying a DC voltage.
Counting means for counting, and when not measuring, applying an AC voltage to the voltage applying means,
During measurement, a DC voltage is applied to the voltage applying means, and
Before the detecting means detects that a predetermined voltage has been reached.
Judgment of humidity based on the count value by the counting means
Control means for controlling the voltage of the capacitor at an arbitrary amplification degree.
Amplifying means for amplifying the cow,
Detection at the amplification degree according to the
measuring device.