JPH04186190A - humidity measuring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a humidity measuring device for measuring absolute humidity, relative humidity, etc.

[Conventional technology]

Conventional humidity sensors mainly use sensing methods that use resistance and capacitance changes due to adsorption and desorption reactions of ceramics and organic polymers. Also, one of the two hot thermistors is placed in a dry air case and the other one is placed in a dry air case.
The two hot thermistors are placed in the atmosphere to be measured, and a current is passed through the two hot thermistors to generate heat □.
Another method used was to measure the temperature difference between thermistors and use that temperature difference as absolute humidity.

[Problem to be solved by the invention]

However, the above sensing method was inferior in chemical resistance (methane, ethane, ethylene, ammonia, acetone, alcohol, formalin, etc.), dew condensation cycle, and long-term stability at high temperatures, and could not ensure reliability. Also,
The above two methods using hot thermistors are highly reliable, but have the extremely difficult problem of requiring thermistors with characteristics that are uniform at about 0°1 to 0.01°C.
Since this method relies on sorting, etc., there are problems such as difficulty in reducing the price. This invention was made in order to solve the problem as described in item 1 above, and its purpose is to obtain a humidity measuring device that has high reliability and can be manufactured at low cost.

[Means to solve the problem]

The humidity measuring device according to the present invention includes a heater placed in a target atmosphere, a temperature sensor that detects the temperature of the heater, an atmosphere temperature sensor that detects the temperature of the target atmosphere, and a pressure of the target atmosphere. and a control signal for controlling the temperature of the heater to a set value according to the detected value of the temperature sensor, and performs a predetermined calculation based on the detected values of the temperature sensor, the atmosphere sensor, and the barometric pressure sensor. Accordingly, an arithmetic device for calculating the absolute humidity and/or relative humidity of the target atmosphere is provided.

[For use]

A highly reliable and highly accurate humidity measuring device can be obtained at a low cost without using particularly high precision heaters, temperature sensors, and atmospheric pressure sensors.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 1 is a heater, a hot thermistor,
A heating element such as a hot wire heater or a ceramic heater whose heat generation amount can be controlled by current or voltage is used. 2 is a temperature sensor that measures the temperature due to the heat generated by the heater 1, and is a temperature sensor that can measure temperatures of about 60°C to 300°C with good reproducibility, such as a thermistor, thermocasople, resistance thermometer, semiconductor temperature sensor, or crystal temperature sensor. is used. 3 is a sensor package in which the heater 1 and the temperature sensor 2 are arranged as close as possible, and the package can withstand temperatures of about -20°C to 300°C, and also contains methane, ethane, ethylene, ammonia, etc. It is made of a material that is not affected by chemicals such as acetone, alcohol, and formalin, and can be easily molded during the manufacturing process, such as low-melting glass. This sensor package 3 is sufficiently shielded by a filter so that it is not affected by the surrounding wind. With this filter, the gas region between the sensor device and the filter is formed in such a way that natural convection occurs. 4 is a constant current circuit that energizes heater 1, and operational amplifier 5
and a resistor R+. Reference numeral 6 denotes an ambient temperature sensor for measuring the ambient temperature (T), which is installed in a position where the influence of temperature rise due to heat generated by the heater 1 is sufficiently small. Sensors such as temperature sensors are used. 7 is an oscillator, a capacitor CI+ 33.4 inverters 8. Switches SWI, SW2. SW3 and resistor R6
Consists of etc. The switch SW3 is the temperature sensor 2.
Ambient temperature sensor 6 and resistor R6 are selectively switched. Further, it is assumed that the capacitor S3 constitutes a part of an atmospheric pressure sensor using a capacitive pressure sensor. 9 is a prescaler that divides the oscillation frequency of the oscillator 7, and 10 is an arithmetic unit including a microcomputer that controls the heater 1 to a set temperature based on the output of the prescaler 9 and calculates relative humidity, absolute humidity, etc. , pulse interval timer 11. It has a PWM (pulse width modulation) signal output port 12 and a memory (not shown). 13 is a DC voltage circuit that superimposes a PWM signal as a control signal on a predetermined DC constant voltage signal, and MO3FET14. Resistance R2~R
s, R7, Zener diode 15 and operational amplifier 1
Consists of 6th grade. FIGS. 2(A) and 2(B) show the structure of the sensor package section 3, in which the heater 1 and the temperature sensor 2 are
is formed of a thin film thermistor. The heater 1 and the temperature sensor 2 are provided one day above the SiO□ layer provided on the SS substrate 17. Also, heater 1
Both ends of the temperature sensor 2 and the temperature sensor 2 are connected to two pairs of electrodes 19.20 provided on the SiO□ layer 18, and lead wires 21.22 are led out from each electrode 19.20. This sensor package section 3 is entirely covered with a low melting point glass 23. Next, the operation will be explained. The circuit shown in FIG. 1 is operated in the loop from (1) to (0) below. Note that in reality, sensor signal input processing and arithmetic processing are processed in parallel using interrupt processing to improve processing efficiency, but interrupt processing is included here to facilitate understanding. (2) When the switch SWI is turned on, the switch SW2 is turned off, and the switch SW3 is set to the resistor R6 side, the oscillator 7 oscillates by the capacitors C1 and R6. The oscillation frequency (FO) at this time is expressed as (Formula 2). Tl=C1*S2* (α+β) ... (Formula 1) FO
=1/To...(Formula 2) α=1n
((Vd-Vl)/(Vd-F2)) ・= (Formula 3
) β-1n ((F2-Vg)/(Vl-Vg))
...(Formula 4) vd: H1 output voltage of the inverter F2: HI level threshold input voltage of the inverter v1:
Inverter's LO level threshold input voltage vg: Inverter's LO output voltage ■, switch SWI is on, switch SW2 is off, switch SW3 is set to ambient temperature sensor 6 side, CI and ambient temperature sensor It oscillates due to the resistor S2 of 6. The oscillation frequency (Fl) at this time is (26). Tl=C1*S2* (α+β)...(Formula 5)%Formula%(6) ■When switch SWI is turned on, switch SW2 is turned off, and switch SW3 is set to heater 1 side, the resistance of C1 and heater 1 It oscillates due to S1. The oscillation frequency (F2) at this time is (28). Tl=C1*S2* (α+β) ... (Formula 7) F2
=1/T2 ... (Formula 8) ■, switch SW1 is turned off, switch SW2 is turned on, switch S
When W3 is set to the R6 side, the oscillator 7 oscillates due to the capacitors S3 and R6 of the atmospheric pressure sensor. The oscillation frequency (F3) at this time is expressed as (Equation 10). T3=33*R6*(α+β)...(Formula 9) F3=
1/T3...(Formula 10) ■, ■~
(2) Oscillation frequency Fl, F2. The frequency of F3 is divided by the prescaler 9 to an arbitrary value, and the time of one cycle of the divided rectangular wave signal is set by the pulse interval timer 1 inside the microcontroller.
1 is measured by an external timer. The arithmetic unit 10 performs ratiometric conversion using the measured values of the oscillation frequencies of (1) and (2) to (2). This conversion cancels all errors related to inverter 8. Then, the detection value Ct of the ambient temperature sensor 6
, the detection value ch of temperature sensor 1, and the detection value C of atmospheric pressure sensor
p (Formula 11-). Calculated using (Equation 12) and (Equation 13). c t =FO/F 1 =S 2/R6...(Formula 1
1) Ch=FO/F2=S1/R6...(Formula 12)c
p=FO/F3=S3/CI...(Formula 1
3) PID control calculation is performed from the difference (Ch-cs) between the value (Ch) of (Equation 12) and the set value (Cs) corresponding to a certain temperature and the time data of the pulse interval timer 11. The control amount (M) obtained by the calculations of ■ and ■ is calculated by the calculation device 1.
0 from the PWM signal output port 12, the PWM signal output as a control signal is received by the MO3FET 14 having low on-resistance and high off-resistance characteristics, and the PWM signal output peak value is converted into a predetermined voltage. The PWM output obtained in ① and ② is superimposed on the DC constant voltage signal by the DC voltage superimposition circuit 13, and the PWM output is
The DC constant voltage signal value is adjusted so that it is controlled to a fixed setting value (Cs) stored within the microcomputer at approximately 0%. In addition, in order to obtain a sufficient dynamic range for humidity measurement, the peak value of the PWM signal output should be adjusted within the range that allows heater temperature control within environmental changes (absolute humidity changes, environmental temperature changes, atmospheric pressure changes, and gas composition changes). as narrow as possible
(Set the high output voltage of PWM output low). The constant current circuit 4 for driving the heater is pulse-driven with a signal obtained by superimposing the PWM output of [phase] and (2) on a DC constant voltage signal. ■From the relationship between the heat capacity of heater 1 and the heater drive power,
The heater 1 has the effect of a time delay (low-pass filter) with a certain defined time constant value. Utilizing this effect, the pulse signal (2) is directly applied to the heater (1). @ and ■ change the signal output of the temperature sensor 2 that measures the temperature due to the heat generated by the heater 1, and the operations from ■ to @ are repeated until the fixed setting value (
The control amount (M) when the difference from the value (Ch) of (Equation 12) <ch - cS) converges to near zero within the accuracy range is stored in the microcontroller's internal memory ( R.A.
M). 0, calculated using a function (F) made in advance at the time of factory adjustment from three parameters: the output of the atmospheric pressure sensor (Cp), the output of the ambient temperature sensor 6 (Ct), and the true atmospheric pressure (P). , find the true atmospheric pressure (P). P=F (CpXCt) ... (Formula 14)■,
The output of the ambient temperature sensor 6 (Ct) and the true ambient temperature (
The true ambient temperature (T) is calculated from the two parameters T) using a function (G) made in advance during factory adjustment.
seek. T=G CCt) ... (Equation 15) [Phase], the controlled variable (M) stored in the memory (RAM) inside the microcomputer at @, the atmospheric pressure (P) of [Phase], and the ambient temperature (■) Absolute humidity (Ha) is calculated from four parameters, T) and true absolute humidity (Ha), using a function (Q) that was created in advance at the time of factory adjustment. Ha=Q (M, P, T) ” (Formula 16) [Phase]
, converts the known relationship between the ambient temperature (T) and the saturated water vapor pressure (Es) into a function (U), and stores it in the memory of the arithmetic unit 10.
(mask ROM). From the ambient temperature (T) at the time of measuring the function, the saturated water vapor pressure (Es) at that temperature is determined. The known relationship between absolute humidity (Ha) and relative humidity (Hr) obtained from this saturated water vapor pressure (Es) and [phase] is converted into a function (■) and stored in the memory (mask ROM) of the arithmetic unit 10. Let me remember it. The function is calculated to determine relative humidity (Hr). Es=U(T)... (Formula 17) Hr=
V (Es, Ha) - (Equation 18)@, Regarding the dew point temperature calculation, the absolute humidity (Ha) obtained in [phase] and the ambient temperature (
T), the water vapor pressure in the measured gas is a known function,
Temperature that is the saturated vapor pressure of water (dew point temperature: Ts)
A function (W) is created to obtain , and it is stored in the memory (mask ROM') of the arithmetic unit 10. The function is calculated to obtain the dew point (Ts). Ts = W (Ha, T) - (Formula 19) Next, the adjustment processing algorithm will be explained. (1) The factory adjustment process (characterization) is as follows:
This is done by ~■. ■The product configured as shown in Figures 1 and 2 is heated to
Place it in a tank that can generate or measure humidity and atmospheric pressure with high precision. The temperature, humidity, and air pressure of this tank are generated by dividing them into two points, the minimum value and the maximum value, or multiple points between them, for each parameter within the usage range of the product. (2) A function (F) is created for each product from the pressure (Cp) of the atmospheric pressure sensor, the output (Ct) of the ambient temperature sensor 6, and the generated true atmospheric pressure (P). (2) Create a function (G) for each product from the output (Ct) of the ambient temperature sensor 6 and the generated true ambient temperature (T). ■The temperature of heater 1 is kept constant by feedback control of the generated true ambient temperature (T), the generated true atmospheric pressure (P), and the generated true absolute humidity (Ha). The control amount (M) and (Q) for each product are created for each product. ■Since the relationship between relative humidity (Hr) and dew point temperature (Ts) is known, instead of creating a function for each product,
Since this function is common to all products, it is stored in a mask ROM without creating a function in the adjustment process. (2) Field adjustment (correction of effects due to fluctuations in gas components) is performed as follows. (2) When installed in equipment in the field, the gas composition may differ from the one in the factory adjustment process. This system may be more sensitive to changes in gas composition than to changes in humidity. However, if the gas component does not fluctuate in the field and this gas exists independently without interacting with the humidity (0120), the measurement gas must be treated with a dehumidifying agent (P2O3, etc.) once when starting up the device to ensure accuracy. Dry it inside and send it to the moisture sensitive part of the product. The absolute humidity display value or output value at that time is adjusted to zero and corrected.

【Effect of the invention】

According to this invention, a heater is provided in the target atmosphere, and the temperature of the heater is controlled to a set value according to the detection value of the temperature sensor that detects the temperature, and the temperature sensor, the atmosphere temperature sensor, and the barometric pressure sensor are controlled. Since the absolute humidity and/or relative humidity of the target atmosphere is calculated by performing predetermined calculations based on each detected value, the following effects can be obtained. (2) It can be constructed from conventional temperature sensors, heaters, and atmospheric pressure sensors, and since it is not necessary to make the absolute accuracy of each sensor higher than in other methods, the cost of each sensor is low. This is because the temperature of the heater 1 only needs to be set around a certain temperature, and what is important is that the temperature is kept constant with high accuracy. Therefore, the temperature sensor 2 that measures the temperature of the heater 1 does not need to be highly accurate. Further, the atmospheric pressure sensor is a sensor for correcting the effect that thermal conductivity is influenced by atmospheric pressure, and since the amount of influence is originally small, the accuracy of the atmospheric pressure sensor is not greatly affected. ■Higher reliability can be ensured compared to conventional humidity sensors. This is because the sensing method does not involve adsorption or desorption reactions, and only the part that comes in contact with gas (heater package 3) is used.
Condensation does not occur because a chemical material (glass or ceramic with a smooth surface) is used, and the parts that come in contact with gas are heated with heater 1. Therefore, high reliability can be ensured. ■Multi-functionality is possible because it uses the idea of a composite sensor. This is because by using three sensors, five measurements of absolute humidity, relative humidity, dew point, temperature, and atmospheric pressure can be made from this combination of outputs. Since the high reliability of (2) and (4) can be ensured, high accuracy is possible.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a humidity measuring device according to an embodiment of the present invention, and FIG. 2 is a plan view and a sectional side view showing a heater package of the device. 1 is a heater, 2 is a temperature sensor, 6 is an ambient temperature sensor,
10 is a calculation device. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Patent applicant Yamatake Honeywell Co., Ltd. Agent Patent attorney 1) Hiroshi Sawa (2 others)

Claims (1)

[Claims] A heater 1 placed in a target atmosphere, a temperature sensor 2 that detects the temperature of the heater, an atmosphere temperature sensor 6 that detects the temperature of the target atmosphere, and an atmospheric pressure sensor S_3 that detects the pressure of the target atmosphere. A control signal is generated to control the temperature of the heater to a set value in accordance with the detected value of the temperature sensor, and a predetermined calculation is performed based on the detected values of the temperature sensor, the atmosphere temperature sensor, and the atmospheric pressure sensor to control the temperature of the heater. A humidity measuring device including an arithmetic device 10 that calculates the absolute humidity and/or relative humidity of the atmosphere.