JPS5942825B2 - Digital ventilated wet/dry bulb hygrometer - Google Patents

Description

[Detailed Description of the Invention] The accuracy and reliability of the present invention are comparable to those of well-known ventilated wet/dry bulb hygrometers, and furthermore, it is capable of continuous relative humidity recording, automatic control, digital display, digital processing, etc. The present invention relates to a digital ventilated wet and dry bulb hygrometer.

As is well known, ventilation wet-bulb hygrometers have high accuracy and reliability, but they cannot be used as they are for continuous recording of relative humidity, automatic control, digital display of data, digital processing, etc. There are some bridge systems that can be used for continuous recording or automatic control, but they are not only inconvenient for direct digital processing of data, but also because the purpose of use is specified, so they are not common.

On the other hand, electrical resistance hygrometers that use electrical resistance are capable of continuous recording, automatic control, and direct digital display and processing of data, but are significantly inferior to ventilated wet-bulb hygrometers in terms of accuracy and reliability. Moreover, the moisture sensing element deteriorates in a short period of time, so it must be replaced frequently. The present invention has been proposed in view of the above, and is a digitalized ventilation wet/dry bulb hygrometer that can measure with relatively high accuracy. In other words, by focusing on the fact that if the operating temperature and humidity are limited, dry-humidification is independent of temperature and becomes a function only of relative humidity, a linearizer circuit using a thermistor element is used to linearize the temperature vs. output voltage characteristic. The corrected output is used to calculate the dry/wet ratio, convert relative humidity, etc. using an arithmetic circuit, and the relative humidity is directly displayed digitally. The present invention will be described below with reference to the illustrated embodiment. A wind tunnel 2 is formed inside a cylindrical case 1,
A pro-ar motor 3 is provided at one end of the wind tunnel 2, and when the pro-ar motor 3 is driven, outside air passes through the wind tunnel 2.

In the wind tunnel 2, a wet bulb thermistor element 4 and a soft bulb thermistor element 5 of the same standard are placed. The wet and dry bulb section 8 for detecting humidity is constructed by immersing the bulb in the water. Since the water in the water reservoir 7 constantly permeates into the water-containing sheet 6 by capillary action, when outside air passes through the wind tunnel 2, each thermistor element 4, 5 exhibits a different resistance value.

In FIG. 1, each thermistor element 4, 5 is connected to a lead wire 10 via a mounting terminal 9, and is connected to another electric circuit through a connector 11 at the tip of the lead wire 10. Thermocouples, diodes, transistors, etc. can also be used in place of each thermistor element. FIG. 2 shows a circuit configuration diagram of the present invention, and can be summarized as follows.
A linearizer circuit 12 linearly corrects the temperature vs. resistance characteristics of the thermistor elements, and the temperature is proportional to the wet bulb temperature (θw) of the wet bulb thermistor element 4 and the dry bulb temperature (θD) of the dry bulb thermistor element 5. With both output voltages from the linearizer circuit 12 as input, the dry and wet bulb Q (however, Q-(θ-C)/
(θo-C), where C is a constant), and relative humidity conversion that converts the output voltage of the arithmetic circuit 13 proportional to the dry/wet ratio (Q) into an output voltage proportional to the relative humidity. A circuit 14, an A-D converter circuit 15 that digitally converts the analog output voltage from the relative humidity conversion circuit 14, and a display section 16 that calculates and digitally displays the pulse output from the A-D converter circuit 15. Become.

The linearizer circuit 12 has a wet bulb section 17 and a dry bulb section 18, and the wet bulb section 17 has a resistor R5 and a wet bulb thermistor element 4 connected in series to a midpoint a between resistors Rl and R2 connected in series. One end of the circuit in which the resistor R6 is connected in parallel is connected, and the other end of the circuit is connected to a parallel circuit of the operational amplifier A1 and the variable resistor VRW. In addition, the dry bulb section 18 connects one end of a circuit in which the resistor R7 and the dry bulb thermistor element 5 are connected in series and the resistor R8 is connected in parallel to the midpoint b between the resistors R3 and R4 connected in series. The other end is connected to a parallel circuit of an operational amplifier A2 and a variable resistor RO. In the linearizer circuit 12 described above, the temperature measurement method using both thermistor elements 4 and 5 will be explained.
(K), the reference temperature is TO (0K), the resistance of the wet bulb thermistor element 4 is Rw (T), the resistance of the dry bulb thermistor element 5 is RD (T), each thermistor constant is B (0K), the reference R is the resistance of each thermistor 4, 5 at the temperature.

Let w,ROO be given by, so R5=ARO
w, R6-BROw, R7-A5R'00, R8-b'
If R'00 is assumed, then R if the reference temperature is the same.

Since w=WOO=RO, the combined resistance R of the resistors R5 and R6Rw becomes.

On the other hand, in Fig. 2, the voltages at points a and b are Ei and E, respectively.
i/, and assuming that this is an equal voltage, the output w(T) of the operational amplifier A1 at T=0K is, and TO(・
The output Vw(TO) of the operational amplifier A1 at K) is given by:

From equations (3) and (4) above, holds true.

In order for the above equation (5) to have linearity with respect to temperature change, the following must be true.

To find the coefficients A and b of equation (5) Then, when solving the simultaneous equations, holds true.

The values of A and b are obtained from the above equation (8) to determine the values of the resistors R5 and R6.

The calculations described above are for determining the values of the resistances R, , R6 in the wet bulb section 17, but the exact same calculations are performed for the dry bulb section 18 to determine a'', b' and the resistances R7, R6.
Determine the value of R8.

Determine the value of each resistor R5, R6, R7 as above,
Configure a linearizer circuit. Note that resistors Rl, R2 and R3, R4 are determined to have appropriate values to obtain appropriate input voltages El, Ei', and each variable resistor VRW, R
D is the reference temperature T.

Each output w(T
The resistance values are set so that O) and VO(TO) are approximately below the maximum output. According to the linearizer circuit 12 configured as described above, the temperature versus output voltage characteristic of each thermistor element becomes a straight line. and a certain temperature range,
If the relative humidity range to be measured is limited, the dry-wet ratio (Q) will appear as a value that is almost independent of temperature, and moreover, the dry-wet ratio and relative humidity will correspond within a certain error range. Therefore, by determining the wet/dry ratio (Q), the relative humidity can be measured.

The arithmetic circuit 13 calculates the dry-wet ratio (Q) described above, and the linearizer circuit 12 is connected to the switch S1 of the wet bulb section 17.
and the wet bulb temperature (
θw) and dry bulb temperature (θ.

) are applied through the switch WDs Sl and S2, respectively, voltages V (T) and V (T) that are proportional to the voltages V (T) and V (T), respectively.

Then, the semi-fixed polymers RCl and RC2 of the arithmetic circuit 13 set a voltage proportional to a constant C when calculating the dry/wet ratio, and each arithmetic amplifier A3A4 is set to θ by the set constant C.
C and θ. -C is calculated, and the calculated result is applied to the divider A8 to calculate the wet/dry ratio. Therefore, the output voltage of the divider A5 is a value proportional to the dry-wet ratio (Q), and this value indicates a one-to-one correspondence between the dry-wet ratio and the relative humidity, regardless of temperature. The output voltage proportional to the dry/wet ratio from the divider A5 is directly the output of the arithmetic circuit 13, and this output voltage is applied to the next relative humidity conversion circuit 14. The relative humidity conversion circuit 14 is composed of a diode, an arithmetic amplifier, etc., and converts a voltage proportional to the dry/wet ratio applied from the arithmetic circuit 13 to a voltage proportional to the relative humidity to be measured.

In addition, this relative humidity conversion circuit re-corrects the linearity of the above-mentioned conversion characteristics, and also corrects the error with the water vapor pressure to determine the relative humidity, and corrects the error when the wet bulb temperature freezes to obtain the measured value. This increases the accuracy of The output of the relative humidity conversion circuit 14 is applied to an A-D converter circuit 15 for A-D conversion, and applied to a display section 16 for direct digital display by an internal counter circuit.
Alternatively, it can be used directly as online input to a computer or the like.

As is clear from the above, according to the present invention, the temperature vs. output characteristic is linearly corrected by a linearizer circuit using a wet bulb thermistor element and a dry bulb thermistor element of the same standard.
The corrected output is used to calculate the dry/wet ratio, convert relative humidity, etc. using an arithmetic circuit, and is then directly displayed digitally. In addition, the linearizer circuit only needs to calculate two fixed resistance values at the design stage based on the thermistor element constants in advance, and thermistor elements of the same standard are compatible and can be compensated with high precision over a wide range. be able to. In addition, the linearizer circuit of the present invention is extremely superior in terms of correction accuracy, stability, simplification of adjustment operations, and economy due to the small number of parts, and is capable of direct continuous recording of measured values, automatic control, digital display, It can also be processed and has high practical value.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic perspective view of a wet/dry bulb section, and FIG. 2 is a circuit configuration diagram. 2...Wind tunnel, 4...Wet bulb thermistor element, 5... ．． ．． Dry bulb thermistor element, 8...
...Wet and dry bulb sound for humidity detection 1S. 12... Linearizer circuit, 13... Performance circuit, 14...
... Relative humidity conversion circuit, 15 ... A-D converter circuit, 16 ... Display section.

Claims (1)

[Claims] 1. A wet/dry bulb part for humidity detection in which a wet bulb thermistor element and a dry bulb thermistor element of the same standard are placed in a wind tunnel through which outside air passes, and a linearizer circuit including one operational amplifier for each thermistor element, and a wet bulb section and a dry bulb section each having a series-parallel circuit of two fixed resistors and the thermistor element at the input of the operational amplifier; An arithmetic circuit that calculates the dry/wet ratio by inputting the output voltage of the linearizer circuit proportional to the temperature from both thermistor elements, and a relative humidity conversion circuit that converts the output voltage proportional to the dry/wet ratio into a voltage proportional to the relative humidity to be measured. A digital ventilated wet/dry bulb hygrometer comprising an A/D converter circuit that digitally converts an output voltage proportional to relative humidity, and a display section that displays digitally.