JPS59141038A - Dew point detecting apparatus - Google Patents

Abstract

PURPOSE:To attain to enhance the measuring reliability of a dew point, by detecting the difference between resonance frequencies of a hermetically sealed crystal vibrator and a crystal vibrator exposed to gas to be detected. CONSTITUTION:When a power source is closed, the difference between resonance frequencies of crystal vibrators Q1, Q2 is set in a setting circuit ST1 as an initial value which is, in turn, compared with the output frequency of a mixer M in a comparison circuit CM1 and, when both values are same, output is generated from a drive circuit DR and a heater cooler A is operated as a cooler. Because the vibrator Q2 is exposed, dew is formed on the surface thereof at a dew point and the mass thereof is increased while the resonance frequency thereof is lowered as shown by the drawing. On the other hand, because the vibrator Q1 is hermetically sealed, there is no dew formation and, therefore, the difference between the resonance frequencies of both vibrators becomes large and, when the difference reaches a predetermined values DELTAf more, cooling is stopped while the oscillation frequency of the vibrator Q1 is taken in an operation circuit CU to be converted to a dew point. At the same time, the output of a temp. detecting circuit TM is taken in the circuit CU to measure atmosphere temp. while the absolute humidity and relative humidity are calculated from the dew point and the atmospheric temp. to be displayed by a display apparatus DS.

Description

[Detailed description of the invention] The present invention relates to a dew point detection device.

Conventionally, a variety of so-called dew point hygrometers have been used that measure temperature from the dew point of a gas, but all of these have complex structures and often require skill to measure, resulting in low reliability of readings. For example, in dew point and humidity correction using visual judgment, it is difficult to judge the dew point and the error is very large. In addition, there are other instruments such as a Kuran tube dew point hygrometer and a lithium chloride dew point hygrometer, but even with these, the accuracy of the dew point is limited to ±1°C. SUMMARY OF THE INVENTION Therefore, the present invention provides a dew point detection device capable of highly accurate dew point detection with a simple configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, one embodiment of the present invention will be explained based on all the drawings. In the spear 1 diagram, Ql + Q2 is respectively the spear 2 diagram t1 +
The crystal oscillator exhibits a linear temperature characteristic as shown by t2, and the crystal oscillator Ql is hermetically sealed, while the crystal oscillator Q2 is for detecting dew condensation and is exposed. A is a cooling and heating device, and a crystal oscillator Q1. Cool or heat Q2. M is the mixer, CMI, 0M2 is the comparison circuit, STt, ST2 is the setting circuit, L is the notice board, D
R is a drive circuit. Q3 is a crystal oscillator for temperature detection,
TM is the temperature detection circuit, and CU is the absolute temperature or relative humidity.

DS is a display device.

Next, the operation will be explained in detail. When the low power source is turned on, one pulse is supplied to terminal P of the setting circuit STl.

The output frequency from the mixer M at this time, that is, the difference between the oscillation frequency mantissas of the crystal sensors Q+ and Qz is set as an initial value by the setting circuit 5TIK. Then, in the comparison circuit CMH, the output frequency of the mixer M and the initial frequency of the setting circuit S1''1 are compared, and if the two are substantially the same, an output is generated from the drive circuit DR based on the output of the comparison circuit CM1. The output V causes the power U to generate heat and the cooler A operates as a cooler to cool the crystal oscillator Q l+ Qz.

Since the crystal oscillator Q2 is exposed, when the dew point is reached, dew condenses on its surface, increasing the buildup, and the resonant frequency decreases as shown in the second diagram. On the other hand, the crystal sensor Q1 is hermetically sealed, so there is no condensation on its surface.

Therefore, the difference in resonance frequency between the two becomes large.

When this difference exceeds the predetermined f@Δf, the comparison circuit CMl
The output from the unit will stop and cooling will stop. This comparison circuit (]
By stopping the output of M1, the oscillation frequency of the crystal resonator cL1 is taken into the arithmetic circuit CU, and this frequency is converted into a dew point. At the same time, the output of the temperature detection circuit TM is output from the arithmetic circuit OU.
The air temperature is measured. The absolute humidity and relative humidity are determined from the dew point 2 and the temperature and are displayed on the 21"L display DS.

By the way, once dew condenses on the crystal resonator Q2, measurement cannot be performed until it dries. Therefore, the setting circuit ST2 is configured to set the quartz crystal sensor Q1 when the crystal oscillator Q2 is dry. Set a value f1 that is slightly larger than the frequency of the difference in Q2 to 2. Therefore, when the switch S is closed, the comparator circuit CM2 compares the output of the setting circuit ST2 and the output of the mixer M, and if the difference between the two is greater than f1, the lamp L
lights up to warn that measurement is impossible, and the heating/cooling device A operates as a heater by the output of the drive circuit DR to heat the crystal sensor Q2. This force n heat dries the crystal resonator Q2, and when the difference in oscillation frequency with the crystal sensor Ql becomes smaller than f1, the output of the comparator circuit CM2 stops.

Note that the electrodes of the crystal oscillator Q2 are made of Au.

Although it is protected with an oxide film, since it is exposed, the surface gets dirty and the resonance during drying changes.

Therefore, as described above, the output frequency of the mixer M is set as an initial value in the setting circuit STI for each electronic receiver.

By the way, as a crystal camera element, I
If a device that changes in KHz is used, the dew point measurement accuracy can be kept within 0.1°C.

As described above, according to the present invention, highly reliable dew point measurement can be performed with a simple configuration, and it is not affected by dirt and is easy to handle and maintain.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a characteristic diagram showing the frequency-temperature characteristics of the crystal sensor used in this example. Ql...Hermetically sealed crystal camera. Qz...Exposed crystal camera, A...Heating and cooling device 1M...Mixer.

Claims (1)

[Claims] Two crystal oscillators exhibiting approximately linear temperature characteristics, one of which is hermetically sealed with gold, and the other exposed to the entire gas to be detected; a cooler that cools each of the crystal oscillators; A control circuit is provided which generates an output when the difference in the number of co-alternating cycles exceeds a predetermined value. - A dew point detection device characterized by determining the dew point of a gas to be detected.