JPS6257937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dew condensation detection device used in a dew point meter or the like.

Generally, a dew point meter measures the dew point when a certain amount of dew is deposited on a dew condensing surface. Therefore, in order to control the temperature of the dew condensation surface by operating the cooling or heating device so that the amount of dew condensation is constant, a dew condensation detection device is provided that obtains a signal corresponding to the amount of dew condensation.

A crystal resonator type dew condensation detection device utilizes the fact that the resonant frequency of a crystal resonator changes depending on dew or frost attached to its surface. In this type of conventional device, an oscillation circuit is constructed using a crystal resonator, and the presence or absence of dew condensation is detected by detecting a state in which oscillation is stopped. however,
Oscillation is likely to stop due to causes other than condensation, such as stray capacitance of cables and lead wires between the crystal resonator and electric circuit that make up the surface to be detected (condensation surface), and a reduction in Q due to the installation method. Dew condensation could not be detected reliably, and the amount of condensation could not be detected.

The purpose of the present invention is to solve the above problems,
It is an object of the present invention to provide a dew condensation detection device that operates reliably and can obtain a signal corresponding to the amount of dew condensation.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the apparatus of the present invention. In FIG. 1, 1 is a sensor section including a crystal resonator 11. As shown in FIG. Resistors 12 and 13 are connected to the crystal resonator 11 in series and in parallel, respectively. An input signal is applied to one end of the crystal resonator 11 through a resistor 12, and the other end is connected to a common point. A voltage signal across the crystal oscillator 11 and a resistor 13 connected in parallel thereto is output as an output signal from the sensor section 1. The impedance of the crystal resonator 11 drops significantly near the resonance point, and when it deviates from the resonance point, it is suppressed by the resistor 13 connected in parallel. Therefore, the impedance characteristic of the sensor section 1 becomes a downwardly convex curve like curve A in FIG. f ₀ in the figure corresponds to the resonant frequency of the crystal resonator 11. Curve A also shows the relationship between the frequency of the input signal of the sensor section 1 and the amplitude of the output signal. Hereinafter, the curve A will be referred to as the impedance characteristic of the sensor section 1.
2 is a voltage controlled oscillator for exciting the sensor section 1. The voltage controlled oscillator 2 is controlled by the control voltage.
Its oscillation frequency changes linearly. 3 is a control circuit that inputs the output signal of the sensor unit 1 and generates a control signal to be given to the voltage controlled oscillator 2 so that the oscillator f _c of the voltage controlled oscillator 2 follows the resonance frequency f ₀ of the crystal resonator 11 It is. This control circuit 3
is a swept wave oscillator 31 for frequency sweeping the oscillation frequency f _c of the voltage controlled oscillator 2, an impedance characteristic detecting section 32, and an output signal e ₁ of the impedance characteristic detecting section 32 as the sweep frequency f _s of the swept wave oscillator 31. It is composed of a synchronous detection circuit 33 that performs wave detection, and an amplifier 34 that amplifies the output signal e ₂ of this synchronous detection circuit 33 and supplies it to the voltage controlled oscillator 2 as a control signal. The impedance characteristic detection section 32 is composed of an amplifier 32a that amplifies the output signal of the sensor section 1, a rectifier 32b that rectifies the amplified output, and a filter 32c that removes the high frequency component of the output of the rectifier 32b. The amplitude demodulation of the output signal is performed according to the impedance of the signal. For this reason, it has been given the name impedance characteristic detection section.

In FIG. 2, waveform B shows the oscillation waveform ( _es ) of the sweep wave oscillator 31. The direction of the arrow on the vertical axis of waveform B is set in the positive direction of the time axis (hereinafter, the same applies to waveforms C to E). The oscillation frequency f _c of the voltage controlled oscillator 2 changes periodically within a certain minute frequency band by the sweep wave oscillator 31 . For example, when f _c < f _p , the impedance characteristic of the sensor unit 1 has a negative slope as shown by the curve A, so the waveform of the output signal e ₁ of the impedance characteristic detection unit 32 is as shown in the waveform C in Fig. 2. become,
The phase difference between the oscillation signal e _s of the sweep wave oscillator 31 and the output signal e ₁ of the impedance characteristic detection section 32 is 180
Because of the difference, the synchronous detection circuit 33 is
The output signal _e2 takes a negative value. Also, when f _c > f _p , the impedance characteristic of the sensor section 1 has a positive slope, so the signals e ₁ and e _s are in phase as shown in waveform D in Figure 2, and the synchronous detection output signal e ₂ is positive. takes the value of When f _c = f _p , the signal e ₁ becomes a double frequency of e _s as shown in waveform E in Figure 2, and the synchronous detection output signal
e ₂ becomes zero. This output signal e ₂ is amplified by an amplifier 34 , and the output signal V _s of this amplifier 34 is superimposed on the oscillation signal e _s of the oscillation signal 31 of the sweep wave oscillator 31 and added to the input of the voltage controlled oscillator 2 . Therefore, the output signal V _s of the amplifier 34 is
It acts as a control signal for the voltage controlled oscillator 2 so that the synchronous detection output signal e ₂ is always zero, that is, the oscillation frequency f _c of the voltage controlled oscillator 2 is equal to the resonant frequency f _p of the crystal resonator 11 .

Next, when dew occurs on the surface of the crystal resonator 11, the resonant frequency f _p changes according to the amount of dew condensation. At this time, the control signal V to the voltage controlled oscillator 2
_s acts, and the voltage controlled oscillator 2 continues to excite the sensor unit 1 while maintaining the condition f _c =f _p .
The output signal V _s of the amplifier 34 changes according to the change in the resonant frequency f _p of the crystal oscillator 11, and the resonant frequency f _p depends on the amount of dew condensation, so V _s is obtained as the dew condensation amount signal.

Moreover, FIG. 4 is a block diagram showing another embodiment, in which the excitation frequency f _c of the voltage controlled oscillator 2 is always f _c =f _p
Therefore, the frequency f _c can be converted into a voltage by the frequency-voltage converter 4 and used as a dew condensation amount signal.

In this way, the device of this embodiment separately excites the crystal resonator 11 of the sensor section 1 with the voltage controlled oscillator 2,
A change in the resonant frequency f _p of the crystal resonator 11 due to dew condensation is detected, and the excitation frequency f _c to the crystal resonator 11 by the voltage controlled oscillator 2 is automatically followed by this resonant frequency f _p to continue the excitation state. At this time, the change in the resonant frequency f _p corresponding to the amount of dew condensation is extracted as a dew condensation amount signal. Therefore, unlike conventional devices, oscillation does not stop due to causes other than dew condensation, and a dew condensation amount signal can be reliably obtained.

Further, in the above-described embodiment, the voltage controlled oscillator 2 is used as the externally excited circuit, but other types may be used as long as the oscillation frequency changes according to the control signal. Furthermore, the control circuit 3 is configured by a sweep wave oscillator 31, an impedance characteristic detection section 32, a synchronous detection circuit 33, and an amplifier 34, but the sweep frequency component of the output signal of the sensor section 1 is detected, and the detected output signal is Any device may be used as long as it generates a signal corresponding to the positive or negative phase and magnitude of the amplitude of the output signal of the sweep wave oscillator 31 and outputs it as the output signal of this control circuit.

FIG. 5 is a block diagram showing the main parts of another embodiment of the sensor section 1. In FIG.

One end of the crystal oscillator 14 is an input terminal of the sensor section 1, the other end is an output terminal, and a resistor 1 is connected in parallel to both ends of the crystal oscillator 14.
5 is connected. Further, a resistor 16 is connected between the output terminal and the common point. When an excitation signal is applied from the voltage controlled oscillator 2 to the crystal resonator 14, the voltage across the resistor 16 is taken out as an output signal from the sensor section 1. The impedance characteristic of the sensor section 1 is as shown in FIG. Even in the embodiment device in which the sensor section 1 has such characteristics, a control loop can be constructed so that f _p = f _c at all times.

As described above, the device according to the present invention includes a sensor section that has a crystal oscillator whose resonant frequency f _p changes due to dew condensation and is placed in the atmosphere to be measured, and excites the crystal oscillator of this sensor section. A separate excitation circuit whose excitation frequency f _c changes according to a control signal and an output signal from the sensor section are input so that the excitation frequency f _c of the external excitation circuit follows the resonant frequency f _p of the crystal resonator. and a control circuit for giving a control signal to the externally excited circuit, and outputs a signal corresponding to the resonant frequency f _p of the crystal resonator as a dew condensation amount signal. According to this invention, it is possible to reliably obtain a dew condensation amount signal without causing oscillation to stop due to causes other than dew condensation.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the device according to the present invention;
FIG. 2 is a diagram showing the impedance characteristics of the sensor section 1 and waveforms for explaining the operation, FIG. 3 is a diagram showing the relationship between the output signal of the synchronous detection circuit 33 and the frequency, and FIG. 4 is a diagram showing the relationship between the output signal and frequency of the synchronous detection circuit 33. FIG. 5 is a block diagram of the main part of another embodiment of the sensor section 1, and FIG. 6 is an impedance characteristic diagram of another embodiment of the sensor section 1. DESCRIPTION OF SYMBOLS 1... Sensor part, 2... Voltage controlled oscillator, 3... Control circuit, 31... Sweep wave oscillator, 32... Impedance detection part, 33... Synchronous detection circuit, 34... Amplifier, 4... Frequency-voltage converter.

Claims (1)

[Claims] 1. A sensor section that has a crystal oscillator whose resonance frequency changes due to dew condensation and is placed in the atmosphere to be measured;
a separate excitation circuit that excites a crystal resonator of the sensor section and whose excitation frequency changes according to a control signal; and an external excitation circuit that uses the output signal of the sensor section as an input signal and whose excitation frequency resonates with the crystal resonator. In the dew condensation detection device, the dew condensation detection device includes a control circuit that provides a control signal to the separately excited circuit so as to follow a frequency, and outputs a signal corresponding to a resonant frequency of the crystal resonator as a dew condensation amount signal, wherein the sensor 1. A dew condensation detection device characterized in that the section is composed of a crystal resonator and a resistor connected in series and parallel to the crystal resonator.