JPH0522149B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frost condensation detection device used in refrigerator defrosters and various other industrial equipment.

[Prior Art] As is well known, frost forms on the surface of a heat exchanger incorporated in a refrigerator, air conditioner, etc. under certain conditions. If the device continues to operate while this frost condition is left untreated, the efficiency of energy consumption will drop significantly, resulting in not only being uneconomical, but also often leading to malfunctions.

Conventionally, as means for detecting frost condensation, methods using a vibrating body, methods utilizing a change in dielectric constant of an element due to frost condensation, methods using optical detection, and the like have been developed.

FIG. 5 and FIG. 6 respectively show a frost condensation detection device using a vibrator, one that detects a change in the resonant frequency of the vibrator, and one that detects a change in the amplitude of the vibrator.

In FIG. 5A, a piezoelectric vibrator 3 is mounted on the upper surface of a hollow cylindrical housing 1 via an elastic support 2, and an output terminal 5 is connected to an electrode 4 that holds the piezoelectric vibrator 3 between its upper and lower surfaces. has been derived.

FIG. 2B shows a circuit configuration, in which the output of the vibrator 3 is amplified on one side through a resistor R and on the other side by an amplifier 6, and is then supplied to an oscillation frequency discrimination circuit 7 and then taken out as an output. To explain its effect, if frost or dew condensation forms on the surface of the vibrator 3, the resonant frequency obtained from the vibrator 3 will change depending on the amount, so if this amount of change exceeds a predetermined value, At a certain time, it is determined that there is frost condensation.

FIG. 6 shows a configuration of a detection device using a piezoelectric vibrator, which detects the occurrence of frost condensation based on the amplitude change of the vibrator 3. The basic configuration of the device is the same as that shown in Fig. 5 above, but this device focuses on the fact that when frost condensation occurs, the vibration of the vibrator 3 is suppressed by its weight. If a change occurs, it is assumed that frost condensation is present.

FIG. 7 shows a waveform diagram of the oscillation output of the piezoelectric vibrator 3 and the detection output of the device in the devices shown in FIGS. 5 and 6.

Figure A shows the oscillation output waveform of the device according to Figure 5, and the resonant frequency is approximately 2 at the same time as frost formation occurs.
FIG. 6B shows the oscillation output waveform of the device shown in FIG. 6, and it can be seen that the amplitude of the output signal of the vibrator 3 decreases at the same time as frost condensation occurs.

When such a change in the resonance frequency and resonance amplitude is recognized, the device outputs a signal notifying the occurrence of frost condensation, and in response to this, a predetermined defrosting or dehumidifying device is activated. Go.

FIG. 8 shows an example of the configuration of a frost condensation detection device using a change in dielectric constant.

Figures A and B show the structure and appearance, respectively, and have the structure of an insulating substrate 10 on which comb-shaped electrodes 9 are printed.

C in the same figure shows a detection circuit, an AC voltage is applied to the detection section from an AC signal source 12, the output of the detection section is supplied to an impedance detection circuit 13, and the output is sent to a defrosting or dehumidifying device (not shown). It is connected.

In the above configuration, when frost condensation occurs on the surface of the detection part, the AC impedance between the comb-shaped electrodes 9 changes, so this is changed by the impedance detection circuit 1.
3 is detected, it is presumed that there is frost condensation.

FIG. 9 shows an example of the configuration of an apparatus using optical means.

2A has a light emitting element 14, a light receiving element 15, and a reflecting surface 16. Light emitted from the light emitting element 14 is reflected on the reflecting surface 16 and enters the light receiving element 15. When frost condensation occurs on the reflective surface 16, the refractive index of the light from the light emitting element 14 or the angle of incidence of the light incident on the light receiving element 15 shifts, resulting in a decrease in the amount of light incident on the light receiving element 15. become. When this change in light amount is observed, it is determined that frost condensation has occurred.

In FIG. 1B, light is transmitted and received between the LED 17 and the photodiode 18. When frost condensation occurs in the optical path formed by the LED 17, which is a light emitting element, and the photodiode 18, which is a light receiving element, the amount of transmitted light changes. The level determination circuit 19 compares this amount of change with a reference value, and when it is equal to or greater than the reference value, a notification is made that frost condensation has occurred.

[Problems to be Solved by the Invention] With the configuration of such a conventional device, the following problems cannot be avoided, and therefore sufficient practicality cannot be obtained.

First, those using the piezoelectric vibrators shown in FIGS. 5 and 6 easily malfunction due to the adhesion of dust or other substances to the vibrators or the influence of vibrations applied from inside and outside.

In addition, with devices that utilize dielectric constant changes or optical methods, it is difficult to miniaturize the detection unit, and regular maintenance is required to maintain detection accuracy at a predetermined level, resulting in a lack of reproducibility. However, the circuit configuration of the device becomes complicated, and manufacturing costs cannot be kept low.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a frost condensation detection device that is small and inexpensive, has excellent detection accuracy, and has good reproducibility.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a variable constant current source whose output current amount can be set to an arbitrary value, and a heat generating current and temperature rise that cause a temperature rise due to self-heating. a temperature-sensitive resistor to which a negligible comparative reference current is alternately supplied from the variable constant current source; and a temperature-sensitive resistor in which the heating current is supplied and the comparative reference current is supplied. an arithmetic circuit that determines the temperature difference between the body and compares it with a predetermined reference value, and determines that there is frost or dew condensation when the temperature difference of the temperature-sensitive resistor falls below the reference value. It is characterized by

[Function] According to the present invention configured as described above, in a non-frost condensation state, the temperature difference of the temperature sensitive resistor that occurs between the time when the heating current is supplied and the time when the comparison reference current is supplied. is held constant.

When frost condensation occurs on the surface of the temperature-sensitive resistor, the temperature of the temperature-sensitive resistor when the heating current is supplied decreases due to the heat conduction effect of the frost or dew, and the temperature when the comparison reference current is supplied decreases. The difference between

The arithmetic circuit compares this temperature difference with a preset reference value, and if it is smaller than the reference value, it assumes that frost and dew condensation has definitely occurred, and outputs a signal notifying this.

[Examples] Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Here, in this embodiment, a thermistor is used as the temperature-sensitive resistor.

FIG. 1 shows a block diagram of the overall configuration of the apparatus of the present invention.

In the figure, a thermistor 10 with one end grounded
Two different values of heating current and comparison reference current are alternately supplied from the variable constant current circuit 12.
The thermistor 10 in the embodiment has a B constant of 3350, 25
A type with a resistance value of 5KΩ at °C is used. The heat dissipation coefficient of this thermistor in air is
2mW/°C, in ice it is about 50mW/°C.
The resistance value at 0°C is 14KΩ.

The heating current is a current value iB that, when supplied, causes the thermistor 10 to generate sufficient temperature (~0.5°C) due to self-heating.On the other hand, the comparison reference current is a current value iB that causes the thermistor 10 to generate sufficient temperature (~0.5°C) due to self-heating. This means the current iA at such a value that there is almost no change in the temperature in the air.

According to the present invention, different current values iA and iB are supplied to a single temperature-sensitive resistor in a time-divided manner, and the amount of heat dissipated is different depending on the surrounding situation at that time, that is, when there is frost condensation and when there is no condensation. The voltage value corresponding to the temperature difference detected from the thermistor is obtained by temporarily delaying one and matching the detection timing of the other. There is.

Therefore, in this embodiment as well, one of the two alternately selectable detection values is delayed by voltage hold and is subsequently supplied to the comparison circuit at the same timing as the other detection value.

Furthermore, according to this embodiment, the heating current iB is set to a higher current value than the comparison reference current iA, so if the comparison is made as is, there will be a difference between the two in the non-frost condensation state. , in order to match this, in this embodiment, when the comparison reference current iA is detected, it is amplified to match the detected value to the same level as the detection value when the heating current is detected.

That is, as is clear from FIG. 1, the output of the thermistor 10 is amplified by the amplifier circuit 14, and then held by the next hold circuit 16 for a predetermined period of time.

In the embodiment, this hold signal is held when the comparison reference current iA is supplied to the thermistor 10, and the amplification degree α of this amplifier circuit 14 is given by the following equation.

α=iBR ₀ /iAR ₀ =iB/iA The output of the amplifier circuit 14 enters the hold circuit 16. This hold circuit 16 is provided to avoid the situation where, as mentioned above, two current values are applied in a time-series manner, so it is impossible to compare the voltage generated in the thermistor 10 by the two current values. The voltage generated in the amplifier circuit 14 when the value iA is supplied is temporarily held, and the thermistor 10 is supplied with the current value iB after a predetermined time.
It functions to enable comparison with the voltage generated in the next stage comparison circuit 18.

The comparison circuit 18 compares the temperature difference that occurs when the currents iA and iB are supplied to the thermistor 10, and when the purpose is to determine only frost formation, the temperature T ₀ of the surrounding environment of the thermistor 10 indicates that frost formation occurs. Determine whether the temperature is below 0°C.

A signal for alternately switching between iA and iB the current values supplied from the timing signal generation circuit 20 to the thermistor 10 for the variable constant current circuit 12, the amplifier circuit 14, the hold circuit 16, and the comparison circuit 18, respectively; A signal for monitoring a voltage change, that is, a temperature signal, to the thermistor 10 when current is supplied, a hold signal that provides a timing to hold the output of the amplifier circuit 14, and a signal that provides a comparison timing are uniformly supplied at predetermined intervals. .

Based on the output from the comparison circuit 18, the determination circuit 22 determines that a frost condensation state exists when the temperature increased portion is below a reference value. In addition, as mentioned above, in the case of detecting only frost, the ambient temperature T ₀ is 0°C.
The following conditions are added.

Figure 2A shows thermistor 1 in an actual device.
A perspective view of the exterior around 0 is shown. In the figure, the thermistor 10 has a support shaft 2 that passes through the side wall of a hook-shaped plate 24.
It is attached to the tip of 6.

In the non-frost and dew condensation state, the thermistor 10 is located in the air as shown in Figure B, but when frost and dew condensation occurs, the thermistor 10 is surrounded by frost and dew as shown in C. I can understand that.

Hereinafter, the operation of the device of the present invention will be explained with reference to FIG. 3, which shows a specific circuit configuration of the device according to FIG. 1.

In FIG. 3, a comparison reference current iA and a heating current iB are alternately supplied to the thermistor 10 from a variable constant current circuit 12 consisting of transistors Q ₁ and Q ₂ at different timings in time series.

A timing circuit 20 is provided to switch the variable constant current circuit 12, and the timing circuit 20 in the embodiment includes an oscillator 30 and a gate 32, and the two current values are adjusted according to the oscillation period of the oscillator 30. The supply timing of iA and iB is alternately switched.

That is, the output of the oscillator 30 is supplied from the gate 32 to the collectors of both transistors Q ₂ through the resistor 34, and when this output is "L", the current flows through the resistor 34 to the collector of the transistor Q ₂ . increase. Transistor Q ₁ ,
Q ₂ constitutes a current mirror and therefore,
The current value iA flowing through the collector of transistor _Q1 up to that point is increased to the heating current iB.

Further, the output of the thermistor 10 is connected to the negative input of the comparison circuit 18 as described above, and the output when the comparison reference current iA is supplied to the thermistor 10 is supplied to the amplifier 14.

The amplifier 14 in the embodiment is an amplifier circuit 36 thereof.
A changeover switch 38 is provided at the front stage of the
A switching signal that opens the switch 38 when the output of the oscillator 30 is "L" is supplied from the timing circuit 20 described above.

Therefore, the amplifier circuit 14 in the embodiment can take in only the output when the comparison reference current iA is supplied to the thermistor 10.

The output of the amplifier 14 is supplied to a hold circuit 16, and its output is supplied to the positive input terminal of the comparison circuit 18.

Therefore, the comparison circuit 18 uses the hold circuit 16 to temporally delay the output of the thermistor 10 when the comparison reference current iA and the heating current iB are respectively supplied to the thermistor 10 at different timings in time series. Both outputs are compared with their timings matched.

The amplification factor of the amplifier 14 is set so that the signal value supplied to the comparator circuit 18 in the non-frost condensation state is the same value, and as a result, the comparator circuit 18 has an output that is However, if frost condensation occurs on the thermistor 10, the negative input value of the comparator circuit 18 will decrease, so a signal corresponding to the heat generation temperature difference at this time is supplied to the second comparator 42, and the reference value is A signal is output when the temperature difference due to heat radiation exceeds a predetermined value.

As described above, according to the present embodiment, the frost condensation detection signal is output from the comparison circuit 18, but furthermore, in this embodiment, the zero temperature detection circuit 50 is provided for obtaining a signal at the time of frost formation. The output of the hold circuit 16, that is, the output of the thermistor 10 when the comparison reference current iA is supplied, is compared with a reference value, and a signal is output when the ambient temperature of the thermistor becomes 0° C. or less.

In the embodiment, both detection signals are ANDed together by gate 52 and fed to a processing circuit, not shown.

Here, when the comparison reference current iA is supplied to the thermistor 10, the negative input value of the first comparator 40 is lower than the positive input value by 1/α, so this difference is output to the second comparator 42. There is a risk that false signals of frost and dew condensation may occur.

For this reason, a switch 72 is connected downstream of the discrimination circuit 22. A timing signal from the oscillator 30 in the timing circuit 20 is supplied to the switch 72 via the gate 70.
By opening the switch 72 when the comparison reference current iA is flowing through the thermistor 10, malfunctions are prevented.

In addition, at the subsequent stage of the switch 72, there is a transistor Q 3 and a transistor Q ₃ whose collector and base are connected to Vcc.
_Q4 is connected, and the output from the discrimination circuit 22 is amplified and sent as a frost condensation notification signal to the subsequent processing circuit.

In the above embodiment, the case where the purpose is to detect only frost formation was explained as an example, but it is of course possible to detect both frost and dew condensation or only dew condensation by removing or changing each of the threshold levels. It is possible.

According to the present invention, the thermistor used as the frost condensation detection means is not easily affected by external fluctuations, is inexpensive, small, and has excellent mechanical strength, so it can be used very easily without increasing the size of the device. It is possible to realize highly reliable detection of frost condensation conditions.

FIG. 4 shows the configuration of a second embodiment of the device of the present invention.

The characteristic feature of this embodiment is that the output port signal of the μ-CPU 60 is used instead of the oscillation circuit to instruct the variable constant current circuit 12 to switch the current supplied to the thermistor, and the temperature signal detected from the thermistor 10 is transferred to the A/D converter. The feature is that the data is digitally converted by the converter 62 and then processed in the μ-CPU 60 all at once. μ−
The arithmetic processing results in the CPU 60 are output to the output circuit 6.
4 and is output as a frost condensation signal.

Although the arithmetic processing process of the detection signal is different, the basic principle of detecting frost and dew condensation state remains the same, and the same effect as in the first embodiment can be obtained.

[Effects of the Invention] As explained above, according to the present invention, the temperature difference caused by using a single thermistor and alternately supplying the heating current and the comparison reference current to the single thermistor can be used to reduce the heat generated during frost condensation. Since the configuration detects the occurrence of frost condensation based on the shrinkage caused by conduction, it is possible to provide a frost condensation detection device that is small, robust, inexpensive, and has excellent detection performance stability, and is free from external fluctuation factors. It is possible to realize reliable detection of frost condensation without causing malfunction due to the influence, without increasing the size of the device.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the device of the present invention, FIG. 2 is a diagram showing the structure of the detection unit according to the invention and the state at the time of frost condensation, and FIG. 3 is a circuit configuration diagram of the device according to FIG. FIG. 4 is a configuration diagram showing a second embodiment of the device of the present invention, and FIGS. 5 to 9 are configuration diagrams and characteristic diagrams of conventional frost condensation detection devices. 10...Thermistor, 12...Variable constant current circuit, 14...Amplification circuit, 16...Hold circuit,
18... Comparison circuit, 20... Timing signal generation circuit, 22... Discrimination circuit.

Claims (1)

[Scope of Claims] 1. A variable constant current source whose output current can be set to any value, a heating current that causes a temperature rise due to self-heating, and a comparative reference current that is so small that the temperature rise can be ignored. Calculate the temperature difference between the temperature-sensitive resistor alternately supplied from the variable constant current source and the temperature-sensitive resistor between when the heating current is supplied and when the comparison reference current is supplied, and this is determined based on a predetermined standard. What is claimed is: 1. A frost and dew condensation detection device, comprising: an arithmetic circuit that compares the temperature difference between the temperature-sensitive resistors with a reference value; 2. The frost condensation detection device according to claim 1,
A circuit that detects that the voltage value depending on the ambient temperature obtained when a comparison reference current is applied to a temperature-sensitive resistor is on the lower temperature side compared to the reference voltage value given by the freezing temperature of water. A frost condensation detection device further comprising: determining that the frost is present only when the ambient temperature is lower than the freezing temperature of water and the frost is present.