JPH042865B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refrigerator control device suitable for a refrigerator that has a wide temperature control range and requires strict temperature accuracy.

For refrigerators that have a wide temperature control range (-25°C to +25°C) and require strict temperature accuracy, such as refrigeration units for marine transportation, the temperature detection element for temperature control is usually Platinum resistance thermometers are used because they have high precision and excellent linearity, but from a practical standpoint, they also have the following drawbacks.

(1) It must be an extremely expensive element.

(2) Because the temperature coefficient is small (approximately 0.4Ω/°C), it is easily affected by the resistance of the lead wires and the contact resistance of the connection parts, which may reduce accuracy and reduce stability (reliability). It becomes a problem on the surface.

(3) Methods to improve the drawback of (2) above include a method of compensating for error resistance in the adjustment stage and a method of using a bridge circuit configuration (4-wire type). It is powerless against changes in contact resistance due to influences, and the latter has the disadvantage of further increasing the already expensive nature.

The present invention has been proposed in view of the above points, and its purpose is to provide an inexpensive, high-performance temperature control device for use in refrigerators that have a wide temperature control range and require strong temperature accuracy. The aim is to realize something that is accurate and highly reliable.

The present invention provides a refrigerator equipped with a temperature control circuit that detects the temperature of air to be controlled with a temperature detection element, and controls the operation of a compressor by comparing the detected value with a set value set by a temperature setting device. In the control device for
As the temperature detecting element, a temperature detecting element having a non-linear output characteristic with respect to temperature in the temperature control range required for the refrigerator is used, and the non-linear output characteristic of the temperature detecting element is converted into a linear one. The temperature control circuit has a temperature correction circuit that corrects output characteristics, and controls the operation of the compressor by comparing an output value from the temperature correction circuit with a set value of the temperature setting device. The gist is a control device for a refrigerator that is characterized by its low cost, generally used as a temperature detection element, and usually has a wide temperature control range, and when temperature accuracy is strictly required.
We use an element with non-linear output characteristics at temperatures where non-linearity is noticeable and accuracy cannot be ensured as is, and a temperature correction circuit is installed to correct the non-linear characteristics of this element to linear characteristics. By doing so, problems in terms of accuracy are covered, so that it is possible to obtain a control device that is inexpensive, highly accurate, and highly reliable.

The present invention will be explained below based on examples.

In FIGS. 1 to 4, 1 is a compressor, 2 is a condenser, 3 is a throttle device, and 4 is an evaporator, which constitute a refrigeration cycle. Reference numeral 5 denotes a control device that controls the compressor 1 via a temperature control circuit 8 based on the temperature detected by the thermistor resistance thermometer 7 that detects the temperature of the indoor air 6 and the temperature set by the digital temperature setting device 9. It has become possible to control ON/OFF. In addition, in the above-mentioned refrigeration cycle and control device, only relevant parts are shown and other parts are omitted.

Figure 2 shows the temperature detection circuit, where V ₁ is a constant voltage source and V ₂
is the bridge output voltage, R ₁ is the series resistance, Rt is the internal temperature air resistance, AD ₁ is the analog/digital converter, and Dt ₁ is the nonlinear internal temperature digital quantity.

FIG. 3 shows a temperature correction circuit, which has a correction temperature digital value storage circuit 10, a linear correction amount selection circuit 11, and an addition circuit 12, and converts a non-linear internal temperature digital value Dt ₁ into a linear internal temperature This is a circuit that corrects the digital amount Dt.

Figure 4 shows a temperature comparison circuit, in which the internal temperature digital amount Dt and the set temperature digital amount Ds are measured by a comparator C.
When the internal temperature digital amount Dt is large, an operation command is issued to the compressor 1, and when it is small, a stop command is issued.

In the above configuration, the high-temperature, high-pressure refrigerant gas compressed by the compressor 1 which is operated in response to instructions from the refrigerator control device 5 radiates heat in the condenser 2, is condensed and liquefied, and reaches the expansion device 3. The depressurized refrigerant enters the evaporator 4, and the indoor air 6 flowing through the evaporator 4
It absorbs more heat, evaporates and vaporizes, and returns to the compressor 1, completing the refrigeration cycle.

During this period, the temperature inside the refrigerator air 6 has a nonlinear temperature-resistance characteristic, and the temperature coefficient is several hundred Ω/℃.
This is sensed as resistance by the large thermistor resistance temperature detector 7. This sensed resistance is converted and detected by the temperature control circuit 8 and compared with the set temperature digital amount Ds of the digital temperature setter 9. When the temperature inside the refrigerator becomes lower than the set temperature digital amount Ds, the temperature control circuit 8 stops the operation of the compressor 1 and stops the cooling operation. Further, when the temperature inside the refrigerator increases due to heat intrusion from the outside and becomes higher than the set temperature digital amount Ds, the temperature control circuit 8 issues an operation command to the compressor 1 again and restarts the cooling operation.

The operation of the temperature control circuit 8 is shown below in Figure 2.
This will be explained with reference to FIG.

Figure 2a shows a temperature detection circuit in which when the power is turned on and the constant voltage source _V1 is activated, the bridge output voltage _V2 has a correlation with the internal temperature air resistance Rt sensed by the thermistor resistance temperature detector 7. A non-linear voltage is generated.

Fig. 2b shows the relationship between the internal temperature air resistance Rt and the internal temperature, Fig. 2c shows the relationship between the output voltage V ₂ and the internal temperature (non-linear voltage), and Fig. 2d shows the digital It shows the relationship between the amount Dt ₁ and the internal temperature (non-linear internal temperature digital quantity).

In this circuit, the bridge output voltage V ₂ is determined by the following equation.

Bridge output voltage V ₂ = Series resistance R ₁ / Thermistor resistance temperature detector resistance Rt + Series resistance R ₁ × Voltage of constant voltage source V ₁ Note that the above equation originally includes the thermistor resistance temperature detector 7.
Although the lead wire resistance and the contact resistance of the connection part are taken into account, the thermistor resistance temperature detector 7 has a large temperature coefficient.
Therefore, it has been omitted because it has no effect even if ignored. Further, in this example, a temperature sensing element with negative characteristics is used.

Now, the non-linear bridge output voltage _V2 , which has a correlation with this temperature, is compared with the set temperature digital value Ds of the digital temperature setting device 9, and in order to match the level, it is converted to the internal air temperature using the analog/digital converter _AD1 . It is converted into a correlated, non-linear internal temperature digital quantity Dt ₁ . Next, Fig. 3a shows a temperature correction circuit, and the non-linear internal temperature digital quantity _Dt1 detected by the temperature detection circuit of Fig. 2a is made easier to compare with the more linear set temperature digital quantity Ds. A correction temperature digital quantity memory is taken into the linearization correction amount selection circuit 11 for the purpose of the present invention, and the linearization correction amount selection circuit 11 predefines the temperature error amount from the straight line of the standard thermistor resistance temperature detector 7. A corrected temperature digital quantity corresponding to the non-linear refrigerator temperature digital quantity Dt ₁ is selected from the circuit 10, and added to the non-linear refrigerator temperature digital quantity Dt ₁ by the adder circuit 12 to obtain a linear refrigerator temperature digital quantity Dt 1. The internal temperature is corrected to the digital quantity Dt. FIG. 3b shows the relationship between the internal temperature digital quantity Dt and the internal temperature (linear internal temperature digital quantity). Next, Fig. 4 shows a comparison circuit, and the internal temperature digital amount Dt linearly corrected by the temperature correction circuit shown in Fig. 3a is the set temperature digital amount Ds.
is compared with comparator C, and the internal temperature digital quantity is calculated.
If Dt is large, an operation command is issued to compressor 1.
If the temperature is too small, a stop command is issued to the compressor 1 to control the temperature.

As described above, in this embodiment, the following effects can be obtained because a control device that uses a thermistor resistance temperature detector that is inexpensive and has a large temperature coefficient and is digitally corrected is used.

(1) Accuracy equivalent to that obtained when using a platinum resistance thermometer is obtained.

(2) Temperature errors due to lead wire resistance and connection resistance are eliminated, improving stability (reliability).

(3) Since an inexpensive temperature detection element is used, the overall cost can be reduced.

In the above embodiment, a thermistor resistance temperature detector is used as an example of the temperature detection element, but the temperature detection element is not limited to this. It does not matter if it is an element. Furthermore, it is not necessary to limit the element to one whose output is a "resistance change" with respect to temperature, but may be one whose output is a "voltage change" such as a semiconductor temperature detection element, for example.

[Brief explanation of drawings]

Figures 1 to 4 show an embodiment of the present invention, in which Figure 1 is a configuration diagram of a refrigerator, Figures 2 a, b,
c and d are diagrams showing the temperature detection circuit, a is a circuit diagram,
b is a diagram showing the relationship between internal temperature air resistance and internal temperature; c is a diagram showing the relationship between output voltage and internal temperature;
d is a diagram showing the relationship between the non-linear digital quantity and the temperature inside the refrigerator, Figure 3 a and b are diagrams showing the temperature correction circuit, a is a circuit diagram, and b is a diagram showing the relationship between the linear digital quantity and the temperature inside the refrigerator. FIG. 4 is a circuit diagram of a temperature comparison circuit. 1: Compressor, 2: Condenser, 3: Squeezing device, 4:
Evaporator, 5: Control device, 7: Thermistor resistance temperature detector, 8: Temperature control circuit, 9: Digital temperature setting device, 10: Correction temperature digital quantity storage circuit, 1
1: Linearization correction amount selection circuit, 12: Addition circuit.

Claims (1)

[Claims] 1. A refrigerator control device equipped with a temperature control circuit that detects the temperature of the air to be controlled using a temperature detection element, and controls the operation of a compressor by comparing the detected value with a set value set by a temperature setting device. In this method, a temperature detection element having a non-linear output characteristic with respect to temperature in the temperature control range required for the refrigerator is used as the temperature detection element, and the non-linear output characteristic of the temperature detection element is converted into a linear one. the temperature control circuit which controls the operation of the compressor by comparing an output value from the temperature correction circuit with a set value of the temperature setting device; A control device for a refrigerator characterized by the following.