JPS6223415B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a temperature detection circuit. [Technical Background of the Invention and Problems Therewith] In recent years, with the spread of microcomputers, it has become common to use them to control the temperature of air conditioners and the like. Figure 1 shows an example of the circuit configuration.
, a bridge circuit, and a comparator C to form two sets of temperature signals, that is, a setting signal and a detection signal, which are compared and the compressor C is operated according to the comparison result.
This will be explained in detail. The 3-bit digital signal appearing at the output terminals _A1 to _A3 of the microcomputer MC is applied to a superimposed circuit consisting of resistors _R1 to _R3 to form a staircase wave, which is applied to a bridge circuit having a variable resistor VR. A bridge circuit is balanced when it is a staircase wave or at a certain level, and becomes unbalanced when it is outside that level. Therefore, the output of the comparator C ₁ becomes O ₁ or 1, and this output is applied to the input terminal I ₁ of the microcomputer MC. This corresponds to the set temperature. On the other hand, a 3-bit digital signal is applied from the output terminals A ₄ to _{A 6} of the microcomputer MC to a bridge circuit having a thermistor TH, and is sent to the input terminal of the microcomputer MC via the comparator C ₂ of the output of this bridge circuit. Given to I ₂ . As a result, the microcomputer MC internally compares the inputs of the two input terminals I ₁ and I ₂ , and
For example, when the detected temperature is high, the transistor Q
Turn relay RY on and off via , and operate compressor C until the two inputs are balanced. Here, since this circuit performs two sets of A-D conversion, there is a possibility that errors peculiar to digital circuits will appear twice as much, and there is a drawback that detection accuracy is poor. Furthermore, since there are two A-D converters, the circuit configuration becomes complicated, and it becomes even more complicated to further improve the detection accuracy. Also, inside the microcomputer, two sets of A
-D conversion and comparison of two inputs I ₁ and I ₂ are required, which poses a problem in that internal processing becomes complicated. [Object of the Invention] The present invention has high detection accuracy. Another object of the present invention is to provide a temperature detection circuit using a microcomputer and having a simple circuit configuration. [Summary of the Invention] The present invention provides a staircase wave output from a predetermined bit output terminal of a microcomputer through a resistor superimposition circuit to a bridge circuit incorporating a temperature setting element and a temperature detection element, and outputs two steps from this bridge circuit.
Compare the two outputs with a comparator, input this comparison output to a microcomputer, and determine from the comparator output and bit output contents whether the difference between the set temperature and the detected temperature is within the temperature difference range divided by the staircase wave output. This is a temperature detection circuit that detects whether it belongs to a certain part. [Embodiments of the Invention] Examples of the present invention will be described below with reference to FIGS. 2 and 3. FIG. 2 shows an embodiment of the present invention, in which a variable resistor VR for temperature setting and a thermistor TH for temperature detection are incorporated into one bridge circuit, and the output terminal A of the microcomputer MC is connected to the bridge circuit. ₁ and _A2 , and the output thereof is applied to the input terminal _I1 of the microcomputer MC via a comparator C. In this case, the variable resistor VR and thermistor TH are inserted into the same arm of the bridge circuit, but it goes without saying that this can be modified as appropriate depending on how the general bridge circuit is used. FIG. 3 is a circuit diagram of main parts mainly including the bridge circuit and comparator C shown in FIG. 2, and the operation will be explained with reference to FIG. Here resistance R ₁ ,
It is assumed that R ₂ has a relationship of R ₁ > R ₂ .

[Table] The bridge circuit changes in four stages depending on the opening and closing of A ₁ and A ₂ . This four-step change is a change in the resistance value of one piece of the bridge circuit, and this appears as a change in voltage at the terminal of the comparator C of the bridge circuit. This change from state to state corresponds to the value of the difference between the set temperature and the detected temperature. That is, the set temperature T _A (°C), the detected temperature T _B
(°C), then in this bridge circuit, the state is T _A −T _B −α, the state is T _A −T _B , and the state is T _A
-T _B +β, the state corresponds to T _A -T _B +γ.
However, α, β, and γ are constants determined by the resistances R ₁ and R ₂ and have the relationship β<γ. Each state is successively compared with a fixed value by comparator C, and the change in the output of comparator C is detected by the microcomputer.
The temperature is processed by the MC, and the difference between the detected temperature and the set temperature is detected. The detection results using this microcomputer are shown in the table below.

[Table] In this embodiment, when the detected temperature T _A is higher than the set temperature T _B , the relay RY is turned on. Thereby, for example, the operation of the compressor of an air conditioner can be controlled. Although the above embodiment simply turns on and off the relay RY at the point where the detected temperature and the set temperature match, the temperature detection circuit of the present invention is suitable for more complex relay control. This is because the temperature detection circuit of the present invention detects which of a plurality of ranges the difference between the detected temperature and the set temperature belongs to, and performs fine control according to the difference between the detected temperature T _A and the set temperature T _B. This is extremely useful for cooling and heating equipment that requires Further, in this embodiment, the resistor superimposed circuit is constructed with a 2-bit configuration, and the detection results are divided into five stages. However, by increasing the number of bits, the detection results can be further divided. By appropriately selecting the resistance value of the resistor superimposed circuit, it becomes possible to arbitrarily set the classification of the difference between the detected temperature and the set temperature. [Effects of the Invention] Since the present invention incorporates a temperature setting element and a temperature detection element into one set of bridge circuits, the number of bridge circuits, comparators, etc. can be halved compared to conventional circuits of this type, and the number of microcomputer The number of input/output ports is small, making wiring easy. In addition, the balance point of the bridge circuit is digitally detected according to the staircase wave output based on the digital signal output by the microcomputer, and the range in which the difference between the detected temperature and the set temperature falls is detected, making it possible to perform complex relay control based on temperature. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a temperature detection circuit using a conventional microcomputer, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a simplified circuit diagram of the circuit of FIG. TH...thermistor, VR...variable resistor, C...
comparator.

Claims (1)

[Claims] 1. A staircase wave output is applied from a predetermined bit output terminal of the microcomputer via a resistor superimposition circuit to a bridge circuit incorporating a temperature setting element and a temperature detection element, and the two outputs from this bridge circuit are compared by a comparator. This comparator output is input to the microcomputer, and the microcomputer determines the difference between the set temperature of the temperature setting element and the detected temperature of the temperature detection element from the bit output content of the output terminal when the comparator output changes. A temperature detection circuit characterized by detecting a range.