JPH041585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a firing angle control circuit for a thyristor element, and more specifically, a firing angle control circuit for a thyristor element in which the firing angle can be controlled by a digital circuit. Regarding.

For example, as a temperature control device for an electric furnace for a thermal analysis device, a thyristor is installed between a heater built into the electric furnace and an AC power source, and the firing angle of the thyristor is controlled. Temperature control devices that control the applied heating power and thereby perform heating control have been widely used. However, since this type of conventional control device controls the firing angle of the thyristor in an analog manner, it is susceptible to changes in ambient temperature or errors in circuit constants, and in addition, it is difficult to control the temperature setting. This method had some disadvantages, such as being difficult to perform accurately. This situation is a common problem not only in temperature control devices but also in motor rotational speed control and power control of other devices.

The object of the invention is therefore to provide a digitally controlled firing angle control circuit for a thyristor element, which eliminates the drawbacks of the prior art described above.

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

FIG. 1 shows an embodiment of a temperature control device using a firing angle control circuit for thyristor elements according to the present invention. The illustrated temperature control device 1 is a device for controlling the heating current of a heater 3 built into an electric furnace 2 and setting the temperature inside the electric furnace 2 to a predetermined set temperature. The heater 3 is connected to a commercial AC power source 5 via a bidirectional three-terminal thyristor (hereinafter simply referred to as thyristor) 4, and between the _T1 terminal of the thyristor 4 and the gate terminal G,
A firing pulse from the temperature control device 1 is applied in a manner described in more detail below, rendering the thyristor 4 conductive for a predetermined period of time during an AC half cycle.

The temperature control device 1 includes a thermocouple 6 that functions as a sensor for detecting the temperature inside the electric furnace 2. The output voltage from the thermocouple 6 is adjusted to a reference temperature by a reference temperature correction circuit 7 consisting of a resistance bridge circuit. After the correction is performed, the isolation amplifier 8
is input. The output from the isolation amplifier 8 is further amplified by an operational amplifier circuit 10 equipped with an offset adjustment circuit 9, input to an A/D converter 11, and converted into digital data _D1 . The A/D converter 11 receives a conversion start command CD ₁ from the central processing unit (CPU) 12.
The input analog signal is converted to digital data, and the message CD ₂ of the completion of conversion is sent to A/
When sent from the D converter 11 to the CPU 12,
Digital data _D1 indicating the temperature inside the electric furnace 2 is
Transferred to CPU 12. Furthermore, the data applied from the CPU 12 to the isolation amplifier 8
D ₂ is a signal for switching the gain of the isolation amplifier 8, and when the thermocouple 6 is switched to another type, the gain of the isolation amplifier 8 is switched according to the characteristics of the thermocouple, and the electric furnace It is possible to maintain a predetermined correspondence relationship between the temperature within 2 and the data _D1 .

The CPU 12 is connected to the key operation unit 13,
By operating the keys on the key operation unit 13, it is possible to enter data regarding instructions for temperature setting, changes in control characteristics, and the like.

The CPU 12 performs a PID calculation based on the actual furnace temperature and the set temperature, and calculates the heating power required to reach the desired set temperature.

In this temperature control device 1, as shown in FIG. 2a, a half cycle of the commercial power supply 5 is divided into 2000 equal parts, 2MHz clock pulses from the clock pulse generator 14 are counted by the counter 31 or 32, and the desired clock pulses are calculated. When the counter 31 or 32 counts the number of pulses corresponding to the firing angle θ, the counter 3
The thyristor 4 is configured to output an ignition pulse from the thyristor 1 or 32 to control conduction of the thyristor 4. Therefore, the calculation result from the CPU 12 is output as the number of pulses corresponding to the required firing angle θ.

For this reason, data indicating the relationship between the firing angle θ and the count number N is stored in the CPU 12, and after the desired firing angle is calculated by the CPU 12, the corresponding action is performed according to this data. The count number N is taken as output data and provided to the ignition control circuit 16 according to the invention.

The firing angle control circuit 16 has a timing detection circuit 17 for detecting the timing of the zero level point of the commercial AC voltage. Timing detection circuit 1
7 has light emitting diodes LED ₁ , LED ₂ connected to the power supply 5 with the polarity shown through a resistor R ₁ ,
Phototransistors Tr ₁ and Tr ₂ are provided corresponding to the light emitting diodes LED ₁ and LED ₂ , respectively. The collectors of each phototransistor Tr ₁ and Tr ₂ are connected to a DC power supply via resistors R ₂ and R ₃ , respectively, and the potential of each collector is applied to a NAND gate G ₁ . Therefore, only when the level of the AC voltage signal becomes zero and both the light emitting diodes LED ₁ and LED ₂ go out, both inputs of the NAND gate G ₁ become high level, and the output of the NAND gate G 1 becomes the AC signal. A timing signal TP that becomes low level is output only at the zero cross timing of (FIG. 2b).

This timing signal TP is applied to the preset terminal PR of the D-type flip-flop _DFF1 , and is also applied to the clock terminal CLK of the D-type flip-flop _DFF2 via the gate circuit _G2 . The D-type flip-flop _DFF1 has its D input terminal grounded, and the firing timing signal AP from the gate _G3 is input to its clock terminal CLK. The D input terminal D of the other D type flip-flop DFF ₂ receives a pulse signal from the CPU 12.
P ₁ is input (Figure 2c). This pulse signal _P1 is a pulse signal with the same frequency as the frequency of the commercial power supply, and if the level corresponding to one zero cross timing is "1", the level corresponding to the next zero cross timing will be A synchronization relationship with the commercial power supply waveform (FIG. 2a) has been established so that the signal becomes "0". Therefore, its Q output and output vary as shown in FIG. 2d and FIG. 2e, respectively. The Q and Q signals of the D-type flip-flop DFF ₂ are input to gates G ₄ and G ₅ , respectively.
Timing signal TP input via gate G ₆
will pass through gate G ₄ during the positive half cycle of the AC signal and through gate G ₅ during the negative half cycle of the AC signal.

That is, the D-type flip-flop _DFF2 and the gate
The circuit constituted by G ₂ , G ₄ , and G ₅ constitutes a timing signal distribution circuit that alternately distributes and applies the timing signal TP to the counters 31 and 32.

Reference numeral 30 designates a programmable general-purpose timer circuit comprising three independent counter circuits 31, 32, and 33, each of which receives a signal based on information stored in a control word register 34. The operating mode and counting method of the counter are set. Writing control to this register 34 is performed by the read/write control circuit 3.
5. In the illustrated embodiment,
Counters 31 and 32 are controlled to operate as rate generators, and counter 33 is controlled to operate as a programmable one-shot circuit.

Therefore, the counters 31 and 32 output an "L" level pulse for one clock every time n clock pulses CLP from the clock pulse generator 14 are input, and the output pulses are as follows: Taken out via gate G ₃ . CPU1
The data of the count number N output from 2 is temporarily placed in the data bus buffer 36.

Timing signal taken out via gate _G5
TP is applied to the counter 31, and during its zero level period, the counter number N placed in the data bus buffer 36 is set in the counter 31 as the value of n. Then, at the same time that the timing signal TP becomes high level, clock pulses from the clock pulse generator 14 start counting, and when the clock pulses from the clock pulse generator 14 are counted up to N, a low level pulse is outputted through the gate _G3 , and the ignition timing signal AP is output. is inputted into the counter 33 as (see FIG. 2 f).

When this ignition timing signal AP is output,
The counter 33, which works as a one shot multi,
An ignition pulse _P0 with a predetermined pulse width is output, the level is inverted by the NOT circuit 20, and the transistor 21
is turned on and applied to the thyristor 4 via the pulse transformer 22. Therefore, at time t= _t1, the thyristor becomes conductive and remains ON for period T.

In this case, the firing timing signal AP output at _t1 is also applied to the clock CLK of _DFF1 , thereby closing the gate _G6 . This makes it possible to reliably prevent the counter 33 from being triggered again during the period when it is operating as a one-shot multiple. The closed state of this gate _G6 is determined by the next timing signal TP.
is input, the Q terminal of DFF ₁ becomes “1”
and is canceled.

In this state, the timing signal TP is
The signal is input to the counter 32 via the gate _G4 , and the counter 32 performs the same ignition control operation as described above.

In this way, by providing two counters 31 and 32 with the same counting function and using them by switching them alternately, data from the CPU 12 can always be set to the counter that is not in use. Therefore, even if the operation of the counter is temporarily stopped during data setting, the firing angle control operation is not affected in any way, and control can be reliably performed in accordance with predetermined data.

Note that in this embodiment, the counter 31 and the counter 3
2 are used alternately, thereby eliminating the influence of the data set on the counting operation of the counter 31.

Programmable general-purpose timer circuit 30 as described above
For example, a commercially available IC
MSL8253P can be used.

In FIG. 1, 23 is a display panel for displaying input data etc. from the key operation unit 13;
24 is a meter for displaying data output from the D/A converter 25 and indicating the deviation value between the set temperature and the actual temperature.

With such a configuration, the firing angle of the thyristor can be controlled in accordance with the count number of the clock pulses, so if the frequency of the clock pulses is set high, the firing angle can be controlled extremely precisely and its setting can be performed extremely easily. Therefore, since highly accurate temperature control can be easily performed, a high-performance temperature control system can be constructed.

Also, if the relationship between the controlled power and the number of pulses N is made into a table and stored in the CPU 12 in advance,
Another advantage is that control in which the control power varies linearly can be performed extremely easily.

According to the present invention, as described above, since the firing angle can be controlled by a digital circuit, the firing angle can be set extremely accurately. It has significant advantages such as being more stable, less susceptible to changes in ambient temperature, and hardly changing over time. Furthermore, even when connected to a computer for control, it has the advantage that the interface circuit becomes extremely simple.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
Figures a through 2g are time charts for explaining the control operation of the apparatus shown in Figure 1. DESCRIPTION OF SYMBOLS 1... Temperature control device, 2... Electric furnace, 3... Heater, 4... Bidirectional 3-terminal thyristor (thyristor), 5... AC power supply, 6... Thermocouple, 12...
Central processing unit (CPU), 14... Clock pulse generator, 16... Firing angle control circuit, 17...
Timing detection circuit, 22...pulse transformer,
31, 32, 33... Counter, TP... Timing signal, AP... Firing timing signal, Po...
ignition pulse.

Claims (1)

[Claims] 1. The first
a timing detection circuit that outputs a timing signal through a gate; and a timing detection circuit that inputs the timing signal to a clock terminal;
A pulse signal having the same frequency as the frequency of the AC power supply from the CPU and having a phase shift is input to the D terminal, the output is turned on and off in synchronization with the input of the timing signal, and the signals Q and Q are inverted with each other. a second flip-flop that outputs a clock pulse; a clock pulse generator that outputs a clock pulse; and a clock pulse generator that counts clock pulses from the clock pulse generator, generates an ignition timing pulse when a predetermined number of clock pulses are counted, and outputs a one-shot signal via a third gate. the first and second counters output to a third counter working as a multiplier, the timing signal is input to a preset terminal, the ignition timing pulse passed through the third gate is input to a clock terminal, and the timing signal is input to a clock terminal; a first flip-flop that outputs a signal that turns on and off according to the firing timing pulse; and a fourth flip-flop that receives the first flip-flop signal and the Q signal of the second flip-flop and outputs it to the first counter. a gate, and a fifth gate that inputs the first flip-flop signal and the second flip-flop signal and outputs it to the second counter. a timing signal distribution circuit that operates one of the timing signal distribution circuits, the third counter converts the output of the first counter and the output of the second counter into a predetermined pulse in response to a signal via the third gate. 1. A firing angle control device for a thyristor element, characterized in that a firing pulse of a certain width is generated and the pulse is input to a bidirectional thyristor.