JPH0215084B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a temperature control circuit, and particularly to a temperature control circuit suitable for application to a temperature control section of a measuring instrument, an analytical measuring instrument, or the like. As temperature control methods, a direct control method and a time proportional control method are known. The direct control method consists of an amplifier that amplifies the output voltage of the temperature sensing element, a switch element driven by the output voltage of the amplifier, and a heating element connected in series with the switch element. The time proportional control method is equipped with an amplifier that amplifies the output voltage of the temperature sensing element, and drives the switch element by amplifying the voltage difference between the output voltage of the amplifier and the sawtooth wave voltage of a constant period. It is something to do. The present invention corresponds to the latter time proportional control method. An example of a conventional time proportional control method is shown in FIG. The output voltage of the bridge circuit 2 including the thermistor 1 enters a first amplifier 3. The output voltage of the first amplifier 3 is connected via a resistor 4 to the inverting input of the second amplifier 5. On the other hand, the in-phase input of the second amplifier 5 is connected to the output of a sawtooth wave voltage generator 6 having a constant period. A resistor 7 is connected to the inverting input and output terminal of the second amplifier 5, and the output side of the second amplifier 5 is connected to the base of a transistor 9 via a resistor 8. The emitter of transistor 9 is grounded,
The collector enters one end of the drive side of the zero cross switch 11, and the other end is connected to a DC power source via a resistor 10. One end of the output side of the zero cross switch 11 is connected to the main AC power supply 13, and the other end is connected to the heater 12.
It is connected to the other end of the main AC power supply via. The time proportional control method has short ON/OFF cycles and repeats ON/OFF every approximately 1 second, so there is no overheating or overcooling, and the advantage is that the temperature control range is extremely small. Since the temperature control width is small in the vicinity, the signal that drives the switch element is also small, and because a sufficient control signal cannot be obtained, the trigger used for the switch element is not activated in both waves but in a half-wave firing state. It had For this reason, when a large-capacity heating element is used, a large current is supplied only in a half-wave from the main AC power supply, which deteriorates the power supply condition and has the disadvantage that good temperature control cannot be achieved. SUMMARY OF THE INVENTION An object of the present invention is to provide a temperature control circuit that can satisfactorily control the temperature without adversely affecting the AC power supply even if the temperature control width near the set temperature is small. The present invention has confirmed through experiments that half-wave ignition occurs when the drive current of the switch element is small, and as a means to eliminate this half-wave ignition, the main AC power supply is completely turned on and off in units of one cycle. This is how it was done. In a preferred embodiment of the present invention, a temperature detection circuit having a temperature sensing element and a temperature setting resistor; a first amplification circuit for amplifying the output voltage of the temperature detection circuit;
A second amplification circuit that compares and amplifies the output voltage of the first amplification circuit and a sawtooth wave voltage generation circuit for performing time proportional control, and a timing signal whose period is one cycle of the main AC power supply. A generation circuit, a determination circuit that determines whether the output voltage of the second amplification circuit is high level or low level, and a holding circuit that maintains the output of this determination circuit until it is established by a timing signal and the next timing signal is input. , a zero-cross switch driven by the output signal of the holding circuit, and a heater circuit that is turned on and off by the zero-cross switch. In a preferred embodiment of the present invention, the timing signal generating circuit is one that half-wave rectifies the main AC power supply and uses the half-wave rectified voltage as the timing signal source. The analog output of the second amplifier circuit is connected to the D terminal of the D-type flip-flop to determine whether the analog output voltage is high or low. A timing signal generation circuit is connected to the T terminal of the D-type flip-flop, and the output of the determination circuit is established by the timing signal and held until the next timing signal is input. As the timing signal generation circuit, a circuit that obtains the timing signal by half-wave rectifying the main AC power supply and further dividing the half-wave rectified voltage into ²ⁿ can also be used. Prior to describing the embodiments of the present invention, knowledge obtained through experiments by the inventors regarding the conventional temperature control circuit as shown in FIG. 1 will be explained with reference to FIGS. 2a to 4c. When the circuit of FIG. 1 is in the control state, the voltage waveforms of the output voltage 3' of the first amplifier 3 and the sawtooth voltage 6' are as shown in FIG. The output voltage 5' is as shown in FIG. 2b. In FIG. 2b, the current waveforms flowing through the transistor 9 and zero cross switch 11 are also similar. When the set temperature is low (L), the time the zero cross switch 11 is turned on is _t1 , and when the set temperature is high (H), it is _t2 . However, the problem is the current waveform to the zero cross switch at times t ₁ and t ₂ mentioned above, which is not completely turned on. Second amplifier 5 and transistor 9
Also a linear amplifier is more than these times completely
It cannot be turned ON. When the waveform becomes as shown in FIG. 2b, the zero-cross switch 11 conducts only a half-wave of the main AC power supply 13 when the ON time ends without the zero-cross switch being completely turned on. This is due to the following reasons. As shown in FIG. 3, the interior of the zero cross switch 11 generally includes a light emitting element D, a light receiving element, a zero cross detection circuit, a triac _TR and its gate circuit A. When sufficient current flows through the light emitting diode D, the output voltage of the gate circuit A is
Since E _g is also large enough, triac T _R can be fired sufficiently. However, light emitting diode D
When the current of is small, the output voltage of gate circuit A
E _g also becomes smaller. On the other hand, as a characteristic of the triax, the firing state changes depending on the polarity of the voltage applied to the electrodes T ₁ and T ₂ and the gate G. For example, as shown in Table 1, when the polarity of the main AC power supply 13 is positive on the electrode T ₁ side and negative on the T ₂ side, it will turn on.

[Table] Gate voltage E _g12 required for arc is main AC power supply 1
Voltage required for ignition when the polarity of 3 is reversed
E It is smaller than _g21 . In other words, when the gate voltage becomes small, a state occurs in which ignition occurs only on a half wave of the main AC power source 13. Figures 4a to 4c explain this state. Figure 4a shows the voltage waveform of the main AC power supply in Figure 3, and Figure 4b shows the output voltage E _g of the gate circuit A in Figure 3. The figure shown in FIG. 4c is a voltage waveform diagram supplied to the heater 12. The gate voltage is P ₁ ,
Heater 1 when it is sufficiently larger than E _g21 like P ₂
2 is supplied with a full wave. Gate voltage is P ₃ , P ₄
Even if the size is the same as E _g21 , a full wave is still supplied. However, as the gate voltage is P ₅ to P ₈ , E _g21 ＞E _g ＞
When E _g12 , only half wave is fired. When the gate voltage becomes small such as P ₉ and P ₁₀ , even though voltage is applied to the gate, it is not ignited and no voltage is applied to the heater. The structure of the present invention was conceived in view of the above findings. FIG. 5 is an explanatory diagram for explaining the configuration of an embodiment of the present invention. Components having similar functions to those in FIG. 1 are given the same reference numerals. In FIG. 5, the collector of transistor 9 has a load resistor 20 and a D-type flip-flop 21.
The D terminal of is connected. Half-wave rectification is performed by a transformer 24 and a diode 25, and the base of a transistor 27 is driven by the half-wave rectified voltage, and a timing signal equal to the frequency of the main AC power source is generated from the collector of the transistor 27. The timing signal produced by transistor 27 is connected to the T terminal of the D-type flip-flop. The output terminal of the D-type flip-flop 21 is connected to the base of a transistor 23 via a resistor 22. The collector of the transistor 23 is connected to one input terminal of the zero-cross switch 11, and the other input terminal of the zero-cross switch 11 is configured to be connected to a DC power supply via a resistor. 26 and 28 are resistors. Next, the operation will be explained. Figure 6a is an output waveform diagram of the transformer 24 in Figure 5, Figure 6b is an output waveform diagram of the transistor 27, Figure 6c is an analog voltage waveform diagram entering the D terminal of the flip-flop, and Figure 6d is an output waveform diagram of the flip-flop. ,
FIG. 6e is a waveform diagram of the AC voltage supplied to the heater. The operation in which the transistor 9 is driven by the output voltage of the second amplifier 5 is similar to the example shown in FIG. The D-type flip-flop 21 receives the signal voltage as either an H level or an L level. Therefore, the output terminal of the D type flip-flop also outputs either H or L. D type flip-flop 21
reads the data input from the D terminal using the timing signal from the T terminal and holds that state until the next timing signal is input, so the drive side of the zero-cross switch 11 is completely turned on for a period of time equivalent to one cycle of the main AC power supply. Or turn it off. Therefore, the output side of the zero cross switch completely turns on one cycle of the main AC power supply by zero cross operation.
Or keep it OFF. transistor 2
The voltage output of 7 is directly connected to the D type flip-flop 2.
It may be connected to the T terminal of 1, but it is also possible to divide the output voltage into 2 ⁿ and then connect it to the T terminal. According to the present invention, it is possible to eliminate the switch ignition caused by only a half wave of the AC power supply, and there is no possibility that the zero cross switch will not operate completely even if the temperature control force near the set temperature is small, which will have an adverse effect on the AC power supply. Good temperature control can be achieved without any problems.

[Brief explanation of drawings]

Figure 1 shows a conventional temperature control circuit; Figure 2a shows a conventional temperature control circuit;
The figure is a waveform diagram of the output voltage of the first amplifier and the output voltage of the sawtooth wave generator in Figure 1, and Figure 2b is a waveform diagram of the output voltage of the first amplifier in Figure 1.
3 is a detailed explanatory diagram of the vicinity of the zero-cross switch in FIG. 1, and FIGS. 4a to 4c are diagrams illustrating the firing state of the zero-cross switch in FIG. 3. Figure 4a is a voltage waveform diagram of the main AC power supply, Figure 4b is a diagram for
The figure shows the output voltage of the gate circuit, Figure 4c is a voltage waveform diagram supplied to the heater, Figure 5 is a circuit diagram of an embodiment of the present invention, and Figures 6a to 6e are explanations of the operation of Figure 5. 6a is a diagram of the output waveform of the transformer, FIG. 6b is a diagram of the output waveform of the transistor of the timing signal generation circuit, and FIG. 6c is a diagram of the analog input voltage waveform at the D terminal of the flip-flop.
Figure 6d is a flip-flop output waveform diagram,
Figure e is an AC voltage waveform diagram supplied to the heater. DESCRIPTION OF SYMBOLS 1... Thermistor, 3, 5... Amplifier, 6... Sawtooth wave generator, 11... Zero cross switch, 12... Heater, 13... Main AC power supply, 21... D type flip-flop, 24... Transformer, 25... diode.

Claims (1)

[Claims] 1. Amplifying means for amplifying the difference between the output voltage based on the temperature detection circuit having a temperature sensing element and the output voltage of the sawtooth voltage generating circuit, and selecting an AC power source for the heater element according to the output of this amplifying means. In the temperature control circuit, a temperature control circuit is provided with a zero-cross switch means that conducts electrically, and a temperature control circuit is provided between the amplifying means and the zero-cross switch means, in which the amplifying means responds to the amplifying means at the time of the previous timing signal until the next timing signal arrives. A temperature control circuit characterized in that a holding means for holding an output state is provided, and a timing signal generating circuit is provided for supplying a timing signal having a cycle of one cycle of the AC voltage of the AC power source to the holding means.