JPS5936737B2 - Temperature control device with zero volt switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device using a so-called zero volt switch (ZVS).

The zero-volt switch is a device developed as a defense against RFI (radio frequency interference). Focusing on the fact that RFI in phase control systems such as triacs and SCRs is caused by a sudden rise in circuit current, the zero-volt switch
A trigger pulse is sent to the thyristor at the moment when the 0ΠZ or 60H2 sine wave reaches zero volts (this is called a zero cross) to reduce the rate of increase in current. In reality, considering the response of the circuit, a certain time width is allowed before and after the zero cross, rather than the literal zero cross, and a rectangular pulse is extracted as the trigger output. A circuit that is already known as a temperature control device using this zero-volt switch IC turns the controlled object on and off at a set temperature determined by a thermistor, etc.
Therefore, if the capacity of the controlled object fluctuates, the capacity of the heater does not match the capacity of the controlled object, resulting in a large temperature fluctuation range.

For example, in the developing section of a diazo dry copying machine, the color development efficiency of diazo photosensitive paper changes depending on the ratio of moisture to ammonia content, so it is necessary to keep this ratio constant in order to obtain the best color development efficiency. For this purpose, it is sufficient to keep the temperature constant, but the amount of ammonia water supplied varies depending on the copy printing speed. Therefore, it becomes necessary to control the heater capacity according to the amount of ammonia water supplied. An object of the present invention is to accurately control a controlled object according to its capacity without high-frequency interference, and embodiments shown in the drawings will be described below.

FIG. 1 shows a developing section of a diazo dry type copying machine, in which aqueous ammonia 10' is sent from an ammonia tank 10 to an evaporation tank 12 by a supply pump 11. The amount of ammonia water supplied at this time is varied depending on the copy printing speed. The ammonia water sent to evaporation tank 1
2 and is heated by the heater 13 to generate ammonia gas 14. Ammonia gas is sent into a developing tank 16 by a circulation fan 15 to color the diazo photosensitive paper. The coloring efficiency of diazo photosensitive paper changes depending on the ratio of water and ammonia content, so in order to maximize the coloring efficiency, it is necessary to maintain this ratio at a certain constant level. In order to keep the ratio of water and ammonia in the ammonia gas constant, it is sufficient to keep the temperature at point A constant. FIG. 2 shows the circuit of a temperature control device for this purpose, where ZVS is a zero-volt switch 1C1, such as CA3O58 made by RCA, and 20 is a triac connected in series with the heater 13.

21 is an oscillation circuit consisting of two timer circuits, and as shown in FIG. 3, the relay 22 is periodically set to 0N. 0FF control.

In this case, the first timer circuit is the ON time t of the relay 22.
1, and the second timer circuit determines the 0FF time T2 of the relay 22, and the 0N time t1 can be changed by the variable resistor R1. The zero volt switch ZVS is connected to the power supply V via the normally open contact 222 of this relay 22, and is therefore controlled according to the opening and closing of the contact 22', and is energized only when the relay 22 becomes ON. Zero volt switch ZVS control input terminal "2" 13,1
A variable resistor R2 for setting the temperature at point A is connected between ``13, 141, 7, 8'', and a thermistor R3 as a heat-sensitive element is connected between ``13, 141, 7, 8''. The resistance value of the thermistor R3 changes depending on the temperature at point A in FIG. The output terminal "41" of the ZVS is connected to the gate of the triac 20. Next, the operation of the circuit shown in FIG. 2 will be explained.

First, it is assumed that R1 is constant, and R2 is set to the target temperature at point A in relation to R3. When the power supply V is turned on, the oscillation circuit 21 is energized and the relay 22 is set to 0N as shown in Figure 3.
．． Controlled to 0FF. Therefore zero volt switch ZVS
Also contact point 22! Similarly controlled by . At this point, the temperature at point A is still low, so the resistance value of thermistor R3 is relatively large. Relay contact 22
When the power supply V crosses zero during the time t1 during which ZVS is energized via
3 is energized. Triac 20 remains conductive until contact 22' is opened or the resistance of thermistor R3 decreases to a predetermined value. Therefore, while the temperature at point A is low, the heater 13 is controlled according to the ON time t1 and OFF time of the relay 22 determined by the timer in the oscillation circuit 21. In order to accelerate the temperature rise, change the variable resistor R1 to lengthen t1. When the temperature at point A exceeds a predetermined temperature, the resistance value of the thermistor R3 falls below the reference value, so the zero volt switch ZVS does not work even if the contact 22' is closed.

Triac 20 is thus turned off during one cycle of the power supply, and heater 13 is not energized even though contact 22' is closed. That is, while the temperature at point A is above a predetermined temperature, the operations of the relay and relay contacts are unrelated to the operations of the ZVS and triax, and the heater 13 is not energized by the relay 22. When the temperature at point A decreases, the value of thermistor R3 increases and ZVS becomes activated in response to relay contact 22'.

Therefore, the heater 13 is again set to 0N by the relay 22. 0F
F controlled. Next, a case will be described in which the variable resistor R1 is changed depending on the amount of ammonia water supplied.

Since the amount of ammonia water supplied changes depending on the copy printing speed, it is actually advantageous to change R1 depending on the copy printing speed. Supply amount of ammonia water and heating it
The electric power of the heater 13 required to keep the temperature at a constant point changes linearly.

Now, if R1 is changed by a value corresponding to the increase in ammonia water and the 0N time t1 of the relay 22 is increased,
Accordingly, the conduction time of the triax, i.e. the heater 13
The energizing time becomes longer. In the opposite case, the energization time of the heater 13 becomes shorter. Therefore, varying the ON time t1 of the relay 22 means that the energization time of the heater,
In other words, this is nothing but controlling the average power consumption. Therefore, by adjusting the variable resistor R1, it is possible to supply electric power to the heater 13 that matches the amount of ammonia water supplied. As described above, according to the present invention, even when the capacity of the controlled object changes, it is possible to form a heater with a capacity that apparently matches the capacity each time, and it also has a temperature adjustment function using a thermistor at point A. This makes it possible to control the temperature of the soil with very high precision, within 1°C.

Of course, the set temperature can also be changed arbitrarily by changing the value of R2. Also, since a zero volt switch is used, there is no high frequency interference. By configuring the variable resistor R1 to change in conjunction with the copy burning speed, temperature control can be automatically performed in accordance with changes in the supply amount of ammonia water (changes in the capacity of the controlled object).

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the developing section of a diazo dry copying machine to which the temperature control device according to the present invention is applied, Fig. 2 is an electric circuit of the temperature control device according to the present invention, and Fig. 3 shows the operation of the timer in Fig. This is a time chart. 13... Heater, 14... Ammonia gas, 20... Triack, 21...
・Oscillation circuit, 22...Relay, 225...
・・Contact, ZVS・・・・Zero volt switch, R
l, R2...Variable resistor, R3...Thermistor.

Claims (1)

[Claims] 1. a zero-volt switch, a temperature-setting variable resistor connected to a first input terminal of the zero-volt switch, and a heat-sensitive element connected to a second input terminal of the zero-volt switch to sense the temperature of a controlled object; A contact point for controlling opening/closing of the power supply circuit of the zero volt switch, and
an oscillation circuit having a timer for performing N/OFF control and setting its ON time and OFF time; means for changing the ON time of the contact by the timer according to a change in the capacitance of the controlled object; and an oscillation circuit connected in series with the heater to be controlled A temperature control device using a zero volt switch, comprising: a semiconductor controlled rectifier element connected to the device and ignited by the zero volt switch.