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China Micro Thermal Switches & thermostat manufacturer

Self-made Pressure Regulating Electric Oven Thermostat Temperature Control Circuit

In production and scientific research, electric oven thermostats are widely used, and temperature measurement and control accuracy are also required. In the application, when the thermostat controller cuts off the electric power of the electric furnace wire, the temperature continues to rise by more than 5 ° C ~ 15 ° C due to the thermal inertia of the electric furnace wire, which is the cause of over temperature. In many places where the incubator is used, only the temperature inside the box is allowed to vary between ±0.5 °C and ±1 °C, such as microbial culture and hatching of chicks.

According to this requirement, the "regulation temperature control circuit" introduced in this paper can be used. It has high temperature control precision, simple and practical circuit, and can be used for constant temperature control below 300 °C, ±O.1 °C ~ ±0.5 °C, and can also be used for early oven technical transformation.

The electrical principle is shown in the drawing. The voltage regulating temperature control circuit is composed of two parts, wherein the two-way thyristor VS, the adjustable electric contact glass mercury thermometer T and the double adjustment network composed of Rl, R2, RP, R3, Cl, C2; The other part consists of a solid-state time relay SsT and a relay K to form a time-switching two-way thyristor voltage regulation network system. After the switches S1 and S2 are closed; The signal light H1 is turned on, and when the thermometer T temperature measuring portion is located at a temperature lower than the set value of T, the contact of T is broken. At this time, the trigger control of the triac VS is controlled by R1, J-2. R3, Cl, C2 and VD to the G pole of VS, VS obtains the trigger current and conducts, the thermostat box resistance wire Rf is heated and heated, and the indicator light H2 is lit.

When the temperature inside the box rises to a set temperature value (20 ° C) from T, the timing time of the solid state time relay SST is up, the start is started, and the relay K is energized. The normally closed contact J-2 is disconnected, and the normally open contact J1 is closed, which changes the conduction angle of the triac VS, thereby lowering the terminal voltage of the load ,, lowering the heating rate, and reducing the thermal inertia. After the timer SsT is actuated, the trigger control circuit of the VS becomes adjustable. When the potentiometer RP is adjusted to increase the resistance of the RP, the conduction angle of the VS is decreased; When the temperature in the tank reaches the set value of T, the platinum wire electrode and the mercury column in T are turned on. The gate G of VS is shorted to cathode A1, and VS loses touch:

Yaxun design self-made voltage regulating temperature control circuit

When the signal current crosses zero, it turns off and H2 turns off. When the temperature drops, the T inner electrode and the mercury column are disconnected, VS triggers conduction again, Rf is energized and heated, and the temperature rises. When the temperature reaches the set value, VS is turned off again, and Rf stops heating. This cycle is repeated to make the oven temperature basically stable.

Component selection
The temperature control component T is an adjustable WXG-11 type electric contact glass mercury thermometer, which can be used for constant temperature control of ±0.1 °C to ±0.5 °C within 0 °C ~ 300 °C. The solid state time relay SST is YHK adjustable two-wire type. An external 2MΩ adjustable resistor is connected between the 2 and 3 pins, and the timing is 6 seconds to 600 seconds, which can be adjusted arbitrarily. SST uses electronic circuitry and features no contact, no spark and long life.
This circuit uses the YHK type 220V1A. Relay K uses JZX-22F/zz 220V5A small AC relay. The remaining components are selected in the usual manner.
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