Furnace Heater Temperature Controller
Temperature control in an electric furnace using the Advanced digital indicating controller, utilizing SCRs (thyristors) and SSRs (solid state relays).
The temperature is controlled as follows: the current temperature inside the furnace is measured with a thermocouple, then the Advanced digital indicating controller outputs a control signal to the SCR and SSR, and the power supplied to the heater is controlled.
Using a SCR (thyristor)
Thyristors can be used in phase control and zero cross control. With phase control, the power supplied to the load can be controlled continuously. This method is used for a wide range of control applications from small capacity devices to large heaters.
Zero cross control is a system which suppresses noises and controls heaters by turning ON/OFF voltage applied on heaters when the AC power supply voltage is at 0 volts.
Using an SSR (solid state relay)
Controling heaters using solid state relays employs time-proportional PID control. With time-proportional PID control, the control output values resulting from the PID calculation are converted to ON/OFF ratios of the cycle time (CT).
Example: What is the ON time when the OUT ratio is 10% and the cycle time (CT) is 2 seconds?
(Answer: 0.2 seconds.)
To set to: PID control, thermocouple type K (range 0.0 to 500.0 ℃), current control output (4 to 20 mA)/voltage pulse output control, set each parameter on the Advanced digital indicating controller.