Panel housing the Thyristors Control Panels the power of the heater to match the thermal requirements of the system for high accuracy control. The Control Panel also contains necessary control and safety features. PID Cont. – Proportional, Derivative, Integral Three Term Indicating. The Panel Housing Thyristor Power Controller for controlling the Heater Controller for accurate control of temperature or viscosity. The signal may be milli-Volt (Thermocouple), Ohms (Resistance Thermometer) or Analogue eg 4-20mA (with transmitter head). PID Cont.