Heater Control Panels

BJ Control Panels have produced a variety of portable and fixed heater control units. These are used mainly in laboratories and industrial research and development departments as well as industrial production areas. Heater panels are produced by BJ Control Panels to cover a vast spectrum of applications and for a wide variety of customers including:

  • Eurotherm (Invensys) Limited
  • Exheat Limited
  • Watlow Limited
  • The Boots Company PLC

They range in size from a few watts of power (at very low voltage) to several hundred kilowatts. The method of control of the heater is as varied as the heaters power rating. Approved methods of industrial heater control include:
  • On/Off Control
  • Burst Fire On/Off Control (Solid State Contactor)
  • Phase Angle Control
  • Burst Fire Control (Variable Time Base)

The simplest form of heater control is on/off. This simply applies power to a heater via a signal from a thermostat or similar temperature sensing device/controller. The heater is energised or de-energised depending on whether or not the monitored temperature is above or below a preset temperature setpoint. This method is not very accurate as the heater is continually switched on and off around the setpoint. The frequency of the on/off cycle can be damped (widening the hysterisis), but this leads to large over and undershoots – this method is however very cheap and is used in the majority of domestic immersion heater applications.
The burst fire On/Off method of heater control is very similar to the simple on/off control but utilises solid state technology to apply power to the heater. The use of solid state devices means that there are no moving parts to wear out (such as relay or contactor contacts). The reason that the burst fire approach is adopted is so that the heater receives very fast pulses of electrical power to achieve the desired setpoint temperature. This method of heater control can be seen in use on most domestic ceramic hobs – where the heating elements can be seen to glow at different frequencies depending on the selected heat output. (e.g. full power – heater glows continuously, half power – heater glows on and off with an equal mark/space ratio)
The phase angle method of heater control employs the same solid state technology already discussed but varies the heat applied to the system by “removing” part of the A.C. waveform applied to the heater. This method of power control can be seen in use in domestic lamp dimmers – where the light output of an incandescent bulb can be varied by turning a control potentiometer.
Burst fire control of a heater is by far the best but most complex method of heater control. It maintains the required setpoint very accurately and lends itself easily to PID (proportional- integral – differential) control. It employs solid state circuitry to provide varying frequency pulses to the heater to achieve the required results. It is the industry standard method of heater control when high accuracy is essential.
 
  Laborotory type portable heater control units.
 





 
  Industrial style fixed heater control panel.