How to control electric heaters in thermoregulating units?

Which are the possible solutions to control and manage electric heaters employed in thermoregulating units? There are in fact three possible options, offering a more and more fine and accurate control of temperatures.

The first option for the control of electric heaters in thermoregulation is to use an electronic thermoregulator, that ensure the fine regulation of the temperature set-point by commanding a contactor, hence electric resistors, with a certain frequency. Clearly, if the resistors have a high frequency of intervention, especially in case of high power resistors, the service life of the contactor will be limited.

Contacts in a contactor are indeed designed to ensure a certain operating life, with a number of cycles, and beyond it the contacts get damaged. It happens that contacts get welded together inside the contactor, so that they don’t respond anymore to the thermoregulator, pushing the thermoregulating unit up to excessive high temperatures.

There are obviously some safety systems, such as safety thermostats, that provide the interruption of power and then halting the system. In this first option, thermoregulation has then some physical limitations, due to the maximum number of intervention allowed by the electro-mechanical contactor.

 

 

A second option is to employ a static relay, which is electronically managed avoiding electro-mechanical contacts. This solutions also enables to operate micro-openings and micro-closings, achieving a more fine and sophisticated temperature regulation.
Anyway, even a static relay can get damaged and thus remaining in a closed status, pushing the thermoregulating unit over the maximum safety temperature. Also in this case, the safety thermostat will operate, and usually in our Tempco thermoregulating units we implement a line contactor managed by the safety thermostat, providing the safety halting of the system when maximum temperatures allowed are exceeded.

At last, a third option is to employ a SCR (silicon controlled rectifier) static relay, with power adjustment. These device allows an even more fine and precise control of the temperatures. Instead of working with on-off activation of the thermoregulator, an SCR allows indeed a modulation of power supply, from a minimum value up to a maximum temperature value. Exactly as if it was an inverter, but applied to electric heaters.

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