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Understanding SCR Power Controls

When selecting SCR Power Controls, it is important to have a basic understanding of how SCRs work. This will help you select the right SCR for your application.


A silicon controlled rectifier (SCR) is a solid state switching device which can provide fast, infinitely variable proportional control of electric power. Not only does this give maximum control of your heat process, but it can extend heater life many times over other control methods. Since the SCR is solid state, it can cycle on and off over a billion times, if properly used.

The advantages of SCR Controls over other temperature control methods

  • Improved response time.
  • Closer process control.
  • Extended heater life.
  • Reduced maintenance costs.
  • Silent operation. No arcing and sparking.
  • Reduced peak power consumption.

Remember, a heating element is made of wire in most cases. If you use a mechanical relay to turn on your heater, it will cycle on or off within 30 seconds or longer. The heater will expand and contract, getting more and more brittle each time. This is called thermal shock. Temperature overshoot may also occur. Relays also arc, spark and will burn out on a regular basis.

Mercury displacement relays can cycle from 3-15 seconds. While it controls better than a mechanical contractor, overshoot and thermal shock will still occur. If cycled too fast, Mercury relays can overheat and explode causing Haz-Mat problems.

Contact Avatar Instruments today.