SCR power controls can extend the life of your heaters by reducing thermal stress on your heaters. The heaters are maintained at a more constant temperatures reducing size changes in the heating elements due to temperature changes. Both zero fired and phase angle SCR controllers can improve the heater life.
Zero fired units turn the power to the heater full on and off for full line cycles very rapidly . Since the on/off cycles are very fast the element temperature does not respond by changing temperature during each cycle. Example: If the temperature requests 50% power the SCR will be on for one full line cycle then off for one full line cycle. The average power will be 50%. An analog ammeter or voltmeter will flutter at some level. Zero fired units cause virtually no electrical noise in operation due to switching at zero volts in the sine wave.
Phase angle SCR power controls vary the power by chopping up the incoming sine wave. A volt or ammeter will indicate a smoothly changing level. Phase angle SCRs are required for transformer coupled loads and loads with significant resistance changes with temperature. Phase angle controls can include various options such as current limiting,