Digital power controller esp. for heater loads - has A=D converter and zero voltage switches controlling power to binary stepped heating elements

摘要

The power controller provides very fine incremental power adjustment without mains interference even with high powers. If is esp. suitable for controlling heaters. The controller consists of an input unit (1) to which desired temperature, actual temperature, heating rate (temp. rise with time) and correction rate (follow-up speed) signals are fed. The analogue signals from the input unit are converted to digital form in an A/D converter (2) having an 8-bit output. These outputs are coupled via opto-insolators (3) to individual zero voltage switches (4). These in turn control the amount of power fed to the individual heating elements (5). The zero voltage switches switch the AC power on and off only at the zero-crossing instant and the power is supplied in the form of bursts of a few cycles at a time.