Precision Control Systems 930 - Manual (Page 19)

Model 930 ControlIR TM Instruction Manual Operating Instructions
Research, Inc. Page 15 of 25
The output voltage of a phase angle controller does not change linearly with respect to
the number of degrees the SCR conduction phase angle changes. Therefore, the SCR
controllers have a built-in load feedback circuit to linearize the relationship between
the control signal and the voltage output. The feedback circuit also adjusts the power
controller output to compensate for changes in line voltage and load impedance (this is
called “line and load regulation”).
Phase angle power control offers a number of attractive features. Because the power
controller output level is adjusted by varying the SCR on time within each AC half-
cycle, the controller’s output is quite constant, rather than being divided into multiple-
cycle periods of on time and off time. In addition, a variety of feedback and output
indication (metering) circuits can easily be incorporated into the controller.