SCR (Silicon Controlled Rectifier)
Control
This discussion refers to the SIEG XMT-1115 and 1135 and
the KB Electronics KBLC-120
This circuit is basically a SCR bridge rectifier with the motor
as the output load. The output of the SCRs (and hence motor power) is
control by synchronized line frequency pulses which gate the SCRs to an "on"
state. The width of the pulse controls motor speed.
Fault Protection: Motor current is sensed and if a preset
limit is exceeded, the gate to the SCRs is shut down. The motor control
can not be restarted until an action on the control panel is taken.
Failure of the bridge rectifiers will cause the system fuse to blow. (Note
- if the system is over fused, damage to the PC board traces can occur)
On-Board Controls: The KBLC has five on-board controls.
Two set the max and min power level. The "Accel" sets the how fast the
control responds to a change of the speed adjust setting. "CL" sets the
motor current limit that, if exceeded, will cause the system to shut down.
"IR" is load regulation adjustment. The XMT series have a range set
adjustment, a fault current adjustment and a load regulation adjustment.
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