Technical information

8 – THEORY OF OPERATION
Phase Control
131
8.6 Phase Control
When the Starter Type parameter is set to Phase Control, the MX is configured to operate as a phase controller or voltage follower.
This is an open loop control mode. When a start command is given, the RUN programmed relays energize. The firing angles of the
SCRs are directly controlled based on voltage or current applied to the Analog Input.
Figure 26 – Phase Control Mode
MX Phase Control Mode
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Analog Input (%)
SCR phase angle (%)
SCR phase
angle
command
A reference input value of 0% results in no output. A reference input value of 100% results in full (100%) output voltage. The actual
input voltage / current that results in a given output can be adjusted through the use of the Analog Input Offset and the Analog Input
Span parameters.
The Phase Control mode has many uses. Two typical applications are use in master/slave starter configurations and as a basic phase
controller.
Phase Controller:
When in Phase Control mode, the MX can function as a general phase controller. Phase control can be used to directly control the
voltage applied to motors, resistive heaters, etc. When in Voltage Control mode, the phase angle of the SCRs and hence the voltage
applied is directly controlled based on the measured analog input signal. The MX’s reference command can be generated from any
0-10V, 0-20mA, or similar sources such as a potentiometer, another MX, or an external controller such as a PLC.
Master/Slave Starter (Lead/Follower) Configuration:
In the master / slave configuration, one “master” starter can directly control the output of one or more slave starters. To utilize the
master / slave configuration, one starter needs to be defined as the “master” starter. The Starter Type parameter of the “master”
starter should be configured appropriately as a Soft Starter (normal or ID), Phase Controller, or Current Follower. If configured as a
soft starter, the acceleration and deceleration profiles need to be configured for proper operation.
To configure a master / slave application:
1. The analog output of the master MX control card needs to be connected to the analog input(s) of the slave card(s).