Harris Intelligent Transmitter Platinum-i Series - SCR Crowbar; Mechanical Shorting Switch; PA Cabinet Control Logic; Analog PA Cabinet RF Config

______________________________________________HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
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The back door is interlocked for protection from contact with AC mains voltage and the
high currents available from the 50 volt power supplies. Opening the interlock removes
+12 volt coil voltage from the auxiliary relay K2 resulting in no coil voltage for K1, the
AC contactor.
7.2.1.2.1 SCR crowbar
This crowbar works in conjunction with the door interlock to discharge the 1.4 Farad
capacitor bank. When the back door is opened, the B section of the door interlock
switch connects the 50 volt bus to the gate of SCR through current limiting resistors.
This turns on the SCR which connects discharges the filter capacitors through one ohm
current limiting resistors. When the main contactor is energized, the auxiliary contact
shorts this voltage to ground. When the 50 volt supply is totally discharged, the gate
voltage is zero and the current flow is zero and the SCR will no longer conduct. When
the back door is opened, wait about ten seconds before re-closing to allow the current
through the SCR to be zero, allowing the reset to an open circuit.
7.2.1.2.2 Mechanical Shorting Switch
When the door opens fully, the mechanical shorting switch located at the hinge side of
the cabinet will close, further discharging the filter capacitors. This is independent of
the SCR circuit, acting as a backup.
7.2.2 PA Cabinet Control Logic
This is commonly called the slave controller. The master controller in the control
cabinet sends each slave controller on and off commands. The slave controller has a
multiple input multiplex system that allows the main control system to control the
multiplex switch position, sequentially sending status and monitoring voltage samples
to the control cabinet for meter reading. Detailed information on the PA cabinet logic is
in the control logic section 6.
NOTE:
Module theory of operation is covered in section 9.
7.3 Analog PA Cabinet RF Configurations
7.3.1 15 KW Vision only PA Cabinet
This cabinet is driven at a medium power level by the modules in a separate driver
cabinet. Therefore this cabinet contains 17 visual power amplifier modules, a 17 way
divider and 17 way Gysel combiner. High Band and Low Band transmitters have the
Same configuration. Detailed drawings of this configuration are in section 800 of the
drawing package.