4.2 Control Electronics (Multiplexed Analog Input)
12
The control electronics for the 1.2Kw Pack consists of a Motherboard, four COBO
Rack Ramp Cards, one COBO Rack Power Supply Card, and a Control Panel
assembly which is screwed on in front of the other control components, and
hides them.
A. Motherboard
The Motherboard serves to connect the control components together. It
also contains the phase references for phases B and C, and a clock cir-
cuit which allows testing the pack by bringing all dimmers in the pack to
FULL
B. Ramp Card
Ramp Cards provide control signal demultiplexing and analog to pulse
width conversion.
Up to 192 dimmer levels are time multiplexed on the ANA (analog) line of
the control cable (control terminal
4). Levels vary from 0-SVDC, repre-
senting dimmer output levels of 0-100%. A differential clock on the CLK-
(minus clock) and CLK+ (plus clock) lines (control terminals
1 and 3)
synchronizes the dimmer rack with the control console. The multiplex-
ing scheme conforms to the USITT AMX192 Dimmer Signal Specifica-
tion.
6W and 12W dimmers require 2 clock cycles or dimmer posi-
tions.
Each Ramp Card contains the following circuitry:
1) clock receiver and reset detector
2) counter/decoder circuit
3) analog buffer
4) analog demultiplexer
5) A.C. zero crossover detector
6) square law curve generator
7) output solid state relay driver
8) power supply
C. Power Supply Card
The Power Supply Card conditions AC power from power phase A, and
supplies the AC line reference source for the phase A Ramp Card.
The Power Supply Card also has an SSA for fan power, which is ener-
gized from the Ramp Card when system clock signals are present. A
fuse on the Power Supply Card provides overload and short circuit
protection for this SSA.
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