Jands HP6, Техническое руководство

Страница: 26 / 96

Equipment Description 3-9
Revision 2 - 26 April, 2000 HP SERIES DIMMER TECHNICAL MANUAL
Read and Write control lines for the SRAM are generated by the GAL16V8 (IC7). A
MAX691 “watchdog“ chip (IC8) supplies power to the RAM ICs from the 5V supply
rail, but changes over to the 3V Lithium backup battery when the 5V supply drops below
a set level.
CAUTION
Danger of explosion if battery is incorrectly replaced.
Replace only with the same or equivalent type
recommended by the manufacturer. Dispose of used
batteries according to the manufacturer’s instructions.
3.6.3 DMX input / output
DMX signal is received via switching relays (RLY1, RLY2) that allow the DMX to be
terminated or looped through. When terminated, the CPU has the ability to drive the data
output for future readback systems, however in normal operation the incoming data is
connected directly to the LOOP output.
The balanced DMX input signals are buffered and unbalanced by a 75176 (IC12) before
passing to the serial port of the
µ
P.
3.6.4 Zero crossing detector
The zero crossing detectors synchronise CPU ramp generation to the mains supply. Each
phase transformer output is rectified, divided, and compared (IC14) with a reference
voltage generated from the +5 volt rail. The three comparator outputs should be low-
going pulses roughly centred around the mains zero-crossing point, with a 10 ms cycle
time.
3.6.5 Analog to digital converter (ADC)
As well as being used to generate zero-crossing pulses, the three transformer secondary
voltages are resistively divided and multiplexed into the 8 bit A-D converter ADC0820
(IC4) via the 4051 analog switch (IC6). This mux is controlled by a latch 74HC574 (IC5
pins 14-19). The temperature sensor and a spare input from the Output PCB are also
connected to the mux inputs.
The ADC is read approximately every 2ms in software V1.1F, however this may change
with later software versions.
The phase voltages are compared in the
µ
P to obtain “bad neutral” information. The
temperature sensor voltage is converted to degrees and can be displayed on the front
panel PCB.
3.6.6 Optocoupler drive
The
µ
P directly drives 12 ULN2003 inverter buffers (IC9, IC13) which in turn drive the
BRT12 optocouplers or power oscillators (on the Output PCB) to fire the triacs/SCRs.
These signals pass down the Output card flat cable, along with the power supplies.