Instruction manual

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5.6. PHASE B/C BOARD
The Phase B/C board, A2A4, uses the DC voltage references and programmable clock from the
Phase A/Ref board to generate the Phase B and C oscillator waveforms. External sense circuits
control the Phase B and C output amplitudes.
5.7. DISPLAY BOARD
The Display Board, A2A1, is connected to the oscillator mother board by a short ribbon cable. The
Display Board holds the 20 button keyboard and a 32 character liquid crystal display. A knob on
the board allows adjustment of the display viewing angle.
5.8. CURRENT LIMIT BOARD
The current limit board receives the oscillator signals identified as OSC A, OSC B, and OSC C
from the oscillator assembly. Analog switches on this board direct the oscillator signals to the
respective amplifier module. The analog switches switch the OSC A signal to the three amplifier
inputs during 1-phase operation. For 3-phase operation, OSC A, B, and C are switched to the
amplifier A, B, and C inputs respectively. Gain adjustments are located on this board to set the
system gain of the three output phases.
The current limit circuits are also located on this board. These circuits receive DC signals from the
oscillator assembly, CLA, CLB, and CLC, that are proportional to the rms current limit value. The
DC signals are compared to the output current signals TA, TB, and TC which are the outputs of the
current transformer assembly, A7. If an output current exceeds the programmed value, an
attenuator will limit the output voltage to a value that will cause the AC Power System to operate at
a constant output current. If the output voltage drops 10% below programmed voltage during
constant current operation, the oscillator will sense this as a fault, set the output to the default value,
display an AMP FAULT error message, and report the error to the GPIB interface.
The current limit board has analog switches and summing amplifiers that are used for current
measurements. The outputs from the summing amplifiers, CTA, CTB, and CTC, are routed to the
oscillator assembly for measurement. In the 1-phase mode, the current from all three output current
transformers are summed together for measurement. This signal is identified as CTA.
Small line frequency transformers step down the auxiliary three phase secondary of the main input
transformer. The outputs of these transformers are rectified and filtered to create an 8 VDC
unregulated supply, and a ±18 VDC unregulated supply. The 8 VDC supply powers the logic
circuits of the current limit board and the oscillator assembly. The ±18 VDC supply powers the
analog circuits of the same assemblies. As part of this power supply circuitry, the three phase input
voltage, the 8 VDC, and the ±18 VDC are monitored; the power source outputs are disabled if a
problem is detected with any of these voltages.