Instruction manual

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5.4. CPU/GPIB BOARD
The CPU/GPIB board, A2A3, provides the control and measurement functions of the module. A
microprocessor circuit accepts commands from the GPIB and the front panel keyboard. It sends
digital programming information to set the output parameters of the power source. Data from
measurement circuits is accepted and reported to the display and GPIB. Measurement calibration
coefficients are stored in a memory backed up by a battery. The battery has a 10 year life
expectancy.
Measurement circuits on the CPU/GPIB board monitor voltage, current, power, frequency, and
phase angle. Voltage from the rear panel sense terminal block is scaled, converted to a DC voltage
by a true-rms-converter, and sent to the microprocessor by the analog-to-digital converter.
Current sensed by the current transformers is scaled, converted to a DC voltage by a true-rms-
converter, and sent to the microprocessor by the analog-to-digital converter.
The scaled voltage and current waveforms are applied to the inputs of a multiplier. The multiplier
output is filtered to a DC level and digitized by the analog-to-digital converter.
Frequency is computed from the measured time intervals between zero crossings of the Phase A
waveform. Phase is computed from the differences of measured zero crossings between the Phase
A signal and the Phase B or Phase C signal.
A digital-to-analog converter on the CPU/GPIB board sets the DC voltages that are used for the
programmable current limit function.
5.5. PHASE A/REF BOARD
The Phase A/Ref board, A2A5, serves several purposes. A programmable clock sets the output
frequency of the power source. Digital-to-analog converters program references to set the output
amplitude of Phases A, B, and C. A sine wave generator creates a 1024 step waveform which is
filtered to provide the Phase A oscillator signal. An external sense amplifier controls the Phase A
output amplitude.