Cryomagnetics Model 4G Operating Instruction Manual 33
2. Theory of Operation
The 4G is a 4-quadrant power supply with glitch free bi-directional output capability and
programmable voltage limiting in both polarities.
2.1. Circuit Description
The 4G front panel is a microprocessor-based unit that handles all display, keyboard, and persistent
switch heater operation, and all communications with the outside world, including the power
modules. User data is stored in non-volatile memory external to the processor.
The power modules are microprocessor-based units that only communicate with the front panel.
The microprocessor has built-in EEPROM that is used to hold factory calibration. Consequently, it is
not possible to simply change the processor with another. The unit will not work properly with a new
processor until it has been initialized by the factory.
Output current is set by a 20-bit digital-to-analog converter controlled by a software PID algorithm
updated at a 15Hz rate. A 24-bit sigma-delta analog-to-digital converter is used to sense the output
current. The programmable current sweep rate is digitally implemented in the PID algorithm.
The 4G’s display is a bright, full-color 5 1/4” LCD display. It is capable of displaying both graphics
and full alphanumerics. Both voltage and current can easily be read from a significant distance.
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