BEHLMAN BL10000 Series, User'S Manual And Technical Reference Manual

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5.8 THEORY OF OPERATION FOR GPIB \ RS232 INTERFACE ( continued )
Read back of output current and voltage is obtained by monitoring the internal circuits of the power source.
These dc signals are selected via U1 a two channel “one of four” de-multiplexor. Note that the actual number
of channels and inputs used depends on the model of the power source. Again , this is determined by the
EEPROM data . The outputs of U1 are applied to a set of voltage to frequency convertors. The output of these
converters range from 100 Hertz to 200 Hertz. These frequencies are measured by the microprocessor and
scaled to provide the proper current and voltage data to the controlling computer. The output frequency of the
power supply is measured by monitoring its internal clock signal via U4. This input is labeled “Hz-FDBK”.
Control of the output on/off relay and range relay is provided via the interface board via dry contacts from K1
and K2. These small PCB mounted relays are controlled by U18. All signals coming to and exiting from the
interface board and the power source are optically isolated. This adds a measure of safety and prevents ground
loops between the controlling computer and power source circuitry.
All firmware for the interface card is written in INTEL’s PL/M format. A list of supported commands and syntax
is provide in appendix B and C of this manual.