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5.4 System Interface Board
The System Interface Board is located in the top section of the MX15 unit. To access this
assembly, the top cover needs to be removed. The System Interface board, A3, receives the
oscillator signal from the CPU controller assembly for all phases and passes it through to the
amplifier whose gains are controlled by a signal from the over current circuit. The over current
circuit senses the RMS value of the current. If the load current exceeds the programmed value,
the output of this sensing circuit reduces the amplitude of the oscillator drive signal. The output
of the unit then becomes a constant current output, with the output voltage dropping as the load
increases.
The System interface also monitors a variety of status signals from the amplifiers. This includes
PFC good, over temperature signals and DC bus regulation good signals. If any status signal is
false, the system interface board will shut down the MX. At power on, all status signals have to
return good (TRUE) or the MX system power up sequence will be halted.
Finally, the System interface assembly also routes the required system interface bus signals
between multiple MX15 chassis for multi-box configurations (MX30/2 and MX45/3). A DB-37 to
DB-37 system interface cable is used to connect two or more MX15 units in a multi-box
configuration. Each MX15 provides two sets of system interface connectors on the rear-panel.
One is the master out (unit with CPU controller assembly installed), the other the Auxiliary in.
((unit without CPU controller or with CPU controller disabled.) The CPU controller can be
disabled using the internal DIP switch located on the GPIB / RS232C / USB IO assembly.
(Requires removal of the top cover).
5.5 Current / Voltage Sensor Board
The current and voltage sensor board, A4, senses the output current and voltage of the amplifier
and feeds this information back to the system interface board. These same signals are also
used by the controller for all measurement functions. Voltage sense is accomplished either
internally or externally. For best voltage regulation at the EUT, external sense connections
should be made using the External Sense terminal block located at the top of the back-panel.
Alternatively, internal sense mode may be selected. In this case, the voltage is sensed at the
sensor board.
5.6 Low Voltage Power Supply
The Low Voltage power supply is mounted beside the system interface board in the top section
of the MX15 chassis. This assembly generates all required low voltage DC outputs. These
outputs from the LV Power supply provide analog and logic power to all the modules.
a) +/- 19 V to the System Interface board and power modules.
b) + 9 V to the oscillator.
c) + 24 V to all contactors and LV cooling fan.
d) Isolated + 8 V for the GPIB/RS232/USB board.
Two green LED's on the system interface board are lit when the ± 15 V and ± 19 V are in
regulation. If an overload condition causes the output to drop more than 10% or the output has
failed, the corresponding LED will extinguish. This feature is helpful in troubleshooting the unit.
See Service section 6.
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