FOCE Auxilliary Circuits

The auxilliary circuits board provides the following functionality:

1. Scaling for source voltages (+12V and +24V) to the DMM32 DAQ board.

2. Current monitoring for the source voltages (+12V and +24V) to the DMM32 DAQ board.

3. Creates a reset pulse for the computer stack from the Axis 241 Video Server.

Source Voltage Scaling 

The +12V and +24V source voltages are scaled down to 0 to +5V via 1% resistors. This voltage is read by the DMM32 DAQ board.

The curve for +24V is:

Y = 5.622X + 0.025 (where X represents the scaled 0-5V signal and Y represents the actual input source voltage)

The curve for +12V is:

Y = 2.767X - 0.004 (where X represents the scaled 0-5V signal and Y represents the actual input source voltage)

Current Monitoring

The outputs of the Vicor DC-DC modules are monitored by current sense ICs (MAX4173). These parts read the voltage across a sense resistor (in series with the monitored voltage), calculate load current and convert that to a usable output voltage. The part was chosen for a gain of 50 with a sense resistor of 10m ohms. This allows for a full-scale load current of 10 amps with a corresponding output voltage of 0-5V.

 The curve for the +24V load current is:

Y = 1.98X - 0.02 (where X represents the scaled 0-5V signal and Y represents the actual load current in amps)

The curve for the +12V load current is:

Y = 2.027X +0.012 (where X represents the scaled 0-5V signal and Y represents the actual load current in amps)

Computer Stack Reset

Links

MAX4173

Auxiliary Circuits Schematic