Current Input Mode 

Current Input

The FAC-2100 can read 0/4mA to 20mA currents on any of its analog inputs. An analog input configured in software for current mode will automatically engage a 250 ohm resistor (physically located in the controller) from the A_IN+ pin to GND.

...

The figure below shows a typical hook-up for loop powered 4-20mA transmitters. This configuration uses the internal 28V axillary voltage source to power the transmitter. Note the connection from the analog input return back to ground of the voltage source is made internal to the controller. Also note that the A_IN- pin is not used in this mode.

Image Added

Suggested Analog Input Wiring with a Loop Powered Transmitter

The figure below shows a 4-20mA sensor (not loop powered) connected to the controller where the sensor is powered by an external source. Note that a similar connection is made when using a 4-20mA loop sensor that is externally powered.

Image Added

Suggested Analog Input Wiring with an Externally Powered 4-20mA Sensor

Over-Current Shutoff

When the input is in current mode the device will automatically protect itself from currents that exceeds approximately 25mA. When this condition is detected the circuitry will automatically disconnect the 250 ohm resistor and thereby open the circuit (this will also turn off an attached loop transmitter). A short time later the 250 ohm resistor will be reengaged to see if the fault has cleared. If not, the cycle will repeat.