ApplicationLoop-powered isolators are used to isolate process signals transmitted between field instrumentation, Programmable Logic Controllers (PLC), Distributed Control Systems (DCS) and Data Acquisition Systems (DAS). Outputs from these systems can also drive one or more isolator channels of the Q500. Field devices such as flow, level or temperature transmitters may also drive a Q500 isolator channel.

The 1800VDC isolation capability of the Q500 prevents ground loops from causing errors in 4-20mA current signals and may reduce susceptibility to Radio Frequency Interference (RFI). Isolation also provides protection from high voltages and current spikes which may damage expensive Supervisory Control And Data Acquisition (SCADA) equipment, such as a PLC or DCS.

Operation
The ActionI/Q model Q500 operates as a looppowered isolator, with each channel deriving its power from the input loop current, 0(4)- 20mA. The effective load of a Q500 isolator channel on a loop is 300W plus the output load resistance. For example, if the load on an output of the Q500 is 500W, then the current loop connected to the input of the Q500 would need to drive 300W plus 500W (i.e. 800W) at a maximum current of 20mA, or 800W x 20mA which equals 16.0V.

The Q500 is protected from reverse input polarity and output short circuit. A span pot is provided for each channel to calibrate the output to the load.

1. Connect the input to a calibrated milliamp source. Connect the output to the actual device load or to a load (between 100 and 500W) equivalent to the actual device load value. Monitor the output current with a milliamp meter in series with the load or monitor the voltage across the load.
2. Set the calibrator to 20mA and adjust the span potentiometer for 20mA output.
3. Set the calibrator to 4mA and confirm that the output is 4mA.