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within the proportional band (Period 3) and the on-time of the relay is regulated proportional to the
distance up to the setpoint. This is illustrated with the two “bars” below the curve, where it is shown
that the on-time drops as the value comes closer to the setpoint. At the point (4) the value is exactly
in the middle of the proportional band where the on-time and off-time of the relay are equal (The relay
is on half the time).
Finally when the setpoint is reached the relay is kept off and will not be set on again until the measured
value drops below the setpoint. This is illustrated with period (5)
Wiring Schematic for FX-300 Measurement Transmitters (FX-300-pH, FX-300-CON or FX-300-
ISE) when used together with FX-300-REL Relay Module and a 4-20mA Output is Required to
connect with additional Data Acquisition or Control Devices
If you wish to “insert” an external device into the current loop, it can be done by removing the bridge
jumper and connecting the two terminals to the external device (“+” to device input and “–“ to device
output, which may also be device ground). If no external device is to be connected, the bridge jumper
must be in place to ensure normal operation of the FX-300-REL relay module.
8 Additional Measurement & Function Modules
FX-300-REL Relay & Control
