14
3.3 Wiring the 4-20 mA Output
Standard Wiring Configuration: 4-20 mA Output
See the photo on previous page for complete output labeling instructions
NOTE: Some configurations DO NOT have the 4-20mA bridge terminal block shown below.
Leave the factory installed jumper from the mA output terminal block (if supplied) intact unless you
are connecting to an external device that passively measures current.
EXTERNAL DEVICE
ANALOG INPUTS MUST BE ISOLATED and must not apply voltage to the active current
loop, doing so will damage the transmitter and is not considered a warranty repair issue.
Keep in mind that all FX-300 transmitters are 3-wire devices. This means they have an ACTIVE 4-20mA
analog current loop output, like a 4-wire type device. The data acquisition or control device to which this
active 4-20mA output is connected should passively measure the current. Most PLC’s have a hardware
or software toggle that allows you to select whether the 4-20mA received is from a 4-wire (or 3-wire)
active type device or else if it is a 2 -wire device which must be energized from the PLC power supply.
The current output from the FX-300 MUST ALWAYS be connected to isolated analog inputs. If
your PLC, SCADA or other external device does not have isolated analog inputs, then you must
add an isolator for each current loop to be used
.
The ground cannot be shared on both the analog current output from the FX-300 (since it is a 3-
wire device) and on the analog input on the PLC. The ground for each analog input on the PLC
must then always be isolated.
3 Installation
