LumaSMART
®
User Manual
Installation of the LumaSMART® Controller
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49
Current Loop Considerations
The LumaSMART provides surge protected isolated current sources for remote monitoring of temperature
(including providing loop power). However, the isolation is not intended to withstand continuous offset voltages
between the Loop Transmitter and Loop Receiver of greater than 20 volts. The recommended limit is 15 volts.
Before inserting the connector between the Transmitter and Receiver, you should check the wiring with a volt
meter to ensure it does not exceed the limit. The voltage (using both the AC and DC scale) between the receiver’s
(-) input pin and the GND pin of the SERIAL connector should be checked to ensure that the 15 volt limit is not
exceeded.
Note:
The measurement of the voltages mentioned above MUST be done when the transformer to
which it is attached is operating and loaded! Measurements while the transformer is offline have
no value.
The cable shield must cover the entire length of the cable. The only permissible unshielded portion of the cable is
the few inches needed to break out the signal wires and terminated them to their respective connection points of
the equipment on each end.
Analog Output Current—Self-Powered (4 to 20 mA or 0 to 1 mA)
∗
If the receiver equipment provides a specific signal ground terminal (not Loop minus) for the current loops, it
should be tied to the cable shield.
∗∗
If the dedicated loop ground is not provided, the cable shield should be tied to Chassis/Earth Ground.
Caution:
Attach the cable shield to ground at one end only, not at both ends.
Verification that the receiver is properly configured as a passive receiver can be performed by measuring the DC
voltage across the (-) minus and (+) plus input pins. If the voltage is not 0, then the receiver is most likely
configured incorrectly as it is supplying the voltage to drive the current loop. Ideally, the Loop Receiver is isolated,
just as the Loop Transmitter.
Caution:
Connecting an external current loop transmitter or any other voltage source to the
LumaSMART Current Loop outputs can cause permanent damage!
