REV 0.0 April 18, 2023
Page 6
3.
Single DC Powered Sensor
The following example is a variation of the previous two, except that the line-powered DC supply is remotely located
and the Gateway does not supply the power to the sensor.
The junction box is required, since there are conductors from three cables that need to be routed to the sensor. In this
case, the Gateway supply output pair (red/black) is not connected.
Note that the common (black wire) of the Gateway supply cable is internally connected to the common of the Gateway
sensor cable (black of the red/black pair). Only one of these should be connected for signal common.
This example illustrates the case where the sensor body is not providing an earth-ground connection, so the shield wire
must be connected to Terminal 3 in the sensor. This may occur if the sensor is mounted on a non-metallic tank or uses
a sensor aiming mount that electrically insulates the housing from earth-ground.
Figure 3 – Simple DC Sensor Connections (No Current Output)
Note that if the DC power supply is located at a significant distance, and the junction box has an available earth-
ground connection much closer to the Gateway and sensor, it may be more desirable to ground the shield wire at the
junction box instead of at the power supply.
Over long distances with multiple RS485 connections, it is preferred to earth-ground the shield at one end or the other.
There are exceptions, of course, depending on the total length of the cable, proximity of electrical noise sources (such
as motors) and the quality of the grounding connection available. For instance, a sensor grounded through a metal tank
mounted on dry ground may not be as effective as a connection to the earth-ground from the AC line supply (as in
Figure 2) – the latter typically implemented with a buried grounding rod or plate.
