Figure 4 0-20ma, 2 wire, field sourcing current, Figure 5 0-20ma, 3 wire, field sinking current, Trusted – Rockwell Automation T8834 Trusted 20 Channel Isolated AI/DI FTA External Power User Manual

Page 14: Ai/di fta external power t8834

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Trusted

AI/DI FTA External Power T8834

Issue 2 Aug 06

PD-T8834

Figure 4 0-20mA, 2 Wire, Field Sourcing Current

Here, an isolated power supply in the panel provides power to the module input circuitry via the zener
diode and 4K75 resistor. The field device is self powered but its range can go down to 0mA and so it
cannot be used to power the input circuit.

Figure 5 0-20mA, 3 Wire, Field Sinking Current

In this example, the device is ranged down to 0mA and cannot power the input circuit. It also requires a
power supply from the FTA. In this case, the device draws the current loop to ground, and so the
current loop is connected below the 100R resistor.

Isolated PSU

TB1 A

TB1 B

100R

7V5

CON1 VPOWER

CON1 COMMON

CON1 VSENSE

TB2 +

TB3 +

TB2 -

TB3 -

4K75