Rockwell Automation T8834 Trusted 20 Channel Isolated AI/DI FTA External Power - Manual (Page 13)

Trusted
TM
AI/DI FTA External Power T8834
Issue 2 Aug 06 PD-T8834 13
5. Field Circuit Design
The T8834 FTA is capable of a variety of circuit configurations. When choosing a circuit, the following
points should be taken into account:
• A current of around 2mA should flow through the zener diode, to provide power for the module
input circuitry.
• The regulated current loop should pass through the 100R precision sense resistor from top to
bottom as shown in Figure 1.
• The field device may need power supplied through the loop, or with separate supply, or with
separate supply and return.
• The current loop may be returned to the FTA or sunk into the field circuitry.
The following diagrams provide some suggested field circuit arrangements.
Figure 3 2-20mA, 2 wire, Field Sourcing Current
This arrangement may also be made with a T8833 FTA. It expects the field transmitter to be self-
powered, to provide both sides of the current loop to the FTA, and to have at least 2mA of power at low
range for the input circuit.
TB1 A
TB1 B
100R
7V5
CON1 VPOWER
CON1 COMMON
CON1 VSENSE
TB2 +
TB3 +
TB2 -
TB3 -
4K75