Rockwell Automation T8834 Trusted 20 Channel Isolated AI/DI FTA External Power - Manual (Page 14)

Trusted
TM
AI/DI FTA External Power T8834
Issue 2 Aug 06 PD-T8834 14
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
Isolated PSU
+ -
TB1 A
TB1 B
100R
7V5
CON1 VPOWER
CON1 COMMON
CON1 VSENSE
TB2 +
TB3 +
TB2 -
TB3 -
4K75