Trusted 20 Channel Isolated AI/DI FTA Loop Powered
1. Description
Rockwell Automation Publication ICSTT-RM294E-EN-P
Issue 5
3
1.
Description
Figure 1 T8833 Layout
The Trusted 20 Channel Isolated Analogue Input FTA (T8833), provides termination for a
maximum of 20 input channels from various types of field devices which generate a current
loop signal. When used with a Trusted TMR Isolated Analogue Input Module (T8433) each of
the inputs is loop powered and individually isolated. Figure 2 below shows the configuration
of a single channel.
Figure 2 Single Channel Schematic
The FTA is configured so that the 4‐20 mA field current loop signal connects to TB1 A and
the loop return connects to TB1 B. The current loop signal is then converted into a voltage
by the circuit in Figure 2. This voltage is split into a 7.5 Vdc low current power supply to
power the isolation amplifiers on the input module (VPOWER) and the precision 0‐2 V
current sense signal (VSENSE) connected to the input module. Both of these voltages are
referenced to (COMMON).
This means that input module operates on the loop power of the field devices. This way
each field device is isolated from the other devices and from ground.
TB1 A
TB1 B
100 Ω
7V5
CON1 VPOWER
CON1 COMMON
CON1 VSENSE
+
