Rockwell Automation T8833 Trusted 20 Channel Isolated AI/DI FTA Loop Powered - Manual (Page 7)

Trusted
TM
AI/DI FTA Loop Power T8833
Issue 3 Aug 06 PD-T8833 7
1. Description
The Trusted TM 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
TM T8433 TMR Isolated Analogue Input module 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 7.5V DC low current power supply to power the isolation amplifiers
on the input module (VPOWER) and the precision 0-2V 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.
The connector linking the 20 channels on the input module to the FTA is terminated at CON1 which is
a 96-way socket. A row of screw terminal connectors (TB1) are used to connect the field wiring.
Unused inputs should be terminated by wiring a 24V supply via a resistor (2K or 2K2) to the A terminal
and wiring the B terminal to the associated zero volts.
TB1 A
TB1 B
100R
7V5
CON1 VPOWER
CON1 COMMON
CON1 VSENSE
+