Rockwell Automation T8433 Trusted TMR Isolated 4-20 mA Analogue Input Module - 20 Channel - Manual (Page 10)

Trusted
TM
Module T8433
Issue 11 Apr 10 PD-T8433 10
1.1. Isolated Input Field Termination Unit (IIFTU)
The Isolated Input Field Termination Unit (IIFTU) is the I/O module sub-assembly containing the field
connector and the TMR isolation amplifiers. The IIFTU connects the isolated field signals into the TMR
isolation amplifier array and onto the three IFIU slices.
Each isolation amplifier slice in the array obtains its operating power from the 4-20 mA current loop
input signal itself. The T8433 module will normally be used in conjunction with a T8833 or T8834 Field
Termination Assembly (FTA). The FTA converts the 4-20 mA current loop signal into a voltage
through the use of rugged under-stressed high-reliability passive components. This voltage is split into
a raw isolated 7.5V DC low current power supply signal, and a precision 0-2V current sense signal by
the FTA.
When two modules are installed in an active/standby pair, their IIFTUs are connected directly in
parallel, and share the same signals.
When installed in a Trusted TM Controller or Expander Chassis, the IIFTU field connector mates to the
Field I/O Cable Assembly attached at the rear of the chassis. The cable serves to connect the module
to it’s associated FTA, and is an important component of the system.
The SmartSlot link is passed from the HIU to the field connections via the IIFTU. These signals go
directly to the I/O cable assembly and maintain isolation from the I/O signals on the IIFTU. The
SmartSlot link is the intelligent connection between active and standby modules for co-ordination
during module replacement.
1.2. Input Field Interface Unit (IFIU)
The Input Field Interface Unit (IFIU) is the standard 42 channel sub-assembly that is used in a variety
of other input modules in the Trusted
TM I/O family. Each module has three FIUs, one per slice. For the
TMR Isolated 4-20 mA Analogue Input module, the FIU contains two analogue to digital (A/D)
converters for each of the 20 field inputs. The redundant A/D values are provided to the application for
an optional layer of information.
The IFIU receives power from the HIU and isolates it for use on IFIU, and it is also used to power the
IIFTU buffer array. The IFIU provides additional power conditioning for the precision reference
voltages required by the IFIU A/D and diagnostic D/A circuitry. An isolated 6.25Mbit/sec serial link
connects each FIU to one of the HIU slices.
The FIU also measures a range of on-board “house-keeping” signals that assist in monitoring the
performance and operating conditions of the module. These signals include power supply voltages,
current consumption, on-board reference voltages, board temperature, and condensation.