Rockwell Automation T8448 Trusted TMR Zone Interface Module - 40 Channel - Manual (Page 20)

Trusted
TM
Module T8448
Issue 14 Apr 10 PD-T8448 20
3. Application
The Zone Interface Module has been designed to provide a cost effective and high integrity interface
with a Fire and Gas Zone. Each Zone within an application will have a unique combination of signals.
In order to reduce the amount of hardware required, the Zone Interface has been made configurable
using a simple software configuration package. The Zone Interface Module operates in conjunction
with the Trusted
TM
Versatile Field Termination Assembly 8842.
The Termination assembly uses plug-in fuses and links to allow selection of different field loop
conditioning combinations.
Under software control, the Zone Interface Module can select any channel to be input or output. When
a channel is selected as output the module provides a full TMR high integrity fault tolerant switch. In
the input mode the channel becomes a voltage input analogue interface. Each field input is triplicated
and the input voltage is measured using an analogue to digital converter. In the Input mode, different
resistor combinations on the Versatile Field Termination Assembly (VFTA) are used to condition the
field loop and provide the voltage input to the module.
For volt-free or zener-limited inputs, the internal input energise test will fail. To avoid fault indications
due to inputs that cannot be lifted in voltage by the module due to intrinsic shorting, a 1K 1W resistor
is required on the channel wiring between the module and the FTA. Note that this will change the
voltages seen by the module, and will require different monitoring thresholds. This resistor may also be
placed in series with the field contacts as a line monitoring component. The energise tests are required
by TUV for AK6 operation to verify the input circuitry
.
One Channel in each power group can be selected on the Versatile Field Termination Assembly to be
a fire detector power output. The power is distributed to the 7 remaining channels of that group and is
controlled by the Trusted
TM application logic. Removing power from the field loop resets fire detecting
field devices. It is usual to configure the module as groups of 7 fire inputs. However, the linking of the
VFTA can allow the Reset group to be any combination from 1 to 39 channels, evenly or randomly
distributed throughout the module, given that the total load on the output channel does not exceed 2A.
Gas inputs are interfaced by converting a 4-20mA current loop into a 1-5V signal on the VFTA, but the
inputs operate across a wider range in order to allow for poor field calibration and the calibration/fault
modes of field devices.
Each digital input voltage can be compared to user adjustable thresholds so as to generate up to 5
distinct states (for example Open circuit loop, Normal, Alarm, Short Circuit loop). Each of these
thresholds has adjustable hysteresis and can be positioned anywhere within the operating range of the
input. This allows for detection of field loop faults as well as alarm states.