Alarm Module - Operation & Configuration; Introduction; Device Details - Eaton Crouse-Hinds Series Instruction Manual

18
7 ALARM MODULE - OPERATION & CONFIGURATION
7.1

Introduction

As with all redundant systems, early notification of the failure of a system component
is important so that the fault can be rectified before a second fault is allowed to occur.
A second fault is likely to interrupt the process, so restoring redundant operation is vital
in maintaining high levels of system availability. With MTL Fieldbus Barrier, notification
of the health of the redundant barrier modules can be made available to the host
control system via the fieldbus network.
Host notification is achieved using an Alarm Module mounted on the Fieldbus Barrier
carrier. The alarm module is a Foundation Fieldbus Device that is connected to the
fieldbus segment using one of the six available spurs, and appears on the segment
'live list' along with other devices that are supported on the segment. The device
monitors both barrier modules and signals the healthy/failed status of each spur via
fieldbus Digital Input (DI) function blocks. Each barrier module is assigned its own DI
function block; the control system must therefore monitor the status of both DIs in
order to detect a spur or a module failure.
The integrated fieldbus device is also able to provide additional diagnostic information
that is not normally available in conventional fieldbus barrier installations. Importantly,
each of the Fieldbus Barrier modules is able to detect a short-circuit or a low impedance
between the plus (+) or minus (–) connections of any spur and the shield (S) of the
spur cable. Undetected "short to shield" faults jeopardise the reliability of a fieldbus
network, because a second fault may cause the loss of one or more active spurs.
With MTL Redundant Fieldbus Barrier, as well as being indicated by the module's
status LEDs, a "short-to-shield" fault is also indicated via status bits contained in the
fieldbus alarm module's Analog Input (AI) function blocks. This can therefore give early
indication of faults via the fieldbus control system, allowing early rectification.
Note: The fieldbus alarm module also incorporates a temperature sensor, which can, if
required, be used to ensure that the ambient temperature around the Fieldbus Barriers
does not exceed the 75°C value required to promote reliable operation and compliance
with certification requirements.
7.2

Device details

The fieldbus alarm device is an ABB type TTH300.
When supplied as part of a 9387-FB-R Redundant Fieldbus Barrier assembly, or
separately as an 9379-ALM alarm module, the device's alarm thresholds are pre-
configured to correspond to the output signals of the MTL Fieldbus Barrier modules.
Further device configuration should not be necessary.
It contains the following FF blocks:
Qty Block
1 Resource block
4 AI (analogue input) block
1 ePID block (PID controller with expanded features)
2 DI (digital input) block
1 AO (analogue output) block
1 Temperature transducer block
1 Extended diagnostics transducer block
1 HMI transducer block (LCD)
As mentioned earlier, the key block types of interest in this application are the DI and
the AI and these are covered in turn below.
INM9380-RD Rev 2