Rockwell Automation T8442 Trusted TMR Speed Monitor - Manual (Page 16)

Trusted
TM
Module T8442
Issue 8 Apr 10 PD-T8442 16
1.3.3. SIFTA
Each T8442 Speed Monitor Module hot swap pair requires a single T8846 SIFTA when installed in a
Trusted
TM system.
The SIFTA has nine identical speed transducer signal conditioning circuits arranged as three groups of
three.
Each of the three groups is an isolated entity, with its own field power and I/O signal interfaces.
A single transducer signal on the SIFTA is taken to three monitoring circuits on the T8442. A fault
causes that transducer to fail safe.
Multiple sensors must be employed for SIL3 applications.
The input transducer fault containment region contains the SIFTA and field cable. It extends from the
transducer to the module/field cable interface.
1.3.4. SOFTA
A single SOFTA assembly provides the relay switching elements for one over-speed output and one
over-acceleration output.
A T8442 Speed Monitor module interfaces with three SOFTA assemblies.
For each output channel, an isolated Hall Effect current sensor is connected in series with each of the
two parallel contact switching paths. The outputs from these sensors connect to the T8442 SFTU via
the field interface cable and are used for relay contact diagnostic and fault detection purposes.
Force guided contact, safety relays are used on the assembly. The physical properties of these relays
ensure that welded primary contacts can be detected by monitoring the auxiliary contact status signal.
This status signal is passed back to the T8442 SFTU via the field interface cable for diagnostic and
fault detection purposes.
Each of the two outputs provides two connection options via separate pairs of screw terminals. The
normally closed pair is for use with energize-to-trip loads. The normally open pair is for use with de-
energise-to-trip loads (preferred). Note: only one pair of output terminals may be used from each
output.
Power, relay drive, contact current sense, and contact status signals all interface directly to the T8442
via the field interface cable.