Rockwell Automation T8891 Trusted Speed Monitor OFTA (SOFTA) - Manual (Page 9)

Trusted
TM
Speed Monitor OFTA T8891
Issue 2 Mar 07 PD-T8891 9
2. Assembly
A single Trusted T8442 TMR Speed Monitor interfaces with three T8891 SOFTA assemblies.
A single SOFTA assembly provides the relay switching elements for one over-speed output and one
over-acceleration output.
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 via the
TC801 field interface cable and are used for relay contact diagnostic and fault detection purposes.
Force guided contact, safety relays are used on the SOFTA assembly. The physical properties of these
relays ensure that welded primary contacts can be detected by monitoring the auxiliary contact status
signal. The contact status signal is passed back to the T8442 via the TC801 field interface cable for
diagnostic and fault detection purposes.
The output contact can be used as a normally-open (de-energised relay) or a normally-closed (de-
energised relay) contact for connection to the field load. They are electrically isolated from all other
signals on the T8891 SOFTA and T8442 Speed Monitor.
For critical shutdown applications only the normally-open contacts should be used.
Power, relay drive, current sense and contact status signals all interface directly to the T8442 via the
TC801 field interface cable.