Rockwell Automation T8094 8000 Series TMR System Safety Manual - Manual (Page 94)

SAFETY MANUAL
D oc N umber T8094
I ssue 27 – June 2013
Page 73 of 103
8.2.1.2 Analogue Inputs
Analogue transmitters are used to monitor safety parameters and inherently provide an
increased level of diagnostics with respect to a simple fail-safe digital input. Analogue
signals always provide values within a set operating range. For safety related
transmitters this should be 4-20mA or 1-5 volts allowing for fault indication below say
3mA (0.75V) and 20mA (5V). If over-range detection is required a 0-10V input module
must be used. All monitored faults from the analogue signals must be used by the
application software to produce fail-safe results (e.g. failed transmitter demands a
shutdown).
The number of analogue transmitters used to monitor a safety parameter will be
dependent on the system integrity level (safety classification) requirement of the loop,
the 100% proof test cycle of the loop and the level of diagnostics available from the
transmitter.
The field analogue signal is wired to the Analogue Input Termination Card. Where the
safety integrity levels require that more than one transmitter be used to monitor a
safety parameter, then the additional analogue input signals should be wired to
separate Termination Cards where practical. The Simplex circuitry on the termination
card must be considered for reliability as part of the transmitter loop (e.g. fuses and
monitoring resistors where fitted). Refer to Figure 7.
The signal is connected from the termination card to the Triguard SC300E input
module via a standard system cable, which connects to the socket on the appropriate
Hot Repair Adapter Card (THR) or chassis connector.
Through the Hot Repair Adapter Card, where required, and the chassis backplane
connector the input signal is connected to the appropriate configured analogue input
module slot position, where an appropriate Analogue Input Module would be located.
All the chassis slot and, where required, their hot repair partner slots configured for the
Analogue module must also have the polarisation keys fitted and configured for this
type of module as specified in the Module and Chassis User Manuals.
Figure 7 - Current to Voltage Conversion
Where separate transmitters are used to monitor the same safety parameters to meet
increased integrity levels these should be configured to separate Analogue Input
Modules where practical.
Switch inputs with end of line and series line-monitoring resisters fitted may be
connected as analogue inputs. These line-monitored inputs provide increased
diagnostic information to the safety system giving discrete analogue values (step
changes) for open circuit, switch open, switch closed and short circuit conditions.