
● The SITRANS P pressure transmitter is only used in applications with a low demand for
the safety function (low demand mode).
●
Communication with the HART protocol is used only for the following:
– Device configuration
– Reading diagnostics values
– However, it is not used for operations critical to safety. In particular, the simulation
function must not be activated in safety-related operation.
● The safety-related parameters/settings have been entered by local operation or HART
communication before commencing safety-related operation. They are checked on the local
display.
(see "Settings" section)
● The safety function test has been concluded successfully.
● The transmitter is blocked against unwanted and unauthorized changes/operation.
● The current signal of 4 to 20 mA of the transmitter is evaluated by a safe system.
● Fault rates are calculated on the basis of a Mean Time To Repair (MTTR) of eight hours
(order option C20) or 72 hours (order option C23).
See also
Settings (Page 140)
8.3 Device-specific safety information for redundant operation (SIL 3)
8.3.1 Safety function
Safety function for pressure transmitters
The safety function of SITRANS P refers to the measurement of pressures. An additional safety
allowance of 2% of the measuring range (complete span) must be added to the application-
specific measuring error for an output current of 4 to 20 mA.
Total tolerance (safety function) = ± [application-specific measuring error + 2% safety
allowance].
Pressure transmitter safety allowance: the maximum effect of an uncritical individual error on
the measured value.
The diagnostics function will respond within 4 seconds in the worst-case scenario.
Functional safety
8.3 Device-specific safety information for redundant operation (SIL 3)
SITRANS P, DS III series with HART
Operating Instructions, 09/2012, A5E00047092-08 143
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