See also
Certificates (Page 248)
General functional safety (
)
Functional safety in process instrumentation (
)
10.1.3
Safety function
The fail-safe behavior of the device is the pressure measurement or the measurement of
certain process values which can be calculated from the pressure value.
The 4 to 20 mA analog output can be used as part of a safety instrumented function (SIF).
Ensure that you have only connected one device per channel and that the device is not in
multidrop mode.
Besides the application-specific measuring errors under default reference conditions, an
additional safety accuracy of ± 2% of the maximum measuring range must be added:
Total tolerance (fail-safe behavior) = ± [application-specific measurement error + 2 % safety
accuracy].
Example
A silo is to be securely monitored to check that the level does not exceed 10 meters.
Application-specific measurement error: 0.1%
Safety accuracy: 2.0%
Total tolerance: 2.1%
2.1% of 10 meters is 21 centimeters. When process monitoring is set to 9.79 meters, safe
shutdown is guaranteed even in the event of a random individual error within the safety
accuracy.
Note
Use of remote seals
If remote seals are used, the application-specific measurement error is the product of the
pressure transmitter and remote seal measurement errors.
Safety allowance
The diagnostics function reacts within 2 seconds after detection of an error.
Note
For use outside the standard reference conditions, contact Siemens to define an additional
safety accuracy.
Functional Safety
10.1 Safety concept
SITRANS P320/P420 (mA/HART)
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Operating Instructions, 06/2018, A5E44852162-AA