Functional Safety; Safety Concept; Random And Systematic Errors; Sil-Compliant Product Version - Siemens SITRANS P Operating Instructions Manual

Functional Safety

Introduction
This section includes the required additional information for parameter assignment,
commissioning and maintenance of the device in a safety-instrumented system.
10.1

Safety concept

The device was developed in accordance with the Safety Integrity Level (SIL), which is defined
as a relative level of risk reduction offered by a safety function.
The individual device has a hardware fault tolerance of 0 (HFT = 0) and a systematic suitability
of 3. The device is classified as Type B device.
● The device meets the requirements of SIL 2 in single-channel safety-related systems.
● The device meets the requirements of SIL 3 in two-channel safety-related systems, when a
comparison function for checking the output of the two redundant devices comprising a
redundant system is implemented.
10.1.1

Random and systematic errors

Random errors can occur at any time. An example is an electronic circuit that is faulty
immediately.
Systematic errors occur under specific conditions and are reproducible, if the same conditions
arise again. An example is a software error that occurs under certain conditions.
There are random and systematic errors in hardware, but only systematic errors in software.
Note
Limitations in redundant systems
Redundancy significantly reduces the probability of a failure of the safety function due to a
random error but not the probability of systematic errors.
10.1.2

SIL-compliant product version

Information on specific versions that are permitted for use in safety-related systems according
to IEC 61508 can be found in the manufacturer's declaration of conformity for the device (SIL
declaration of conformity, Functional Safety according to IEC 61508).
SITRANS P320/P420 with 4 to 20 mA/HART
Operating Instructions, 11/2019, A5E44852162-AC
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