Information On The Determination Of Safety-Relevant Parameters; Decommissioning The Transmitter - WIKA T32. S Serie Guide De Sécurité

2. Safety
WARNING!
The methods and procedures used for these tests (test scenarios) must
also be documented like the test results. If the outcome of the function test
is negative, the whole measuring system must be shut down. The process
GB
must be put into a safe condition using appropriate measures.
WARNING!
After the proof test of the instrument, start a functional check of the
entire safety function (safety loop) in order to test whether the transmitter
ensures the safety function of the system. Functional checks are intended
to demonstrate the correct function of the whole safety-related system,
including all instruments (sensor, logic unit, actuator).

2.9 Information on the determination of safety-relevant parameters

The failure rates of the electronics were determined through an FMEDA in
accordance with IEC 61508. The calculations have been based on component
failure rates per SN29500. Specifically for temperature resistance sensors and
thermocouples connected to the temperature transmitter, the failure rates determined
by Exida.com LLC are used.
The following assumptions have been made:
The transmitter is only operated in Low Demand Mode applications
■
The mean ambient temperature at the temperature transmitter during the period of
■
operation is 40 °C
The MTTR following an instrument failure is 8 hours.
■
Following ISO 13849-1, a maximum service life in the safety application for the
transmitter of 20 years is assumed. Replace the instrument after this time.

2.10 Decommissioning the transmitter

WARNING!
Ensure instruments that have been taken out of service are not
accidentally recommissioned (e.g. through marking the instrument).
After decommissioning the temperature transmitter, a functional test of
the entire safety function (safety loop) should be initiated, in order to test
whether the safety function of the system is still ensured. Function tests
are intended to demonstrate the correct function of the whole safety-
related system, including all instruments (sensor, logic unit, actuator).
16 WIKA safety manual temperature transmitter T32.xS