Periodic checks
12
TTH200, TTR200, TTH300, TTF300, TTF350 SM/TTX200/TTX300/SIL-EN
7 Periodic
checks
Safety inspections
The safety function for the entire safety loop must be checked regularly in accordance with
IEC 61508. The inspection intervals are defined when calculating the individual safety loops for
a system.
Users are responsible for selecting the type of check and the intervals within the specified
period. The PFD
AV
value depends on the selected inspection interval. For the PFD
AV
values in
the SIL declaration of conformity, the inspection interval T[Proof] for checking the safety function
is 1 year. For other inspection intervals with corresponding PFD
AV
values, refer to the section
titled "Management summary FMEDA".
Inspections must be conducted in a manner that enables users to verify the proper function of
the safety equipment in combination with all components.
One possible procedure for recurring tests to detect hazardous and unidentified device errors is
described in the following section. This test is able to detect 99 % of the "Du" errors affecting the
transmitter.
Checking the safety function
To check the safety function of the device, proceed as follows:
1. Bridge the safety DCS or take other appropriate measures to ensure the alarm is not
triggered unintentionally.
2. Deactivate write protection (refer to the relevant operating instructions).
3. Use the EDD / DTM simulation command (Diagnostics / Simulation / Current Output) to set
the transmitter's current output to a high alarm value.
4. Check whether the current output signal reaches this value.
5. Use the EDD / DTM simulation command to set the transmitter's current output to a low
alarm value.
6. Check whether the current output signal reaches this value.
7. Activate write protection (refer to the relevant operating instructions) and wait at least
20 seconds.
8. Shut down and restart the device.
9. Check the current output with reference temperature; use 2-point calibration for the LRV
value (lower measuring range limit 4 mA) and the URV value (upper measuring range limit
20 mA).
10. Remove the bridge from the safety DCS or use another method to restore normal operating
conditions.
11. After performing the test, the events must be documented and archived accordingly.
An appropriate simulator (Pt100 simulator, reference voltage sources) can also be used to
check the transmitter without sensor. The sensor has to be tested in accordance with the SIL
requirements of the customer application. SensyTemp TSP temperature sensors can be tested
in accordance with the OI/TSP by means of a quick check.
