Decommissioning and withdrawal from service
© exida.com GmbH TURCK 04-07-14 R001 V2R0.doc; February 8, 2013
Stephan Aschenbrenner Page 23 of 25
Appendix 1.1: Possible proof tests to detect dangerous undetected faults
Isolating Transducers
Proof test 1 consists of the following steps, as described in Table 9.
Table 9 Steps for Proof Test 1
Step Action
1 Bypass the safety PLC or take other appropriate action to avoid a false trip
2 Send a HART command to the Isolating Transducers to go to the high alarm current
output and verify that the analog current reaches that value.
This tests for compliance voltage problems such as a low loop power supply voltage or
increased wiring resistance. This also tests for other possible failures.
3 Send a HART command to the Isolating Transducers to go to the low alarm current
output and verify that the analog current reaches that value.
This tests for possible quiescent current related failures
4 Restore the loop to full operation
5 Remove the bypass from the safety PLC or otherwise restore normal operation
This test will detect approximately 50% of possible “du” failures in the Isolating Transducers.
Proof test 2 consists of the following steps, as described in Table 10.
Table 10 Steps for Proof Test 2
Step Action
1 Bypass the safety PLC or take other appropriate action to avoid a false trip
2 Perform Proof Test 1
3 Perform a two-point calibration of the connected transmitter
This requires that the transmitter has already been tested without the Isolating Transducers and
does not contain any dangerous undetected faults anymore.
4 Restore the loop to full operation
5 Remove the bypass from the safety PLC or otherwise restore normal operation
This test will detect approximately 99% of possible “du” failures in the Isolating Transducers.
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