11
D5290S-078
- 5 A SIL 3 Relay Output Module
G.M. International ISM0152-8
The proof test shall be performed to reveal dangerous faults which are undetected by diagnostic. This means that it is necessary to specify how dangerous undetected faults, which
have been noted during the FMEDA, can be revealed during proof test. The Proof test consists of the following steps:
Testing procedure at T-proof
Steps
Action
1
Bypass the safety-related PLC or take other appropriate action to avoid a false trip when removing the unit for test.
2
Verify the input-to-output functionality, considering the input signal and each relay output contact state:
□
Out S_1 (NO contact) at terminals “13”-“14”: when input is energized, Out S_1 must be closed;
while shutdown of the input channel, Out S_1 must be open;
□
Out S_2 (NO contact) at terminals “15”-“16”: when input is energized, Out S_2 must be closed;
while shutdown of the input channel, Out S_2 must be open;
□
Out P_1 (2 NC contacts in parallel connection) at terminals “17”-“18”: when input is energized, Out P_1 must be open;
while shutdown of the input channel, Out P_1 must be closed;
□
Out S_3 (NO contact) at terminals “23”-“24”: when input is energized, Out S_3 must be closed;
while shutdown of the input channel, Out S_3 must be open;
□
Out S_4 (NO contact) at terminals “21”-“22”: when input is energized, Out S_4 must be closed;
while shutdown of the input channel, Out S_4 must be open;
□
Out P_2 (2 NC contacts in parallel connection) at terminals “19”-“20”: when input is energized, Out P_2 must be open;
while shutdown of the input channel, Out P_2 must be closed.
The channel functionality must be verified for a min to max input voltage change (21.6 to 27.6 Vdc).
In addition is possible to check the Out P_1 and Out P_2 (which are the parallel connection of 2 NC contacts), imposing (by internal DIP-switches n°1, 3, 5)
the short circuit of each single relay coil and to verify the ohmic continuity of the contacts, as described in the following procedure.
1. Do not supply the input channel (terminals “1”-“2”, or “3”-“4”) of module under test and verify that the ohmic continuity at the output contact terminals
“17”-“18” (Out P_1) or “19”-“20” (Out P_2) is present (i.e. the parallel connection of the 2 NC contacts is closed: the
1
st
requisite is verified
). But this
condition could also be true if only one contact is closed and other is blocked (for welding) into closed or open position: this will be verified testing the
channel when input is supplied (see the 2
nd
point). Instead, the absence of ohmic continuity implies that all relay contacts are blocked (for welding) into
open position.
2. Supply the input channel (terminals “1”-“2”, or “3”-“4”) of module under test and verify that the ohmic continuity at the output contacts terminals
“17”-“18” (Out P_1) or “19”-“20” (Out P_2) is absent (i.e. the parallel connection of the 2 NC contacts is open: the
2
th
requisite is verified
).
The presence of ohmic continuity implies that at least one relay contact is blocked (for welding) into closed position: this could only be verified after
disassembling and individually testing each relay. Instead, to verify if a contact is blocked (for welding) into open position, use internal DIP-switches
(n°1, 3, 5) to put in short circuit one relay coil at a time (starting with the 2
nd
coil by DIP-switch n°3, then going on with the 3
rd
one by DIP-switch n°5
(for “17”-“18” Out P_1) or with the 1
st
one by DIP-switch n°1 (for “19”-“20” Out P_2)), verifying that the ohmic continuity is always present between
terminals “17”-“18” (Out P_1) or “19”-“20” (Out P_2). In this situation, the absence of ohmic continuity implies that a relay contact (the only one with
de-energized coil) is blocked (for welding) into open position.
3
Remove the bypass from the safety-related PLC or restore normal operation inserting the unit.
This test reveals almost 99% of all possible Dangerous Undetected failures in the relay module.
