8
D5244
- SIL 2 - SIL 3 Digital Relay Output , Loop Powered
G.M. International ISM0271-5
Description:
Input Signal from PLC/DCS is normally High (24 Vdc) and it is applied to pins 1-2 in order to Normally Energize (NE) or Normally De-energize (ND) loads.
For NE load, the Input Signal from PLC/DCS is Low (0 Vdc) during “de-energized to trip” operation, in order to de-energize the load.
For ND load, the Input Signal from PLC/DCS is Low (0 Vdc) during “de-energized to trip” operation, in order to energize the load.
The following table describes the status (open or closed) of each output contact when the input signal is High or Low for both NE and ND loads.
Safety Function and Failure behavior:
D5244S is considered to be operating in Low Demand mode, as a Type A module, having Hardware Fault Tolerance (HFT) = 0.
The failure behaviour of D5244S is described by the following definitions:
□
Fail-Safe State: it is defined as the relay output being de-energized (that is, the NO-COM contact being open and the NC-COM contact being closed);
□
Fail Safe: failure mode that causes the module / (sub)system to go to the defined fail-safe state without a demand from the process;
□
Fail Dangerous: failure mode that does not respond to a demand from the process (i.e. being unable to go to the defined fail-safe state), so that the relay output remains
energized (that is, the NO-COM contact remains closed and the NC-COM contact remains open);
□
Fail “No Effect”: a failure mode of a component that plays a part in implementing the safety function but is neither a safe failure nor a dangerous failure.
When calculating the SFF, this failure mode is not taken into account;
□
Fail “Not part”: failure mode of a component which is not part of the safety function but which is part of the circuit diagram and is listed for completeness.
When calculating the SFF, this failure mode is not taken into account.
Failure rate date: taken from Siemens Standard SN29500.
Failure rate table:
Failure rates table according to IEC 61508:2010 Ed.2 :
PFDavg vs T[Proof] table
(assuming Proof Test coverage of 100%), with determination of SIL supposing module contributes
≤
10% of total SIF dangerous failures:
PFDavg vs T[Proof] table
(assuming Proof Test coverage of 100%), with determination of SIL supposing module contributes >10% of total SIF dangerous failures:
Systematic capability SIL 3.
Operation
Input Signal
Pins 1 - 2
Pins 14 - 15/16
Pins 13 - 15/16
NE Load (SIL2)
Pins 15/16 - -Vload
ND Load (SIL2)
Pins 15/16 - -Vload
Normal
High (24 Vdc)
Closed Open Energized
De-Energized
Trip
Low (0 Vdc)
Open
Closed De-Energized Energized
Failure category
Failure rates (FIT)
λ
dd
= Total Dangerous Detected failures
0.00
λ
du
= Total Dangerous Undetected failures
35.23
λ
sd
= Total Safe Detected failures
0.00
λ
su
= Total Safe Undetected failures
109.72
λ
tot safe
= Total Failure Rate (Safety Function) =
λ
dd
+
λ
du
+
λ
sd
+
λ
su
144.95
MTBF (safety function, single channel) = (1 /
λ
tot safe
) + MTTR (8 hours)
787 years
λ
no effect
= “No effect” failures
92.45
λ
not part
= “Not Part” failures
2.00
λ
tot device
= Total Failure Rate (Device) =
λ
tot safe
+
λ
no effect
+
λ
not part
239.40
MTBF (device, single channel) = (1 /
λ
tot device
) + MTTR (8 hours)
476 years
λ
sd
λ
su
λ
dd
λ
du
SFF
0.00 FIT
109.72 FIT
0.00 FIT
35.23 FIT
75.70%
T[Proof] = 1 year
T[Proof] = 6 years
PFDavg = 1.55 E-04 - Valid for
SIL 2
PFDavg = 9.28 E-04 - Valid for
SIL 2
T[Proof] = 20 years
PFDavg = 3.09 E-03 - Valid for
SIL 2
Functional Safety Manual and Applications
Application D5244S -
with Loop Powered Mode
2)
Normal state operation
De-energized to trip operation
14
PLC
Output signal
ON - 24 Vdc
15/16
SIL 2
NE Load
+ V load
- V load
13
14
PLC
Output signal
OFF - 0 Vdc
15/16
+ V load
- V load
13
SIL 2 Normally Energized Relay Condition for ND Load
Normal state operation
De-energized to trip operation
13
PLC
Output signal
ON - 24 Vdc
15/16
+ V load
- V load
14
13
PLC
Output signal
OFF - 0 Vdc
15/16
+ V load
- V load
14
SIL 2 Normally Energized Relay Condition for NE Load
SIL 2
NE Load
SIL 2
ND Load
SIL 2
ND Load
