www.miinet.com
Moore Industries-International, Inc.
- 127 -
User’s Manual
238-760-00K
May 2019
Functional Safety Dual Input Smart HART® Temperature Transmitter
STZ
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SECTION 8
Figure 8.5.
The STZ in SIL 3 Application.
SIL 3 Application Example
The STZ has been approved for SIL3 systematic capability. This means it can be used in a
redundant architecture in a SIL3 application. The figure below is an example of the STZ in a SIL3
application with STA Logic Solver acting as a 1oo2 voter.
In this case every loop component appears twice. The logic is an ‘OR’ for fail safe instruments; if
any element in either set asserts a trip condition, the loop will trip as each dual sensor, STZ and
STA are intended to perform the same function. If one of the elements fails the redundant set
should still perform the safety function.
Advantages:
- Improved reliability of trip action
- Reduced vulnerability to a single dangerous failure as compared to a 1oo1 loop.
SENSOR
1
SENSOR
2
NC1
CM1
NO1
NC2
CM2
NO2
NC3
CM3
NO3
P
ROCESS
R
ELAY
F
AULT
R
ELAY
1
+PS
-PS
1
2
3
4
ADDR
ADDR
ADDR
ADDR
STZ
NC1
CM1
NO1
NC2
CM2
NO2
NC3
CM3
NO3
P
ROCESS
R
ELAY
F
AULT
R
ELAY
1
READY INPUT
TRIP 1 TRIP 2 FAULT
SELECT
DOWN
UP
COM
STA
SAFETY
TRIP
ALARM
TAG
READY INPUT
TRIP 1 TRIP 2 FAULT
SELECT
DOWN
UP
COM
STA
SAFETY
TRIP
ALARM
TAG
+TX
I
SENSOR
1
SENSOR
2
+PS
-PS
1
2
3
4
ADDR
ADDR
ADDR
ADDR
STZ
+TX
I
STA
STA
STZ
STZ
F
INAL
ELEMENT