www.miinet.com
Moore Industries-International, Inc.
- 71 -
User’s Manual
225-748-01L
February 2017
www.miinet.com
Programmable Current/Voltage Safety Trip Alarm
STA
HLPRG
SEC
TION 8
High Integrity Analog Output
The configuration shown in Figure 8.5. offers the highest AO integrity. Any input or STA fault will
drive the AO signal out of range. However this configuration is vulnerable to spurious trips as
STA safe failures will also drive the AO signal out of range.
Tx or I+
COM
NC3
CM3
NO3
READY INPUT
TRIP 1 TRIP 2 FAULT
SELECT
DOWN
UP
COM
STA
SAFETY
TRIP
ALARM
TAG
126.39
DEG C
Analog
Output
Fault
Relay
LO
AD
Figure 8.5.
High Integrity Analog Output example
Analog Output in the Safety Path
When the Analog Output is used in the safety path, the fault alarm must also be monitored to
detect STA failures. In Figure 8.4 below, the fault alarm is wired separately in a high availability
architecture. The fault alarm can also be wired in series with the Analog Output to provide a high
integrity architecture..
Figure 8.4.
The STA with Analog Output (AO) in the Safety Path
Tx or I+
COM
NC3
CM3
NO3
READY INPUT
TRIP 1 TRIP 2 FAULT
SELECT
DOWN
UP
COM
STA
SAFETY
TRIP
ALARM
TAG
126.39
DEG C
Analog
Output
Fault
Relay
LO
AD
LO
AD
Note:
When power is lost the AO will fail low. For this reason in a safety application, the logic
solver must be either configured to detect a ‘fail low’ condition (anything less than 4.0mA is
detected as a fault) or ‘fail windowed’ condition (anything outside the 4-20mA range is detected
as a fault).
Note:
For STA units with V1.3 firmware or greater, the AO can be used in the safety path.
