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Reference Manual
00809-0100-4021, Rev DA
November 2004
Rosemount 3144P
7-2
Prior Use SIS
SAFE FAILURE
FRACTION
The Safe Failure Fraction calculation for the combination of the 3144P and
the process sensor must consider the effects of the transmitter’s process
sensor diagnostics. The following is an example only. The 3144P FMEDA
report should be consulted for actual transmitter failure rates. Sensor failure
data may be found in various references, or may be based on the user’s
experience history. All failure rates are listed in FITs.
Example
Transmitter Only:
Lambda H = 33
Lambda L = 334
Lambda DU = 74
Lambda Total = 459
Sensor Only:
Lambda Total = 200
%L = 99% (open circuit 70% + short circuit 29%)
%DU = 1% (drift 1%)
Lambda L = 1980 (99% of 2000)
Lambda DU = 20 (1% of 2000)
Transmitter plus Sensor:
Lambda DU = 94 (Lambda DU Transmitter + Lambda DU Sensor
Lambda Total = 2459 (Lambda Transmitter + Lambda Sensor)
Safe Failure Fraction = 96.2% (Lambda DU / Lambda Total)
INSTALLATION No special installation practices are necessary with the 3144P in a PU Safety
Instrumented System. However, a full review of the Failure Mode and Security
switches is required. Follow the standard installation requirements (see
Section 2: Installation).
Switches Failure Mode Switch
The transmitter monitors itself during normal operation using an automatic
diagnostic routine. If the diagnostic routine detects a sensor failure or a failure
in the transmitter electronics, the transmitter goes into high or low alarm,
depending on the position of the failure mode switch.
The analog alarm and saturation values that the transmitter uses depend on
whether it is configured to standard (set by the factory) or NAMUR-compliant
operation. These values are also custom-configurable in both the factory and
the field using the 375 Field Communicator. The limits are:
•21.0 ≤ I ≤ 23 for high alarm
• 3.5 ≤ I ≤ 3.75 for low alarm
The values for standard and NAMUR operation are as follows:
Transmitter Security Switch
The transmitter is equipped with a write-protect switch that can be positioned
to prevent both accidental and deliberate change of configuration data.
Characteristics Standard Operation NAMUR-Compliant Operation
Fail High 21.75 mA ≤ I ≤ 23.0 mA 21.0 mA ≤ I ≤ 23.0 mA
High Saturation I ≥ 20.5 mA I ≥ 20.5 mA
Low Saturation I ≤ 3.90 mA I ≤ 3.8 mA
Fail Low I ≤ 3.75 mA I ≤ 3.6 mA