Emerson Rosemount, Reference Manual

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188
Reference Manual
00809-0100-4021, Rev GC
Section 7: Prior Use (PU) Safety Instrumented System
April 2014
Prior use (PU) safety instrumented system
7.2 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 3144P FMEDA
report should be consulted for calculated transmitter failure rates. Sensor failure data may be
found in various references, or may be based on the user’s experience history. A copy of the
FMEDA can be found at
http://www.emersonprocess.com/rosemount/safety/safetyCertTemp.htm
7.3 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 ).
7.3.1 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 an electronics failure, the transmitter goes
into high or low alarm, depending on the position of the failure mode switch.
The analog alarm and saturation values used by the transmitter depends 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 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
accidental and deliberate change of configuration data.
7.3.2 Changing switch position
The Failure Mode and Security switches are located on the top center of the electronics module
(see
Figure 7-1 on page 189 ) which is on the electronics side of the transmitter housing. For
transmitters with an LCD display, the electronics module is located behind the LCD display
faceplate.
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