169
Reference Manual
00809-0100-4026, Rev HA
Section 8: Safety Instrumented Systems (4-20 mA Only)
November 2014
Safety Instrumented Systems (4-20 mA Only)
8.2.2 Skill level of personnel
It is assumed that the personnel installing, configuring, and operating the system have the
knowledge equal or greater than that of a qualified Instrument Technician familiar with
safety-related systems, process control applications, and general instrument use.
Note
The Rosemount 5400 Series transmitter is not safety-rated during maintenance work,
configuration changes, multidrop, loop test, or other activity that affects the Safety Function.
Alternative means should be used to ensure process safety during such activities.
8.3 Functional specifications
The Safety Function is based on the analog output 4-20 mA, used as the safety variable. It is
configured to activate the alarm function if an error occurs or if the measured value goes
beyond the measurement range set by the user.
In the case of the Rosemount 5400 Series, the definition of the Safe State Safety Function is:
The distance measurement is performed as intended inside the safety accuracy limits,
that is with a deviation of < ±2 % of the measuring range.
The safety analog output signal is set outside the normal 4-20 mA range (Low or High
Alarm). The Rosemount standard alarm setting
is: <
3.75 mA or > 21.75 mA.
Only the 4-20 mA output can be used in the Safety Function. The HART protocol can only be
used for setup, calibration, and diagnostic purposes, not for safety critical operation. The
measurement signal used by the logic solver must be the analog 4-20 mA signal proportional to
the level generated.
8.4 Installation
The device should be installed and configured as a level sensing device per manufacturer’s
instructions. The materials must be compatible with process conditions and process fluids. No
special installation is required in addition to what is described in this section, the standard
installation practices outlined in Section 3: Mechanical Installation, and the Rosemount 5400
Series Quick Start Guide (Document No. 00825-0100-4026).
Environmental limits are available in Appendix A: Reference Data.
Note
False echoes within the radar beam from obstructions may lead to a situation where the
Rosemount 5400 Series can no longer be used for safety related functions with the listed failure
rates, SFF, and PFD
AVG
. However, reduced proof test intervals can help to detect such unwanted
causes.
The loop must be designed so the terminal voltage does not drop below the minimum input
voltage, see values in Ta ble 8 -2, when the transmitter output is 21.75 mA. The input voltage U
i
for HART is 16-42.4 Vdc (16-30 Vdc in IS applications, and 20-42.4 Vdc in Explosion-proof /
Flameproof applications).
To Next Page
Loading...
