Siemens SITRANS SL - Application Restrictions; Temperature and Pressure; Purging

Device-specific Safety Instructions
Safety Manual
Operating Instructions, 06/2012, A5E03433511-05
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3.3 Application restrictions
Installation and configuration of the SITRANS SL must be completed following the
instructions detailed in the Operating Instructions of the device /1/. All application limitations
and restrictions described in that manual must be observed.
3.3.1 Temperature and pressure
Safety recommendations for process temperature and process pressure
Process temperature and process pressure measurements have an influence on the
concentration measurement by SITRANS SL and thus must be considered upon installation
of the analyzer. The measurement of temperature and pressure must reflect the process
conditions at the measurement point. Otherwise the error in concentration measurement
increases.
If the process conditions for temperature and pressure can not assumed to be constant,
external sensors for temperature and pressure are highly recommended. SITRANS SL
provides two analog input channels (4 to 20 mA) for external temperature and pressure
signals. Any external sensor for temperature and pressure must meet the requirements for
SIL 1 with a maximum total tolerance (safety function) of ±5 %.
To calculate the error in the concentration measurement which is caused by an error of
process temperature and/or process pressure measurement contact SIEMENS support
providing the operating conditions of the measurement point and the total tolerance (safety
function) of the external sensors.
3.3.2 Purging
Safety Recommendations for Purging
Purging of sensors is always required for applications with oxygen as gas to be measured. In
this case the sensors require continuous purging using nitrogen. For detailed information,
refer to respective chapters in the user manual.
Upon installation of the analyzer the use of an external monitoring system must be
considered. This system must be designed to constantly monitor the purging flow and to
ensure that all possible faults are signalled to the Safety PLC.