Revision 1 SLN 700 SmartLine NCR Level Transmitter User’s Manual Page 43
Safety Instrumented Function (SIF): A set of equipment intended to reduce the risk due to a
specific hazard (a safety loop).
Safety Integrity Level (SIL): A discrete level (one out of a possible four) for specifying the
safety integrity requirements of the safety functions to be allocated to the E/E/PE safety-
related systems where Safety Integrity Level 4 has the highest level of safety integrity and
Safety Integrity Level 1 has the lowest.
Safety Instrumented System (SIS): The implementation of one or more Safety Instrumented
Functions and is composed of any combination of sensor(s), logic solver(s), and final
element(s).
Secondary Variable (SV): A secondary dynamic feature of the process which may change
rapidly and is measured. (HART only)
Stillwell / Stilling well: A chamber that enables level measurement in turbulent conditions.
Tertiary Variable (TV): A tertiary dynamic feature of the process which may change rapidly
and is measured. (HART only)
Time-Domain Reflectometry (TDR): For Level measurement, it is a measurement technique
used to determine distance by measuring the time it takes to send electromagnetic
measurement pulses along a probe (for example, a metallic probe), reflect off a surface (liquid
or solid) and travel back to the source.
Upper Product: The lighter liquid when two liquids exist in a vessel (e.g. oil in an oil/water
measurement application)
Upper Range Value (URV): A Basic configuration parameter which allows users to enter the
measuring value for which the analog output will be scaled to 20 mA (HART only).
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