Definition:
An instrument in functional safety is any sensor or device used to detect a condition to trigger the SIF into performing its action.
Many process instruments follow NAMUR conventions, such as NE 43, where a transmitter signals an internal fault by driving its 4-20 mA output below 3.6 mA or above 21 mA instead of reporting a believable value.
Key Points:
- Includes all types of instruments. Such as with transmitters or simple switches
- Can be very high end to very low tech instruments.
- Most high-tech instruments are essentially computers with their own diagnostics.
Example:
A high-level switch on a separator vessel is an instrument.
See Also: final element, logic solver
Cited Source:
- IEC 61511-1:2016, Clause 3.2.34