Instrument Design Principles
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Instrument Design Principles
Instrument performance/accuracy shall be sufficient to fulfil process/unit performance requirements.
Variation of instrument types and ranges (e.g. thermowell lengths/transmitter ranges) shall be kept to
a minimum.Analogue instruments shall be used for switch functions.
Smart type instruments should be used.
For each installation, the communication protocols shall be
harmonised.Galvanic isolation barriers shall be used for I/O signals. These barriers should have full smart signal
transmission capability.For simple local control purposes only, the field instruments including controllers may be of a
pneumatic type.Where local indicators are required, local indicators and transmitters shall be combined.
Separate
local indicators may only be installed if necessary for local operation.Any arrangement of instruments shall allow for the removal of a sensor/detector head while
maintaining the integrity of the other sensors, e.g. in addressable systems.Instruments shall meet requirements to EN 50081-2 and EN 50082-2 regarding electromagnetic
compatibility.Flange connection for inline instruments shall follow piping class and specification ref.
ANSI B16.5
Pipe Flanges and Flanged Fittings.All in-line flow elements (when part of the process line) shall be flanged for removal from the
process line.Pressure vessel design (e.g. accumulators for on/off valves) shall follow NORSOK standard L-002
Piping Design, Layout and Stress Analysis.The most frequently used measuring principles are specified in separate sections of this document.
Other types may be used on special applications.For field instruments not specifically dealt with in this standard, the design shall be based on
recognised international standards where applicable.
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