UFC 3 -430-11
14 February 2001
Electronic transmitters with internal microprocessors are known as "smart
transmitters". These transmitters provide on-board sensor linearization, data correction
coefficients, measurement ranging, system diagnostics, and instrument configuration.
These transmitters communicate to the control system via a communication bus (e.g.
HART or Fieldbus).
5-2.12
Electrical Instrument Switches. Typical applications for electrical
instrument switches are alarms and shutdowns. Contacts should open to alarm or shut
down for fail safe operation. Provide switches that are suited for the environment.
Provide switches that are dust tight and vibration proof for all locations. Provide NEMA
4 rated switches for outdoor locations with non-corrosive atmospheres and NEMA 4X
rated switches for corrosive atmospheres. Provide SPDT contacts as a minimum.
5-2.13
Analyzers. Include all analyzers necessary to meet federal, state, and local
environmental monitoring requirements. Analyzers used in a boiler plant include the
following:
In-line
Sample diverted from the stream to the analyzer and then returned to the
stream
Sample diverted from the stream to the analyzer and then discharged to the
atmosphere or a drain
5-2.13.1 General Guidelines. Use in-line analyzers where practical. As a second
choice use an analyzer where the sample is diverted to the analyzer and then returned
to the stream. Use an a nalyzer where the sample is discharged to the atmosphere or
drain as a last choice. Provide a relatively constant differential pressure device, such as
a pump, as a bypass to divert a sample that is to be returned to the stream. Avoid
bypassing around a control valve.
5-2.13.1.1
zero and full span in the range in which the analyzer will be operating. Provide
automatic calibration at power-up, at manual command, and at preprogram med
intervals.
5-2.13.1.2
Application. When to use analyzers and what type of analyzer to use
depends upon environmental and value engineering concerns for a given boiler size.
These issues are discussed in paragraph 3 -17 and 6 -4. Analyzers should be used for
trim or alarms. Avoid using analyzers as a sole means of control or shutdown.
5-2.13.1.3
Packaging. It is possible to obtain multiple analyzers packaged in one
system. For example, flue gas analyzers are available that combine oxygen,
combustib les and methane measurement in one package. This packaging concept
would reduce installation complexity and may provide cost savings.
5-9
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