The HART Command Set provides uniform and consistent communication for all field devices. The command set includes three classes: Universal, Common Practice, and Device Specific. Host applications may implement any of the necessary commands for a particular application.
Universal Commands
All devices using the HART Protocol must recognize and support the universal commands. Universal commands provide access to information useful in normal operations (e.g., read primary variable and units).
Common Practice Commands
Common Practice commands provide functions implemented by many, but not necessarily all, HART communication devices.
Device Specific Commands
Device Specific commands represent functions that are unique to each field device. These commands access setup and calibration information, as well as information about the construction of the device. Information on Device Specific commands is available from device manufacturers.
The table below gives a list of the common HART commands encountered:
Universal Commands
|
Common Practice Commands
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Device Specific Commands
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|---|---|---|
Read manufacturer and device type
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Read selection of up to four dynamic variables
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Read or write low- flow cut-off
|
Read primary variable (PV) and units
|
Write damping time constant.
|
Start, stop or clear totalizer
|
Read current output and percent of range
|
Write device range values
|
Read or write density calibration factor
|
Read up to four predefined dynamic variables
|
Calibrate (set zero, set span)
|
Choose PV(mass, flow or density)
|
Read or write eight character tag, 16 character descriptor, date.
|
Set fixed output current
|
Read or write materials or construction information
|
Read or write 32-character message.
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Perform self-test
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Trim sensor calibration
|
Read device range values, units and damping time constant.
|
Perform master reset
|
PID enable
|
Read or write final assembly number.
|
Trim PV zero
|
Write PID setpoint
|
Write polling address
|
Write PV unit
|
Valve characterization
|
Trim DAC zero and gain
|
Valve set point
|
|
Write transfer function (square root/linear)
|
Travel limits
|
|
Write sensor serial number
|
User units
|
|
Read or write dynamic variable assignments
|
Local display information
|
