Allen-Bradley 1719 Ex I/O User Manual page 52

Chapter 5 1719 Ex I/O HART Analog I/O Modules
52
changed via configuration. In other more simple devices, the assignment is done
at the factory and cannot be changed.
An example for a Flow Meter might be:
• PV - Primary Variable. Flow Rate in Liters per Minute.
• SV - Secondary Variable. Process Temperature in °C.
• TV - Third or Tertiary Variable. Product Density in Grams per Cubic
Centimeter.
• FV - Fourth or Quaternary Variable
An example for a Valve Positioner might be:
• PV - Primary Variable. Commanded position in %.
• SV - Secondary Variable. Actual position in %.
• TV - Third or Tertiary Variable. Air Pressure in PSI.
• FV - Fourth or Quaternary Variable. Loop current in mA.
In addition to the measurement value, HART devices can provide status
information that indicates the quality of the measurement.
Process Data Status
11 Good
01 Poor Accuracy
10 Manual/Fixed
00 Bad
For example, if a valve positioner cannot open any further, it should set its
HART.ChxSVStatus to 2#11100000 to indicate that the actual position value in
the SV is Good (accurately measured) but is the subject of a High Limit. This
status information can be used for windup control in PID loops and for other
diagnostic purposes.
Rockwell Automation Publication 1719-UM001C-EN-E - August 2018
Device Family Specific Status
More Device Variable Status Available
Limit Status
11 Constant
01 Low Limited
10 High Limited
00 Not Limited