Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 114)

114 Rockwell Automation Publication 1756-UM533C-EN-P - February 2011
Chapter 7 Configure the Modules with RSLogix 5000 Software
– Current Fault - The analog current doesn't match the readback of the
current received over the HART communication. This might be caused
by an inaccurate field device, faulty wiring, or water in the conduit.
Sometimes a rapid change in the signal results in a transient current
fault as the analog and digital representations are sampled at slightly
different times and at different places in the signal path.
– Configuration Changed - The Field Device configuration has changed
and new Field Device configuration information can be obtained from
the module via CIP MSG GetDeviceInfo, which will clear this bit.
– ResponseCode - HART Communication Status or Response Code.
0 means success. See Appendix C for details.
– FieldDeviceStatus - HART device health, such as PV out of range or
device malfunction. See Appendix C for details.
– UpdatedStatusReady - indicates new device diagnostic information is
available, which can be obtained by sending a CIP Message with
Service 4C.
HART Dynamic Variables
Most HART devices are capable of measuring several different process
characteristics or of deriving other measurements from directly sensed
measurements. For example, many differential pressure transmitters can also sense
the process temperature and can calculate the flow, or they might calculate the
volume in a tank based on a measurement of its head pressure and knowledge of
tank geometry and product density.
The most important of these direct or derived measurements is assigned to the
PV (Primary Variable) and the analog signal will represent its value. Additional
measurements can be read from the HART field device over the HART
communication protocol. HART provides a standard message for reading four of
the dynamic variables, called PV, SV, TV, and FV (sometimes called QV). These
four dynamic variables are the four measurements of interest to a controller.
These four dynamic variables - PV, SV, TV, and FV - are automatically collected
from the HART field device and placed in the module’s input tag in
HART.ChxPV (for Analog and HART PV data format) or Chxx.PV (for Analog
and HART by Channel data format). In some HART devices, the choice of
which of the available measurements to assign to PV, SV, TV, and FV can be
changed via configuration. In other more simple devices, the assignment is done
at the factory and cannot be changed.