Operating functions via HART
7.4 Selecting the measurement type
SITRANS P300 with HART communication
7-4
Operating Instructions, 06/2005, A5E00359579-02
7.4.3
Variable mapper
Introduction
In SITRANS P300, the dynamic variable that determines the behavior of current output is
always called the Primary Variable (PV). You need to use the mapper for a number of
purposes, including selecting which device variable is to be switched to PV. The variable
selected as PV using a PC program such as SIMATIC PDM or using the HART
Communicator is scaled once again in the analog output stage to a zero value and a limit
value. These two values then correspond to the current values 4 and 20 mA.
As soon as the PV is switched over using the mapper, these zero and limit values in the
analog output stage are preset to the limit values of the new device variables. You can
define these limit values within the individual block functions.
The dynamic variables "Primary", "Secondary", "Tertiary" and "Quarternary" (PV, SV, TV,
QV) can be interconnected with any active device variables. Various different measurement
type examples are conceivable with a 4 bar pressure transmitter.
See also
Measured value status (Page 7-10)
7.4.4
Measurement type "Pressure"
Introduction
The "Pressure" measurement type contains the "Sensortrim" function and is always active as
the default measurement type. If the measurement type selector is set to "Off", no further
measured variables will be inferred from the measured variable "Pressure". All device
variables apart from the first four are marked as inactive and are given the status
CONSTANT. These four variables are mapped by default to the dynamic variables PV, SV,
TV and QV.
Switching an inactive device variable to the Primary Variable (PV) generates an fault
message since the variable does not contain a valid measured value at that point in time.
This message is shown in SIMATIC PDM or in the HART Communicator.
