On some instruments, it is very clear about assigning HART variables, like the newly introduced FC430 Coriolis meter. PV = whatever is assigned to the analog output; SV, TV, and QV are assignable from a pool of 12 variables, via LUI menu item 4.6 or PDM.

The PS2 suffers nearly non-existent documentation when it comes to HART diagnostics and PDM in general.

But an analogy with regards to the DSIII pressure transmitter should be valid.

Figure 01 in the FAQ "How do you use the HART secondary variables in addition to the actual HART process value in PCS 7?" is a screen shot of PDM screen

at this URL:
https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&objId=23818073&load=treecontent&lang=en&siteid=cseus&aktprim=0&objaction=csview&extranet=standard&viewreg=WW

You don't have to enlarge the image because the HART variables in their table are shown just below Fig 01.

The default variable assignments are
PV = pressure (presumably as corrected, since untrimmed pressure is QV)
SV = Sensor temperature
TV = Electronics temperature
QV = untrimmed pressure

PDM should show the same set of four HART variables for the PS2 positioner as for the DSIII pressure transmitter, along with descriptions.

I've wondered whether the 'abbreviation' used by Siemens for the diagnostic variables, like T3 for number of operating hours in temperature range 3 might act as HART tags to be used with a HART command to call'buried' diagnostic values.

Somebody out there uses HART diagnostics, somehow . . .
If I can get a HART modem on a PS2 in the next couple days, I'll try to gather some info on which variables are assignable.

In answer to Jeff's original question about "the actual valve position as a HART variable", the primary HART variable, PV, is what Siemens calls Readback and is the actuator/valve's position value in percent.

I checked position in a static state, with air pressure removed so the valve position was frozen. The PS2's display read 26.0%, and all three software HART secondary masters (Viator utiliy, PDM and Pactware) all showed 26.0% as the primary variable.

So actual valve position is the primary variable is position.

Since PDM trends setpoint, I'm guessing that setpoint might be SV, the secondary variable, but I have no tool to address an SV to prove the point.

Neither PDM nor Pactware list HART assigned variables, at least in any manner that can be clearly interpreted.

How one utilizes SV, TV, and QV shall remain a mystery.
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The attached pdf file shows
- screen shots from PDM, Pactware and Mactek's utility reading the primary variable
- all PDM's entries for the PS1, over 100. Should anyone have a magic decoder ring that can ID the HART variables, please let us know.