RE: Logarithmic conversion / Breakpoint tabes

["Mark Rivers" <rivers@cars.uchicago.edu>]

Hi Gavin,

> I have an Ai record which gets raw data from a pressure (vacuum?)
sensor
> measured by the PLC. The raw data ranges from 0 to 256000 and
represents
> a Torr of 1e-11 through to 1e-3. I am wanting to convert this into the
> engineering units, but as far as I can see only linear styles of
> conversion are supported. I could make a breaktable with some values
in
> it, but if I understand correctly the gaps between the points will be
> interpolated linearly, and will therefore suffer some error.

For the vacuum gauge controllers we use (HPS MKS) I wrote device support
in C.  That was necessary because there are things that need to be done
at iocInit, like asking what type of gauge is connected to each of 4
inputs (to set HOPR and LOPR), what units the gauge is using (torr mbar,
etc.).  With device support it is easy to do the conversion in C and put
the result into the VAL field of the ai record, returning 2
(DO_NOT_CONVERT).

Mark