RE: Logarithmic conversion / Breakpoint tabes

["Dalesio, Leo `Bob`" <dalesio@slac.stanford.edu>]

I used breakpoint tables back - as it uses less CPU - but on the Power PC - I think that the calc record is just fine.
Bob 

-----Original Message-----
From: Gavin Smith [mailto:gsmith@tic.toshiba.com.au] 
Sent: Monday, March 28, 2005 10:37 PM
To: tech-talk@aps.anl.gov
Subject: Logarithmic conversion / Breakpoint tabes

Hello All,

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.

In addition to inputs, I need to have a couple of Ao's, representing maximum allowable pressures, etc. My current thinking is to have a calc record for each sensor to evaluate something like CALC,"exp(A/3200-4)", and for the outputs having an ai feeding a calc feeding an ao record for each one.

How are other people handling this in their systems?  Extra records, big breakpoint tables or some other way?

Thanks,
Gavin Smith.

(I'll be away from the office till next week sometime, so don't think I'm snubbing anyone by not replying to them straight away).