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Subject: RE: Logarithmic conversion / Breakpoint tabes
From: "Owens, PH \(Peter\)" <[email protected]>
To: "Gavin Smith" <[email protected]>, <[email protected]>
Date: Tue, 29 Mar 2005 10:45:26 +0100
I have some AIs like that.
I deal with the input using a CALC record
just as you suggest for your outputs.

Pete.

-----Original Message-----
From: Gavin Smith [mailto:[email protected]]
Sent: 29 March 2005 07:37
To: [email protected]
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).



Replies:
Re: Logarithmic conversion / Breakpoint tabes Maren Purves

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