Experimental Physics and
Industrial Control System

Rolf Keitel <[email protected]> · Wed, 30 Mar 2005 10:54:44 -0800

We have something similar, but really weird, with ion gauge controllers
by Varian, which give a 0-10V readback with 1 V / pressure decade.
Within the decade, however, the pressure readback is linear!!.

We use an analog record to convert the raw ADC value to voltage, then
follow with a subroutine record, which does the funny calculation.

- rolf -
Gavin Smith wrote:
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).

--
+-------------------------------------------------+
| Rolf Keitel, TRIUMF         Tel: (604) 222-7453 |
| Group Leader ISAC Controls  Fax: (604) 222-7307 |
| and Electronics Development                     |
| Vancouver, B.C., Canada                         |
+-------------------------------------------------+

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System