Experimental Physics and
Industrial Control System

"David Dudley" <[email protected]> · Tue, 14 Nov 2006 08:37:27 -0600

Two point scaling I understand.  What I haven't figured yet is where I put it in.

Where(how) do I set the deviceHigh and deviceLow variables, or is that expected in the device driver?  And if it is in the device driver, does that mean that I'm going to have to have a separate device entry for each device that has a different dynamic range?

Dynamic range calculations are not handled inside EPICS?

I've got a number of different dynamic ranges for the different devices here, do they all have to be separately scaled inside the device driver to a standard range, or can EPICS be set to adjust for the dynamic ranges?

Most of the software (make that *all*) I've used previously had the ability to have the RAWLOW and RAWHIGH values set, and they they did the scaling themselves.  Seems an omission if EPICS can't do that?

David

>>> "Mark Rivers" <[email protected]> 11/13/06 8:22 PM >>>
Device support must have a "convert" routine that does a calculation like the following to compute .ESLO and .EOFF

        precord->eslo = (eguf - egul)/(deviceHigh - deviceLow);
        precord->eoff = (deviceHigh*egul - deviceLow*eguf)/
                        (deviceHigh - deviceLow);

Mark

________________________________

From: David Dudley [mailto:[email protected]] 
Sent: Mon 11/13/2006 8:07 PM
To: [email protected] 
Subject: Scaling Database entries

OK guys,

My modbus driver is starting to work, and now I'm linking up with some of the PLC's in the plant.  Now, I've started working on building the database for the first site.

Here's my question:

I've got some AI signals that come from one of the PLCs.  Raw values on some are scaled 0-32000, while others are scaled 800-32000, and others have raw values from -32768-32767.  I see the definitions for the EGUL and EGUF values, but how do I set the RAW input ranges?  Also, I've got some flow meter values that have to be scaled from linear to square root values..

David Dudley
City of Corpus Christi

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System