Re: aiRecord conversion

[Michael Davidsaver <mdavidsaver@bnl.gov>]

On 8/28/2012 1:08 PM, Eric Norum wrote:

On Aug 28, 2012, at 9:42 AM, Bruno Seiva Martins <brunoseivam@gmail.com> wrote:

...

The documentation at https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14_Analog_Input#special_linconv describes this pretty well:

special_linconv(precord,after)

This routine is called whenever any of the fields LINR, EGUF, EGUL or ROFF is modified. To support linear conversion, EOFF and ESLO must be set accordingly. The record support sets EOFF to EGUL before calling this routine, which is the very common case when RAWL is zero below.

A useful formula for calculating EOFF and ESLO is this one:

EOFF = (RAWF * EGUL - RAWL * EGUF) / (RAWF - RAWL)
ESLO = (EGUF - EGUL) / (RAWF - RAWL)

Here, RAWL and RAWF are the lowest resp. highest possible raw value. For instance, a 16 bit bipolar ADC might have RAWL=-0x7fff, RAWF=0x7fff.

Did RAWF and RAWL ever exist in a 3.14 release?

A quick search through VCS history shows that these fields only existed briefly between 3.14.0-alpha2 and -beta1 (circa 2001).

It would be nice to have them, then linear conversions would be unambiguous defined by fields and we could do without special_linconv().

Michael