Re: aiRecord conversion

[Bruno Seiva Martins <brunoseivam@gmail.com>]

Hi Eric,

I believe you refer to [1]. I was referring to the text that I found in [2], which is the top Google result for "epics record reference". Those texts present different formulas:

[1] val = val * ESLO + EGUL

[2] val = val * ESLO + EOFF

So there seems to be an inconsistency in the documentation. I'll try to set both EOFF and EGUL, as Ralph suggested.

Thanks!

[1] https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14_Analog_Input

[2] http://www.aps.anl.gov/epics/EpicsDocumentation/AppDevManuals/RecordRef/Recordref-8.html#HEADING8-0

Bruno Seiva Martins

On Tue, Aug 28, 2012 at 10:45 AM, Eric Norum <eric@norum.ca> wrote:

Perhaps you misread the wiki page.  EGUL does not take part in the conversions.  

Here is the salient portion of the wiki page:

The record processing routine performs the following algorithm for all records except those that use the Soft Channel device support routine. Be aware that step 3 is performed only when the record specifies LINEAR:

1. Val= RVAL + ROFF

2. Val = Val * ASLO + AOFF

If the conversion algorithm is LINEAR, the raw value is converted via the equation:

3. val = val * ESLO + EOFF

If the conversion is via a breakpoint table, the new value is obtained.

On Aug 28, 2012, at 5:48 AM, Bruno Seiva Martins <brunoseivam@gmail.com> wrote:

Hi all,

I am having trouble trying to adjust the conversion parameters of an analog input record for a A/D converter.

My AD accepts voltages ranging from -10 to 10 volts and has a resolution of 12 bits.

For -10 volts, it produces a digital output of 0

For 10 volts, 4095

I configured the conversion fields as follows:

EGUF: 10

EGUL: -10

AOFF: 0

ASLO: 1

EOFF: 0

ESLO 0.004884   // which is (EGUF - EGUL) / 4095

ROFF: 0

LINR: LINEAR

Those values seem right to me but, for example, RVAL=1005 gets converted to VAL=4.9084, when it should be VAL=-5.0916. The problem seems to be that the conversion formula isn't taking into account the EGUL field.

According to the EPICS record reference for aiRecord:

The record processing routine performs the following algorithm for all records except those that use the Soft Channel device support routine. Be aware that step 3 is performed only when the record specifies LINEAR:
1. Val= RVAL + ROFF
2. Val = Val * ASLO + AOFF
If the conversion algorithm is LINEAR, the raw value is converted via the equation:
3. val = val * ESLO + EGUL

Seems like the step 3 is not being completely executed, or considering EGUL = 0...

Does anybody know what is wrong? Probably I'm missing something really obvious, but I couldn't figure it out...

Thanks in advance,

Bruno Seiva Martins

-- 
Eric Norum
eric@norum.ca