Experimental Physics and Industrial Control System

Marty Kraimer wrote:
> 
> Last week during a visit at DESY, Gabor Csuka
> suggested that the ai and ao records should have two additional
> fields RAWH and RAWL. The reason is that often it is possible
> to create common device support for a set of modules that differ
> only in the number of bits and/or polarity.
> 
> I expressed concern that this opens door to an unlimited
> set of configuration fields. After discussion I had to agree
> that these two fields  are generic enough that perhaps
> we should add them. They would not impact any existing support
> but future support could use them.
> 
> For example if a device is a bi-polar 12 bit adc the fields would
> be
> 
> RAWH 2047 RAWL -2048
> 
> If the device is a 14 bit unipolar adc the fields would be:
> 
> RAWH 16383 RAWL 0
> 
> Comments anyone?
> 

I don't think records should have these fields.  The device
support module should know this information by reading a register
from the ADC board.  If there is a concern that someone may change
the operation of the ADC from bi-polar to unipolar while the system
is up, then the configuration registers of the ADC board can be
read each time the "read" function of device support is invoked.

I realize that things like PLCs that just spit values out over a
serial-type link are a problem.  One solution is to use the parm
field of the input link,  another solution is to use a "Config"
function in the vxWorks startup.cmd file (many Argonne device
support modules use this method).  Marty suggested that the PLC be
programmed to always send out 16 bit unsigned values - even if the
ADC is only 12 bit.

I have found that a user that is putting together a database that
takes input from an ADC does not want to manage a field that specifies
the raw range of the ADC.  The user may be using a cheap 12 bit
ADC in their test stand and have an expensive 16 bit ADC in the
actually running system. In this case the user probably does not want
to be concerned about changing the database when it needs to be loaded
into a different crate.

Many people put together generic processing routines that take
reading from ADCs and perform algorithms.  These databases can
be used with a large variety of ADCs.  It seems like a pain to
need to adjust fields for each different installation.

-- 
Jim Kowalkowski
708/252-9410
[email protected]

Argonne National Laboratory
Advanced Photon Source - Accelerator Systems Division
Controls and Computing

Replies:

Re: Should ai, ao records have RAWH, RAWL? watson

References:

Should ai, ao records have RAWH, RAWL? Marty Kraimer

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