Re: Doubts about DISS field

[Andrew Johnson via Tech-talk <tech-talk at aps.anl.gov>]

Hi Marco,

On 6/29/22 3:32 PM, Marco A. Barra Montevechi Filho via Tech-talk wrote:

I am altering an old OPCUA IOC that was running here in the lab and i noticed that someone configured several records with the DISS field set to "INVALID". When the IOC is running, all of these records have the fields .SEVR set to "INVALID" and this was messing with some interfaces made with pydm. The records have no HSV, LSV or similar fields defined and cagetting into DISV and DISA fields revealed that they are at default value.

I'm assuming the DISS field is responsible for the .SEVR INVALID value, but searching in the web all i could find about DISS was: "When this record is disabled, it will be put into alarm with this severity and a status of DISABLE_ALARM." and this is not clear for me: shouldnt the records only have "INVALID" value at .SEVR if they were disabled (which is not the case since DISV and DISA are at default)?

I altered the DISS field to DISABLE_ALARM and now the records display NO_ALARM. Is this coherent? Am i altering any other functionality of the IOC without knowing?

The severity from the DISS field is used and the record's STAT field set to "DISABLE_ALARM" when the record is prevented from processing because the value read into DISA through the SDIS link matches that found in the DISV field. Where were the SDIS links of those records pointing to? Was their STAT field showing "DISABLE_ALARM" (or possibly the value 18, since CA only supports up to 16 enumeration states)?

This mechanism is described on slide 37 of my Database Principles training lecture.

Often a record's SDIS link will be pointed at a binary or calc record that is used to enable or disable parts of the IOC database, because the equipment it controls is not used in that configuration, or the binary value may reflect whether the device is currently connected or not.

Just changing the DISS severity won't allow those records to process if they were being disabled using the SDIS/DISA/DISV mechanism. I suggest you investigate that further since there may be more to that database than you originally thought.

HTH,

- Andrew

-- 
Complexity comes for free, Simplicity you have to work for.