Experimental Physics and
Industrial Control System

On 4/6/21 12:01 PM, Alfio Rizzo via Tech-talk wrote:
> Hi
>
> I would like to have some clarification about the MDEL field.
>
> If I understood correctly from the online documentation,
>
> If I set a value > 0 , the PV monitor (camonitor or pvmonitor)
>
> should be triggered if and only if
>
> ABS(ValPrev - ValCurr) > MDEL
>
> where ValPrev and ValCurr is the previous and current value of my PV.
>
> So, I have made some simualtion, but apparently the monitor is triggered also when the condition before is not satisfied.
>
>
> Do I miss something ?

In addition to the value change event (DBE_VALUE), most clients also subscribe
to the alarm change event (DBE_ALARM).  So eg. a 'camonitor' will by default show
an update if either the MDEL deadband is exceeded, or if the alarm state changes.

You can use the '-m' argument of camonitor to probe this.  See 'caget -h' for other
options.


> $ camonitor PiraniGauge_RB
> PiraniGauge_RB                 2021-04-06 21:50:55.628735 0.0398545 HIHI MAJOR
> PiraniGauge_RB                 2021-04-06 21:51:04.628750 0.0374571 HIGH MINOR
> PiraniGauge_RB                 2021-04-06 21:51:08.628789 0.0342738 
> PiraniGauge_RB                 2021-04-06 21:51:18.628817 0.0247016 LOW MINOR
> PiraniGauge_RB                 2021-04-06 21:51:22.628811 0.0218172 LOLO MAJOR
> PiraniGauge_RB                 2021-04-06 21:51:35.628792 0.0222724 LOW MINOR
> PiraniGauge_RB                 2021-04-06 21:51:39.628829 0.025354 
> PiraniGauge_RB                 2021-04-06 21:51:50.628785 0.0357844 HIGH MINOR
> PiraniGauge_RB                 2021-04-06 21:51:54.628773 0.0385044 HIHI MAJOR
> PiraniGauge_RB                 2021-04-06 21:52:06.628815 0.0379849 HIGH MINOR
> PiraniGauge_RB                 2021-04-06 21:52:11.628786 0.0341212 
> PiraniGauge_RB                 2021-04-06 21:52:21.628730 0.0245598 LOW MINOR
> PiraniGauge_RB                 2021-04-06 21:52:25.628775 0.0217217 LOLO MAJOR
> PiraniGauge_RB                 2021-04-06 21:52:38.628715 0.0223802 LOW MINOR
> PiraniGauge_RB                 2021-04-06 21:52:42.628800 0.0255035 
> PiraniGauge_RB                 2021-04-06 21:52:52.628759 0.0350866 HIGH MINOR
> PiraniGauge_RB                 2021-04-06 21:52:56.628754 0.0380378 HIHI MAJOR


Subscribe only to DBE_VALUE.

> $ camonitor -m v PiraniGauge_RB
> PiraniGauge_RB                 2021-04-06 21:57:28.828710 0.039463 HIHI MAJOR


cf. record support code for ai where the monitor event for .VAL originates.

https://github.com/epics-base/epics-base/blob/348d1bba176117178eb2c59cd0be193e1cf104ca/modules/database/src/std/rec/aiRecord.c#L461

recGblResetAlarms() handles alarm change

https://github.com/epics-base/epics-base/blob/348d1bba176117178eb2c59cd0be193e1cf104ca/modules/database/src/ioc/db/recGbl.c#L208

recGblCheckDeadband() handles floating point deadband

https://github.com/epics-base/epics-base/blob/348d1bba176117178eb2c59cd0be193e1cf104ca/modules/database/src/ioc/db/recGbl.c#L354