Experimental Physics and
Industrial Control System

"Ernest L. Williams Jr." <[email protected]> · Tue, 13 Apr 2004 07:12:44 -0400

On Tue, 2004-04-13 at 06:08, Ralph Lange wrote:
> >>>>> "Andrei" == Andrei Liyu <Liyu> writes:
> 
>   > [...]
> 
>   > At second, bi-direction data is not need usually. Operator in LOCAL
>   > (rack place) and REMOTE (from computer) sets new value and than sees it.
>   > This is two operations, two values ...
> 
>   > Andrei.
> 
> I do not agree.
> 
> 
> Scenario 1 (quite usual during commissioning):
>   Some part of the machine is not working correctly. The device
>   specialist goes there, switches everything local, optimizes until
>   things are running.
>   -> Without some bidirectional functionality you are left to write down
>   all setpoints locally and hack them back into the system manually
>   (quite error-prone) else you will lose beam as soon as you touch
>   something.
> 
> Scenario 2 (usually with large "intelligent" sub-systems such as PLCs):
>   No strict hierarchy, i.e. the EPICS system is just one client of the
>   system and not the only master.
>   -> Without some bidirectional functionality your EPICS screens will
>   most likely not show the current status of the system. Touching setpoint
>   sliders will most likely produce unwanted output jumps.
> 
> Scenario 3 (usually with small "intelligent" sub-systems such as
> embedded device controllers):
>   To create a "bumpless" reboot behaviour, the EPICS IOC should be able
>   to read back the setpoints from the device. The collected values
>   should end up in the same records that are used to control the
>   device. (Else you still get bumps when you touch a slider.)
> 
> 
> I think these are three good reasons why bi-directional behaviour is a
> desireable feature. (I'm sure there are more...)

Can you achieve most of what you want by using a collection of database
records and closed-loop/supervisory feature of output records?
 --- When in local mode put the appropriate record in closed-loop mode
and have it obtain values from the intelligent device (e.g. the
setpoint)

--- When in remote mode, choose "supervisory mode". This obtaining the
desired setpoint from the operator or other CA client.

If the above is possible, you should be able to achieve bumpless
behaviour.

Ernest

> 
> Ralph
-- 
Ernest L. Williams Jr. <[email protected]>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System