Experimental Physics and
Industrial Control System

Hi Rolf,

 

Thanks.  I just checked, and it looks like the motor.db Enable/Disable does set .DISP as you describe, along with .SDIS.  When disabled, both medm and probe throw out a warning when changing .VAL is attempted, and the requested (changed) value is ignored.  caput behaves similarly.

 

Kurt

 

 

 

The statement below is not correct. If a record is disabled, both CA clients and other database records can write to a record's .VAL field. If the record is later re-enabled and processes, this may lead to unexpected consequences or discontinuities.

If you just want to prevent CA clients to modify a record's .VAL field you should set the .DISP field to 1.

HTH - rolf -

Hi Ray,

 

“motor.db” loads a bo record, “$(P)$(M)_able”, that the motor record’s SDIS field points to.

 

We use this to enable/disable the motor record.  When disabled, writes to the motor record’s .VAL field are not allowed.

 

Kurt

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Matt Newville via Tech-talk
Sent: Tuesday, October 3, 2023 10:06 AM
To: Peterson, Kevin M. <kmpeters at anl.gov>; Gregory, Ray <gregoryrd at ornl.gov>; tech-talk at aps.anl.gov
Subject: Re: preventing changing an EPICS motor's commanded position

 

Ray, 

 

Perhaps what you're looking for is simply to set the Motor Record low and high limits to the drive value you want to maintain.  

You could also set the SPMG field to 0 or 'Stop'.  That would allow someone to change the VAL field (which is what you said you wanted to not allow), but it will prevent the Motor from actually moving until SMPG is changed back to 2 or 'Go'.   Both of these use the exposed interface to the Motor Record, so in principle can be changed at any time.   But they are also not uncommon things to do for motors that you want to not accidentally move. 

 

 

 

On Tue, Oct 3, 2023 at 8:17 AM Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov> wrote:

Ray,

Can you provide more details about what "disabling the axis" means?  The
behavior of the motor record's CNEN field, which is labeled "Torque" on
the motorx_all screen, is controller dependent; for some controllers
CNEN enables/disables drive power, for other controllers CNEN switches
between open and closed loop control, and some drivers do nothing when
CNEN is changed.

Kevin

On 10/2/23 12:32, Gregory, Ray via Tech-talk wrote:
> Hi,
>
> How can I prevent changing an EPICS motor record’s commanded position
> (.VAL field) without disabling the axis?
>
> Thank you,
>
> Ray
>
> Ray Gregory
>
> Oak Ridge National Laboratory
>

 

--

--Matt Newville <newville at cars.uchicago.edu> 630-327-7411