Experimental Physics and
Industrial Control System

"David Dudley" <[email protected]> · Thu, 01 Feb 2007 08:43:26 -0600

I'm currently starting to work on adding support into my modbus device driver for Analog Arrays.  Is there any documentation on the AAI and AAO records?

It has been suggested before that perhaps I should consider the Waveform record, but I have a little problem.  I need to read a string of 16 bit registers in a single group (sort of a 'simultaneous sample' thing), and I don't see the capability of doing this will a standard AI record (do I need to write special device support for Waveform?  Maybe that's the problem).

Also, even if I generate whatever is needed for Waveform records for input, how do I manage output?  I need to be able to write a 120 register block out at the same time in order to insure consistency.  Seems to me, that's an Analog Array Output (AAO) record, if I ever saw one.

On an unrelated note, I'm curious about a few things.  I don't see any way to do tests with the database.  I have a need to do things like "read an input - Test for a value - output a trigger if true", as a simple grouping.  I don't see any way to programmatically decide whether or not to execute a FWDLNK, which I think is what I want to do (or is that what the SEQ block can do?  Documentation is kind of weak.).

Finally, I don't see any way to do 'discrete PID' controls.  Guess I should just shut up and write blocks to do what I want, which I think consist of the following (any way to do these already would be appreciated).

1. Multiplex a input array into a single value (think I found that in the SEL block, but why is the limit 12 on so many of these blocks?).
2. Demultiplex a value to a selected FWDLNK (don't see this one, unless the SEQ block does it.  But it doesn't have multiple FWDLNKs).
3. IF or other conditional test block (if condition meets criteria, do FWDLNK, else don't).
4. PID Control with Discrete output controls (jog up/jog down, for PID Control).
5. DB Log command to output current value to a database point.

Also, is there any structure built into the system to provide a 'orderly startup / orderly shutdown' operation?  The stuff I have background with all provide the capability of loading an initial state and storing the current state when the system is started up and shut down, as well as the capability of doing a 'checkpoint' type operation.  Need that to do continuous control type operations.  Can't have a remote IOC defaulting everything to invalid conditions if it has a short power failure or other problem that causes a reload.

I would expect that most of these capabilities are available in EPICS already, since I'm certainly not the first one to be doing control with the software.

Lastly, do most IOC's have the SEQUENCER software incorporated in them?  Seems to me that a lot of the things I would expect to do in combinational-logic don't seem to *exactly* exist in the DB.  Do all logic things need SEQ support?

David

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System