Experimental Physics and
Industrial Control System

[email protected] (Kay Kasemir) · Wed, 24 Nov 1999 16:14:19 -0700

At 03:02 PM 11/24/99 -0500, you wrote:
>Happy Thanksgiving Day,
>I would like to make a few PV's available (read-only) to our collaborators
>through a web browser, strictly low performance.  What approach has been
>used for this?  Do I need to program in Java and use JCA ?  Or,  are there
>unix/scripting  tools that can be applied?

One common problem with CGI approaches is that they are comparably slow.
So if you display an analog value as a single number,
it might not be of much use because it's a singular snapshot.

In those cases it's better to display a strip chart type of history plot.
If that chart shows the value's history of e.g. 10 minutes,
you don't care if the CGI approach can only update once every few minutes.

The next question, of course, is: How can you produce an online strip-chart?
The two basic options are:
1) write your own java code that communicates to some server
   (you can't use the CA client library directly via JNI
    because you're using the browser's built-in java machine)
2) use some other programs (DM, MEDM, StripTool, TCL, MatLab, ...)
   that can - via available extensions - read PVs & plot them,
   take a snapshot (e.g. GIF image) and display that on your web page.

What we are experimenting with here at LEDA is LabVIEW:
It has a CA client interface, can produce history plots
*and* provides a build-in web-server,
so you circumvent the need to take snapshots,
do the housekeeping for the generated gifs etc.
There might be other similar tools available.

-Kay

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System