Kay,
Who can I contact to find out more about the 'scope application?
--
Paul Sichta
Princeton Plasma Physics Laboratory
609-243-3477
-----Original Message-----
From: Kay-Uwe Kasemir [mailto:[email protected]]
Sent: Wednesday, September 06, 2006 8:48 AM
To: tech talk
Subject: Re: StripTool2_5_10_0 display of waveform records?
On Sep 6, 2006, at 02:30 , Jon Brinkmann wrote:
> Does StripTool2_5_10_0 display waveform records?
Hi:
It doesn't, and it couldn't.
The general problem with EPICS and waveforms is that
the information provided via ChannelAccess is
insufficient, since there are at least four types
of waveform usage:
1) Fast ADC
Your waveform might come from a fast ADC.
For example one that takes samples at 100kHz,
and is triggered every 2 seconds.
Via channel access, we can get the waveform samples
and the time stamp, which might indicate the
start or end of acquisition. But for a proper
display over time you also need the
inter-sample-distance (=1/100kHz).
2) Position scan
Beam position monitors are one example where your
waveform represents data that was sampled
at various positions. Again CA provides the
waveform and a time stamp, but what's the position
information? Was the first array element taken at "0 mm",
the next one at "0.0001 mm" and so on?
3) Histogram
Your waveform data might represent a histogram.
What are the 'bucket' locations/sizes?
4) Image
Waveforms are sometimes used to store images.
So a 10000 sample waveform might really represent
a grayscale image of 100 x 100 pixels.
How do you tell the width and height when you
only have 10000 samples and a time stamp?
5) Binary data
Waveforms are sometimes also used to transfer
arbitrary binary structures, especially to overcome
the limited 'command'/'response' support in EPICS.
The server and client use for example gensub records
to encode/decode them.
==> In all of these cases, a general purpose client
has no clue how to properly display the waveform.
At the SNS, there is a 'scope' application for displaying
waveforms of type 1 (fast ADC). It assumes that any waveform
PV "fred" given to it is of that type, _and_ it requires
two additional, scalar PVs which serve information about the
start and the inter-sample-distance of the waveform data
in a way that nails it down relatively to our hardware timing system.
I'm sure other sites have come up with similar ideas,
be it that you manually enter the additional info,
or expecting additional PVs based on a naming standard,
or deriving display meta-information from the waveform PV's name.
-Kay
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