Experimental Physics and
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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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ANJ, 02 Sep 2010 |
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