Products > Test Equipment
Standardised Way To Test Oscilloscope Screen Update Rate
tautech:
--- Quote from: EEVblog on April 29, 2024, 07:57:55 am ---
--- Quote from: tautech on April 29, 2024, 07:36:43 am ---With mouse plugged into the scrope the scroll wheel is available for making numeric field adjustments.
--- End quote ---
That's interesting, must not have implemented that in the web interface
--- End quote ---
Yep.
Now requested to be supported in all models.
pdenisowski:
--- Quote from: EEVblog on April 29, 2024, 06:07:03 am ---High speed camera and frame anlaysis is one way obviously.
--- End quote ---
If "screen update" means "pixels changed" (assuming a continuously changing input), then I think that's the only way :)
We (R&S) actually make a visual monitoring system, mostly for EMS testing, that detects display changes (max speed is 30 frames / second). One metric that it reports is how long something stops moving ("motion freeze")
https://www.rohde-schwarz.com/us/products/test-and-measurement/emc-test-software/rs-advise-visual-inspection-software_63493-149761.html
https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/AdVISE_bro_en_3607-3168-12_v0500.pdf
I assume a similar approach could be homebrewed by simply grabbing frames at a very high speed, doing a "diff" on them, and then measuring the time difference between "diffs"
RoGeorge:
--- Quote from: EEVblog on April 29, 2024, 07:57:55 am ---
--- Quote from: tautech on April 29, 2024, 07:36:43 am ---With mouse plugged into the scrope the scroll wheel is available for making numeric field adjustments.
--- End quote ---
That's interesting, must not have implemented that in the web interface
--- End quote ---
An USB mouse only sends the displacement+buttons when polled, and the standard HID poll rate is something about 100Hz (don't recall the exact rate, it's in the HID specs). That is low enough to affect pro gamers, so there are non compliant USB ports, and non compliant USB drivers that can poll a mouse at 200Hz or more.
Another thing, LCD panels are very hard to drive at fast refresh rates, and they are usually working at less than the CRT used to. Most LCD and/or IPS panels are at 50/60Hz refresh rate, yet they do not flicker to the eye (like a 50/60Hz CRT would), because of the remanence. Flat panels are very hard to drive at more than 200Hz, and gaming monitors at >150Hz are very expensive.
My guess is the refresh rate in an oscilloscope panel would be a casual 30 or 60Hz, I don't see why I would need more than that, but I didn't measure.
The "slower" update might look so because the memory depth is higher. A waveform is redrawn on the screen at each trigger, but only after the memory is full (or at least that is how it seems to be for my Rigol DS1054Z). Because of this, at the same sampling rate, same oscilloscope will appear "slower" when the memory depth is set to higher values.
For slower ADC sampling rates, it might even take seconds to fill something like the 14 mil samples (the max memory in a DS1054Z).
mikeselectricstuff:
--- Quote from: pdenisowski on April 29, 2024, 10:59:34 am ---
--- Quote from: EEVblog on April 29, 2024, 06:07:03 am ---High speed camera and frame anlaysis is one way obviously.
--- End quote ---
If "screen update" means "pixels changed" (assuming a continuously changing input), then I think that's the only way :)
--- End quote ---
No need for a high speed camera though - you have full control of the source signal, so you can create test signals and use a simple single-point optical sensor on a specific area of the screen.
nctnico:
--- Quote from: mikeselectricstuff on April 29, 2024, 11:35:12 am ---
--- Quote from: pdenisowski on April 29, 2024, 10:59:34 am ---
--- Quote from: EEVblog on April 29, 2024, 06:07:03 am ---High speed camera and frame anlaysis is one way obviously.
--- End quote ---
If "screen update" means "pixels changed" (assuming a continuously changing input), then I think that's the only way :)
--- End quote ---
No need for a high speed camera though - you have full control of the source signal, so you can create test signals and use a simple single-point optical sensor on a specific area of the screen.
--- End quote ---
The more I think of it, the less I'm convinced this is actually easy to measure. In the end the rendering engine of an oscilloscope needs to pack multiple acquisitions into a rendered image which is not necessarily equal, but likely synchronised to the screen refresh rate to avoid tearing effects. If you look at the trigger output signal from an oscilloscope, you often see a whole bunch of triggers, dead time and another burst of triggers. The dead time is likely the time needed to create the rendering from (pre-processed) acquired data.
Still, sending a single pulse into an oscilloscope and measuring the time until it is rendered onto the screen (using a simple optical sensor) could lead to some interesting data on what the latency (min / max) is between signal input and display rendering.
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