Rigol DS2072A oscilloscope (need to help to perform a simple measurement task) - Page 1
Forum section: electronics / testgear

author: SharpEars
author_rank: Unknown
timestamp: January 03, 2016, 10:02:09 pm
content: I have a monostable multivibrator that generates a pulse. I want my DS2072A oscilloscope to measure the length (in seconds) of the (high part of the) pulse generated by the multivibrator. The question is how do I set up this simple exercise. I guess I am not familiar with measuring discrete bursts. If I leave it in auto mode it keeps measuring and draws the pulse at odd parts of the screen (depending on when I trigger the pulse). I would like for it to do the following:When the pulse transitions from low to high (rising edge, 0-5V) start the measurement at the left side of the screen. When it transitions from high to low, stop the measurement. Display results on the screen, so that I can measure the length of the pulse in seconds. I guess this is one-shot mode (maybe?), but I am very confused on how to perform this simple task.I also want to be able to easily repeat this exercise, as I adjust a pot to change the length of the pulse generated by the multivibrator.Summary:Press a button on the scope to begin measurementPress a button on the breadboard to trigger the pulse (i.e., low to high transition, high for a period of time, high to low transition)The scope should show the pulse from the previous item (i.e., start measurement on the low to high transition, stop on the high to low transition)Prepare for the next measurement, starting at Step 1 (perhaps with the push of a button on the scope to clear the display)

author: Someone
author_rank: Super Contributor
timestamp: January 03, 2016, 11:06:55 pm
content: Quote from: SharpEars on January 03, 2016, 10:02:09 pmYou're most of the way there, single shot mode (or triggered but not using auto-trigger) is the start but the scope will not adjust the horizontal time to match your signal, you need to set the horizontal time to the range you need before making the trigger. The automated pulse width measurements of the scope should make easy work of a simple pulse such as this once its captured with a sensible horizontal timebase.

author: SharpEars
author_rank: Unknown
timestamp: January 04, 2016, 01:48:48 am
content: Quote from: Someone on January 03, 2016, 11:06:55 pmI can't figure out how to actually trigger it to start measurement in single-shot mode (nor how to reset it if a measurement is present).

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 04, 2016, 02:09:21 am
content: The scope will trigger in single-shot mode when the input signal exceeds the trigger level setting. To reset it, press the "single" button again, and the screen will clear and the scope will wait for another trigger event.What kind of pulse duration are we talking about?Here's a single-shot capture of the pulse from a 555 based monostable multivibrator. I set the horizontal trigger ("delay" or whatever your scope calls it) at the first division from the left edge, set the vertical trigger amplitude to 1 volt, pressed the "Single" button on the scope, then triggered the multivibrator. The scope triggers when the pulse exceeds 1 volt, and places that edge where I told it to with the "delay" or horizontal trigger position setting. Then the sweep continues on to the right edge of the screen, and stops. Since I have some idea of the pulse length, I set the horizontal timebase so that the full pulse will be displayed on the screen in a reasonable manner.

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2016, 02:18:04 am
content: Quote from: SharpEars on January 04, 2016, 01:48:48 amDo you have the Trigger set to the channel of interest?Screenshot pleaseDo these units have a Pulse trigger mode? If so set the parameters to obtain a stable waveform.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 04, 2016, 02:32:22 am
content: I don't know about the DS2072A, but the DS1054Z (unlocked) does have a pulse trigger mode. But I don't see why you'd use it for this application, unless you only want to trigger on some particular width of pulse, rather than on the leading edge of whatever pulse the monostable puts out.

author: AG6QR
author_rank: Frequent Contributor
timestamp: January 04, 2016, 05:50:45 am
content: Quote from: SharpEars on January 04, 2016, 01:48:48 amDon't touch the "auto" button.First, set up the triggering to trigger on the rising edge of your pulse. This may be as simple as setting the trigger level about halfway between the low level and high level of the signal, and leaving the rest of the triggering set at default (usually, default is a rising edge trigger).When triggering is set up, push the "single" button on the front of the scope. The scope will sit there and wait for a triggering event. When it sees one, it will record what it sees and display it on the screen, and keep it frozen there until you push some other button on the scope.Once you have the pulse on the screen, you may adjust the time base or the vertical scale to zoom in or out or pan around on the waveform that you sampled. If you change things too much, you might notice you start to lose resolution, or you run off the end of what was sampled. This happens because you're zooming around in what was previously sampled, and it was sampled at a fixed rate and vertical resolution. If you want to resample, just hit the "single" button again, and then trigger another pulse on your DUT. This will measure the pulse again, at whatever resolution your scope is now set to.Play with this until you're really comfortable with it! It's one of the most powerful features of a DSO, when compared to an analog scope. It can be useful for things like capturing devices talking to each other via RS-232 or similar. Also, for capturing start-up glitches on power supplies, or any other single-shot event.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: January 04, 2016, 06:47:20 am
content: Quote from: SharpEars on January 03, 2016, 10:02:09 pmQuote from: SharpEars on January 04, 2016, 01:48:48 amIt sounds like you are trying capture long (seconds) pulses. One thing to watch out for when trying to single shot capture on slow time base is after you press the single button it can take a while before the scope is ready to actually trigger on your waveform. Forum member marmad talks about it in this threadhttps://www.eevblog.com/forum/testgear/first-impressions-and-review-of-the-rigol-ds2072-ds2000-series-dso/msg515875/#msg515875. You can shorten the time it takes for the scope to be ready to trigger by moving the trigger position over to the left side of the screen by using the horizontal movement knob.On the top left of the screen where it shows Run/Stop (and other things), when you first press the Single button it will show "RUN" in green. While the scope is in that state its not ready to trigger on your signal (it is still recording the signal though).Once the "RUN" changes to a green flashing "WAIT" the scope is ready to trigger and capture. At that point you can start the pulse from you multivibrator and if your trigger is setup correctly the scope should trigger and then display the captured waveform.Edit: Meant to mention that once the scope is in the "WAIT" state it will wait indefinitely until the waveform meets the trigger conditions. You don't have to try and send your pulse immediately after pressing the Single button.

author: SharpEars
author_rank: Unknown
timestamp: January 04, 2016, 04:17:56 pm
content: Quote from: alsetalokin4017 on January 04, 2016, 02:09:21 amThanks for the advice, I will give it a try when I get home. This is about a 2 second pulse duration being measured.

author: SharpEars
author_rank: Unknown
timestamp: January 04, 2016, 04:21:45 pm
content: Quote from: CustomEngineerer on January 04, 2016, 06:47:20 amWow, thanks for the explanation and pics. I guess the whole RUN/WAIT thing is very confusing. I thought I had to present the symbol while it was in the "RUN" state, but it's the "WAIT" state that is important. How confusing!

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: January 04, 2016, 04:43:40 pm
content: It is definitely confusing at first. I initially thought the same thing and made the same mistake. On fast enough time bases you dont even notice because it gets to the wait state almost immediately after hitting the single button. But if you have the time base set to 1sec/div with the trigger position set on the center line (default) it can take up to 7 seconds after you press the single button before the scope is ready to trigger/capture.

author: SharpEars
author_rank: Unknown
timestamp: January 04, 2016, 08:21:57 pm
content: Quote from: CustomEngineerer on January 04, 2016, 04:43:40 pmAnd this last part is what really REALLY confused me - (i.e., why was the scope behaving so slowly).

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: January 04, 2016, 08:58:51 pm
content: If you move the trigger to the left side of the screen (using horiz position knob) you can get the time from pressing the single button to ready to trigger down under a second.Edit: Forgot I mentioned this above, sorry for repeating.

author: gmb42
author_rank: Frequent Contributor
timestamp: January 05, 2016, 08:20:41 am
content: Quote from: CustomEngineerer on January 04, 2016, 04:43:40 pmI believe the delay is because with the trigger horizontal position set to the centre, you have all the left hand side of the display as a pre-trigger buffer, i.e. with a 1sec/div timebase that's 7 div * 1 = 7 secs that the scope has to capturebeforeit can trigger. Moving the trigger horizontal position to the left reduces the pre-trigger buffer, making the scope ready to trigger much faster.I guess the scope could be ready to trigger after run was hit and then only display the actual pre-trigger buffer that was captured, I'm not sure what other scopes do.

author: SharpEars
author_rank: Unknown
timestamp: January 05, 2016, 02:39:14 pm
content: Part of the problem is that having a hacked scope with max memory (and it being set to use that memory) means that it takes forever to traverse the left half of the range when the trigger is centered. But in the end, it seems like moving the trigger point all the way to the left is probably the thing to do.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: January 06, 2016, 07:11:11 am
content: Quote from: gmb42 on January 05, 2016, 08:20:41 amThats what the DS2000As do. When you hit the Single button the scope actually starts capturing (doesn't show anything at this point yet) while it is filling the pre trigger buffer, but it will not trigger and display the waveform until it has completely filled the pre trigger buffer and gone into the WAIT state. You can see this by generating a couple of pulses right after you hit the Single button before the scope is ready to trigger and then as soon as the scope is ready generate one more pulse and the scope will start showing the waveform starting at the trigger position, but it will also show the pulses that you generated before it was ready to trigger. Even if you don't generate a signal that meets the trigger condition for a while after the scope gets into the WAIT state the scope will keep the pre trigger buffer filled by continuously capturing.