#66: How to make a rise-time measurement on an oscilloscope
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- เผยแพร่เมื่อ 10 พ.ย. 2012
- This video shows how to make a rise-time measurement on an oscilloscope. It briefly discusses the importance of ensuring sufficient samples exist on the edge when using a digital scopes. The video mainly focuses on how these types of measurements were made before the digital scopes did these measurements automatically.
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Thanks! I have such an old scope, but no practical knowledge of using it beyond the basics, and neither any kind of instruction manual. This helped me uncover parts of the functionality I hadn't understood so far.
Almost every time I watch one of your videos, I'm like "Meh, I know this stuff", but I watch it anyway... And every single time I learn something new. I never thought about using those markers on my analog scope graticule to measure rise/fall time. Fantastic stuff, I love your videos. :)
Thanks for this! I refurbished (mostly) a 465 and have yet to purchase a digital scope. The procedure you demonstrated worked well. We didn't get into the measurement of transition edges in the US Army tech school 30 years ago (that I remember) so now I know.
Am I being too romantic when I say that I really want to get an old Tek 465B and fix it up? I am a hobbyist and a beginner who has only been watching electronics videos for about 6 months. The only piece of test equipment I currently own is a multimeter. So much of the advice out there says I should forget about these old CROs and just pick up a cheap Rigol. I really don't want to do that! I find it far more appealing to work with a machine that doesn't have all of the fancy software to automatically bring up the waveform and spit out dozens of different measurements for me. I want to take those measurements myself directly on the waveform, and then do the calculations myself. I think I learn a lot more that way and I am definitely not afraid to learn. I'm in my last year of a mathematics degree so I have no worry about learning any of the math involved in electronics or in radio.
Thank you. This demonstration was very helpful. Especially like that delayed sweep feature of the third scope.
Your videos are very cleared explained!
Very well explained, thanks for sharing.
Great video , thanks.
Thanks again Alan.
It is of great interest , watching your video(s)
Thank You!
very good video mate. Very well explained (as usual). That 485 is a beauty, too bad in this sh*thole of ours we cannot get semi decent gear for a reasonable price.
Oh, well... I wouldn't call myself *experienced*... I'm still a student who sometimes thinks he knows stuff. Looks like I can still learn from videos that some people would consider "basic". :)
Hi. As (almost) always great video! Got a question, but not about the video's topic. In the video you have a 50 ohm terminator attached to the input of channel 1. However it looks like a BNC barrel connector (M/F). I have never seen one like this usually a terminator is for terminating, right (ending a "T" loop)? Why barrel to it? Why did you need it? Why term the input of a scope anyway? Why not just turn the channel off or set to ground?
Thanks,
Ken
That is a 50 Ohm barrel connector where the 50 is from the center to the ground barrel. Serves the same purpose of a "tee" with a terminator cap. The barrel terminator is needed because that scope model has no 50 Ohm setting on the channels. And you need a terminator for super fast rise-times because there is a 50 Ohm cable of length too long compared to the rise time of the signal. Otherwise, there would be a large reflection and lots of ringing.
Ken Cosi
This can be measured with an ohmmeter.
If we measure risetime for a 5V peak to peak signal VS say 10V peak to peak signal, would the rise times be different? Risetime is a function of the bandwidth of the scope and the detector right?
Normally when you measure risetime you would want the scope's inherent risetime to be 3-5x faster than the signal you're measuring so that it doesn't artificially slow the signal. Risetime is independent of voltage swing unless the circuit is slew rate limited.
Hello again
found this not too far from me 1 Ghz. Agilent HP54110D with all probes he says 200.00 fro probe alone I can get it for all for $ 500.00 ,what do you think
thankyou very much
Firstly thank thank. Just listening to you talking about this. clears up a lot of past misunderstanding and also create new questions for me. thank you.
one of the questions is, can excessive ringing at beginning of rise and fall be the cause of overheating on resistors? This is a problem I'm dealing with now. Some resistors are overheating about 300-400 F.
Their normal operating temp in this circuit seems to be a little over 200.
It is very doubtful. The heating of a resistor simply a function of the power being dissipated (Vrms*Vrms/R), and ringing on the edges won't contribute to that much more power being dissipated.
@@w2aewis there another scenario that causes high dissipation besides high power or current going through? I did measure power or I thought I did.
I used ohms law to get
the current. (168=(47k)X(I)=0.00357), then (168 X .00357= P=(.6)
I know the resister are at least 3 watt
And they measure with in good tolerance of their value of 47K..
@@AB-yu2tj The POWER dissipation is the source of the energy that results in heat (i.e. same reason a light bulb gets hot). The amount of heat generated at a given power level is a function of the thermal resistance - which depends on the physical size/construction of the resistor, the mounting configuration, the heat-sinking provided by the circuit board connections, air-flow, ambient temperature, etc.
@@alanwolke6253 does skin affect or other affecting resister at hi frequency play a factor in over heating it..
I measured frequency from a little below 50k to below 200k. It does not seem to stay stable.
But I might not have the right instrument to measure frequency, though.
@@AB-yu2tj At those frequencies, no.
I'm not sure if its called rise time measurement when you measure various switches open contacts to close contact time interval because some switch mechanisms are Fast acting and some are slow acting. I'm guessing this is called the rise time? when measuring the time interval from open contacts to close contact time interval? I have used a DVM meter and set it to measure frequency and toggle the switch to measure the frequency and convert the frequency into time. Using an oscilloscope you can toggle the switch and measure the rise time of the switch on/off time interval. Some switches are fast acting and others are slow acting
What if I want to measure the time it takes from receiving an external trigger to the 100%?
If you have a digital scope, you can easily position a cursor at the point where your signal reaches 100% and the time-value will be the measurement you're looking for (since most digital scopes assign 0 seconds to the trigger point. If you have an analog scope, you'll have to count divisions from the trigger location to the point where the signal reaches 100%, then multiply this by the TIME/DIV setting.
How do you measure the Max Rise Time the actual oscilloscope can measure? because when adjusting the function generators Pulse Width range from 10mS and keep lowering it like to 1mS or 100uS to 10uS the Oscope Rise time can't measure it because of the Digital ADC converters or the software not sure, but have you notice this problem and what is the called? The Max Rise Time won't change value because that is how fast the Oscope can measure the rise time of the function generator Pulse width but I don't know the term or name this is called when the Oscope can't measure very short rise time.
Risetime and scope bandwidth are intimately related. The general rule of thumb that applies in most general purpose application is that the scope's inherent risetime is approximately equal to 0.35/bandwidth of the scope. Thus, a 100MHz scope has an inherent risetime of 3.5ns. A scope can not measure a risetime faster than its inherent risetime. For example, if you have a signal that has a real risetime of 1ns and you measure it on a 100MHz scope, it will measure something a little larger than 3.5ns. Digital scopes add another wrinkle. In order to measure risetime, the sample rate of the scope has to be fast enough to put a few sample on the rising edge itself. When you are running the scope at slower horizontal scales, the waveform sample rate may drop due to scope memory limitations. Also, many scopes perform the measurements on the display sample points, not the actual acquired samples in memory. By doing this, the risetime measurement will change when you change the scope's horizontal scale! This is poor behavior, but it is done by many scope makers to make the processing faster/easier. Tektronix scopes always make the measurements on the underlying acquired sample points (not the displayed sample points), so the measurements still remain accurate (provided the acquisition was setup with an appropriate sample rate and memory setting). When the scope risetime measure changes with horizontal scale due to the sample density, the effect is called undersampling.
@@w2aew Thanks for the info because I have notice this also about the ADC sample rate time and the Oscope Bandwidth being related to the max rise time. Different Oscope brands make the rise time measurements differently by the sample points. I don't know how to change the sample points, sample rate, memory setting to NOT change with the horizontal scale of the sample density. Try to make a video lesson about this because it gets very confusing if you don't set up your Digital Oscope correctly when measuring very short rise time pulses. The Horizontal scale when changing it will inherently change also the sample points, sample rate, etc it does this by default/automatically when I'm not sure if certain Oscope brands even allow you to changing the sample point settings, sample rate settings, etc.
@@w2aew Also Oscope has a measuring called "Pulse counter" PS but it always will count the pulses wrong and in correct, The newer Digital Oscopes have Pulse Counters but you have to go into the sample rate settings, sample points settings, etc to set it up correctly I think in order for the Pulse counter to work correctly, If you apply a pulse that has 100 pulses the Oscope Pulse counter it not count 100 pulses it will say its 30 pulses and the next cycle it will say 45 its random. How do you fix this problem?
I love O'scopes ;) (old scopes)
Hah. You call that old analog stuff? My first scopes were recurrent, not triggered sweep. And I have a Tek 536, on a cart, sitting out in the garage... It's been a while since I fired that one up and I'm not sure how I'd take that measurement on that one offhand, but I could probably figure it out.
How do measure it on 0% to 100%? is it feasable to calculate it through a 3 simple rule (direct proportional calculus)?