| Products > Test Equipment |
| Basic scope requirements except need to see ~10 ns pulses |
| (1/7) > >> |
| stephencox:
I know there are a ton of posts seeking purchasing advice, but I've read through a bunch of them and I don't think my situation has been covered. I am an academic (scientist, not an EE) and I am shopping for a new oscilloscope after changing labs and research focus. I previously worked more directly with RF and had access to much better test equipment. Now my needs are pretty basic for the most part and would be satisfied by a $2000 scope (plus some expensive high voltage probes) with one major exception: I work with electron multipliers and need to be able to look at 10–1000 mV pulses with a rise time of 1.5–3 ns and a total pulse width of ~20 ns. It can be very useful to trace these signals down the amplification chain from the source to troubleshoot both electronics problems and external sources of noise. I don't need to be able to produce a textbook image of the pulse, but I need to be able to see it well enough to see that it's really a single pulse, for example. I recently tried to troubleshoot one of these with a cheap 40 Mhz scope that was already in the lab and could not even get it to reliably trigger, let alone visualize the pulses. Most recently I used a Tektronix MDO3034 for this purpose, and the bandwidth was sufficient for my purposes. The direct equivalent is now ~$15000 from Tektronix. I do still have some RF equipment but I'm unlikely to be troubleshooting it without an engineer beyond trying to isolate things to reduce noise, so I'm wondering whether I should consider a cheaper option. For example, I am wondering if I should consider buying a slower Tektronix scope for daily/high voltage use and something less nice to use but with the necessary bandwidth for this one specific job. I'd be much happier spending around $5000 if I can get away with it. |
| nctnico:
You'd probably need a scope with at least 300MHz of bandwidth. If it is just for looking at pulses, almost anything is useable so it should be possible to stay under the $5k mark if you look at other brands. |
| TimFox:
Are you concerned only with pulse-pair resolution (how close the pulses can be while still resolved as separate) or do you need other information about pulse width, pulse height, or rise time? |
| tggzzz:
--- Quote from: stephencox on March 06, 2024, 05:00:33 pm ---... and need to be able to look at 10–1000 mV pulses with a rise time of 1.5–3 ns ... --- End quote --- You should be a bit more explicit about what you mean by "look at". In particular, what aspects of the pulses will you be measuring and what are the fidelity requirements. You will be able to see a pulse is present and its relative time of occurance even with a 50MHz scope :) Having said that, the key points are indeed the risetime and amplitude. The rule of thumb is that tr=0.35/BW, where the risetime and bandwidth are the combination of the scope plus probe plus signal. Hence 1.5ns=>250MHz. The rule of thumb is that the risetimes increase as root-sum-of-squares, so the combination of two components with a risetime of 1.5ns is 1.414*1.5ns. That should give you sufficient information to enable you to determine the required scope+probe bandwidth. Given that bandwidth and the impedances, you should be able to calculate the noise. The noise won't be trivial, but may well be OK - depending on your fidelity requirements. |
| stephencox:
Thank you all for the replies so far. It sounds like I'm not missing some magic solution, so I'm looking at either a ~$15000 Tektronix scope or maybe a combo of a $2000 Tektronix scope for something nice and usable for daily use and then a still pretty expensive scope from a budget manufacturer that can do 350+ MHz for the one specific task. --- Quote from: TimFox on March 06, 2024, 05:41:50 pm ---Are you concerned only with pulse-pair resolution (how close the pulses can be while still resolved as separate) or do you need other information about pulse width, pulse height, or rise time? --- End quote --- --- Quote from: tggzzz on March 06, 2024, 05:45:39 pm --- --- Quote from: stephencox on March 06, 2024, 05:00:33 pm ---... and need to be able to look at 10–1000 mV pulses with a rise time of 1.5–3 ns ... --- End quote --- You should be a bit more explicit about what you mean by "look at". In particular, what aspects of the pulses will you be measuring and what are the fidelity requirements. You will be able to see a pulse is present and its relative time of occurance even with a 50MHz scope :) Having said that, the key points are indeed the risetime and amplitude. The rule of thumb is that tr=0.35/BW, where the risetime and bandwidth are the combination of the scope plus probe plus signal. Hence 1.5ns=>250MHz. The rule of thumb is that the risetimes increase as root-sum-of-squares, so the combination of two components with a risetime of 1.5ns is 1.414*1.5ns. That should give you sufficient information to enable you to determine the required scope+probe bandwidth. Given that bandwidth and the impedances, you should be able to calculate the noise. The noise won't be trivial, but may well be OK - depending on your fidelity requirements. --- End quote --- It's a little tough because I am mostly using this for troubleshooting and so I probably can't even imagine all of the potential problems that I might see in a sufficiently resolved pulse shape. That said, I can definitely be more clear. In addition to pulse-pair resolution, which only requires ~20 ns resolution, it is useful to be able to see stacked pulses that the pulse-counting electronics also can't resolve, and to do that I need to be able to resolve ~the rise time of the pulse rather than the width. That's how I end up at the requirement of around 350 MHz as you outlined. And I can say from experience with the MDO3034 that I could see the pulses relatively well and was able to resolve both dead time and ringing/double counting issues this way in the past. |
| Navigation |
| Message Index |
| Next page |