May be oscilloscope? - Page 1
Forum section: electronics / projects

author: tbutton
author_rank: Newbie
timestamp: February 01, 2012, 07:32:42 pm
content: My task is: find X as accurately as possible.The maximum.Source (generates a rectangular pulse with amplitude = 20 V, frequency = 0.3 MHz) -> the object of study -> signal receiver (receives a rectangular pulse, amplitude = X, frequency = 0.3 MHz). An additional condition: the data must be recorded in the computer in real time.A minimum.Record and save a signal amplitude (X) with every 0.01 sec (working with not one, but with 10,000 pulses). Also in real time.Why oscilloscope? I would like to acquire a useful device = solution.Which oscilloscope to cope with the problem of min / max?What instrument would you choose?Your suggestions: how to solve the problem better?Thank you very much for your feedback!

author: erupter
author_rank: Contributor
timestamp: February 01, 2012, 11:10:13 pm
content: A scope is overdoing it.If you are not interested in the actual form of the signal, but rather in the time characteristics alone, a simple microcontroller logger could do it.You state you want a sample every 0.01 secs (100 Hz), but your original signal has a freq of 300 KHz... there is a factor of 1000 unaccounted for here which does not have anything to do with the 10000 pulses you cited. What are those?If you do 300 KHz / 100 Hz = 3000. So what is 10000?What are you trying to do?If the original signal is a square wave, why are you interested in the amplitude?What characteristics of this square wave are you interested in?

author: tbutton
author_rank: Newbie
timestamp: February 02, 2012, 08:07:05 am
content: Thank you!"So what is 10 000?" You are right 3000:) Until then, I've tried other frequencies, so mixed up.About task:Two choices: good and bad. 300 kHz - good and 100 Hz - bad.The amplitude of the final wave gives information about the properties of _the_object_of_study_"What characteristics of this square wave are you interested in?" - Only the amplitude.What oscilloscope do you recommend?Rigol 1052E solve the problem? I can not understand where to find the speed of their measurements. 100 Hz or less? Can I save the information in .txt?

author: erupter
author_rank: Contributor
timestamp: February 02, 2012, 09:33:12 am
content: Oscilloscope's main advertising parameter is their analog bandwidth (Rigol's is 25 MHz).No o'scope in any resonable price range is able to save data in real time.For this you need a logger.A dsPic or PIC32 logger may reach the 300 KHz frequency you want.Although keep in mind that wanting 300'000 samples and accurately tracking a 300 KHz signal are two very different things.BUT if you're ABSOLUTELY SURE the signal IS AND REMAINS a square wave, an oscilloscope is utterly useless.A simple data logger is all you need.Different is the case in which you use the square wave as an input to a black-box style device and want to characterize its response.In that case you need precision, and the data logger (while still your only choice since you want to actually save data) must be a more refined device than the first one.This data loggermay fit your needs.

author: tbutton
author_rank: Newbie
timestamp: February 02, 2012, 04:55:12 pm
content: Thank you very much!But I want the oscilloscope:))What an oscilloscope a better choice?Owon SDS6062 (http://www.owon.com.cn/eng/smartDS.asp) orRigol 1052E (http://www.dealextreme.com/p/rigol-ds1052e-5-6-tft-lcd-50mhz-2-channel-digital-color-storage-oscilloscope-30573).Your opinion?

author: olsenn
author_rank: Frequent Contributor
timestamp: February 02, 2012, 05:38:18 pm
content: Don't listen to "erupter"; the Rigol DS1102E is 100MHz bandwidth, only costs $400, and it can be connected to a pc over USB or RS-232 and do data logging. I'm not sure what the purpose of those requirements are, but all oscilloscopes will have plenty of bandwidth to measure a 300KHz square wave. As a general rule of thumb, choose an oscilloscope to have a bandwidth of AT LEAST five times the analog bandwidth of the maximum frequency square wave you want to analyze (300KHz * 5 = 1.5MHz)Think about what you need, how soon you need it, and how much you're willing to pay for it, prior to choosing an oscilloscope. If this 300KHz square wave is all you need to measure, go for the cheapest scope you can find... if you need a scope at all, but if you want something that will keep up with your demands for future projects, go for something nice!

author: erupter
author_rank: Contributor
timestamp: February 02, 2012, 06:01:05 pm
content: Quote from: olsenn on February 02, 2012, 05:38:18 pmThanks mate, I really appreciate your deep comprehension of my posts.Buying a 500$ instrument capable of following an arbitrary signal up to 25 MHz just to record a square wave at 300 KHz...Yes that's gorgeous!Why spend 100$ when you can spend 500$?Don't listen to me, I'm a cheap guy...Quote from: olsenn on February 02, 2012, 05:38:18 pmAs ANY OTHER DSO OSCILLOSCOPE, the proposed model DOESN'T save data in realtime as requested by the OP.It can save the memory when in a paused state.This memory amounts to 1Million samples if I remember correctly, which amounts to 0.01 s at the 100 MHz sampling frequency.Or about 3 cycles of the original signal.

author: Unknown
author_rank: Unknown
timestamp: February 02, 2012, 09:46:50 pm
content: I wouldn't say a scope is useless for this application, although not ideal and certainly not the cheapest. It is far more versatile than a data logger, however. When did the price on the Rigol rise to $500?Not sure what the measurement rate is on the Rigol DS1052E. I would be happy with 100 Hz, it's certainly nowhere near 300 kHz. I'm also not sure at what speed it will be able to stream those measurements to the PC, anyone with a Rigol scope ever tried this? Those Agilent DSO-X scopes would probably be better (though the measurement update rate may not be the same as the waveform update rate), but even more expensive.The issue with just using an ADC with a micro is that you have to sample the square wave to determine the amplitude, so you need to sample much faster than the 300 kHz fundamental frequency. Probably something like 1.5 MSPS or so, if noise is low. If the signal is fairly noisy and you need to average several points to determine the high and low value, then you need to take even more samples. This is going to need a fairly beefy uC, especially if some processing and data transfer needs to take place.Quote from: erupter on February 02, 2012, 09:33:12 amAnalog bandwidth 70 kHz. Real-time continuous streaming 1kS/s or greater (they don't say how much). Continuous streaming (not sure what the difference with real-time streaming is) 100 kS/s with their SDK. That's not going to work well for a 300 kHz signal. For high-speed data logging, they recommend... a DSO. The cheapest of the non-handheld ones is $260, which is getting closer to the Rigol scope ($350?). In continuous streaming mode it can do 1 MS/s typical, which might just barely be enough.Quote from: erupter on February 02, 2012, 06:01:05 pmSampling a 300 kHz signal at 100 MHz is of course very inefficient. At something like 10 MSPS, it would be able to store about 30,000 cycles of data. Probably not enough, but no 3 cycles either. I agree that a DSO is not usually designed for continuous logging.

author: tbutton
author_rank: Newbie
timestamp: February 03, 2012, 10:16:26 am
content: Thank you!!!"The cheapest of the non-handheld ones is $ 260, which is getting closer to the Rigol scope ($ 350?)".Yes ... but scope much more useful."... Agilent DSO-X ..." I would like to, but ... I have only $500What do you think about Owon ? (http://www.owon.com.cn/eng/smartDS.asp)andhttp://www.dataq.com/data-acquisition-starter-kits/data-acquisition-starter-kits.htmPlease comment (Is it real?)As far as I know, by the theorem of Nyquist-Shannon sampling theorem, it is necessary that a sampling rate of at least 3 times greater than the maximum frequency of the signal, ie about 1 MHz.What is confusing is that the measurements should be carried out:a) For a rectangular pulseb) Every 0.01 secondsI think may be obtained to reduce the requirements: <1 MHz?

author: Unknown
author_rank: Unknown
timestamp: February 03, 2012, 11:02:18 pm
content: Quote from: tbutton on February 03, 2012, 10:16:26 amThe Owon SDS series appears to be decent, based on the reviews posted on this forum. There is at least one video review and quite a lot of information by rf-loop about them on this forum. They're more expensive than the Rigol DS1052E, have better specs, but I've no idea if they're much better for this application. I believe they also had some annoying firmware issues.Quote from: tbutton on February 03, 2012, 10:16:26 amI don't see any reason why these wouldn't be real, but the sampling rate is at least one order of magnitude too low for 300 kHz signals.Quote from: tbutton on February 03, 2012, 10:16:26 amCorrection: it should be more than twice thebandwidthof your signal. A 1 MHz square wave has much more than 1 MHz of bandwidth. When an ideal square wave is decomposed as a Fourier series, it will have an infinite number of odd harmonics. In the real world square waves are not ideal and have a finite rise time (edge rate), this rise time is what determines the bandwidth. A rule of thumb is a bandwidth of 0.35 / Tr.You're not sampling the square wave to produce an accurate representation, but just want to measure amplitude, so you should be able to get away with much less and should be able to ignore the fast edges. You just need enough points per cycle so you'll be certain that you have at least one good point in the flat part representing the maximum and one for the minimum. Hence my guess of something like five points per cycle.Quote from: tbutton on February 03, 2012, 10:16:26 amFor an oscilloscope, the repetition rate of the measurement is the difficult part. A decent 50 MHz scope should give an OK representation of a 10 MHz signal, but doing that hundreds to thousands time per second may not be possible. For a data logger, the frequency of the signal is the difficult specs, since you need to sample this signal continuously.

author: tbutton
author_rank: Newbie
timestamp: February 04, 2012, 07:55:05 pm
content: "I don't see any reason why these wouldn't be real, but the sampling rate is at least one order of magnitude too low for 300 kHz signals."What sample rate do you recommend?Is there a device with _sample_rate_ <= $ 100?