Products > Test Equipment
PicoScope 2000
irakandjii:
I am very grateful for this review, It will help me with my final selection of a diagnostic tool. I am looking at the 3405D Mso or the 5442B or the 2208B if it can do the job.
I have been investigating these scopes for a few weeks. My needs are heavily biased towards protocol investigations and analysis.
This puts serial decoding at the top of my list of priorities. But closely followed by bandwidth and frequency analysis.
It turns out that ALL of the standard bench scopes I looked at below $2000.00 US have significant short falls for this purpose, leaving Picoscope as a sole contender. I did find Keysight scopes >6k $ US that would work but that is a whole other universe for me.
Problem: I have long path lengths for multiple serial busses, some upwards of 4 meters. To make things worse these busses are vulnerable to flexing, stretching, vibration and significant thermal variations. Think sensors or remote devices on the ends of a robot arm working outdoors in the Canadian sub-arctic (+45 degC to -50 degC) in high winds. p.s. Its why I want a robot. A human standing in that is subject to pain.
Standard scopes typically save no more than 500 mSec or so of signal and in many cases far less. Allowing for very short exchanges to be diagnosed. The math follows:
Total Time of Acquired sample = (Time scale per division X Number of divisions per screen X the number of Screens in memory) / Sample Rate
I need very long diagnostic samples (ideally 10-20 sec.) that can be reviewed and analyzed for faults back in the lab. I require the samples to include protocol decode info plus the analog signals (for fault isolation). To handle "the very long" worst case diagnostic scenarios I came to the conclusion that streaming the data to an external PC would be optimum. The picoscopes can stream approx. 12 MS/sec for USB 2.0 models and 125 MS/sec for USB 3 models. ( I would write my own application using the SDK). I am now trying to figure out if there are dead spots in the stream analogous to the screen refresh dead spots on regular scopes. Regular scopes just don't stream.
For best case, 128-256 MS memory would be sufficient and cover a lot of use cases. This scale of memory is generally missing in regular scopes.
I am very interested in the impact of the PC hardware, my plan is to use an original Surface Pro as the PC interface. It is unclear to me if this will be sufficient.
I look forward to seeing this post progress
MrW0lf:
PicoScope 2408B DC ACCURACY
While checking my AD584kH, AD588 voltage standards against stuff I got, developed technique to substantially exceed specified DC accuracy of this scope (±3% of full scale ±200uV), making use of math channels.
General idea: High sampling rate will generate noise, which will induce "artificial accuracy" when averaged.
Setup with some example values:
Scope horizontal setting: max RTS sampling rate, large amount of points (1GSa/s, 1M)
Vertical setting: good enough for measured (DC) voltage, make use of DC offset if single polarity (+-10V, -5V for ~12V stuff)
Make math channel formula that irons out DC error ((A+4.984)*1.0056)
Apply DC averaging auto-measurement to math channel.
Configure stats reading count that will give stable reading (64 in test, but much less ok for regular use).
Calibrate using high accuracy DMM for 0 and max volts. Watch out for ground loops!
After initial effort all this can be saved as settings file and reloaded any time.
Do not use "Zero offset", because this does not get saved ("DC offset" does).
Just as "sanity check" included pretty ok 4-digit DMM for comparison - UNI-T UT210E.
There is some (temperature related) drift with scope, but for hours it seems to hover in the couple mV vicinity for +-10V range. Looking at test results, this technique results in DC error mostly far <1%, without even utilizing full scale of 8bit ADC. Could be used to monitor battery voltage etc on dedicated channel no worse than average DMM.
MrW0lf:
--- Quote from: irakandjii on March 09, 2017, 05:03:19 pm ---I am very grateful for this review, It will help me with my final selection of a diagnostic tool. I am looking at the 3405D Mso or the 5442B or the 2208B if it can do the job.
--- End quote ---
Think 3405D MSO is everything mine is + some on top of that + MSO. 5000 series is interesting with flexible bit resolution up to 16bit... but according to my findings even 8bit one do not exactly suffer from inaccuracy... 100MHz analog seems just about right, balances with MSO part which is max 500MSa/s = 100MHz/200Mbit also.
Edit: So much going on already forgot. You do not get cut out of 16bit game with MSO! Just pick any external ADC, feed into digitals and if your ADC voodoo is good its up to 16bit extra channel. For simple analog sensor listening youre already in with Arduino Uno/Due:
https://www.eevblog.com/forum/testgear/what-you-do-with-math-channels-on-oscilloscope/msg1106353/#msg1106353
Heres final version with faster scripts etc:
https://www.eevblog.com/forum/testgear/what-you-do-with-math-channels-on-oscilloscope/msg1130997/#msg1130997
Managed 59kSa/s@8bit with Uno, 687kSa/s@12bit with Due.
This works in standard software using math channels. Developed on my old 2205 MSO.
So with 3405D you get 4x8bit analog channels + 1x12bit sensor channel + 4x1bit digitals to spare. Or any other combination with digitals... Of course if you fire it all up at once it bogs down sampling rates making 50MHz max scope (Nyquist limit for 125MSa/s).
So you could calibrate formulas in standard GUI and then insert into your custom app. If you ever do this would be excellent to get some feedback about how it worked in real life.
--- Quote from: irakandjii on March 09, 2017, 05:03:19 pm ---Its why I want a robot. A human standing in that is subject to pain
--- End quote ---
We here in Estonia know all about that ;) Robot building is quite popular :-DD
--- Quote from: irakandjii on March 09, 2017, 05:03:19 pm ---I am now trying to figure out if there are dead spots in the stream analogous to the screen refresh dead spots on regular scopes. Regular scopes just don't stream.
--- End quote ---
Think no spots. Stream is stream, it goes into similar mode on ultra slow timebases. Going for USB 3 good idea also. I can look into that a bit on coming days. Doing this review-thing is very interesting because I learn new stuff every day.
--- Quote from: irakandjii on March 09, 2017, 05:03:19 pm ---I am very interested in the impact of the PC hardware, my plan is to use an original Surface Pro as the PC interface. It is unclear to me if this will be sufficient.
--- End quote ---
My second PC is similar - Lenovo Yoga 14 - folds into (a bit heavy) tablet. Runs good there. Unless you go completely crazy with math channels processing load is very little.
--- Quote from: irakandjii on March 09, 2017, 05:03:19 pm ---I look forward to seeing this post progress
--- End quote ---
Think next part will be something for timing nuts (femtoseconds >:D). After that will look into streaming and processing load then. Thanks for good feedback! :-+
MrW0lf:
--- Quote from: MrW0lf on March 09, 2017, 06:03:57 pm ---this technique results in DC error mostly far <1%
--- End quote ---
Did fire up same settings today. After "cold startup" zero point was drifted about -25mV vs U1282A. Waited for ~0.5h. Results with 64x averaging (values in volts, single +-10V (20Vpp) range as yesterday):
U1282A2408Bdiff% of range0.0045-0.005-0.00950.04754.92094.915-0.00590.02959.9389.927-0.0110.05514.90914.9-0.0090.045
After writing this 0-level is drifting between -2...0mV.
This cries for built in cal-tool, could cal all ranges easily with PSU/DMM at hand.
irakandjii:
Fantastic!
I will follow up on the MSO + ADC once I get the unit. My requirement for 12 bit+ is a future need. I want to play with some ultra-sonic gear and see if I can get some improved object or location sensing. Your proposed solution will work wonders for that and give me more flexibility.
Looks like the 3405 MSO is the way to go. As far as I can see the differences are: memory amount, memory architecture HAL 3, more analog channels, USB 3. I wanted both MSO and 4 analog channels. I wanted 4 analog channels so I can decode any of the available protocols in Analog mode.
Thanks again and the new data looks great!
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