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Capture data directly to disk

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Capture data directly to disk

Postby pisoiu » Mon Mar 20, 2017 3:10 pm

Hi,
I recently purchased a 2406B scope. Among other uses, I need it for data logging.
I have some devices which works in automotive environment and from time to time they suffer from random errors mainly due to noise on power supply lines. This behavior happens usually when the devices are not available for direct analysis, like working on them on my desk. Also, the erratic behavior may disappear at next restart of the car's engine. So the only solution is to hook up an usb scope to the signals with problems, connect it to a laptop permanently mounted on the car and record data directly to the laptop's hard drive. Several days of data must be recorded automatically, nobody will be able to make a click on the recording system. After that, data has to be analyzed. The size of data is definitely higher than my scope's buffer or even the highest buffer scope from your portfolio. How can I do that with 2406? As a note, I use a similar system for recording digital data, a logic analyzer from tech-tools.com and their digiview software is able to do that, but in this case I need to record analog data.
Thank you.
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Re: Capture data directly to disk

Postby Martyn » Tue Mar 21, 2017 7:13 am

Collecting extended periods of data can be challenging, and will be governed by what data you really need to collect.

Does the data have to be continuous or can there be small gaps between buffers ?
Are you interested in all of the data, or just the data where problems occur ?
If just the problem data, is there a suitable trigger event ?
How many channels are needed and what is the required sampling rate ?
What types of signals are you looking at ? What is the device you are investigating ?
Would a custom application written using the SDK be suitable, or do you need the PicoScope 6 features ?

Dependant upon the answers the 2406B may or may not be suitable.
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Re: Capture data directly to disk

Postby pisoiu » Tue Mar 21, 2017 7:40 am

Hi,
Small gaps due to usb transfer are not a problem. The signals in questions are power lines of a gsm modem and its power supply from 12/24v. There are some power glitches there which sometimes exceeds certain limits and creates problems.
I do not always know what to look for, so it is very hard for me to create a trigger condition. Therefore, the capture should be continuous, saved to disk, and later I should load it into picoscope to examine all the signals. The sample speed I need is not very high, I think 100ksps are more than enough and I need at least 2 channels.
As far as I can tell, picoscope does not look suitable for recording, maybe only for playing/analyzing recorded data. I would like to avoid sdk, as I do not have very good programming skills (I only know a little VB6), but if there's no other way...
Thank you.
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Re: Capture data directly to disk

Postby Martyn » Tue Mar 21, 2017 10:15 am

A possible option for you would be to use the Masks and Alarms features in PicoScope 6.

FIrstly you would capture a waveform that is known to be good, you then apply a mask around this waveform, and finally you set up an alarm condition that will record the capture to disk only when the mask fails, before restarting the capture.

At the end of the run you would have a number of stored capture files that show a faulty condition, which will be time stamped to second resolution, and you avoid having a disk full of known good waveforms.

Do you think this may help ? If so we can assist with setting up the masks and alarms.
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Re: Capture data directly to disk

Postby pisoiu » Tue Mar 21, 2017 1:27 pm

Unfortunately this is not an option, there are two reasons for that: one is that there is more than one 'good' waveform. As you may know, gsm modems transmit data with variable output power, depending on network condition. The consumption and therefore the pattern of the power lines depends on this factor. The second reason is that the power line fluctuation depends not only on the modem current but also depends on the power supply behavior, mostly the transient response. This changes over time because of temperature which affects important parameters of the components. We have large swing of temperatures in a single day, sometimes as much as 80 degrees celsius.
I really need to capture everything, even with small pauses due to usb transfer.
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Re: Capture data directly to disk

Postby bennog » Tue Mar 21, 2017 6:36 pm

You can do it with streaming data at 100ks.
There are 3 problems.
- You should use the SDK (or someone who is willing to do it for you)
- The amount of data you sample.
2 channels at 100ks will produce 400 kB of data per second.
so you will get 1440 MB per hour and 34.5 GB per day.
- You can not use the picoscope software to analyze you data.

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Re: Capture data directly to disk

Postby pisoiu » Tue Mar 21, 2017 10:09 pm

The size of data is not a big problem, hard drives with such capacities are common.
Analyzing data in picoscope was just an idea but probably other solution would be to view it with sound editing software such as cooledit, if I convert scope data to raw/wav format.
SDK is my fear but I will use it if I have no other way. Do you know any examples with SDK written in VB6? I know it a little and I may be able to do the app myself. The oficial 32/64 bit SDK does not contain VB6 examples.
Thank you.
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Re: Capture data directly to disk

Postby bennog » Sun Mar 26, 2017 2:32 pm

I doubt cool-edit or equivalent is able to handle sound recordings of 48 hour or longer.
Wav files in origin where 48 kS / sec the pico caputuring is 100 kS so 24 hour of pico caputre is 48 hour wav file.
Most so not all editing apps will not be able to handle this.

I should split the file in 2 or 4 hour chunks and then analyse them later on.
in the SDK is a streaming sample of C# you can modify simply for your needs.
C# has the most similarity's with VB so you should be able to read and modify it.

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Re: Capture data directly to disk

Postby pisoiu » Mon Mar 27, 2017 9:39 pm

Thank you.
I thought splitting them in small chunks is a good idea. I had some experience in the past with such sound editing sw and loading big files is just not a good idea.
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