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Picoscope - datarate to PC

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Picoscope - datarate to PC

Postby Guest » Tue Dec 18, 2007 10:13 am

Hi,

We'd like to measure the peak amplitudes of 2 ch simultaneous and store the readings to HDD as fast as possible. We need to store only the peak value (a few bytes) and not the full sweep. The scope should collect these values continuously for up to 10 minutes at the fastest possible rate.

If necessary, we can provide an external trig signal and also an external analog peak detector, although we would prefer to avoid any external electronics. We have some knowledge in C/C#/C++.

The peak readings should be appended in a file on the HDD for the whole period up to 10 minutes.

What model PC scope do you recommend for this?
What is the maximum datarate (peak readings per second) we can expect?

Regards grandpa
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Postby ziko » Tue Dec 18, 2007 11:57 am

Hi grandpa, thank you for your email.

I have a few questions regarding your query:

1) You say two channels simultaneously, do you want them at exactly the same time or do you not mind say a 50ns delay between them?
2) You say you want to log up to 10 mins as fast as possible, how fast do you wish to sample, and how fast is the signal you are trying to measure?
3) You say you just want to measure just the peaks, do you want a time stamp for the peaks?

Kind regards
Ziko

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Picoscope - datarate to PC

Postby Guest » Tue Dec 18, 2007 12:46 pm

Hi Ziko,

Thanks for quick response and good questions!

General:
The pulses we want to catch are "analog" with a rise time of 10-20nS and a fall time of 100-200nS. The 50% width varies with amplitude with an average of 50-100nS, roughly. The amplitude as well as the period are arbitrary. Some occur almost overlapping in time, others are up to 1mS (milliS) apart. Some times they occur simultaneous on both ch, some times not. We only need to catch the ones that come simultaneous. It is sufficient to catch pulses that come 10-100uS (microS) apart. We will obviously loose whatever comes during this dead time, but that's ok.

Further info re your questions:
1) The peaks occur within 20nS of each other and the top (flat part) is less than 10nS. We can, if necessary, add an analog peak detector and hold the peak up to 500nS or, preferrably shorter time.
2) According to the info above, we would like to measure both ch every 10-100uS, faster is better. The sampling of both ch should take less than 500nS. If the saving to HDD keeps up with the 10-100uS period, fine, if not, the data has to be buffered up to 10 minutes.
3) We don't need a time stamp.

Interesting application, right?

Regards grandpa
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Postby ziko » Thu Dec 20, 2007 3:37 pm

Hi Grandpa,

Sorry for the slight delay we were busy figuring this one out! You are correct, it is an interesting application.

It seems as if this is perfectly plausible if you wish to write your own software. You would just need to trigger on an event and start doing your capture. If you wish to analyse your data (i.e. peaks of overlapping pulses within a certain time window) then you can do that after you have done your aquisition.

There is a lot of information in what you have sent and it is not very clear what you require, so if you can answer the following questions it would be greatly appreciated:

1) Exactly what sample rate do you want?
2) Over what length of time do you want to sample (continuously or not)
3) How far apart are pulses are on a single channel (smallest gap, i.e worst case scenario)

Kind regards
Ziko

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Picoscope - datarate to PC

Postby Guest » Fri Dec 21, 2007 1:34 pm

Thanks again Ziko,

We start to realize that this is not really easy. Therefore, we will use an external analog peak detector and electronics to provide a trig signal when simultaneous pulses occur.

Your questions:
1) Exactly what sample rate do you want?
2) Over what length of time do you want to sample (continuously or not)
3) How far apart are pulses are on a single channel (smallest gap, i.e worst case scenario)

My answers:
1)
The peak values are held for 500nS. Anywhere during this time we need 2-4 samples (readings) of each ch. 10-20 MS/s sounds reasonable to me.
2)
500nS or less. We do not want a stream of continuous samples into the HDD as this will grow huge files. All we need is the 2-4 samples after each external trig event.
3)
With the external electronics, we will supply a trigpulse every 100uS (or faster, if possible for your scope, every 10uS would be real nice). The real pulses come faster, but we will simply disregard what happens in between to allow the scope to catch up.

Best regards
grandpa
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Postby ziko » Fri Dec 21, 2007 2:46 pm

Hi Grandpa,

After extensive discussions unfortunately you cannot do this with any of our devices. The main limitation is the time between the trigger events (for the device to rearm itself), will be 600us. Other problems are the length of time it can capture data for as it will need to go into Rapid Block mode, where it fills the memory of the device and then dumps it onto the hard drive. It will then need to arm itself again after transferring the data which may take 50-60ms.

So to sum up capturing a single trigger event is no problem whatsoever its just the next pulse would come too soon before the device has armed itself again.

Kind regards
Ziko

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Picoscope - datarate to PC

Postby Guest » Fri Dec 21, 2007 3:29 pm

Hi again,

I didn't expect this to be possible. That's why I spent a lot of time checking.

Your scope can obviously be used for more common tests in our lab.

I have also made a sketch of the signals, so if that would be useful, you can send me a message at bjorn_bgresearch_no and, I will attach a pdf of it in the reply. I was unable to register to your forum today. Pls replace the _ as needed.

Thanks a lot,
have a Merry Christmas

Regards grandpa
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Postby ziko » Thu Dec 27, 2007 1:18 am

Hi Grandpa hope you had a merry christmas.

Could you send any attachements to support@picotech.com.

Kind regards
Ziko

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