DAQ HELP WITH SELECTING CARD FOR LOGGING SCOPE / LABVIEW

[bob1111]

What I need:

A scope system that will hook up to labview or comparable with 4 channels and ability to sample at least at 50M samples/sec or so. I will need to log and compare data from separate channels recorded simultaneously. I also will need to output another frequency that will sweep from 0-500 pulses/sec with an amplitude of .1V or so.


That .1V output along with the other channel inputs will all need to be logged and compared. For instance, I will need to compare my output signal to CH1 at 200 pulses/sec and compare the peak offset, if any.

I will be capturing square and sine wave data.

I am hoping what I am describing is a relatively basic 4 ch scope and probably not even in the high speed category.... I am just wondering if the output signal will be a problem. I know some cards do this.

I would prefer to buy a DAQ type device for this for use with a laptop rather than buying a complete scope. I will admit that my partner is much more knowledgeable in this area but he is too busy to shop around.

When I visit NI website, I get lost FAST wiwth so many choices. I need a little hand holding I guess to learn this stuff. I am also open to other options as well. Don't have to go this route but ultimately need to send and receive frequencies and record all of it.


OH - I did want to ask a dumb question. I see some scope advertised as say "4mhz" sampling and some as "30msps". How does the frequency compare to the msps? is 4mhz the same as 4msps? Am I off track?

I would also add that I am not experienced with DAQ and any signal conditioning and such would have to be brought into the light. I want to move forward with tougher DAQ tasks but want to get the basics by doing this one first.

 

[bob1111]

After posting, I see some errors. We can probably work with 20-50M samples/sec and would like to have a min of 4 channels. 8 would be great.

It would be best if we have some options on the signal generator side. 0-5V preferred.

We are just doing some testing a playing here so trying not to break the bank with this build. ebay or used find would certainly be nice for this.

 

[zappedagain]

There are DAQ cards out there and NI loves to sell their hardware. You will have a lot of software to write to get the same functionality as a scope (but NI might have a plug in that they will sell you too!). I suggest you contact one of the rental houses and rent a scope for a month or three. You can get one with an interface to the PC and drastically reduce the amount of software required. It will also help you define your hardware requirements.

4 MHz sampling is the same as 4 msps. Where you need to watch out is some scopes will talk about their analog bandwidth in hertz, and that is not the same as the sampling clock, especially when using oversampling techniques. Ideally by Nyquist it could be half the sampling frequency, but that isn't very realistic as it assumes infinite roll-off in the anti-aliasing filter.

Hope that helps,

John D

 

[bob1111]

Thanks for the reply. What we have found in our discussions is my target 4Mhz is a bit on the high side and we probably would never need to step past 200Khz.

I am certainly open to other solutions for a logging scope. I will admit I have some stick shock on some NI boards. Really would rather buy than rent.

I agree software could be an issue. A sister company has Labview that we could use but we are not proficient with it and not sure how easy it is to setup for things like this. I know NI preaches that they are really designed to interface with LV well but not sure.

Will the output signal create a problem in finding a suitable setup? We need to log it's frequency and compare timing from it to our other inputs.

 

[BobM3]

You could try

http://www.picotech.com.

 

[FreddyNurk]

I'd probably suggest for a small(ish) sum that you consider renting a scope for a little while and at least get familiar with some of the functions that are likely to be available to you.

A couple of other considerations that may or may not pop up; are all the signals sharing the same common reference? Are all of the signals likely to be well within the equipment's (i.e. scope for now) input ranges?

I've seen a LabView setup with a full custom front end of sensor interfaces (about 8 Differential probes, 8 Rogowski Current probes) all connected via separate DAC units and then fed into an NI 16 channel PCMCIA card. It worked really well when it was behaving properly, and a complete pig to diagnose when it wasn't (was a driver issue with the then outdated PCMCIA card).

LabView can definately do what you're after, the development curve might be a little steep at first though. It is possible (though I admit I haven't tried it) to use a moderately expensive CRO (say a Tektronix) with a GPIB interface and then use that instead of looking at custom DAC front ends, such as in the example I quoted above.

Another option may be to use a Pico as suggested, they're fantastic for the price and portability.

Above all though, I'd spend a little time working out how to use the sort of equipment that you're likely to end up with, and then work out what your processing requirements are. A final consideration may be that some of the moderately priced CROs do offer screen capture and similar functions. I don't know if they offer data extraction however.

 

[zappedagain]

Newer scopes have USB ports and are even easier to interface with. Most of the rental companies have decent programs set up if you want to rent first and then buy later.

John D