lock-amplifier Error -200278

[Nan Yang]

Hi,

I am trying to use a virtual lock-in amplifier to detect AC signals from noise. I have downloaded the NI Lock-in amplifier start-up kit" and some examples. But when I run the exmple" Multichenel locl in-DAQmx", it dose not work, and said:

Error -200278 occurred at DAQmx Read (Analog 2D DBL NChan NSamp).vi:1

Possible reason(s):

Attempted to read a sample beyond the final sample acquired. The acquisition has stopped, therefore the sample specified by the combination of position and offset will never be available.

Specify a position and offset which selects a sample up to, but not beyond, the final sample acquired. The final sample acquired can be determined by querying the total samples acquired after an acquisition has stopped.

What dose this mean? Also, is this "Multichenel locl in-DAQmx" a completed lock in amplifier I can use ( it seems there is no reference input controler on the front panel) or I get to set up my own lock-in using the "start-up kit"?

Thank you!

nan

[Yardov]

Hello Nan,

Welcome to the forums. This error means that your program tried to read the buffer but this buffer was already replaced by more samples. Basically, you were not reading fast  enough.

I am not sure what hardware you have, is always useful to know, but I tried with an M-Series (6251) and with the default parameters I am not getting any errors. I am including a very simple test example that will help you generate your test signals. Use this to generate on AO1 and AO2 and route them to AI0 and AI1.

Good luck,

[Nan Yang]

Thank you very much for your help! it works today after we change some parameter.

But now the problem is: it is not a lock-in what we want. it can only acquire the signal buried in noise but what we want to do is to compare a signal with its initial one after some process. This new signal may be lag and attenuated, and of course, it is also buried in noise.

I found that in the "NI lockin start up kit", the "LockInDEMO.vi" has a reference input channel, which may be what I want.  But because I am using "labview8.2", the vi can not work and asks for some subvis like:

AI clock config.vi; AI start.vi; AI config.vi; AI read (scaled array).vi; AI read.vi; AI clear.iv

I think these should be in a lower version. So can you tell me where I can get these subVIs from the website to help me run the lockin, or where I can get a new but same kind of lock-in which can work under "labview 8.2", or how can I replace these old subvis using those of labview8.2?

Your help will be very appreciated!

regards,

Nan

[Yardov]

Hi Nan,

There are some demos out there that uses the same three VIs which are the "engine" of the lock in amplifier. The one you have should be on traditional DAQ (name of the driver) and you should use the one I posted before. This one works with DAQmx and LabVIEW 8.2 (if you noticed, that is the LabVIEW version of the VI I posted).

Depending on the dynamic range of your hardware, that application will give you accurate results. With an M-series the phase has some 5% error but the frequency is very accurate with a SNR of about 44 dB.

[Nan Yang]

Thanks for your reply!nan

Message Edited by Nan Yang on 05-02-2007 06:58 PM

[Nan Yang]

Hi Gerardo,

Sorry, I am a very new labview user and  I am still confused. I am now using labview8.2, and I want to open the demos (especially the one named " LockinDemo")  in the " NI lock-in amplifier start up  kit", but it asks for some subvis:

AI clocl config.ai; AI start.vi; AI congig.vi; AI read (scaled array).vi; AI read.vi; AI clear.vi.

So if I download " traditional DAQ" and install it to the computer, then I can open the demos with labview8.2?

Or I should download " DAQmx" and install it, then I can open the demos with labview 8.2?

Can you give me the suitable link?

regards,

Nan

[Nan Yang]

My card is NI PCI-6035E.

[Yardov]

Hello Nan,

That example requires Traditional DAQ and you do not have the driver. This is why you cannot find those VIs.
I think you are not downloading the example I told you to. Here is the link and address: http://zone.ni.com/devzone/cda/epd/p/id/4532 
This example uses DAQmx which is compatible with your card and will help you get started directly using the example I posted before.
If you do not find some VIs, then you do not have the driver. 

Finally, since your card is a 12 bit card, you should not expect to have very accurate results. Just for quantization, you have already about 64 dB SNR (signal to noise ratio).

Message Edited by Yardov on 05-04-2007 11:00 AM

[jmoya]

I have had success in designing a lock-in amplifier with the Elvis II+ and the valuable assistance provided by you. Using the scope input I can work with frequencies up to 5MHz. Now, I have two questions to ask:

1) The DAQ of scope of the Elvis II+ is 8 bits, and being the smaller range of +/-20 mV, the resolution is about 156 uV. If what I say is correct, why I can read up to approx. 20 uV with my lock-in? (This data is true as it was compare with a real Lock-in instrument)

2) I need the virtual lock-in to read the reference signal internally, and have not succeeded in developing a sine-wave generator with a capacity up to 5 MHz. The actual signal generation I use is the FGEN of Elvis II+, meanwhile the reference signal is acquired by the scope via one scope channel. I would like to leave vacant that channel of the scope and to send via software internally the signal to the Lock-in libraries. Can you help me? (none of my attempts has read as well as the reference signal generated by the FGEN and acquired by the scope).

[Jacob_K]

The specifications on our instruments are at the levels that we can guarantee for sure will be true.  When using successive approximation digitization signals it is possible that the reading will fall very close to the true value.  Although because of the step size we can only be certain that it is within 156 uV of that value.   This is similar to rounding.  If a true value is 9.001 and our device is only accurate to the tenths we would read 9.0 which we could then say that we are within .001 of being accurate, but we would get the same answer if our signal were 9.049 which would mean we were .049 of being exact.

As far as I know there is no such path internally that you are looking for.

Jacob K