basic question to continuous signals

[Anni]

Hello.

Unfortunately I got no answers of my questions after reading in help documents and articles.

Technical details: Labview version 7.1; we want to receive signals from different channels of a lock-in amplifier. We have a PCI 6220 and a a/d converter.

First of all I had the error -50103, but I could solve it, when I put the two signals together in one task. All in one the program runs, but I have some questions in basics.

For example: When I choose a number of samples per channel of 100 with a rate of 50 Hz the signals run not continuously. I see some information in the chart, then a few seconds there is nothing and after that the signals go on. With a number of samples per channel of 1500 the curve gets worse. But I want a continuous signal, whatever number of samples per channel I choose. Is it generally possible that my signals will be continuously/directly run in my chart? Maybe with arrays, but if yes how could it work? It really seems to me, that “DAQ read” saves some information in for example buffers and then shows it in a chart, then saves and show and so on. But that’s not what I want.

Please can anybody answer my questions?

Thank you very much.

[Dennis_Knutson]

It's basic arithmetic. If you specify a sample rate of 50 samples per second and request 100 samples, then it will take 2 seconds for the board to acquire that number of samples and return them (100/50). If you request 1500 samples, it will take 30 seconds to return that number (1500/50). The samples you see in the chart are continuous but the update rate of the chart is determined by the ratio of the number of samples and the sample rate. You can specify a higher sample rate or specify a lower number of samples.

[Anni]

Hi.
Thank you allot for your answer.
But that´s not good for me ;(
I have a problem with the update rate of the chart. So there is no possibility to see every time a continuous signal or choose a chart
that can show the signals continuous every time independent of the values of sample rate or number of samples??
The reason why we want to see the signals continuous is that we want to make really long measurements and we must see directly what happens.

[Dennis_Knutson]

I guess I don't understand the problem. If you choose to read all of the samples available, then your data is continuous. The only time your data isn't, is when the number of samples requested is less than the sample rate.

Be aware also that a chart has a limited history that you set at the beginning of the program. Once the number of samples acquired is equal to the history value, old values are removed in order to display new ones.

[ceties]

Why don't you just use continuous data acquisition? Than you acquire samples with the rate you select until you hit the stop button. Search some of the LabVIEW examples (LabVIEW-Help-Find Examples...) for instance: Cont Acq&Chart Samples-Int Clk.vi

[Anni]

Ok. Thank you very much. I will try it.