continuous data acquisition with tds 2002

[levback]

Hi all,

We have a TDS2002 Oscilloscope and NI-USB6259 DAQ card. We apply a PWM signal (25 Khz) from the DAQ card analog output and we want to measure the continous signal from the Oscilloscope using Serial Port. We installed the drivers for the Instruments and they work well. We use two Basic Function Generators, one for the square wave output and one for duty cycle adjustment(We need to continously change duty cycle between two values) of the output square wave. We apply the DAQ output as an input to a boost converter circuit and we measure the output of the circuit with the scope. However, we could not obtain the output of the scope continously using LabView 8.2. We also want to save the output data and PWM signal into a file and we will process it in MATLAB later. When we use a while loop, we could obtain a clear PWM signal. We tried to get the data from the scope and we could only get one screenshot from the scope. We want to obtain data for at least 30 seconds continously.Can anybody help us to do this work?

We first tried to measure the data from the DAQ input, however we could only get 30 samples in a second. We need to sample the data at least 500 KHz frequency. If somebody can offer a solution to read from the DAQ card at that frequency, it would be appreciated.

Thanks,

[Dennis_Knutson]

I'd say you were doing very good to get 30 samples per second with a scope and serial connection. You would do better with a GPIB connection but you would still not be able to acquire continuously. You have to send a command to the scope to acquire, it has to acquire, you then have to send a command to transfer the waveform, and when the transfer is complete, you start again. While it is transferring, it is not acquiring. I don't beleive this scope has an internal buffer which will keep acquiring while you do the transfer. Why aren't you using the 6259 for the acquisition? It's got a 1.25MS/s sample rate and is capable of continuous capture. You can also, with proper coding, stream the data to disk.

[levback]

Dear Dennis,

We get very fast data from the scope but the problem isto get the data continously. On the other hand, we get data from the DAQ with 30 samples/sec. It says it has a 1.25 MHz  sampling rate.However, we could not achieve more than 31 samples/sec.could you offer me a good solution?

[Albert.Geven]

Hi

Data_aquisition is perfectly possible with your 1.25 DAQ Card, at least I assume it is a M-series card.
You probably initialalise each measurement instead of setting up a continuous strea.
Did you look at the examples shipped with LabVIEW?