Data Acquisition with TDS220

[Lozer]

Dear all,

 As a part of my Master Thesis I've fabricated a Transient Hot Wire system to measure the thermal conductivity of fluids. Voltage output from the system is to be measured with a time interval of 5-20ms but not more than 20ms. That means after each 5 milli second I have to save a voltage reading from the oscilloscope in to a file  in my computer. I have downloade drivers for TDS220 (Techtronix Storage Oscilloscope) from NI website itself. In my lab I have LabView versions both 7.1 and 8. I've used the Examples came with the driver package and modified it. But the problem is it does not allow to pick data in intervals less than 500ms. The example programme itself takes 500ms to read one data from the oscilloscope. How can I overcome this. 

Please Help me out. I'm really stuck with this.

Thank you very much.

Neeraj K

Magnetics Laboratory

Cochin University of Science and Technology

India.

[Dennis_Knutson]

It would help if you attached the modified code but if you are trying to continuously acquire every 5 msec, you may be using the wrong instrument. The scope has to be triggered, then perform an acquisition of however many points you have configured it, then do a transfer. This will take considerably longer than 5 msec over GPIB. You could possibly use a hardware trigger to capture some specific time interval but for continuous acquistion, you should be looking at a pc based solution. An NI DAQ card is one option.

[Lozer]

Hello Dennis,

    Thanks for your advice. I am planning to buy a DAQ card from NI. But I don't have any experience with the card based acqisition. Can you explain me what all am I need to have in order to acqire data from my experimental system? 

Please note that my requirement is to measure voltage imbalance in a wheatston bridge, in each 5 ms, since the voltage increases rapidly and the experiment won't run more than 8 seconds. I need as much as datapoints I could get. Please suggest me a low cost (I'm a student I can't afford a sophisticated one) DAQ card, and please explain me what all accessories I need to have inorder to measure the voltage and plot it against time. What I already have are Core2Duo based PC (Server) and LabView8.

Thank you.

[Coq_Rouge]

If you use a low frequency AC excitation of the bridge you may use a sound card. Just as a last resort solution. I will not recommend using a sound card in any commercial no sound application. But in a student assignment it may work.

You should talk to your professor about this. He/she may be able to help you with your resource problem. It is much better than just sitting on your thumbs. 

[Lozer]

Huh, that is the funny part. My professor only told me to ask in NI forums and find out myself if I want to do the project. Can anybody suggest an NI DAQ ?

[Dennis_Knutson]

The least expensive from NI is the 6008. There are other brands available. Google is your friend.

[Lozer]

You think this is all I need? and is it capable of giving a reding of 1 per 5ms ? Also the current in the circuit may go as big as 100-200 mA. wouldn't that trouble the card? I use a DC votlage source so no dealings with AC.

Message Edited by Lozer on 05-26-2010 10:21 PM

[Dennis_Knutson]

You were looking for cheap. I gave you cheap. It's certainly fast enough. You are the one with akk the details of what you need to measure. Look at the specs at the link I gave you. And, is the scope the only instrument you have now? Some DMMs can do a scan.

[Lozer]

When I said cheap, I meany cheap that is handy

Indeed I have gone through the specs and there is nothing about input current in the 'Analog input section'. pardon my ignorrance, but is it like directly pluging in the output leads of my device to the card  when we say 'Analog input'? or I need yet another connector block for this? If so, is there a low-cost card which can measure maximum up to 15V and 200mA DC?

[Dennis_Knutson]

200ma is way outside the limits of the 6008. Sorry, but I am not familiar with each and every NI device. Have you trid your local NI Sales Engineer?