What animal should I use GPIB or DAQ?

[Gaudier]

               MyProject

The proposed work consist of developing and implementing a measurement system able to capture the signals provided by the different probes used in the plasma laboratory and store them into a computer, along with performing various calculations using those signals. The system should be able to display the measurement as well as the result of the computations and provide for further development leading to the inclusion of new measurements and computation. As measurement element, the system should be able to use a Pico-ammeter, a manual swapping devise or a digital scope. The programs and interfaces should be able to display the acquired data in a computer, compute the significant variables needed by the plasma laboratory, store the data acquired during operation in a identified, reliable way, allowing to produce a graph display, instant measurements, printouts, and some easy math operations using the data collected. What  would be better for this project a GPIB or a DAQ?

[AnalogKid2DigitalMan]

You mention picoammeter and digital scope, these instruments traditionally have GPIB interfaces (and maybe serial or USB too). So I would suggest that as a starter interface. You did not go into hardware details, but you may also need a DAQ card to turn discrete devices on and off, supply pulse trains, sample lower bandwidth analog signals, etc.

To make the project easier, you may want to check NI's site for instrument drivers for the meter and scope you may want use.

I am assuming you will be using LabView, if you have no experience I would suggest at least basic formal training if possible. And go through the canned tutorials, help, and user guides.

Good Luck, it sounds like a cool (maybe hot, due to plasma? ) hands-on project!

[Dennis_Knutson]

For a slightly different recomendation, I would suggest you start by determing the actual specifications for the instruments. In some cases, that will decide the interface for you. For example, if you need to measure pico-amps to a x% accuracy, you may find that only a GPIB instrument exists. Or you might need an extremely high sample rate for the scope and that too, will limit your choices. On the other hand, average sample rate scopes are available in GPIB, PCI/PXI, USB. GPIB scopes have their own power supply, display, knobs that can be twiddled, portable, are more expensive, and relatively slow to transfer data. Computer based scopes use the computer's power supply and monitor, no knobs, less portable, are cheaper, and transfer data very fast. Actually, if you look at some of the newer scopes from Tek and Agilent, what you will find is that inside is a computer mother board running some version of Windows and have some data acquistion cards in regular PCI slots.

Personally, in my applications, I favor the computer based instruments because of the cost and data transfer benefits.

[Marni]

Dear Gaudier,

Some excellent points have been made. The DAQ cards do not have the resolution for picoamps, but the GPIB cards tend to be a lot slower. Have you considered a PXI system with Modular Instruments products? National Instruments has FlexDMMs, Digital Scopes, and programming is really easy with LabVIEW. There are some great examples that come with LabVIEW that enable you to bring in the data, display it, manipulate it, store it, etc. This combination will have the speed and accuracy that you are looking for. Have a great day!

Sincerely,

Marni S.