Current measurement and display of RC circuit

[jatin10]

Suppose I have  a RC circuit and a known supply. The current in an RC circuit would vary. How can I measure the current in this case?

I want to display the current measured on a chart from the time t=0 to the time the capacitor is fully charged. If I use the DMM vi present in the examples of ELVIS and plot the measured current on a strip chart, at what frequency will the strip chart plot the current i.e what is the rate of plotting? Can we control it? If yes, how? Can we attain the rate of 10 samples per millisecond in ELVIS I?

[nyc_(is_out_of_here)]

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@jatin10 wrote:

Suppose I have  a RC circuit and a known supply. The current in an RC circuit would vary. How can I measure the current in this case?

I want to display the current measured on a chart from the time t=0 to the time the capacitor is fully charged. If I use the DMM vi present in the examples of ELVIS and plot the measured current on a strip chart, at what frequency will the strip chart plot the current i.e what is the rate of plotting? Can we control it? If yes, how? Can we attain the rate of 10 samples per millisecond in ELVIS I?

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ELVIS is covered in the http://forums.ni.com/t5/Academic-Hardware-Products-NI/bd-p/10

[jatin10]

Thank you for replying,

I seaeched the above mentioned forum but still my query remains unsolved.

Can someone please solve my problem? I would appreciate your painstaking efforts.

[johnsold]

This sounds somewhat like a school assignment. We do not do your homework for you because you would not learn anything that way, in addition to being dishonest. Even if this is not a school assignment, showing what you have tried to do and asking specific questions about how to improve your VI will tend to get you answers more quickly.

I am not aware of the capabilites of ELVIS, so these comments are general.

How are you getting multiple readings from the DMM? Some kind of loop? Then what determines how fast the loop iterates? Can you get multiple samples per iteration or just one? What is the maximum sampling rate of the ELVIS hardware? The answers to these questions and some thought should get you closer to the answers to your questions.

Lynn

[jatin10]

Thank you for your not so helpful reply. 

I thought that the forum encouraged problem solving technicalities. Moreover I am not asking you to prepare my vi. It's just that after too much research, I still find that Elvis manual needs to explain more on current measurement. Moreover the forums do not usually have posts regarding current measurements which is one of the most challenging topics which people tend to avoid.

If you could help me in some proper way, I would appreciate your painstaking.

Thank you

[Dennis_Knutson]

Quite frankly, you should be posting to the board that Lynn mentioned. Elvis is an academic product and you won't find many users of that hardware on this board. Your initial questions also seemed related mostly to sample rates and general LabVIEW and not so much current measurement.

[jatin10]

Thank you for replying Sir

I know how to measure current from ELVIS. It states that Current Low terminal needs to be grounded while Current High is to be placed at point of interest. Using this, i observe the value of current on the DMM. However, if I wish to plot these values using a strip chart, I do not get a desired result. Here, comes my problem of sampling. Since I am working on a windows platform, I can't set the duration of my loop update(in FOR or While loop) below 1ms. If i set it to say 0.001ms, it takes it to be 0.

Since i want the measurements to be at a higher rate, so that they get plotted conveniently on graph, I am stuck.

I wil soon attach a vi that will further clarify my problem..

In the meanwhile, sir please help in any possible way if you could understand the root of my problem( which is current measurement and display from elvis at a higher rate)

Thank you

[johnsold]

Now you have clearly described a specific situation which can be addressed.

The shortest wait time which can be specified in a For or While loop is 1 ms. To get samples faster than that requires the hardware to take multiple samples for each time the software reads. Can the ELVIS DMM do that? I seriously doubt that any inexpensive DMM can sample at 1 MHz.

Basically you want to set the hardware sampling rate to the speed you want, such as 1 MHz. Then you start the sampling, typically as a continuous process. Inside a loop you read the samples in blocks. For 1 MHz sampling you might read 10000 samples every 10 ms. After acquiring the samples you want, exit the loop and shut down the acquisition task.

If you will be using sampling rates on the order of 1 MHz and the duration of the acquisisiton is more than a few seconds, you will need to be careful about memory management.

Lynn

[jatin10]

Thank you Lynn,

I will work on the approach and see if i get what I desire...