Continuous integration of Analog Input

[jakel314]

Hi all, I'm pretty new to LabView and have been given a project part of which I'm not sure is doable, basically an arbitrary waveform voltage is sent out and we're looking to record the current values received back, simple enough, the tricky part is we would like to cut the voltage source at the point when a certain amount of charge has passed through our object, basically integrating the current and when it hits a target value cutting the source. I have not yet found a way to continuously integrate input data, the only thing i have found is after capturing an entire wave,

Does any one know if continuous integration is possible? if so where can i find a vi or would i have to create my own,

Thanks for all the help

-J

[m3nth]

To "continuously integrate" in the digital world always means to monitor at discrete integrals--that's part of having the data digitized. The smaller those discrete integrals, the better the accuracy of your integration. You will always be integrating a set of data points ("an entire waveform"), but in my understanding, the length of your acquisition in the current setup is excessive in comparison to the time you would like to pass before cutting your source off.

What is the maximum amount of time the voltage cutoff can lag the actual charge accumulation event? From what you've stated, your present configuration fails this criteria.

What I would look at if I were you:

The Time Domain Math Express VI (Block Diagram > Express > Arithmetic & Comparison > Time Domain Math) has an option to perform a waveform integration on a signal. The guts of the integral are just to add one number after another after another until everything in the data set is added to a single value (which is then multiplied by the dt value for correct time units). It can also perform a "continuous" integration by "remembering" where it left off--ie, it saves the last value when it has completed processing the data set. Then when it gets called the next time, that number is the starting value.

Using an integral should work for you but what you would want to do I imagine is keep your acquisition times very low so you are monitoring at intervals that make it seem more "continuous" instead of "discrete".

Something else to consider (don't know what hardware you're using) is that the NI scope cards such as the 512x family offer on-board measurement capabilities, one of which is integration (which means it gets performed in hardware and you just read back the number).

[Sparc]

The guts of the integral are just to add one number after another after another until everything in the data set is added to a single value (which is then multiplied by the dt value for correct time units).

What he said. To integrate the values from a DAQ board just sum all the samples and multiply by how long the acquistion took. To do it "continuously" keep the last sum around, add the new DAQ samples to it and multiply by the time since the DAQ started (or whenever you have defined to be t0). Rinse. Repeat.

Sparc

[Michael Aivaliotis]

Hi all, I'm pretty new to LabView and have been given a project part of which I'm not sure is doable, basically an arbitrary waveform voltage is sent out and we're looking to record the current values received back, simple enough, the tricky part is we would like to cut the voltage source at the point when a certain amount of charge has passed through our object, basically integrating the current and when it hits a target value cutting the source. I have not yet found a way to continuously integrate input data, the only thing i have found is after capturing an entire wave,

Does any one know if continuous integration is possible? if so where can i find a vi or would i have to create my own,

Thanks for all the help

-J

Have you seen the "point-by-point" analysis? This will do what you want but you need to change your output accordingly. The Acquisition and Analysis probably needs to happen in a closed loop.