using long term data from high res multimeter for analysis? - Page 1
Forum section: electronics / projects

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 18, 2014, 05:02:05 pm
content: Would it be possible to use a datalogging multimeter as a kind of low frequency high resolution FFT? For low noise FFT, kind of like using it a dynamic signal analyzer for like 0-10 hertz to check out the behavior of something when using it or near DC? I am guessing a dynamic signal analyzer is essentially a ADC sampling at some frequency to cover the ~100KHz range. Even though the sample rate for multimeter measurements is not great surely it could be useful for low frequency FFT.would one gather the data into a text file and use excell? I played with computerizing data before this before just using a ADC/PIC combination to make a ADC histogram and I got the feeling that it was inappropriate for large amounts of data (when I did it I think the limit was 30,000). What if you really really want data analysis on a shitload of samples?

author: penfold
author_rank: Frequent Contributor
timestamp: February 18, 2014, 05:46:33 pm
content: Your first concern should be to make sure that the sampling rate at least meets your nyquist rate and then some, depending on the required accuracy i'd go for nearly 10 times, 5 if not critical.The jitter of sampling would be the next big concern, timing error and jitter can cause you big problems in an FFT which can be anything from a raised noise floor to some unusual spikes, I can't remember the factor i normally work to on this but i'm sure somebody will jump in with it.So if your multimeter will sample sufficiently frequently, say near 100 Hz, youre set.If you could RS232 attach your ADC/PIC to a PC then the world is your oyster for maximum number of samples.

author: Selectech
author_rank: Regular Contributor
timestamp: February 18, 2014, 05:47:52 pm
content: A series of articles were published in EDN for doing just that;http://www.edn.com/electronics-blogs/the-practicing-instrumentation-engineer/4401550/Use-a-DVM-to-directly-digitize-low-frequency-noise--Part-1-A good read, follow the links for the other 3 parts.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 18, 2014, 05:50:09 pm
content: So you think that for my purpose I should stick to a "quick and nasty" solution involving a ADC and PIC rather then using the well built front end of the multimeter? Are there any situations where a multimeter should be used rather then a ADC ?I guess its fairly easy to construct a single range high quality multimeter, it gets tricky with range switching and input protection.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 18, 2014, 06:29:40 pm
content: and does he ever list software? I only read three parts. Is there a 4 with downloads ?

author: dannyf
author_rank: Super Contributor
timestamp: February 18, 2014, 06:41:47 pm
content: -30,000).-given that each sample is at least one byte and likely more, that kind of sample would require so much data that a pic in existence today cannot hold it.alternatives:- develop a recursive fft algorithm.- use shorter windows and kalman filter the output.

author: tszaboo
author_rank: Super Contributor
timestamp: February 18, 2014, 07:08:30 pm
content: Quote from: SArepairman on February 18, 2014, 05:02:05 pmThat is nonsense, a 3458A is able to make 100KSPS with 4.5 digit. And with sub sampling, you can go up to 12Mhz with it.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 19, 2014, 11:39:44 am
content: Quote from: NANDBlog on February 18, 2014, 07:08:30 pmsounds like you can ghetto rig an oscilloscope pretty easy out of a fast sampling multimeter thenhowever I think that given the type of input a multimeter has using it into MHz is a bad idea