Hello,
Does anyone know of a Velleman handheld o-scope which can perform FFT for THD from a waveform (or even capable of importing the data to computer). I plan on buying a Velleman, but I would like to calculate the THD for a home audio project and am not sure if any of these can spit out the data I would need to calculate it. Any advice or info would be very helpful. Also, one of the scopes I had in mind was the HPS50, but anything handheld and under $500 would be great. Thanks.
As all our handheld scopes are 8-bit scopes, they are not suited for such puposes.
You will not find bench DSO for less than $20,000 that is suitable for doing THD analysis for serious audio work. Picoscope has some 16-bit units ($10k), or look in to high-end sound cards and good PC software.
Other options include older analog equipment–I use an old HP 3581a Wave Analyser and custom “virtual” X-Y recorder software–or find one of the very fine Tektronix modular distortion analysers. I have a Tek DA4084 that is good down to +/-0.005% overall accuracy. The Tek AA5001 is an excellent instrument, a bit more pricey that the DA4084 but well worth it.
For less automated THD measurement look for the HP 334a and 333a distortion analysers, they are semi-automated instruments, but quite capable to 0.01% THD.
Let me know if you care to know more about any of these options.
I have also been looking at the USB oscope PCSU1000 (which does perform frequency analysis) to run off of my laptop. However, when I looked through its manual, these calculations require the computer have an arithmetic coprocessor. Is this referring to a graphics card or is it something different altogether?
Currently, I am an electrical engineering and student I commute an hour each way every day, but I want something to work on projects and senior design stuff at home (I’ll save the amount I’d spend in gas). Any info would be great. Thanks again.
Our PC scopes are also 8-bit instruments…
Any contemporary 32-bit processor used in a Windows based PC has a built-in math co-processor.
It is important to understand that nearly all oscilloscopes, PC based or benchtop, in the sub $1000 range (and many costing more than that) use 8-bit ADC’s. This limits their dynamic range to 48dB–I.e. even with a FFT analysis the lowest THD you would be able to view spectrally would be 0.4%.
But please don’t get me wrong here. I have a PCSU1000, and the PCGU1000 function generator, as a pair they offer one of the best bode plotting tools I have ever used and I would highly recommend the set for any electronic engineering student. Generating response curves for audio gear is as quick and easy as any tool I’ve used, here’s an analysis of a small 10Wpc amplifier I built:
The amplifier has a “loudness” contour control, these are the response curves (frequency and phase) at three settings of the contour; 100% (green, top), 75% (blue), and 35% (red).
This graph also highlights another element of working with Velleman and their instruments–unparalleled customer support. I had indicated almost an aside in a somewhat related thread, that it would be great to have an “audio” range sweep (the 10Hz to 30kHz used above) in the bode analysis tool–less than 24 hours later is was available in a new release of the PCLab2000 software.
I have never before worked with a vendor that did, or was even capable of, responding to user input that quickly!
However with regard to THD analysis it remains, somewhat counter-intuitively, that the PC sound card based “instruments” are the best low-cost tools.
Thanks for the info. Even though I have been research on what to buy, you’re input helped out alot.
Out of curiosity, do the images display in real time or are they freeze frame only (a.k.a. Hit a refresh button to update the image once the signal has changed)?
Thanks again.
The images display in real time.
A demo version of the software, which does not require the hardware to operate, can be found here:
http://www.velleman.eu/downloads/files/downloads/pclab2000lt_v1_07.zip