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HV differential probe versus isolation transformer
Luxor92:
Hello, dear users. I've done a couple of designs: frequency control and TRIAC switcher. Both work, but, of course, I am curious to check performance by observing voltage transients on gate and terminals accordingly.. Until recently just wanted to purchase differential probe, but watched a video from Micsig demonstrating how HV diff probe distorts measured signal, when the signal is something more than just a sinewave and now have big doubts. Kindly asking for an advice from those of you who practice such measurements, what is actually more suitable, isolation transformer or HV diff probe? What are drawbacks and benifits of each choice. What do you prefere to use? My loads are: 80W fan for frequency control and 370W motor for switcher.
tggzzz:
Start by reading the references at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ , especiallyt those marked "high voltage".
Luxor92:
--- Quote from: tggzzz on June 21, 2023, 11:11:20 pm ---Start by reading the references at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ , especiallyt those marked "high voltage".
--- End quote ---
Useful articles, thanks alot! Apparently, it will take some of my time to look closely and absorb. Couldn't find any information about making "floating" measuremenst by isolating exactly the load itself (not an oscilloscope) yet. (P.S After reading app notes provided above I am not even sure how to name such measurements, since floating measurements are when non of points connected to ground, and here oscilloscope would be connected to ground). If someone have anything to add, I am here to read :)
schmitt trigger:
Can you post a link to the Micsig video?
I have used diff probes extensively, and as long as you know the limitations, they work fine. Specially for 50/60 Hz signals.
But to your question, I always use an isolation transformer when working with power line circuits. When you are developing a circuit, sometimes I connect other equipment in addition to the scope or DMM. Thus better safe than sorry.
Luxor92:
--- Quote from: schmitt trigger on June 22, 2023, 05:48:33 pm ---Can you post a link to the Micsig video?
--- End quote ---
Sure, here you are.
--- Quote from: schmitt trigger on June 22, 2023, 05:48:33 pm ---...they work fine. Specially for 50/60 Hz signals.
--- End quote ---
Yes for 50/60Hz signals, but as I mentioned in the first message, one of my tasks is to observe transients on gate of IGBT when switching: to check ringing and Miller's plato duration for example. On the linked video we can clearly see how even Tektronix differential probe has pretty poor performance when measuring step function: time [1:42] on the video. UPDATE: just noticed that they use 300mV/div on the video, so oscillations aren't so significant. But once again, it is Tektronix, I have budget for Micsig only, which I have heard do not have such bandwith as they declare:)
--- Quote from: schmitt trigger on June 22, 2023, 05:48:33 pm --- I always use an isolation transformer when working with power line circuits
--- End quote ---
You mean isolation transformer between load and mains even when using HV differential probes, right?
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