at 9:30 your discussion of the RMS value being a bit off spec.. the waveform on the scope, to my eye, doesn't look like the cleanest sine wave. The waveform peaks look like they flatten off somewhat. The RMS value of a distorted sine wave won't be the same as a pure sine wave, and could read a bit higher if the peaks flatten, even if the pk-pk voltage is the same on both waveforms. Just a thought.
Definitely right. Many scopes/meters 'estimate' the RMS by taking the PP voltage (which is relatively easy to detect from a waveform with a peak detector) and multiply this by 2sqrt(2). This is only of course correct for a pure tone sine wave. 'True RMS' meters calculate the power of the signal, which is what the RMS value actually means. It is very interesting how some high precision RMS meters do this ! They let the input waveform literally heat up a resistor, and measure the thermal dissipation with some clever tricks. RMS measurements are a fascinating subject in itself.
No, most differential probes are certainly not isolated. They are simply high impedance to ground for both inputs. I don't have that new model probe, but I have the Micsig DP10007. The specification for it is 4 M ohm from ground to each input or 8 M ohm differential impedance. You can measure this from input to the shell of the BNC. The Micsig specs for new MDP probes are either 8 M or 10 M to ground, and double that for the differential impedance depending on the model.
@@TMaierhofer The Micsig probe under review was sold as a "high voltage" probe so clarity of what isolation means is important. In my experience the term "isolation" in the application of electronic equipment in high voltage and extra high voltage environments means galvanic isolation, i.e. no dc current path. In such environments measuring equipment with "isolated" inputs typically have isolation provided by optical coupling, transformers, "flying capacitors" etc. In that context a 4M or so path to ground is certainly not isolated but as you suggest, in some situations may be high enough to be good enough. Equally in some applications where true isolation is required. 4M or so to ground will be a fail and of course megohms to ground are more significant at higher voltages.
A few years ago when I transitioned to a new company, I found they were using this exact differential probe. A very brief amount of work with it showed me that it is entirely unsuitable for any but the most modest needs. For serious small signal limited bandwidth differential work, I recommend the Tektronix ADA400A or similar. It has selectable bandwidths of 100Hz, 3KHz, 100KHz and 1MHz. At around $3K today, it is overpriced, but it works for debugging small signal instrumentation.
I read an article in an old magazine that stated RMS reading meters may not be perfectly accurate if the AC waveform is not a perfect sinewave. On the scope, I can see a bit of distortion.
Its actualy the other way round as a true RMS meter will be accurate for non sinusoidal waveforms whereas the cheaper Averaging meters make certain assumptions about the waveform and take samples and average those ignoring polarity. If you take the average of a pure sinewave it will of course be zero, I may have botched that delivery but the essence is there. Maybe someone out there can explain better than me !!
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at 9:30 your discussion of the RMS value being a bit off spec.. the waveform on the scope, to my eye, doesn't look like the cleanest sine wave. The waveform peaks look like they flatten off somewhat. The RMS value of a distorted sine wave won't be the same as a pure sine wave, and could read a bit higher if the peaks flatten, even if the pk-pk voltage is the same on both waveforms. Just a thought.
Definitely right. Many scopes/meters 'estimate' the RMS by taking the PP voltage (which is relatively easy to detect from a waveform with a peak detector) and multiply this by 2sqrt(2). This is only of course correct for a pure tone sine wave.
'True RMS' meters calculate the power of the signal, which is what the RMS value actually means. It is very interesting how some high precision RMS meters do this ! They let the input waveform literally heat up a resistor, and measure the thermal dissipation with some clever tricks. RMS measurements are a fascinating subject in itself.
No, most differential probes are certainly not isolated. They are simply high impedance to ground for both inputs. I don't have that new model probe, but I have the Micsig DP10007. The specification for it is 4 M ohm from ground to each input or 8 M ohm differential impedance. You can measure this from input to the shell of the BNC. The Micsig specs for new MDP probes are either 8 M or 10 M to ground, and double that for the differential impedance depending on the model.
I think the term "isolation" means technically very high impedance. If you consider 4M high enough to call it isolated is another question.
@@TMaierhofer The Micsig probe under review was sold as a "high voltage" probe so clarity of what isolation means is important. In my experience the term "isolation" in the application of electronic equipment in high voltage and extra high voltage environments means galvanic isolation, i.e. no dc current path. In such environments measuring equipment with "isolated" inputs typically have isolation provided by optical coupling, transformers, "flying capacitors" etc. In that context a 4M or so path to ground is certainly not isolated but as you suggest, in some situations may be high enough to be good enough. Equally in some applications where true isolation is required. 4M or so to ground will be a fail and of course megohms to ground are more significant at higher voltages.
One of those is definitely on my list, I dithered long enough to now be looking at the new model, some benefit to dithering I guess
A few years ago when I transitioned to a new company, I found they were using this exact differential probe. A very brief amount of work with it showed me that it is entirely unsuitable for any but the most modest needs. For serious small signal limited bandwidth differential work, I recommend the Tektronix ADA400A or similar. It has selectable bandwidths of 100Hz, 3KHz, 100KHz and 1MHz. At around $3K today, it is overpriced, but it works for debugging small signal instrumentation.
@@petepeterson5337 I think it must have been a different probe, as this one was only released just before I did the video.
I read an article in an old magazine that stated RMS reading meters may not be perfectly accurate if the AC waveform is not a perfect sinewave. On the scope, I can see a bit of distortion.
I think it is more of a problem for AVERAGE reading meters, rather than RMS reading.
@@TheDefpom
Well, the article was written in 1954 so perhaps the equipment was not as robust as today? I don't know. 😅
Its actualy the other way round as a true RMS meter will be accurate for non sinusoidal waveforms whereas the cheaper Averaging meters make certain assumptions about the waveform and take samples and average those ignoring polarity. If you take the average of a pure sinewave it will of course be zero, I may have botched that delivery but the essence is there. Maybe someone out there can explain better than me !!
Yes, the cardboard box thing is naff. All they need is a new insert for case they use for the older type differential probes and the current probes.
I just received the 1502 probe (4/29/2024) and it came with a plastic case.
ooof the price tho
Hmmm - yea