On the video you nailed the interesting bits of the UT61 series: the lightning fast capacitance meter (the original UT61E is the king on this, even on capacitors with tens of thousands of µF) and its wide input frequency (which cooked the frequency range unfortunately). I did not improve the safety on mine since, as long as I keep it on the bench, I don't see it being cooked anytime soon. Also, the absence of an auto-power off is great.
Back to the frequency range, the UT61E+ manual indicates that frequencies above 40MHz have unspecified accuracy, thus the marketing department was very optimistic on this feature.
The manual also says the maximum input voltage at that range is derated to 20VRMS maximum, although it says it has a 1000V overvoltage protection. How many volts did you apply?
Right, they don't spec the voltage required for it to work above 40MHz, so I was creeping up on it. I assume that 20V is the maximum required for it to read the proper value. I searched for "derate" and it doesn't appear to be mentioned in the manual I have. I certainly talks about the 1kV overload protection.
I have no idea how much voltage I was putting into the meter. There was nothing monitoring it. I wonder what the impedance of the PTCs would be at 200MHz. Consider most meters have a surge rated resistor in them, their impedance may be more inductive where the PTCs may be more capacitive. I doubt the MOVs would have much of an effect as I had the low voltage clamps engaged. Anyway, what I am getting at is the voltage may not be all that high but the impedance may be low causing excessive power to be dissipated in the PTCs.
Easiest thing is not to put 200MHz on the box and I won't play at 200MHz. But with it on the box I want to see it and I'll smoke the meter trying to get it there.... That should have been expected based on my previous years of videos..
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Plotting the impedance of a 1.5K surge rated resistor and a PTC. These are not the parts used by the UT61E+ but they are parts I have shown and used in other meters. You can see how the PTC is a lot less stable than the resistor. I suspect this is one weakness in using two PTCs in series like the 61E+ in place of the more typical resistor+PTC combo.
Again, the UT181A also uses the two series PTCs, but the manual shows the upper range is 60MHz. In this case, we can verify this really is the upper limit.
https://youtu.be/PjNXbKlr3MI?t=1921