I am apparently more out of touch than I realized, and need someone in the know to please answer a dumb question for me. If an LCR meter with the lowest range of L is 20mH has a 3-1/2 digit display, does this mean it will display down to 1 microhenry? I'm thinking that it would display .001 in the range for mH's, which should be 1 microhenry. Does this sound right to anyone out there who uses such a device? Your help is appreciated.
Dave snipped-for-privacy@hotmail.com
3-1/2 digit max on a 20mH scale would be 19.99mH, so if one looks *only* at digits, then the least significant digit is 10uH, *BUT* the best accuracy one can expect is +/- one digit, making a reading of 0.01mH virtually meaningless.
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Gotcha. Many thanks.
Dave
I wouldn't count on it without checking with the manufacturer. The '1/2' digit is for the 0 or 1 needed in the most-significant digit, but you'll need one more digit to the left of the decimal point for the
0?.00 or 1?.00 place. That leaves you with only two full digits to the right of the decimal point.For measurement in that range, I'm aware of only one affordable LCR meter (really, LC meter) that's useful -- the L/C Meter IIB sold by
-- jm
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Wow. Too cool. I need one of those...
One NANOhenry. Is this really meaningful? how does it get around stray inductance etc?
Thanks for the ref. I'm really going to check this out.
Much thanks,
Dave snipped-for-privacy@hotmail.com
There's a zero button; to measure L, you short the test leads, zero it, then try to connect the unknown inductor without moving the leads around too much. It actually works pretty well in practice, although the 1-nH LSD isn't exactly repeatable with normal test leads.
Same for C, only you zero the meter with the leads open.
Some people have built their own test jigs to eliminate the instability caused by the leads, but I haven't had the need to do that, myself. The meter itself is stable enough to take advantage of its own resolution, which is really saying something.
Obviously the accuracy is much less than the resolution, but for sorting or tweaking parts, that's fine.
Note that it doesn't work on caps bigger than 1 uF, or inductors that get extremely lossy at frequencies in the hundreds of kHz. It's more of an RF-grade complement to the high-range LCR functions on DMMs than a replacement.
-- jm
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