Understanding digital electronic meter ranges

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spindown
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Understanding digital electronic meter ranges

Post by spindown » Fri Apr 15, 2011 7:49 pm

I am interested in determing inductance in the microhenry range. One of the digital electronic meters advertised on Ebay has one range of 2mh(lowest range) but the seller cannot tell me what the lowest value of inductance that could be measured and displayed in that range. How can I determine the information I need from the specifications for this meter? Thanks Paul

dyarker
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Re: Understanding digital electronic meter ranges

Post by dyarker » Fri Apr 15, 2011 8:56 pm

Look up specs on manufacturers web site (brand and model number not given).

Alternate is guess from number of digits in the display (not given). From low range of 2mH I can WAG that display is something and a half digits. Where max displayable of 1.9 is one and a half, 1.99 is two and a half, etc. Regardless of precision in percent, most digital meter specs say LSD (Least significant Digit (right most digit)) is plus or minus one. So if two and a half digit, I would WWAG lowest measureable as "0.02", or 20uH.

A more conservative guess would be 1/10 of MSD, or 100uH.

WAG = Wild A_s Guess, WWAG = Wild squared A_s Guess :grin:

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rshayes
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Re: Understanding digital electronic meter ranges

Post by rshayes » Sat Apr 16, 2011 3:48 am

Measurements in the microhenry range are probably better done with a "Q" Meter or an RF Bridge. A rough measurement can be done by using a parallel capacitor to form a resonant circuit and measuring the frequency with a Grid Dip Meter.

Normal test leads can cause considerable errors in inductance measurement in this range of inductance.

The frequency that the digital meter uses to measure inductance is usually fixed for each decade range and may not be optimum for measuring the inductance of a small coil.

Often, small coils are measured at two frequencies about an octave apart. If both frequencies are below the self resonant frequency, this will allow calculating both the inductance and the parallel stray capacitance, which may be significant at the operating frequency.

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Bob Scott
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Re: Understanding digital electronic meter ranges

Post by Bob Scott » Sat Apr 16, 2011 10:29 am

spindown wrote:I am interested in determing inductance in the microhenry range. One of the digital electronic meters advertised on Ebay has one range of 2mh(lowest range) but the seller cannot tell me what the lowest value of inductance that could be measured and displayed in that range. How can I determine the information I need from the specifications for this meter? Thanks Paul
You didn't say what make or model so I can't say for sure, but......

In the 2mH range, 2mH will be the max of the display and that should look like "1.999". That should measure right down to 1uH while the meter is in the 2mH range.

I have a good resistance meter that has only a "K Ohm" range for resistance. It measures down to 1 ohm (+/- a couple of ohms of error.) because .001K is 1 ohm.
-=VA7KOR=- My solar system includes Pluto.

spindown
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Re: Understanding digital electronic meter ranges

Post by spindown » Sat Apr 16, 2011 7:08 pm

The meter I was referring to is: Circuit Specialist- LC METER,DIGITAL CAPACITANCE AND INDUCTANCE TESTER( CS16243). The specs: for the 2mH range---Resolution:1uH, Accuracy:+-2% of full scale+-1 digit,--Test Frequency: 900Hz, Current through inductance under test :150uA. Basic Accuracy L:+- 1.5%(<0.5uF)+-2.0%(>0.5uF). C:+-2.0%(<0.5uH) +-5.0%(>0.5uH). Thanks for the replies. Paul

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Re: Understanding digital electronic meter ranges

Post by Robert Reed » Sun Apr 17, 2011 2:36 pm

This LC meter probably would not work out for the radio enthusiast. According to the specs you list, it would not offer any meaningful reading below 10 uH and would be questionable below 100 uH. Also 900 hz test frequency is extremely low for small value coils and that in itself would lead to errors in that range. This item would be similar to measuring low value caps with the "cap" section on most DMMs. However, if it performs well on higher value components, it looks like a good buy for that purpose.
Also I found it humorous that the C & L were transposed in the specs and especially the accuracy above 0.5 uH since the digital readout could not even display in tenth uH units :smile:

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