allpwr
New member
- Location
- Falmouth, Maine
Looking for recommendations for testing Generator Alternators. Looking for an affordable Multi meter for measure less than 1 ohm for example .0460 ohms.
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DVM
- Thread starter allpwr
- Start date
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- Not open for further replies.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
160926-1418 EDT
You need a 4 terminal ohmmeter. So make your own.
If you want a resolution of 0.001 ohm, then provide 1 A or thereabouts or more to the "to be measured resistance", and measure the voltage drop across said resistance with a meter with at least 1 millivolt resolution. From the measured current and voltage calculate the resistance.
Use a DC current source or low enough frequency AC source to minimize inductive effects.
The voltage measurement must be made between two points directly on the "to be measured resistance" to eliminate the contact resistance at the current injection points.
See my photos P19 thru P21 at http://beta-a2.com/EE-photos.html .
.
You need a 4 terminal ohmmeter. So make your own.
If you want a resolution of 0.001 ohm, then provide 1 A or thereabouts or more to the "to be measured resistance", and measure the voltage drop across said resistance with a meter with at least 1 millivolt resolution. From the measured current and voltage calculate the resistance.
Use a DC current source or low enough frequency AC source to minimize inductive effects.
The voltage measurement must be made between two points directly on the "to be measured resistance" to eliminate the contact resistance at the current injection points.
See my photos P19 thru P21 at http://beta-a2.com/EE-photos.html .
.
meternerd
Senior Member
- Location
- Athol, ID
- Occupation
- retired water & electric utility electrician, meter/relay tech
Looking for recommendations for testing Generator Alternators. Looking for an affordable Multi meter for measure less than 1 ohm for example .0460 ohms.
Called a DLRO (Digital Low Range Ohmmeter) which does just what was said above. Two current leads and two voltage leads. Used for contact resistance on medium or high voltage switches, very large motor or transformer windings, etc. Can measure down to fractions of a mil-ohm. Not cheap, though. Building your own is cheaper if you aren't doing a lot of measurements and high accuracy is not an issue.
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- Not open for further replies.