mustang guy Posted March 23, 2016 Share Posted March 23, 2016 I think I've worn out my trusty Extech 430. I have been thinking about getting a new MM any way. I was considering the Fluke 87, with it's 0.2% accuracy as a replacement, but I noticed it's maximum resolution is 0.1 Ohms. When you are measuring resistors that are a fraction of an Ohm, then the mighty Fluke 87 isn't good enough. What do some of you recommend? I need Diode, Capacitor, and would like RMS and ESR may be a pipe dream. I have a separate ESR meter, but what the hey. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 23, 2016 Share Posted March 23, 2016 To make accurate sub 1 ohm measurements you need a 4 wire meter. Usually only benchtop ($$$) meters have this capability. https://en.wikipedia.org/wiki/Four-terminal_sensing Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 23, 2016 Author Share Posted March 23, 2016 To make accurate sub 1 ohm measurements you need a 4 wire meter. Usually only benchtop ($$$) meters have this capability. https://en.wikipedia.org/wiki/Four-terminal_sensing OK, you sent me on the right track. The name those have are Milihom meters. There are lots of them available. This will amaze you believe me. I love mine and I have 3 multimeters and none will measure .47 ohm resistors except this. Expensive though. http://www.ebay.com/itm/Mega328-Transistor-Tester-Diode-Triode-Capacitance-ESR-Meter-MOS-PNP-NPN-L-C-R-/271838772700?hash=item3f4ada7ddc The specs on that say "Resistance :0.1 ohm resolution, maximum 50M ohm" Still pretty cool though! Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 23, 2016 Author Share Posted March 23, 2016 Ordered this unit for $100 delivered. I can leave it on the bench and since it doesn't need batteries, it will be waiting for me there whenever I need it. : http://www.ebay.com/itm/172139217849 It is not lab grade, but it's a darn site better than 0.1 resolution! Quote Link to comment Share on other sites More sharing options...
babadono Posted March 23, 2016 Share Posted March 23, 2016 OK, you sent me on the right track. The name those have are Milihom meters. There are lots of them available. All milliohm meters are by necessity 4 wire but not all 4 wire meters are milliohm meters Quote Link to comment Share on other sites More sharing options...
WMcD Posted March 24, 2016 Share Posted March 24, 2016 (edited) Let me suggest you build a little test rig with a say a 12 ohm resistor (or what you have laying around) and a fair sized 12 volt, or so, battery. Put the unknown small value resistor in series with the 12 ohm resistor and put 12 volts across the pair. Then measure the voltage drop across each resistor. The voltage drop should be proportional to the resistance of each resistor and you can calculate accordingly. Your present DVM should be able to give you the true resistance of the 10 ohm to within a percent or so if you have doubts. Your present DVM should be able to read down to 1/100 volt or so. The current drain on the 12 volt battery will be 12/(12 plus your small R) or 1 amp and so and not croak the battery with that 1 amp drain. Note that because the resistors are in series, the current though each is the same, and that is why voltage drop must be proportional to resistance values. You get the idea and can play with the components. WMcD Addition by edit. You've created a bit of a crude current source by this of 1 amp. So even without doing the proportionality we see that a 1 ohm resistor will have a 1 volt drop. A (an?) 0.5 ohm will have a 0.5 volt drop. A 0.1 ohm will have a 0.1 volt drop. Your meter can probably measure 0.01 volt (0.01 ohm), and so you should have pretty good accuracy. Edited March 24, 2016 by WMcD Quote Link to comment Share on other sites More sharing options...
ZEUS121996 Posted March 24, 2016 Share Posted March 24, 2016 This will amaze you believe me. I love mine and I have 3 multimeters and none will measure .47 ohm resistors except this. Expensive though. http://www.ebay.com/itm/Mega328-Transistor-Tester-Diode-Triode-Capacitance-ESR-Meter-MOS-PNP-NPN-L-C-R-/271838772700?hash=item3f4ada7ddc It is a little bit rich for my blood. Maybe I can pick one up used on the bay :huh: Mark Quote Link to comment Share on other sites More sharing options...
djk Posted March 25, 2016 Share Posted March 25, 2016 http://www.ebay.com/itm/NEW-DER-EE-DE-5000-High-Accuracy-Handheld-LCR-Meter-and-probes-set-from-Japan-/131744235082?hash=item1eac917e4a:g:Ba8AAOSwwbdWIgQq Can resolve 0.001Ω Quote Link to comment Share on other sites More sharing options...
efzauner Posted March 25, 2016 Share Posted March 25, 2016 (edited) Lets be careful here. Resolution and accuracy and precision are 3 different things. Sorry to chime in here, I have 30 years experience in Test and Measurement. Imagine a dart board. Resolution would mean that there are many sectors. The smaller the sector or square the better the resolution. So for an ohm meter this means what is the smallest digit. Precision would mean that when you throw the darts they always land close together. So repeated measurements are always close together. But not necessarily with bullseye accuracy Accuracy means you can throw darts and hit the bullsey. So you can be precise, bunching up the darts but be consistently away from the bullseye. This is like a gun sight that is not adjusted properly, Or a measurement instrument that has a known offset or is not calibrated. You can usually account for this. Low precision often means lots of noise. You can be accurate, with the darts in a circle around the bullseye, but not bunched up. So you can be accurate but not precise or repeatable from measurement to measurement. Normally if you average accurate but imprecise dart shots you should be on the bullseye. So what specification is important for this particular low resistance measurement. Resolution is only part of it. You MUST look at accuracy. the VC480 Precision Milliohm Meter on ebay states: 2 Ω range, resolution is 1 mΩ accuracy is ±(0.5%rdg±3) So for the 2 ohm range, measuring a 1 ohm resistor, with 1 mohm resolution, accuracy is 0,5% of the measurement plus 3 x the resolution. Or 5 plus 3 milliOhms or 8 milliOhms Not bad actually It is accurate and Precise! The Fluke 87V has the following specs Resistance Maximum resistance 50 MΩ Accuracy ±(0.2% + 1) Maximum resolution 0.1 Ω So for a 1 ohm resistor, the accuracy is 102 milliohms not good! Yet it is accurate, but not precise enough. Internal circuits cannot generate clean low currents and measure low voltages well because of noise. You can do others yourself. The reason you need 4 connections (this is called force-sense, or Kelvin connection) is to avoid including in the measurement the voltage drop across the leads that carry the current. So you force a known accurate current through one pair of wires, and measure the voltage across the resistor with a separate sense connection. Edited March 25, 2016 by efzauner 2 Quote Link to comment Share on other sites More sharing options...
Fjd Posted March 25, 2016 Share Posted March 25, 2016 (edited) Here are the specifications for the DE-5000 in case anyone is interested in the comparison of accuracy and precision. . Edited March 25, 2016 by Fjd Quote Link to comment Share on other sites More sharing options...
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