Multimeter Vichy VC97 - measuring resistance - Page 1
Forum section: electronics / beginners

author: nForce
author_rank: Frequent Contributor
timestamp: September 08, 2019, 05:42:51 pm
content: Hello, I have this multimeter, and when I am trying to measure resistance below 1 ohm, I don't get any reading. I was looking at the manual, and I don't see that it can measure resistance below 1 ohm. So it actually can't? Does anyone have this multimeter?Thanks.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: September 08, 2019, 05:48:55 pm
content: Mine says .6 ohms when I short the test leads. What does your meter call out when doing this?

author: MosherIV
author_rank: Super Contributor
timestamp: September 08, 2019, 06:28:38 pm
content: Most hand held dmm are no good below 1.Even the best like Fluke87V will not give very acurate readings.

author: nForce
author_rank: Frequent Contributor
timestamp: September 08, 2019, 06:52:50 pm
content: Quote from: joseph nicholas on September 08, 2019, 05:48:55 pmTry to measure 0.27 Ohm resistor. I get value 0.2 or 0.3. What now?

author: MosherIV
author_rank: Super Contributor
timestamp: September 08, 2019, 07:14:28 pm
content: Can you set up 100mA cinstant current?If so, put the resistor across it and measure the resulting voltage on the resistor.

author: The Soulman
author_rank: Super Contributor
timestamp: September 08, 2019, 07:19:25 pm
content: Use a external current source (bench psu with adjustable current?) to drive a known current thru the resistor and measure the voltage dropacross the resistor with your multimeter.Use Ohms law to calculate the resistance.For instance: 100mA thru 0,27 Ohm should read 027,0 mV.Have fun learning.Edit: mosher beat me.

author: mikerj
author_rank: Super Contributor
timestamp: September 08, 2019, 08:54:10 pm
content: Quote from: nForce on September 08, 2019, 05:42:51 pmQuote from: nForce on September 08, 2019, 06:52:50 pmIf your meter is showing a value of 0.2 or 0.3 for a 0.27ohm resistor, then what's the problem?

author: tooki
author_rank: Super Contributor
timestamp: September 09, 2019, 05:49:47 am
content: Quote from: nForce on September 08, 2019, 05:42:51 pmJust what exactly are you hoping for? Accurate sub-ohm precision on 2-wire resistance measurement is a tall order for any multimeter, never mind a $20. And you're already getting it to within 0.1 ohm. To measure sub-ohm resistances you want a meter with 4-wire resistance.Quote from: nForce on September 08, 2019, 06:52:50 pmCelebrate the amazing accuracy a $20 meter can get you nowadays.

author: Jwillis
author_rank: Super Contributor
timestamp: September 09, 2019, 06:09:02 am
content: If you want accuracy below 1 Ohm you need a milli-Ohm meter.Really good ones can be expensive but some affordable ones do exits.I have a VICI VC480C+. The zero adjust is a bit finicky at the lowest setting it works good enough for my needs.

author: BravoV
author_rank: Super Contributor
timestamp: September 09, 2019, 08:51:25 am
content: Ordinary multi-meter that only has 2 wires (even the expensive ones) can not reliably measure sub-ohm resistance, as the probe's wires it self will change if you move around.As pointed, only 4 wires measurement as in most bench DMM or LCR meter that have 4 wires can do that reliably.Example of 4W, at the alligator pair clips, each side has different wire, so 2 clips = 2 pairs = 4 wires.

author: Jwillis
author_rank: Super Contributor
timestamp: September 09, 2019, 07:22:45 pm
content: Quote from: BravoV on September 09, 2019, 08:51:25 amJust to be sure BravoV .The kelvin clip 4 wire meter measures the voltageaddand the current across the resistor and the unit calculates the value. Would that be a correct in the simplest terms ?

author: tooki
author_rank: Super Contributor
timestamp: September 10, 2019, 03:58:49 am
content: Quote from: Jwillis on September 09, 2019, 07:22:45 pmNot exactly. One pair of wires pushes a constant current through the resistor under test, and the other pair measures the voltage drop. Because the voltage measurement uses the meter's high input impedance, essentially no current flows through the sense lines, eliminating the lead resistance.See 4:20 in:https://youtu.be/L9q5vwCESEQ?t=260

author: BravoV
author_rank: Super Contributor
timestamp: September 10, 2019, 04:00:27 am
content: Quote from: Jwillis on September 09, 2019, 07:22:45 pmBasically at the 4 wires, 2 wires "force" a known constant current into the DUT, then the other 2 wires are basically a volt meter measure the voltage drop across it.And then using the basic formula -> Resistance = Voltage / Current , to get the final resistance result.So at most 4W DMM, you will see the terminals sometimes labelled "force" and "sense" , the "force" terminals mean the ones that force a constant current thru the DUT, and then the "sense" terminals are basically a voltmeter measuring the voltage drop.As a hobbyist, in the past started in similar situation as op, with a limitation using single cheap DMM, without using the fancy 4 wires measurement tools, I made my self an adjustable constant current source power supply with 100ma and 1A capability just to use it for measuring low resistance, such as low ohm resistors, or sometimes measuring a cable like ordinary power cable which I suspected whether it was made from cheap fake copper inside.PS : Just posted after Tooki, his post explains it better.

author: bob91343
author_rank: Super Contributor
timestamp: September 10, 2019, 04:04:46 am
content: Just for fun I built a sub-Ohm setup. It uses one IC as a current source and any old DVM to measure the result. I get reliable readings well below 1 Ohm. If I remember correctly it resolves 0.01 Ohm.I don't use it because I have better units. But I still have it and switch it on occasionally. It's so small I have trouble finding it.

author: BravoV
author_rank: Super Contributor
timestamp: September 10, 2019, 04:15:07 am
content: Quote from: bob91343 on September 10, 2019, 04:04:46 amDamn, you just remind me of my old DIY constant current rig, and I lost it too and it has a sentimental value for me.Fun fact for others that starting to venture into low sub Ohm measurement, if you can measure it "reliably", then try cheap fake copper power wire or thin one, once hook up firmly and steady at both ends, then sort of move, drag or pull the wire gently, sometimes you will see the wire resistance varies quite significantly.

author: nForce
author_rank: Frequent Contributor
timestamp: September 28, 2019, 02:19:23 pm
content: Quote from: joseph nicholas on September 08, 2019, 05:48:55 pmHi, I would like to ask you something.When I was testing the multimeter for resistance and continuity, I notice that most of the time the multimeter does not read the value of the resistance. Also for continuity, it does not beep. Occasionally it does work, but not most of the time. When not working I get ".0L" reading. I don't understand why? I reset the meter a few times, but also the same problem.Has someone had any similar issues with the VC97 multimeter? Thanks.