# 4-wire measurement differs between same model multimeter

#### finalmike

Joined Aug 16, 2018
4
I have a part that gives a 90% different resistance when measured on 2 different multimeters of the same model. I read 4 wire supplies current, monitors resulting voltage and calculates resistance according to Ohm's law, but I can't find anything in the manual about setting the currents for 4W. What am I missing?

#### tindel

Joined Sep 16, 2012
934
Make sure they are both set on the same range and hooked up the same. I'd be surprised if any multimeter can drive 4W. It's also possible that one meter is broken. What model are you using?

Joined Jan 15, 2015
7,256
I read 4 wire supplies current, monitors resulting voltage and calculates resistance according to Ohm's law, but I can't find anything in the manual about setting the currents for 4W. What am I missing?
Nothing, the meter sets the current. Just as an example using an Agilent (now Keysight) 34401A DMM if we look at the specifications. Under resistance we see the meter ranges and the test currents, they look like this:

100.0000 Ω 1.000000 kΩ 10.00000 kΩ 100.0000 kΩ 1.000000 MΩ 10.00000 MΩ 100.0000 MΩ 1 mA 1 mA 100 µA 10 µA 5 µA 500 nA 500 nA || 10 MΩ

While hard to read the 100 Ohm range is 1 mA, the 1,000 Ohm range is also 1 mA and so forth. So when I choose a 4 wire measurement the meter applies the current, I don't select it. A two wire measurement is done the same way but the meter measures the drop internally rather than using 4 wires.

What meter do you have?

Ron

#### finalmike

Joined Aug 16, 2018
4
Nothing, the meter sets the current. Just as an example using an Agilent (now Keysight) 34401A DMM if we look at the specifications. Under resistance we see the meter ranges and the test currents, they look like this:

100.0000 Ω 1.000000 kΩ 10.00000 kΩ 100.0000 kΩ 1.000000 MΩ 10.00000 MΩ 100.0000 MΩ 1 mA 1 mA 100 µA 10 µA 5 µA 500 nA 500 nA || 10 MΩ

While hard to read the 100 Ohm range is 1 mA, the 1,000 Ohm range is also 1 mA and so forth. So when I choose a 4 wire measurement the meter applies the current, I don't select it. A two wire measurement is done the same way but the meter measures the drop internally rather than using 4 wires.

What meter do you have?

Ron
I have a Keithley 2000

Joined Jan 15, 2015
7,256
OK, this is your meter. Take a look in the back of the manual in Appendix A you will see what I mentioned earlier. Under DC Characteristics you will see Resistance Ranges, Resolution and the Test Current. If you have a basic hand held DMM and you want to see something just set your DMM to measure current and set it up accordingly. Set your bench meter for 4 wire measurement and measure the current out of the current terminals, SENSE Ω4 WIRE HI and LO. You should see the current as you step the meter manually through the resistance ranges.

Also, when doing 4 wire resistance measurements it is best to use good kelvin clips and make sure your clips are connected correctly to the meter.

Ron

#### ebp

Joined Feb 8, 2018
2,332
The Keithley 2000 has a front panel button for 2 lead resistance (Ω2) and another for 4 lead resistance (Ω4). Plug in a set of Kelvin test leads and push the appropriate button.

#### crutschow

Joined Mar 14, 2008
33,318
Exactly how are you connecting the four wires?

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
What's typical of the numbers your getting for what order of magnitude resistances?

#### finalmike

Joined Aug 16, 2018
4
Exactly how are you connecting the four wires?
One sense/one input wire for either side of the part, with the sense/V pins inbetween the input/current pins where R is being measured across.
OK, this is your meter. Take a look in the back of the manual in Appendix A you will see what I mentioned earlier. Under DC Characteristics you will see Resistance Ranges, Resolution and the Test Current. If you have a basic hand held DMM and you want to see something just set your DMM to measure current and set it up accordingly. Set your bench meter for 4 wire measurement and measure the current out of the current terminals, SENSE Ω4 WIRE HI and LO. You should see the current as you step the meter manually through the resistance ranges.

Also, when doing 4 wire resistance measurements it is best to use good kelvin clips and make sure your clips are connected correctly to the meter.

Ron
Thanks! I will try this

#### finalmike

Joined Aug 16, 2018
4
What's typical of the numbers your getting for what order of magnitude resistances?
It's a test of R vs. part usage/wear so it can start below 1 Ohm. It usually gets measured until it reaches about 10 kOhms at which point we pull the sample.

#### crutschow

Joined Mar 14, 2008
33,318
One sense/one input wire for either side of the part, with the sense/V pins inbetween the input/current pins where R is being measured across.
The sense wires needs to be connected directly to the part terminals, or as close as possible.

Joined Jan 15, 2015
7,256
I may have given you some bum information when I said:
" Set your bench meter for 4 wire measurement and measure the current out of the current terminals, SENSE Ω4 WIRE HI and LO. You should see the current as you step the meter manually through the resistance ranges".
On my own Agilent meter example when set for 4 wire measuring my input + and - become the current source leads and the sense terminals are just that, the sensing terminals. Again, if you are looking at incorrect readings I would check your setup. Page 2-23 of your meter's manual shows the correct 2 Wire and 4 Wire setups for resistance measurements.

Ron

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
You want two probes at your sample. The "sense" wires determine the resistance being measured. The force wires need to be ahead of the sense wires. Connecting (two wires) x 2 at the point of contact won't cut it. You need 4 probes.