Multimeter: How to measure low resistances?

[LucasDK]

Hi,

I would like to be able to measure very low resistances RELIABLY and with some degree of PRECISION.

Measurements of interest would be (for diagnosis):

a) Glow plugs (typical resistance 0,2 ohm)
b) Contact resistance on for instance ground cables (from battery to chassis, to engine, back to chassis etc etc). I would like to measure where there is a bad contact due to corrosion which will result in a voltage drop.

I have the possibility to buy a special multimeter designed for measuring low resistances more precisely. That multimeter applies 0,2 Amps when measuring resistances and should be considerably more than a standard multimeter.

Can anyone elaborate on whether 0,2 Amps is sufficient for measuring low resistances and thus voltage drops for automotive use?

 

[Lubener]

I use a digital volt meter instead to measure voltage drops while the circuit is energized and under an actual running condition. I don't use an ohm meter for that.

 

[joegreen]

First measure the resistance of the leads. Then subtract that from your measurement. That should help. Also if all the glow plugs generally read similar but one is way off that can also be an indicator even if the values don’t match the book

 

[Donald]

Hi,

I would like to be able to measure very low resistances RELIABLY and with some degree of PRECISION.

Measurements of interest would be (for diagnosis):

a) Glow plugs (typical resistance 0,2 ohm)
b) Contact resistance on for instance ground cables (from battery to chassis, to engine, back to chassis etc etc). I would like to measure where there is a bad contact due to corrosion which will result in a voltage drop.

I have the possibility to buy a special multimeter designed for measuring low resistances more precisely. That multimeter applies 0,2 Amps when measuring resistances and should be considerably more than a standard multimeter.

Can anyone elaborate on whether 0,2 Amps is sufficient for measuring low resistances and thus voltage drops for automotive use?

You need a 4 wire ohmmeter. The extra 2:wires allow the meter to take into account the resistance of the leads.

I bought one to measure the resistance of a generator could.

I ended up ordering two by mistake and could give you a deal on the extra new one I have. PM if you are interested.

 

[redbone3]

You need a 4 wire ohmmeter. The extra 2:wires allow the meter to take into account the resistance of the leads.

I bought one to measure the resistance of a generator could.

I ended up ordering two by mistake and could give you a deal on the extra new one I have. PM if you are interested.

After spending the best part of my life as a calibration technician, I can say you are exactly right. The correct terminology is "milliohm meter". However, this amount of accuracy for measuring a glow plug is big time overkill.

 

[Creekside]

In my experience a Fluke 117 will do everything you ask of it. I use one on everything from automotive to 480v AC.

 

[LucasDK]

You need a 4 wire ohmmeter. The extra 2:wires allow the meter to take into account the resistance of the leads.

I bought one to measure the resistance of a generator could.

I ended up ordering two by mistake and could give you a deal on the extra new one I have. PM if you are interested.

Im sorry but I live in Europe. Its not worth buying and sending it
Are you satisfied with your meter and what brand/model is it?

 

[sk_pete]

have the possibility to buy a special multimeter designed for measuring low resistances more precisely

Do you have spec sheets?
Very likely it will have 4 wire system

 

[LucasDK]

Do you have spec sheets?
Very likely it will have 4 wire system

https://www.elfadistrelec.dk/Web/Downloads/_t/ds/2705_eng_ger_tds.pdf

 

[sk_pete]

Good specs, good precision. 200mA is enough as we can see.
I can't think of reasons why higher current would have benefit.
Protective earth testers use 5...30A, but they are not meant as ohmmeters, they test the safety system.

 

[Jetronic]

I use a digital volt meter instead to measure voltage drops while the circuit is energized and under an actual running condition. I don't use an ohm meter for that.

Yes I do the same if it's possible.

measure voltage btween battery ground and glow plug body and you know the voltage drop.