# How do the multimeter measure the resistance

#### engr_david_ee

Joined Mar 10, 2023
25
How a multimeter measure the resistance. When we attach a multimeter for example Fluke 175, then would there be any current flowing through the resistor whose resistance is to be measured ? Is it connected in parallel to the resistor whose resistance is to be measured ? and how much is that current ?

#### StefanZe

Joined Nov 6, 2019
178
Hi, yes there will be a current flowing through the resistor.
The multimeter injects a small current and measures the voltage.

#### Ya’akov

Joined Jan 27, 2019
8,154
Welcome to AAC.

In fact, using a constant current source to measure resistance is the method used by DMMs. The precise current will vary with the range set, in the case of the Fluke 175 in particular, that will range from 1µA on the MΩ range to about 1mA on the lowest range.

#### Ya’akov

Joined Jan 27, 2019
8,154
Welcome to AAC.

In fact, using a constant current source to measure resistance is the method used by DMMs. The precise current will vary with the range set, in the case of the Fluke 175 in particular, that will range from 1µA on the MΩ range to about 1mA on the lowest range.
I should add: since any time there is a voltage applied to a conductor current is a byproduct, any method of resistance measurement will necessarily involve current flow.

#### engr_david_ee

Joined Mar 10, 2023
25
If the constant current provided by the multimeter flows through the resistor, then I guess the multimeter will measure the voltage and then found the resistance by formula, R = V / I. Here is the current I is the supplied current by the multimeter and V is the voltage measured by the multimeter, right ?

#### Ya’akov

Joined Jan 27, 2019
8,154
If the constant current provided by the multimeter flows through the resistor, then I guess the multimeter will measure the voltage and then found the resistance by formula, R = V / I. Here is the current I is the supplied current by the multimeter and V is the voltage measured by the multimeter, right ?
Yes, it’s simply an application of Ohm’s Law, as you have surmised.

#### engr_david_ee

Joined Mar 10, 2023
25
Thank you very much for reply. And how it measure the current ? Usually we connect multimeter in series in the circuit in which we need to measure the current. Would there be a resistance in parallel in the multimeter for current measurement ?

#### Ya’akov

Joined Jan 27, 2019
8,154
Thank you very much for reply. And how it measure the current ? Usually we connect multimeter in series in the circuit in which we need to measure the current. Would there be a resistance in parallel in the multimeter for current measurement ?
The meter will have a burden resistance which it uses to make current measurements. Since it is a known value, you can account for it. However it will mean that during your measurement of the current the displayed value of the meter under test will be wrong, though this really doesn’t matter and if you needed to know the resistance you could simply subtract the burden from the total.

If you simply take two DMMs and connect them together with one in the resistance range and the other in mA current range you can measure both the current used for resistance measurement and the burden of the current range.

• BobTPH