# How measure unknown inductor

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#### zawminoo measuring inductance with multimeter

Hi everybody,

How can I measure an unknown inductor?
I can't use oscillator and can use digital multimeter.
Thank...

Zaw

#### A.Anand Srinivasan how to measure an inductor

inductor values can be measured using LRC meter which looks like a function generator... the main problem of measuring it using digital multimeter is inductor have to be measured using their voltage wrt change in current which needs timing calculation and hence i dont think multimeters which measure inductance and capacitance are compactly(small) available....

#### hbaocr

##### Full Member level 4 1mh inductor

hi, more example,,you can make a serial circuit include resister and your winding.and connect it to AC voltage.Measure Voltage drop on WINDING. you can find the Z.
Z=1/ωL=>L=1/ωZ.

#### A.Anand Srinivasan measuring inductance with a multimeter

hbaocr said:
hi, more example,,you can make a serial circuit include resister and your winding.and connect it to AC voltage.Measure Voltage drop on WINDING. you can find the Z.
Z=1/ωL=>L=1/ωZ.

but that would need current measurement... also inductors require specific settling time and also given the fact that di/dt is not constant for a sine wave.... also the parasitics in the circuit cannot be monitored.... if the parasitics are high enough then it may lead to oscillations....

#### hbaocr

##### Full Member level 4 how digital multimeter can measure the inductor

but that would need current measurement...
hi, VR=voltage drop on R in that circuit.
U can see IR=IL=VR/R=I

#### A.Anand Srinivasan measuring an inductor

what i meant by current measurement is that for the inductor V=L(di/dt) and di/dt is not constant for the sine wave and also since you are using sine wave as input the voltage across the resistor would be varying and also you would need the instantaneous value of your input....

#### rowokii

##### Member level 4 how to measure inductance using multimeter

I've built this LC meter and it works fairly well. It might be a good project for you to try out. Keep the wires short as possible on the analog section. The web site has some leads on how to calculate L if you are interested.

As others have stated, if you want to measure without a L meter, you will need a function generator or another way to creating a sine wave. Parasitics from the DMM or wires might make for big errors depending on what size L you are trying to measure.

Anand, think of the problem in frequency domain where the impedance of the inductor Z = jWL. Hbaocr is suggesting making a voltage divider with a R and L and measuring the AC voltage across the L (or R) to find the impedance of the L, and from there calculate the L itself. You do not have to measure the instantaneous current.

#### A.Anand Srinivasan measuring inductor

I'm not talking about the instantneous current... I'm talking about the instantaneous voltage which you would be needing when you measure the voltage across the inductor... because it is gonna act as a voltage divider i think you would need the instantaneous voltage value....

#### rowokii

##### Member level 4 inductor making of 1mh

Nope, you can set the DMM to measure AC voltage and you should be fine. You will get RMS voltage (hope your DMM is true RMS meter) from which you can get the peak-to-peak.

#### A.Anand Srinivasan how to measure an unknown inductor

if you can resolve the equation for current and post it then i would be able to understand it better because one component has voltage across it proportional to the current and other has it proportional to the differential.... so i'm not able to resolve it properly and am not getting a sine wave(for finding rms) across the inductor....

#### rowokii

##### Member level 4 inductors measuring dmm

Anand,

For sinusoidal signals, you can use modified ohm's law where you use impedance instead of resistance. So, as long as you are looking as AC steady state, you can simply measure voltage levels.

If you really want to do this in time domain, you can. It's straight forward... but it's also a page and a half worth of derivation in my circuit analysis book. Using impedance is a short cut.

As an example:
1V P-P sine wave at 100KHz is connected to a series connected 1Kohm resistor and 1mH inductor. Voltage across the inductor is 1V * voltage divider equation between the 1K resistor and 1mH inductor.

Impedance of the inductor is j*2*pi*100e3*1e-3 = 628.3j.
So, total impedance is 1000 + 628.3j.

Voltage across the inductor is ZL / (R + ZL) * 1V = 628.3j / (1000+628.3j) * 1V.
Since we are only measuring the P-P voltage and take a magnitude of the above and you get 628.3/(1181) = .532V.

P-P voltage across is 1mH is .532V. Your DMM will measure RMS voltage, so your measurement is squrt(2) off (.376V).

Try it out on a spice simulator is you want to double check....

Also, if you want to do the time domain analysis, look it up in your electric circuit analysis book.

Cheers

#### nguyennam measuring unknown inductance

It is not easy to measure the inductance of a inductor which has magnetic core since its inductance varies depending frequency and current/voltage and not be fixed over wide ranges of electrical parameters like resistance of resistors and capacitance of capacitors.

nguyennam

#### smith123

##### Member level 5 how to test a inductor via multimeter

you can measure an unknown inductance by lrc meter

#### deepakg88

##### Newbie level 1 how to measure an unknown inductance

u can use maxwell s bridge arrangement . set ratio of resistances to be constant and then vary known inductance to get a balanced condition.if the ratio of resistances is unity then the unknown inductance will be equal to the known inductance.

u can refer electrical and electronic measurements by ak sahwney

#### thezooz

##### Newbie level 3 how to use a dmm to check inductors

i use R and c make resonand

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