Generally, an LCR bridge should be used to measure the inductance.
Today, I want to share a method to measure inductance with oscilloscope.
First, we need to use these several components to make a circuit.
This is the circuit.
LM7805 provide a voltage of 5V.
The capacitor of 470uF maintain the voltage during discharging.
Non-inductive cement resistor of 0.5ohm as the sample resistor in series the inductor.
Diode 1N4007 as a flyback diode for the inductor.
Protect components in the circuit from inductive voltage to avoid being broken down.
Let's assemble the circuit. Install LM7805 first.
Install capacitor of 470uF.
Install tact switch for discharge the capacitor.
Install flyback diode 1N4007.
Install Non-inductive cement resistor of 0.5ohm.
Install socket strip for connection of inductor to be measured.
Finally, a jump wire as GND.
Weld the circuit.
2-Pin Socket strip for power input.
Add two thick copper wire to both end of the Non-inductive cement resistor as the connection with oscilloscope.
Circuit complete.
Connect oscilloscope to the end of Non-inductive cement resistor.
Use two 18650 batteries in series as the power source.
Connect batteries to the circuit.
First, let's measure an inductor of 470uH.
Put the inductor to be measured into the socket strip.
Click the tact switch.
We get a wave on oscilloscope.
Use lower part of the wave, we could calculate the inductance.
The time internal is 10us
The voltage changing on the sampling resistor is 50mV.
As we know, inductance equal to the voltage across the inductor divided by the changing of the current flow through the inductor per unit time.
After close the switch, the voltage across the inductor is 5V.
From the wave on oscilloscope we can get the changing of voltage across the sampling resistor is 50mV.
Time interval is 10us.
The value of sample resistance is 0.5ohm.
Delta V divided by the value of sample resistance.
We get the changing of current flow through the inductor is 100mA.
Put the calculated data above into the formula of inductance.
Get the value of inductance is 500uH.
It is very closed to the value of 470uH.
The slope of upper part of the wave is larger than lower part obviously.
Let's calculate the inductance according to this period.
The period is 4.8us and the changing of voltage is 56mV.
Make a spreadsheet according to do the calculation just now.
We get the value of inductance reduced more than half.
When the current flow through the inductor excess a certain value,
The value of inductance will reduce quickly.
This current is the Saturation Current of inductor.
Saturation Current is an important parameter of power inductor.
From the wave, we can get this position.
The voltage at this position is 80mV.
Divided by the value of sampling resistor 0.5ohm, we get the current is 160mA.
So the Saturation Current of this 470uH inductor is about 160mA.
To verify this method, let's measure another inductor of 1mH.
Change the inductor to be measured with 1mH. Press the tact switch.
The time interval is 10us and changing of voltage is 23.3mV.
Put all data into the spreadsheet, we get the value of inductance is 1073uH.
It is very closed to the value of 1mH.
Let's check out the value of inductance after the current excess the Saturation Current.
The time interval is 4us and changing of voltage is 23.3mV.
Put data into the spreadsheet, we got the value of inductance is 429uH. Reduced more half too.
Finally, let's check out the Saturation Current.
The voltage at inflection point is about 55mV, so the Saturation Current is about 110mA.
For inductors in same type, the higher inductance have lower saturation current.
After test, this method to measure inductance and saturation current is practicable.
If you don't have LCR bridge, you could try this method.