How to define inductance of the coil

How to define inductance of the coil

The inductance of the coil can be measured directly or an indirect way. In the first case the direct-reading or bridge device will be required, and in the second it is necessary to use the generator, the voltmeter and the milliamperemeter, and then to carry out a number of calculations.

It is required to you

  • - direct-reading or bridge measuring instrument of inductance;
  • - generator of sinusoidal tension;
  • - voltmeter and milliamperemeter of alternating current;
  • - frequency meter;
  • - scientific calculator.


1. To measure inductance by the direct-reading device, connect to it the coil, and then, consistently choosing measurement limits as the switch, choose such of them that the result was approximately in the middle of range. Read result. If the measuring instrument has an analog scale, when reading result take the division price and also the coefficient specified near the relevant provision of the switch into consideration.

2. On the bridge device after each switching of ranges transfer the handle of the regulator of balancing of the bridge to any of extreme provisions, and then rotate it against the stop in an opposite direction. Find such range in which this handle it is possible to balance the bridge. Having achieved disappearance of a sound in the loudspeaker or earphones or reduction of indications of the arrow indicator to zero, read indications on a regulator scale (but not the arrow device). At the same time, as well as in the previous case, consider the price of division and coefficient by which it is necessary to multiply on this range of the indication.

3. For measurement of inductance collect by an indirect way a measuring chain. Connect the voltmeter of alternating current switched to a limit at which to the upper bound of range there corresponds tension in several volt parallel to the output of the generator. There connect also a frequency meter. Also parallel to them attach the consecutive chain consisting of the test coil of inductance and also a mililampermetr of alternating current. Both devices have to show acting, but not amplitude values of the measured sizes and also to be calculated on a sinusoidal form of fluctuations.

4. On the generator include the mode of development of tension of a sinusoidal form. Achieve that the voltmeter showed about two volts. Increase frequency until indications of the milliamperemeter do not begin to decrease. Achieve their reduction approximately to a half of initial value. Choose a limit on a frequency meter, corresponding to the measured frequency. Read indications of all three devices, and then switch-off the generator and sort a measuring chain.

5. Transfer indications of devices to SI units. Divide tension into current. Inductive resistance of the coil at that frequency at which measurement was carried out will turn out. It will be expressed in ohms.

6. Calculate inductance by a formula: L=X / (2πF), where L - frequency, (henry), X - inductive resistance, Ohm, F - the frequency, Hz. If necessary transfer result of calculation to derivative units (for example, a millihenry, microhenry).

Author: «MirrorInfo» Dream Team