Tutorial: Mechanik - elektrotechnik Topic: Basics of electrical engineering the 2nd. year Measuring inductance Prepared by: Ing. Jiří Smílek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/ je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

 Definition:  Inductance is the ratio of the coupled induction flux to the current which passes through the coil.  Coupled magnetic flux to the current that flows through the coil  The basic unit - 1 H (henry) ◦ L- inductance coil ◦ M - magnetic flux coupled coils ◦ I – current passing through the coil ◦ N – number of turns in the coils  The mutual inductance M of two close coils is the ratio of the induced emf in the first coil caused by a current in the second coil or vice versa - M 1 = M 2

 The used method: Deviation method – inductance is measured by an A-metre and V- metre to determine the value of the measured resistance deviation or determine the numeric value. a)Connection for the measurement of smaller inductance/ coils b)Connection for the measurement of larger inductance/coils

 Calculation: Self inductance can be determined from the definition of impedance: Apparent power coils: Coil impedance: Coil resistance

 The measurement procedure: To measure inductance using the indirect method we must know the voltage and the current – calculate R X and Z LX ⇒calculate L X To measure the resistance a DC current must flow in the circuit To measure the inductance an AC current must flow in the circuit ⇒ Method suitable for measuring air coils in operation

 The used method: Deviation method – inductance is measured by an A-metre, V- metre and a W-metre - Inductance coils with an iron core are not constant because they depend on the magnetic flux, that is the current passing through the coil Resistance R reg adjusted current for example of 0.25 A and read current I, voltage U and power P (losses in the turns and the iron). From the measured values we calculate the coils impedance:  The measurement procedure:

 Calculations: From the measured values we calculate: Coil impedance: Active resistance: Inductance: Inductance can also be calculated from the relationship: Of which

 The used method: Bridge method– inductance with a Maxwell-Wien bridge The condition of the bridge balance: After treatment and separation of real and imaginary members:

 Describe how induction is defined ◦  Describe how mutual inductance is defined ◦  Write how you know the types of coils ◦  Write what methods can measure inductance ◦ direct –  ◦ indirect – 

 Explain why an inductance coil with an iron core is not constant ◦  Write a procedure to measure inductance with an iron core ◦  Write the procedure to calculate the inductance from the measured values ◦

 Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, ISBN  Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 –  Dostupné na: konkurenceschopnosthttp:// konkurenceschopnost  Učebnice Elektrická měření – Ing. Pavel Vylegala, SŠE Ostrava, 2006  Učebnice Elektrické měření – SNTL, 1981  Elektrotechnika - Laboratorní cvičení pro bakalářské studium - Doc. Ing. Miloš Hammer, CSc.