Latest Trends in Circuits, Control and Signal Processing
A Rapid Inductance Estimation Technique By Frequency Manipulation
LUM KIN YUN, TAN TIAN SWEE Medical Implant Technology Group, Materials and Manufacturing Research Alliance, Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, Skudai 81310, Johor, Malaysia [email protected]; [email protected]
Abstract: Inductors or coils are one of the basic electronics elements. Measurement of the inductance values does play an important role in circuit designing and evaluation process. However, the inductance cannot be measured easily like resistor or capacitor. Thus, here would like to introduce an inductance estimation technique which can estimate the inductance value in a short time interval. No complex and expensive equipment are involved throughout the measurement. Instead, it just required the oscilloscope and function generator that is commonly available in most electronic laboratory. The governed theory and methods are being stated. The limitation of the method is being discussed alongside with the principles and computer simulation. From the experiment, the error in measurement is within 10%. This method does provide promising result given the series resistance of the inductor is small and being measured using proper frequency.
Key-Words: Inductor, Inductance measurement, phasor, series resistance, phase difference, impedance. • Current and voltage method which is based on the determination of impedance. 1 Introduction • Bridge and differential method which is based on the relativity of the voltages and There are many inductors being used in electronics currents between the measured and reference circuits. In order to evaluate the performance of impedances until a balancing state is electronic system, it is particular important in achieved. determining the inductance values as what happened • Resonance method which is based on to the resistance values. Especially for the system physical connection of an inductor with a which required the accurate operation of frequency capacitor to create a resonant system. like the tuning circuits and filters, the measurement of inductance value does play an important roles in For all that, these methods are not straight forward the designing process. and hard to be implemented except for the first one which is the current and voltage method. This is However, unlike the resistor or capacitor value which because some of them required complex calculation can easily be measured by using a typical multimeter, has to be involved before getting the result. the inductor value cannot be evaluated that way. Meanwhile, some of them required some circuit There are two methods generally used to determine configurations in order for the system to work[4]. the inductance value, which are using the theoretical These circuit configurations make the measurement formulae estimation as discussed in [1]and indirectly and contribute to the errors due to the experimental measurement. The theoretical tolerance of individual circuits elements[5]. As thus, estimation method only limited to certain commonly another simpler method based on the use of function inductors[2]. On the other hand,the inductance can be generator and oscilloscope is being utilized here as measured by using the LCR meter which is belong to an extension for the further expansion on the first the experimental measurement. However, the LCR method. Function generator and oscilloscope meter is not cheap to be purchased and normally not generally can be found in ordinary electronic equipped in the general working laboratory. The laboratory. It can be further utilized to perform this methods being used in measuring an inductance task without the present of any additional circuit falling into three categories[3]: components like resistors and capacitors.
ISBN: 978-1-61804-173-9 13 Latest Trends in Circuits, Control and Signal Processing
2 Theory Assuming the series resistance of the resistor is negligible, impedance of an inductor is defined as
50 Ohm (4) According to the voltage divider rule Unknown Function Inductor Oscilloscope Generator
Fig. 1 Schematic for the configurations For the passive elements R, L and C, we can represent the voltage and current in the phasor or frequency domain[6].
For a resistor, if the current through it is , the voltage across it is given by Ohm’s cos law as Taking , so (1) cos
For and inductor L, assuming the current through it 1 is . The voltage across the 2 inductor iscos Solving for L with 2