17-07-2013, 04:40 PM
LCR meter
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Introduction
It is evident from the name of LCR meter that it is basically inductance ‘L’, capacitance ‘C’ and resistance ‘R’ measuring device. LCR meters are generally used for easy and accurate evaluation of components like capacitors, inductors, transformers and electromechanical devices. The ability of LCR meters to apply specific measurement conditions (test frequency and signal level) is important for R&D and production test environments.
The 4287A RF LCR meter (along with a measurement schematic) installed in MRL is shown in Figure 1 This instrument employs the direct-current-voltage measurement technique, rather than the auto balancing bridge method; therefore, it yields accurate measurements over a much wider impedance (from 0.2 mΩ to 3 kΩ) and frequency (1 MHz to 3 GHz, with 100 kHz steps) range. It has superior measurement repeatability at low test signal level with basic accuracy of 1% at a high measurement speed of 9 ms. More precisely, the 4287A uses the RF I-V measurement method for measuring impedance by measuring the current flowing through a device under test (DUT) and the voltage applied across the DUT. For small inductance (of the order of a few nH), this is a big advantage of this meter. Thus the Agilent 4287A RF LCR meter is a high performance instrument for testing of devices such as SMD inductors and EMI filters which require impedance testing at high frequencies.
Working Principle of LCR Meter
LCR meters for electrical properties measurement at low frequencies are based on Auto balancing bridge method and the one for measurements at high frequencies employ the RF I-V method. In automatic balancing bridge method, the device under test (DUT) is placed in a bridge as shown in Figure 3. The DUT impedance is represented by Zx. The impedance Z2 and Z3 are known, and Z1 is changed until no current flows through D i.e. the terminals of D are made equi-potential.