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LCR Meter Working Principle and Uses
An LCR meter is used to measure the impedance of a circuit or a device. This ScienceStruck article explains the uses, types, and some parameters related to LCR meters.
An LCR meter is used to measure the inductance, capacitance and resistance of a circuit. Hence, the name LCR meter.
When there is a change in the current flowing through a conductor, a corresponding change is induced in the voltage in it and in conductors surrounding it. This property is known as inductance. The ability of a body or a conductor to store electrical charge is known as capacitance. The opposition that a conductor offers to the passage of electric current through it is called resistance.
We pass an AC voltage through a DUT (Device Under Test). Now the LCR meter is used to measure the voltage and the current across the DUT. The magnitude of the impedance can be calculated from the ratio of these two quantities.
Uses of an LCR Meter
A digital LCR meter is used to measure the impedance flowing through a Device Under Test (DUT). It measures the voltage (V) across it, the current (I) flowing through it, and the phase angle between current and voltage. Subsequently, we can determine all the impedance parameters from these three factors.
Thus, an LCR meter measures the following parameters related to a circuit:
- dissipation factor
- quality factor
- phase angle between the current and voltage
What is Impedance?
Impedance is the opposition that a circuit offers to the flow of direct or alternating current through it. It is a vector quantity composed of 2 scalars: resistance and reactance. Reactance is the name given to the opposition by an electronic component to the flow of alternating current due to capacitance and inductance.
Types of LCR Meters
1.Handheld LCR meters:
As the name suggests, these LCR meters are small in size and can be held in the hand; they are lightweight and also portable. They have a multiple test frequency, and the data it captures can be transferred to a PC via a USB port. They are generally used in field operations. They offer an accuracy in the range of 0.2% to 0.1%. The test frequency of a handheld LCR meter varies from 100 Hz, 120 Hz, 1 kHz, 10 kHz, and 100 kHz.
2.Benchtop LCR meters:
They are bulky in size. They can be operated on programmable frequencies. They offer an accuracy of 0.01%. They can be controlled via a computer. Test frequencies are above 100kHz.
Some Terms You Should Know
LCR meters operate within the frequency range from 10Hz to 2Mhz. The DUT is used under its own frequency. LCR meters have to match the frequency of their measurement to the frequency that the DUT is tuned to.
A particular voltage is applied to the DUT. The AC output voltage of an LCR meter has to match it.
If the accuracy of your measurement is high, it takes more time to record that measurement for the LCR meter. Accuracy is hampered if the measurement is recorded in a short time. Most LCR meters provide 3 speeds for measurement: slow, medium, and fast. You have to make a choice between speed and accuracy.
Some Techniques Used with LCR meters
This method is employed for measuring frequencies below 100kHz. The DUT is placed in a Wheatstone Bridge. ZD is the DUT. ZB and ZC are known impedances. Impedance of ZA is varied until no current flows through ZD.
Thus, the four impedances obey the equation:
|ZD / ZA = ZC / ZB
ZD = ( ZC / ZB ) ZA
This way, we can find the impedance of the DUT.
LCR Measurement by Current-Voltage Technique
In this technique, the LCR measurement of a component is done by measuring the current and voltage. Then the impedance values are found out from these two quantities.
There are different arrangements for low impedance and high impedance circuits, which are as follows:
Both analog and digital LCR meters are available. While analog testers are cheaper, the digital variety scores on quality as it is more accurate.