Introduction to the working principle of LCR digital bridge
A digital bridge is an instrument that can measure inductance, capacitance, resistance, and impedance. This is a traditional saying, and the earliest impedance measurement used the true bridge method. With the development of modern analog and digital technology, this measurement method has long been eliminated, but the name LCR bridge has been used to this day. If an LCR bridge using a microprocessor is used, it is called an LCR digital bridge. These are commonly referred to by users as LCR testers, LCR bridges, LCR meters, LCR meters, and so on.
With the circuit signals constantly becoming "high-speed" and "high-frequency". We must know the actual model of LRC and cannot simply regard it as an ideal model.
By accurately measuring the voltage and current loaded onto the DUT, the impedance value of the DUT can be accurately measured. From the graph, it can be seen that the current through DUT is equal to the current through resistor Rr, and the current through Rr can be calculated by measuring Vr.
The measurement of impedance is reduced to the measurement of the phase difference between two sine signals.
Inside the LCR digital bridge, a phase sensitive detector (PSD) can be used to measure the in-phase and quadrature components of Vx and Vr corresponding to a certain reference phasor. Then, they are converted into digital quantities by an analog-to-digital converter (A/D), and complex operations are performed by a computer to obtain the resistance and reactance values that make up the measured impedance Zx.
The digital bridge only inherits the traditional name of the bridge. In fact, it has lost the traditional and classic form of AC bridge composition, and has returned to the circuit and principle of measuring impedance based on Ohm's law for ammeters and voltmeters at a higher level.
How to measure the phase difference between voltage and current
Method 1: Zero crossing comparison+time measurement technique
Measure the time difference between two zero crossings by starting a voltage level with a zero crossing point.
Method 2: Dual channel synchronous sampling technique
Perform operational analysis after sampling through two ADCs.
Method 3: analog multiplier
Multiply two signals.
Since the angle value can be obtained, the impedance value can also be obtained.
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