The digital bridge is an instrument that can measure inductance, capacitance, resistance and impedance. This is the traditional saying. Early impedance measurements used the real bridge method. With the development of modern analog and digital technology, this method has long since become obsolete. But the name LCR bridge is still used today. If it is an LCR bridge using a microprocessor, it is called an LCR digital bridge.

The measurement object of the digital bridge is the parameter of impedance component, including AC resistance R, inductance L and its quality factor Q, capacitance C and its loss factor D. Therefore, it is often referred to as a digital LCR measuring instrument. The measurement frequency ranges from power frequency to approximately 100 kHz. The basic measurement error is 0.02%, usually about 0.1%.

The DUT of the digital bridge is the device under test, and its impedance is represented by Zx, and Rr is the standard resistance. The switch can measure the voltages Ux and Ur of the two separately, so there is the following formula: Zx=Ux/Ix =Rr*Ux/Ur

This formula is a phasor relationship. For example, using a phase-sensitive detector (PSD) to measure the in-phase and quadrature components of Ux and Ur corresponding to the reference phasor, and then pass the analog-to-digital converter (A/D), and then the computer performs complex number operations to obtain the composition of the measured The resistance value and reactance value of impedance Zx.

It can be seen from the circuit and working principle that the digital electric bridge just inherits the traditional name of the electric bridge. In fact, it has lost the composition form of the traditional classic AC bridge, but it has returned to the circuit and principle of ammeter and voltmeter that measure impedance at a higher level based on Ohm's law.

The digital bridge can be used for the verification and transmission of impedance measurement tools in the measurement and testing department, as well as the routine measurement of impedance components in the general department. Many digital bridges have standard interfaces that can automatically classify the components under test based on the accuracy of the measured values. It can also be directly connected to an automatic test system to perform automatic product inspection on the parts production line to achieve quality control of the production process.