Bridges

Impedance bridges are precision measurement instruments based on the Wheatstone bridge principle, used to determine resistance, inductance, and capacitance by balancing the bridge circuit against a known reference. Unlike swept-frequency analyzers, traditional bridges achieve their highest accuracy at null balance, making them suitable for metrological work where traceable, low-uncertainty measurements are required. They serve as reference-grade instruments in standards laboratories, national metrology institutes, and calibration facilities.

Modern variants include automatic capacitance bridges, AC resistance bridges, and transformer ratio arm bridges. These instruments offer exceptional accuracy — often in the parts-per-million range — and are used to verify the value of precision standard resistors, standard capacitors, and inductance standards. Bridges are also applied in sensor measurement systems where strain gauges, thermistors, and other resistive transducers are the sensing elements.

Typical Applications

Calibration of standard resistors, capacitors, and inductors in metrology laboratories
Verification of precision passive components against national measurement standards
Strain gauge and transducer measurement in structural testing and load cells
Low-resistance measurement in precision resistor manufacturing
Temperature measurement using resistance temperature detectors (RTDs) and thermistors
High-accuracy inductance and mutual inductance measurements in electromagnetics research

Popular Brands

IET Labs (formerly GenRad) is one of the most recognized names in impedance bridge technology, offering a wide range of precision bridges for resistance, capacitance, and inductance standards. Keysight and Fluke provide bridge-based instruments suited to calibration lab use, while specialized manufacturers serve national metrology institute and defense calibration requirements.