Scheringbrug

Scheringbrug, also known as the Schering bridge, is a type of alternating-current (AC) electrical bridge used in metrology to determine the dielectric properties of insulating materials. It is particularly employed to measure the capacitance and the dielectric loss (dissipation factor or tan δ) of liquids and solids under test.

Construction and principle: A Schering bridge comprises four arms arranged similarly to other AC bridges. One arm contains the test capacitor formed by the sample placed between two electrodes. Other arms hold known, adjustable components, including a standard capacitor with known capacitance and a resistance network that provides a reference impedance. At a chosen excitation frequency, the bridge is balanced so that the detector indicates zero. From the balanced condition, the unknown capacitance and the parallel loss components can be derived, yielding the sample’s dielectric constant relative to a reference geometry and its dissipation factor.

Applications: The Schering bridge is widely used in dielectric testing for quality control and research. It is employed to determine the capacitance, dielectric constant (relative permittivity), and dissipation factor of insulating liquids such as mineral oils, as well as solid dielectrics. The method is valued for its precision in low-loss measurements at specific frequencies typical for dielectric testing.

History and context: The Schering bridge is part of the broader family of AC impedance bridges developed in the early 20th century to enable precise impedance measurements. Modern instrumentation often implements the same measurement concepts digitally (as in LCR meters), but the Schering bridge remains a foundational approach for characterizing dielectric properties.

See also: AC bridge, Maxwell-Wien bridge, LCR meter.