Measuring Dielectric Properties with AC Bridges

Electrical bridge circuits are commonly used to measure unknown impedance values (resistance, inductance, capacitance) by balancing the bridge. Different types of bridges are designed for specific measurements, especially when dealing with AC signals and reactive components like capacitors and inductors.

Let's look at the common bridges mentioned in the options:

• Wheatstone bridge: This is primarily used for measuring unknown resistance values in DC circuits or AC circuits where reactances are negligible. It's not typically used for measuring capacitance or dielectric loss.
• Kelvin double bridge: This bridge is specifically designed to measure very low resistance values, essentially eliminating the effect of lead resistances which become significant at low values. It is not used for measuring capacitance or dielectric loss.
• Maxwell bridge: The Maxwell bridge is an AC bridge used for measuring unknown inductance by comparison with a known capacitance. It's useful for coils with a wide range of quality factors (Q). It is not used for measuring capacitance or dielectric loss of dielectric materials.
• Schering bridge: The Schering bridge is an AC bridge specifically designed for measuring capacitance and dissipation factor (or dielectric loss) of a capacitor. It's particularly suitable for testing insulating materials and cables at high voltages and frequencies, making it ideal for evaluating dielectric properties. The dielectric loss in a material causes a phase difference between the voltage and current that is not exactly 90 degrees for a theoretically pure capacitor. The Schering bridge can measure this deviation, represented by the loss angle or dissipation factor, and the capacitance value.

Based on the functions of these bridges, the bridge specifically used to measure the dielectric loss and capacitance of dielectric material is the Schering bridge.

Therefore, for measuring dielectric loss and capacitance, the appropriate bridge is the Schering bridge.