Comparators

A comparator compares two operating parameters- operating quantity and restraining quantity. The two types of comparators are amplitude comparators and phase comparators. Regardless of the value of the phase angle, amplitude comparators compare the magnitudes of operating and the restraining quantity. When the magnitude of the operating quantity exceeds that of the restraining quantity, the relay operates and sends the trip signal to the circuit-breaker. Three varieties of amplitude comparators exist. They are integrating amplitude comparator, sampling amplitude comparator and instantaneous amplitude comparator. The two types of integrated amplitude comparators are circulating current type and the voltage opposed type. In sampling comparators, signals are sampled either at the same instant or different instants and then compared. The averaging type and the phase splitting type are the two types of instantaneous amplitude comparators. Phase comparators compare the phase relation between two input signals. Coincidence type phase comparators and vector product type phase comparators are examples of phase comparators. The different techniques employed in coincidence type phase comparators are block spike phase comparison, phase splitting technique, integrating phase comparison and rectifier bridge phase comparison. The two varieties of vector type phase comparators are Hall Effect type and magneto-resistivity type phase comparators.