Logic Rating of Electromechanical Relays

Electromechanical relays were the first logic element used in a computer. Today, small compact reed relays are again being extensively used as logic elements. A logic factor, FL, measures the improvement that a logic device can affect if interposed between a logic source and logic detector. A logic figure of merit, TFM, determined when FL = 1.0 can be used for comparison of the logic performance of logic devices. TFM is developed for an arbitrary electromechanical relay. For a miniature reed relay packaged for printed circuit boards, TFM = 1.7 milliseconds. For comparison, solid-state devices have TFM ≈ 1 nanoseconds and COSMOS (complementary symmetry metal oxide semiconductor) devices have TFM ≈ 20 nanoseconds.