Solid-state relays (SSRs) »J offer improved reliability and performance over that of electro-mechanical relays (EMRs) in applications requiring large numbers of contact closures, interfacing to low power solid-state circuits, maximum speed and control of contact closure, and minimum production of radio-frequency interference. SSRs may not be used as a direct replacement for EMRs in many circuits, however, and a number of the important fac-tors required for satisfactory SSR application and performance are considered.