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Solid State Relays

Solid State Relays WatlowWatlow solid state relays (SSR) offer many of the advantages of solid state power controllers, but at a lower cost. Watlow's extensive knowledge in power controller design led to the development of a special fast cycle input card that enables a solid state relay to operate from a standard 4-20mA instrumentation command signal. Test results show that zero-cross solid state relays in combination with the fast cycle card promote better temperature control and longer heater life than slow cycle relays. Through a time proportional cycle rate of 1⁄10 of a second, heater life will be extended. Both low and high voltage solid state relays are available from 24 to 660VAC. All ac output models include back-to-back silicon controlled rectifiers (SCRs) for a more rugged design than the traditional triac-based solid state relay. The internal design allows it to tolerate high currents and harsh electrical environments of heavy industry. Watlow also offers a switched VDC model for dc heating applications. Watlow provides all of the components necessary for trouble-free operation. This includes two standard convenience items: a thermal foil to ensure proper thermal transfer from the relay to the heat sink and belleville washers to ensure that the relay is mounted with sufficient pressure to enable good heat transfer. Matched semiconductor fuses and heat sinks are available to complete the power switching package.