Watlow 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.