Specification Options




Available Specifications:


{{specification.MaxOperatingTempF}}°F or {{specification.MaxOperatingTempC}}°C

{{specification.MaxWattDensityIn}} W/in2 or {{specification.MaxWattDensityCm}} W/cm2

TRU-TUNE®+ Adaptive Control


Agency Approvals




Ambient Operating Range


Communication Protocols


Control and Limit Loops




Max Monitor Channels


Max Output


Operating Requirements


Output Firing


Phase Configurations




Supported Controllers


Remote Limit Reset


Display Height


Warranty (Years)


Optical Res


F / C
Outside Diameter
(W/in / W/cm2)



{{sensorSpec.TemperatureF}} / {{sensorSpec.TemperatureC}}

{{sensorSpec.OutsideDiameterIn}} / {{sensorSpec.OutsideDiameterCm}}

Power Switching Devices

Watlow solid state power switching devices complement the rapid switching required by PID temperature controllers and help deliver optimum system performance and service life. They are available in 1-phase and 3-phase/2-leg and 3-leg configurations, feature touch-safe terminations, input indicators, zero-cross, random or phase-angle fire options, ratings from 18 to 1,000 amperes and agency approvals including CE and UL® 508. Various configurations offer short circuit current ratings (SCCR) of 200,000 amperes, extensive system and heater diagnostic capabilities, heater bake out, integrated heat sinks, on-board fuses, RoHS compliance and serial communications.

Watlow DIN-A-MITE® and E-SAFE II power switching devices provide convenient DIN-rail mount packages and are a good replacement for mercury displacement relays.

Additionally the EZ-ZONE ST offers an integrated temperature and process controller with optional over- and under-temperature limit and safety shutdown contactor.

Watlow® Silicon Controlled Rectifiers (SCRs):

Minimizing temperature extremes results in less expansion and contraction of the heater element and extends heater life. By reducing the time base, on-to-on cycle time, the resistance heater can provide a smooth, even output.

The power controlling device you use in your thermal system determines the severity of thermal excursion. For example, the electromechanical
contactor (EMC) and mercury displacement relay are limited in their capability to control thermal excursions.

The EMC normally operates on a 30-second or longer time base, allowing the temperature excursion between the overshoot and droop points to increase.

Although longer time-base settings will result in longer life for the contactor, heater life will be reduced significantly. Any shorter time-base settings will shorten the life of the contactor.

The mercury displacement relay (MDR) with shorter cycle times of 3 to 15 seconds still produces a significant temperature excursion, again leading to reduced heater life.

By comparison, solid state relays (SSRs) are able to operate on a one-second time base. This reduces the temperature difference between the overshoot and droop points and increases the life of the heater.

A SCR power controller with burst firing capability and operating on a variable time base of less than one second effectively eliminates temperature excursion.

An SCR power controller with phase-angle firing, regulating power by turning the SCR on within each half cycle, operates on a 8.3 millisecond time base and also effectively eliminates temperature excursion.

Because phase-angle firing can cause undesirable electrical interference, Watlow® recommends the variable time base—burst firing—for all Watlow heaters. Performance and heater life have been tested to be equal.

Thermal Excursion

A temperature controller with an onoff control mode has a characteristic over- and undershoot as it oscillates about set point.

The greater the thermal excursion between the over- and undershoot temperatures, the greater the thermal expansion and contraction of the element wire in the electric
heater. This makes the wire more brittle and causes it to breathe and oxidize. The work hardening of the element causes breakage and heater failure.

Using SCR controllers in your process eliminates overshoot and droop to ensure long heater life and better performance of your system.

Watlow SCRs: Dramatically Increase Heater Life

As time-base cycling rates increase past one second, they become more damaging to the heater element. Faster cycling does not cause as much expansion or contraction of the element wire. SCRs, cycling at less than one second, stabilize element temperature and increase heater life.

To illustrate this, Watlow conducted a heater life test of the effects of timebase cycling on resistance heater element life. Test models used identical cartridge heaters, thermocouples and temperature controllers. The only variable was the power controller type: EMC, MDR and SCR and their minimum time-base cycling rates.

The heaters were operated in open air and at high temperatures to accelerate failure. Test results showed any cycling over one second shortened the life of the heater significantly. Using SCRs extended heater life up to 20 times and more in some instances.

Watlow SCRs: Higher Allowable Watt Densities

SCRs improve heater life regardless of watt density. However, heater life is of greatest concern when using higher temperature and higher watt density heaters. Because these heaters produce a greater temperature differential between the element and sheath than lower watt density heaters, they will have a shorter life.

However, if operated with a proportional temperature controller and an SCR power controller, this difference is reduced as temperature excursions are stabilized through faster cycling. Because the SCR does not allow the element temperature to rise to a destructive level during the cycle's on-time, the higher watt density heater will survive.

Watlow SCRs: Provide Years of Reliable Service

Because the SCR power controller is a solid-state device, there are no inherent wear-out modes, no moving parts to replace. The SCR is capable of many years of service while operating at the fastest time base.

The SCR’s virtually limitless life eliminates the maintenance time and cost in replacing mechanical contactors.