Electromechanical relay technology has been the same for many years. So, has the electrical arcing that can shorten the life of such electromechanical relays. But this engineering "fact of life" has changed thanks to a new technology developed by Watlow engineers that extends the life of relays encompassed within Watlow temperature and power switching controllers used in resistive heating applications that require a high volume of cycles.
Called NO-ARC, the technology has already been incorporated into several new high-profile products including E-SAFE® II hybrid power switch, EZ-ZONE™ PM integrated controller and EHG SL10 process controller and safety limit.
Standard relays typically consist of two separate and independent circuits. The first (a coil) drives the electromagnet. When the switch is on, the electromagnet is on, and it attracts the armature. The armature acts as a switch in the second circuit (the contacts). When the electromagnet is energized, the armature completes the second circuit. Standard relays can experience arcing, or surges in current. When an arc jumps across the contacts, it can melt a small section of the contact surface and contacts can weld together. Over time, this can render the relay unusable.
A NO-ARC relay is a mechanical relay with arc suppression provided through the use of smart electronics. The technology reduces the amount of arcing across the relay contacts and greatly extends the life of the relay. Watlow assistant product manager, Jim Hentges, says that arc suppression is desired to effectively manage thermal properties and provide a robust switch with a long life. Relays without NO-ARC typically have a life cycle of about 100,000 cycles at rated amperage, while the NO-ARC relay will have a life of more than four million cycles.
"When the control signal is provided to the product to turn the relays on, NO-ARC technology energizes a circuit that is in parallel with the contacts to carry the load so the contacts do not have to," Hentges explains. "Then, we do the same thing when the relay is expected to open or turn off."
NO-ARC technology is superior to alternative technologies for many reasons including it can handle high current without a large heat sink. Eliminating the need for a heat sink further reduces ownership costs and the number of components required for operation. Watlow is the first heater manufacturer to introduce this new technology.
Any application that requires millions of cycles will see value in arc suppression technology.
"Many industries are constantly seeking ways to reduce cost, so building in an arc suppression circuit extends the life of relays, reducing the need for product replacement and potential manufacturing downtime," Hentges says.
Watlow products that have incorporated NO-ARC technology include:
- E-SAFE II Hybrid Power Switch
E-SAFE II provides reliable and accurate power switching in a mercury-free product. E-SAFE II offers a switching life of millions of cycles at 35 amperes at a high ambient temperature rating of 70°C (158°F) providing superior performance. NO-ARC technology allows it to switch millions of cycles while decreasing noise and increasing temperature accuracy. The switching mechanism of Watlow's E-SAFE II is a hybrid solid state and mechanical relay. This allows faster cycling and more precise control, which helps contribute to energy savings, extended heater life and lower overall costs.
E-SAFE II is also a UL® Recognized product.
- EZ-ZONE PM Integrated Controller
The EZ-ZONE PM is a 1/32 or 1/16 DIN panel mount controller offering options to reduce the complexity and cost of a control loop. The EZ-ZONE PM controller can be configured as a PID controller, over/under limit controller or these functions can be combined into one integrated controller. Using NO-ARC relay technology the EZ-ZONE PM is able to offer 15 ampere load capacity and offers over two million cycles at rated load (maximum 240V~(ac), five second minimum cycle time).
- EHG SL10 Process Controller and Safety Limit
EHG SL10 is an integrated/adjustable, agency recognized safety limit (UL®1998), temperature controller and heater all in one system. Its compact design, inherent reliability and integrated limit functions make this system a tremendous value. EHG SL10 incorporates a NO-ARC relay as the process output switching device, making it more reliable than traditional thermostats and thermofuses. This controller will typically provide four to five million cycles at 10 amp rating.
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