Optimise Switches For Harsh Industrial Environments

March 22, 2011
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1. Multidirectional switches such as the RS and QS Series feature audible clicks and tactile feedback even when operators wear thick work gloves.

Fig 2. The KMT0 Series switches developed by C&K Components are designed without plating. They’re sealed with Teflon films and adhesives to prevent the ingress of fluids, thus providing IP68 sealing.

Fig 3. The HP Series Hall-effect pushbutton switch features the control capabilities required in industrial equipment.

Industrial equipment demands a lot from its components. Design engineers thus face the challenge of developing rugged and robust electromechanical components to ensure that the equipment is durable as well as cost-effective. New switch designs and materials, along with advances in precision (e.g., Hall-effect technology), are necessary traits to make the components work in increasingly demanding environments.

When incorporating a switch into a piece of industrial equipment, it soon becomes evident that not all switches are created equal. Industrial equipment requires ruggedised switches that can perform in harsh environments, at extreme vibration, and after repetitive impacts.

As industrial applications have evolved, so have switch designs. No doubt, advanced switch configurations are a direct response to evolving industrial equipment. For example, a more productive workday created the need for extended switch life cycles, and more stringent safety regulations required the assurance of proper feedback, resulting in features such as audible clicks and tactile feedback discernible through thick work gloves. Moreover, a desire for maximum uptime called for simplified assembly and low maintenance requirements.

Extended Life Cycles

An obvious solution to downtime is a switch that’s designed to have a long life cycle. These extended-life switches are staples in industrial applications.

For example, industrial pushbuttons are ideal for simple switching functions due to their robustness and long operating lifetimes, with many providing more than one million cycles. In addition, they stand up to the repetitive actions necessary in equipment functions. Industrial pushbuttons are dependable and provide adequate functionality without the bells and whistles, making them a cost-effective solution.

Safety Issues

Just as the equipment needs to be reliable, so does the feedback provided by the switch to the operator. Otherwise, simple human error can cause serious detriments to safety and contribute to downtime. For operators on the manufacturing floor, a switch’s tactile feedback can serve as an additional safety feature, along with front-panel indicator lights and visual on-off indicators like keylocks and toggle switches.

Audible clicks need to be heard even in noisy factory environments, and tactile feedback must be felt through thick work gloves for front-panel switches. Other features that help optimise operator safety include an enhanced design for ease of use. In this case, several switch functions are combined in a bidirectional switch that operates in various directions. Such a switch can exhibit a single function with four switches or double functions with eight switches in four directions: up, down, left, or right (Fig. 1).

Furthermore, switches designed to incorporate illumination can provide a visual cue for added safety. LEDs designed into a switch, yet independent of the switching mechanism, allows for a solid, slow- or fast-blinking LED to indicate equipment status. For application-specific needs, snap-on caps in a variety of colors are available. Consequently, customers can purchase one standard switch with or without LED illumination, as well as incorporate many different colored caps based on their application-specific needs.

Sealed For Integrity

Application-specific sealing is another determinant when specifying a switch. Commonly, industrial-equipment switches are sealed to IP67 or IP68 specifications, which assure protection from contamination by dust and water. As such, switches typically feature three layers of sealing, including internal and external seals, as well as a silicon rubber outer cap for further protection from environmental contaminants.

The internal seal protects the switching mechanism while the external panel seal is designed to prevent liquids from entering the panel or enclosure. For applications that require a higher-degree of protection, such as outdoor applications, an IP69 rating is necessary. An IP69-rated switch is designed to meet level-6 dust and particle intrusion standards, and can be submerged in at least five feet of water for 30 minutes.

As another example, many PC-board-mounted switches must also be sealed to withstand several rounds of soldering and cleaning processes. Industrial/automation applications often these switches underneath overlays for added sealing and protection.

Rugged Switch Materials

Surface-mount processes increasingly drive the demand for materials capable of withstanding higher temperatures. Some applications have raised the surface-mount solder temperature from 235°C to 260°C for through-hole switches. Process sealing has risen to the challenge of meeting these high-temperature requirements.

In addition to high temperatures, materials used in switches designed for harsh environments must be able to withstand chemicals, hydraulic fluids, hydrocarbons, oils, and other potential contaminants. Materials such as polybutylene terephtalate (PBT) are able to provide additional strength against these contaminants.

Other design considerations involve switches with or without plating. There are advantages and drawbacks in each case, but the most versatile solution is to seal the switch using Teflon films with either acrylic or silicon adhesives (Fig. 2). It provides a robust solution with sealing to up to IP67 specifications, and doesn’t allow liquids to corrode the switch.

Accurate Switching Technology

To address accuracy and precision, switch manufacturers developed Hall-effect pushbutton switches. They’re more popular than ever in industrial equipment due to their precision and control capabilities, as well as extended life cycles. Hall-effect switches are solid-state electronic devices with no mechanical parts. By eliminating the mechanical parts more susceptible to breaking, they provide a robust alternative to conventional switches. 

A magnet and an integrated circuit are used to detect the motion, position, or change in the field strength of the switch position, ultimately delivering a clean, fast linear output that’s switched without bounce. Using the magnetic technology overcomes an inherent problem with mechanical contact switches.

The electrical life of the Hall-effect switch is virtually limitless, which is ideal for systems in harsh environments (Fig. 3). The highly sensitive circuit in the switch can achieve accurate and repeatable results in close tolerance applications.

Hall-effect pushbutton switches also provide linear motion, which is rarely seen in a standard pushbutton switch. The linear motion allows for a more precise output signal, depending on the exact position of the switch. It’s also not susceptible to environmental contamination. Furthermore, it can be sealed to IP67 specifications, adding to its durability for industrial applications.

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