By Gary Mountford, C&K General Manager, C&K Components, Newton, Mass.
Although innovative, traditional electromechanical switches are still widely employed in heavy-duty industrial and off-highway equipment, Hall-effect switches are increasingly being used to keep pace with new system designs and can provide the reliability and almost limitless life cycles that are now being demanded.
Heavy-duty industrial equipment, such as front-end loaders, bulldozers, forklifts, agricultural machinery, and forestry equipment are typically equipped with joystick controls for precision adjustment, lifting, lowering, and grasping objects. Adapting regular joystick controls to function in heavy machinery usually involves employing switches with redundant contacts to ensure that if one set of switch contacts fail, a second set of contacts can still perform the switching function. This makes machine operators more effective with their time on the job site and reduces downtime for any repairs that the machinery might need.
Many pushbutton and rocker switches are now using innovative electromechanical components and especially contactless Hall-effect devices because of their exceptional control precision, extended electrical and mechanical life, flexibility, and customization capabilities.
Double-pole single- and bi-directional rocker switches provide redundant contacts, distinct tactile feel, and positive snap-point action.
Innovative electromechanical designs
For typical switching functions in different types of heavy machinery, robust rocker switches are used for dashboard or control functions due to their long operating life (usually more than one million cycles). Rocker switches provide an ideal proportional function; they are cost-effective, and often available with multiple actuator and terminal styles, mounting options, and detent angles to meet application-specific needs. Short-circuit protection (a ridge between the contacts prevents short circuits, even under tensile load of the connection cable) and integrated temperature compensation provide features that extend their durability and reliability even further.
Redundant switch contacts are currently incorporated into the switch assemblies for heavy-duty industrial machinery. For example, a double-pole switch provides redundant contacts so that if one set of contacts fails, the second set ensures that the switch remains functional. This redundancy combined with an external metal housing for the switch lets it carry more current. By providing this type of fail-safe mechanism, the redundant switch design ensures that the machinery or vehicle doesn’t experience unnecessary downtime. For example, some panels combine bi-directional switches, with a single or double function switch that is intended to operate in both directions.
The AP Series SPST (single-pole, single-throw), normally open, momentary action switch is sealed to IP67 specifications and is available in illuminated and non-illuminated versions.
Other assemblies contain quadrant switches with single-functions (four switches) or double-functions (eight switches) in each of four different directions: up, down, left or right. Such types not only contain redundant contacts, but they also have distinct tactile feedback and positive snap-point action. This produces an audible click with feedback that can be felt through thick work gloves on front panels, multi-function grips, and other control units within the equipment.
Along with the basic functionality of the switch itself, innovative switches also often employ various forms of illumination for visual status indication or function of a machine. Adding illumination at the switch level significantly reduces materials costs. For example, some switches with optional illumination let users order the base switch with or without the cap and lens. This gives them the ability to order a single base switch and add multiple colors of snap-on caps that can be used during installation to meet each application-specific need.
Hall-effect switches are solid-state electronic devices with no mechanical parts. This makes them inherently more reliable than traditional mechanical switches. Also, Hall-effect switches typically employ a magnet, an integrated circuit, and active electronic components in a circuit designed to detect the motion, position, or change in the field strength of the magnet to give a clean, fast, and linear output that is switched without bounce. Precision and control are achieved through the magnet providing a controllable linear motion, which is not normally available in a standard pushbutton switch. This linear motion then translates into a precise output signal, which can be varied depending upon the exact position or travel of the switch. When moving or adjusting the control surfaces of the machine or equipment, this precision helps determine the accuracy of the overall control.
In addition to the precision and control capabilities afforded by the use of magnetic technology, the contactless design also guarantees an almost limitless electrical life for the switch, and a mechanical life of more than 10 million actuations. These features, in turn, increase the reliability of the switch such that it will not experience unexplained field failures under normal operating conditions.
The integrated circuit within the Hall-effect switch is highly sensitive and provides reliable interpretation of the Hall-effect sensor output signal, which enables the switch to deliver precise incremental control in close-tolerance applications. In most instances, because the Hall-effect sensors are not affected by dust or temperature extremes, the switch circuit is nearly immune to environmental contaminants and can be sealed to meet IP67 specifications. Because of these design features, Hall-effect switches are uniquely qualified for use in harsh environments and are gaining widespread use in heavy-duty industrial and off-highway equipment. Currently, Hall-effect switches are not as widely specified as traditional pushbuttons, so they provide manufacturers an option for extended life, high reliability equipment controls.
The HP Series sealed switch houses a non-contact, Hall-effect switch system. A high-energy magnet provides a linear magnetic field for the Hall device.
Hall-effect switches, such as those shown, are unique in that they offer a single or dual Hall-effect element for providing an output in two directions or a redundant contact for a single-direction switch. Such devices are also commonly sealed to IP67 or IP68 specifications to prevent contamination by hydraulic fluid, dust, dirt, and water, which are primary concerns in industrial and off-highway equipment. Combating environmental elements is often accomplished with Hall-effect switches that contain an internal seal to protect the switching mechanism, and an external panel seal to keep liquids from entering the panel or enclosure. Silicon rubber caps also prevent the ingress of fluids that could adversely affect the function of standard switches. Also, the materials used in these switches, such as PBT (Polybutylene Terephtalate), are robust enough to withstand exposure to agricultural chemicals, hydraulic fluids, hydrocarbons, UV light, oils, and other potential contaminants.
Flexibility and customization
Innovative electromechanical designs in switch assemblies often afford customers greater flexibility and customization options, depending on their specific needs. Illumination with customizable end caps, for example, not only allows equipment manufacturers to have fewer part numbers to inventory, which simplifies materials and assembly processes, but they also allow greater flexibility with circuit and panel designs.
Hall-effect technology also affords end users a significant amount of flexibility and customization, with varying wire lengths, wire gauges, and choice of connectors. Often, modular construction depends on connectors that allow it to be plugged into the panel and locked firmly in place during installation, simplifying both assembly and maintenance. Modules also need less storage space and they reduce cost because the user can store individual switch elements separately and configure them during final assembly to meet application-specific needs. Multiple mounting styles, including threaded or snap-in types, provide even greater flexibility and customization options.
Filed Under: ELECTRONICS • ELECTRICAL, Switches