Button Down HMI Design

Dependability of Electromechanical Switches and Buttons Is Vital to HMI Reliability

By Control Design Staff

Electromechanical devices, including switches and elements such as indicators and alarms, have undergone major changes over the years to serve specialized HMI panel needs, report Joseph Torzillo, EAO vice president of sales, HMI components; and Lance Scott, EAO president, the authors of a new white paper from EAO Switch.

Further, switch designers have to contend with contact arcing, welding and bounce. "Arcing is a discharge of electricity — a spark — that can occur when contacts make or break," write the authors. "Welding occurs when contact material melts and fuses, causing contacts to stick. Arcing and welding degrades or burns contacts, reducing useful life, and are more severe in dc than ac applications. Solid-gold contacts are more easily melted and eroded by arcing, so they are limited to low-current switching where there is little or no arcing. As switched current increases, hotter arcs form and the potential for erosion and contact welding is greater. Arcing is more severe when handling high inrush currents, i.e., inductive and capacitive loads that require high initial current. Lamps may draw 10–12 times normal operating current when first activated. Relays, solenoids and motors may show high-inductive inrush currents when powering up. Minor periodic arcing with silver contacts is actually beneficial because it keeps contacts free from dirt and corrosion."

EAO says that another challenge in switch design is contact "bounce" or "chatter," a condition in which a contact rebounds for several milliseconds before it finally closes. "This is not a concern for power circuits, but causes problems in logic circuits that may interpret on-off bounces as data streams."

Read the full paper: "Key Components Enhance the Human Machine Interface."

Series 51 stop switch Stop It   
Series 51 stop switch with visual actuation status has a back panel depth of 18.8 mm, is sealed to IP65 standards, and uses industry standard 16 mm mounting hole.
EAO Switch
(203) 877-4577
 flush-mount CW switches Push It   
Industrial-strength, 22 mm, flush-mount CW switches include maintained pushbutton switch operators, rubber boots and nameplates with either black or metallic bezels, and a choice of illuminated pushbuttons, pushbuttons and pilot lights in six colors. Selector and key selector switches are available.
(800) 262-4332
 Multi-voltage pilot light You Light Up My Panel   
Multi-voltage pilot light modules in 16, 22 and 30 mm sizes support 20–240 Vac/Vdc. Low-energy-consumption LED lamps with Lexan lenses in six colors last 100,000 hours. The modules are Type 4/4X rated.
(724) 775-7926
 illuminated e-stop pushbutton Know Your Status   
30 mm mount, illuminated e-stop pushbutton has status indication with an illuminated yellow base when the button is armed and machine enabled to RUN or is running. When the button is pushed, yellow turns to flashing red to indicate an e-stop condition. The yellow can turn to steady red when a STOP condition exists by applying an external signal via the M12 QD connector.
Banner Engineering
(888) 373-6767
 electrical buzzers See the Buzz   
With polycarbonate/ABS housings, 22.5 mm panel-mount continuous-tone, electrical buzzers have LED indicators with red or yellow lenses. Two-wire, high-intensity LED 29 mm diameter beacons are available in panel-mount styles, or M20 threaded base for use with limit and cable-operated switches.
(800) 633-0405
 OMPBD7 22 mm pilot devices Installation a Snap   
OMPBD7 22 mm pilot devices offer modular assembly and interchangeability. A toolless mounting latch mates the front element with the contact blocks and other back-of-panel components. The mounting latch is available in a plastic and metal design. The latches install with a click and are removed by pushing a rotating collar to the right.
Omega Engineering
(800) 622-2378
 A22R 22 mm diameter pushbuttons and selector switches Ease of Use       
A22R 22 mm diameter pushbuttons and selector switches have a metal bezel. The switches allow configuration changes to match contact requirements, and are designed for plug-in replacement.
Omron Automation and Safety
(866) 88-omron
 MetalliCard metal markers labeling system Marks the Spot   
MetalliCard metal markers labeling system provides an in-house print capability on aluminum or stainless steel marker-plates for pushbutton and control panel identification. Installation options include self-adhesive, riveted markers, attached with plate holders. Push button holders work with 22 mm pushbuttons from various manufacturers.
(800) 849-9343
 control stations Your Choice   
Preassembled and ready to install or assembled to order control stations include heavy-duty cast aluminum enclosure that is assembled with 22 or 30 mm pushbuttons. Use up to two contact blocks with the illuminated operators or up to four contact blocks with the non-illuminated operators. This enclosure can be modified to accept any non-illuminated 30 mm operator or pilot light as well.
(908) 806-9400
 C22 pushbutton family C the Light   
C22 pushbutton family has operator and contact blocks together in one housing. The 22 mm design provides the same pressable area as 30 mm buttons. It includes LED illuminated pushbuttons and pilot lights, twist-to-release emergency stops, selector switches, and comes in flat and extended non-illuminated versions.
(877) 386-2273
 E-Box low-profile housing Remotely Safe   
E-Box low-profile housing for single control components at detached or remote locations includes bottom and top parts, contact module with contact block, and an e-stop actuator. Choose gold contacts for 35 V and 100 mA maximum or silver for 250 V and 4 A maximum, available with two normally closed contacts, or one normally closed and one normally open.
C&K Components
(617) 969-3700