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Proper Selection of HMI Components Ensures Reliable Operation and End User Safety
By Joe Torzillo, Vice President of Sales — HMI Components, EAO Corporation
cators, and alarms, are critical aspects of human machine interfaces (HMI). HMIs are used for controlling equipment and systems often found within both consumer and industrial equipment. Designers today face an aston-
E
ishing range of choices in electro- mechanical components that encom- pass not only the type of device, elec- trical specifications, environmental sealing, and mounting and termina- tion styles, but also ergonomic con- siderations, such as configuration, size, illumination, and tactile feel.
The Technology of Switch Design A switch makes or breaks an
electrical connection or diverts cur- rent from one conductor to another, through the motion of an actuating mechanism. A basic switch that makes and breaks a single circuit is said to have one pole. The number of poles a switch has represents the number of separate circuits that can be active through the switch. Switches are available with nor-
mally open (NO) contacts, normally closed (NC) contacts, or combinations
U
lectromechanical devices, such as switches, keypads, key- boards, pointing devices, indi-
of both. When a NO contact is acti- vated the contact closes. When a NC contact is activated the contact opens.
over-silver, gold-plated silver, and gold-on-nickel plating. Silver con- tacts are also available in a variety of forms: solid silver, hard silver, silver-
suitable for various power levels and application requirements. But in search of a more perfect device, switch designers had to contend with three problems: contact arcing, weld- ing and bounce.
Three Challenges Arcing is a discharge of electric-
ity — a spark — that can occur when contacts make or break. 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
Proper switch selection has a direct impact on operator efficiencies and end user safety.
Gold and silver contacts are
used in most switches. Gold contacts come in many forms: solid gold, gold-
over-silver, silver-over-palladium, and silver-nickel alloy. These options provide contacts
easily melted and eroded by arcing so they are limited to low-current switching where there is little or no arcing. As switched current increas- es, hotter arcs form and the potential for erosion and contact welding is greater. Arcing is also more severe when handling high inrush currents. Relays, solenoids and motors may show high inductive inrush currents when powering up. Switches for higher currents
use gold-plated silver or all silver contacts that resist the effects of arc-
Continued on next page
LIGHT WEIGHT HIGHEST DENSITY FINEST RELIABILITY
MI DC-DC Converters
2V to 10,000 VDC Outputs 1-300 Watt Modules
Transformers & Inductors
Surface Mount & Thru-Hole MICRO D AND NAN
D AND NANO MINIATURE CONNECTORS
• MIL/COTS/Industrial Models
•Regulated/Isolated/Adjustable Programmable Standard Models
• New High Input Voltages to 900VDC • AS9100C Facility/US Manufactured
• Military Upgrades and Custom Modules
• Ultra Miniature Designs • MIL-PRF 27/MIL-PRF 21308 • DSCC Approved Manufacturing
•Audio/Pulse/Power/EMI Multiplex Models Available
• For Critical Applications/Pico Modules, Over 50 Years’ Experience
143 Sparks Ave. Pelham, N.Y. 10803-1837
Fax: 914-738-8225 E Mail:
VISIT OUR EXCITING NEW WEBSITE:
www.picoelectronics.com
www.UltimateConnector.com 714-637-7099
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