Tact Switch Fundamentals
Switches : In the simplest form, a switch is a device that opens and closes a circuit. Every machine needs to be turned on or turned off at some point and that’s typically done by activating a switch. There are an incredible variety of switches like rotary switch, slide, snap – action, tilt, push button switch, push wheel switch, rocker switch, paddle, toggle, keylock switch, tactile switches etc.
Tactile Switches :A tact switch derives its name from tactile which means perceptible through the sense of touch. Tactile switches are so named because they give the user tactile feedback in the form of a detent or snap – action when the switch has actuated.
Tactile switches are momentary contact devices that operate when depressed with a force of between 100 and 300 gm. They are also generally single – pole single – throw elements and are designed for high-density operation. The actuation element is an elastomeric actuator top that impinges on a metal contact. Applied force exceeding a threshold pushes the contact onto stationary contacts to complete circuitry.
Contacts are gold or silver depending on design requirements. As with many circuit – board components, tactile switches come in surface – mount and through – hole styles.
Advantages of tact switches : Besides miniaturization, tactile switches are replacing standard push button switches due to low cost, lower power circuitry, variety and surface mount requirements. These switches continue to fall within the definition of mechanical switch products but are typically replacing standard switches used over the past three decades.
Design in Aspects : Design Engineers should relate their switch needs to power requirements, current levels, size, mode of actuation, life, mounting requirements (through hole or surface mount), sealed and surge requirements.
Applications: Tactile action switches find applications in automotive applications, computers, instruments, process controllers, appliances, TV sets, VCR’s, communication sets etc. They may be the part of the front panel, make up a keypad or reside in equipments.
Important specifications :
- Ratings : The electrical parameters, current and voltage are specified at resistive loads.
- Operating Force : It refers to the maximum load at the time of switching over of the contacts (Point A in the figure).
- Return Force : It refers to the returning force of the stem after its full travel when pushed out (Point B in the figure).
- Travel : It refers to the distance of the travel of the operating part before the contact is changed over. Generally it is about 0.3 mm in mechanical contact.
- Bounce : This refers to the state of repeating the contact opening or closing momentarily at the time of the changeover of the switch to ON or OFF. Longer duration of this state may cause malfunction of the signal.