industrial keypadindustrial keypadindustrial keypad

Images credits: Digi-Key | SF Cable

 

Industrial keypads allow users to press keys or enter codes to control equipment and machinery. Specifically, industrial keypads are manufactured to withstand the rigors of industrial processes and environments. Keypads are mainly used to enter numbers, but can be tailored for a variety of uses.

 

Operation

 

Industrial keypads can be distinguished by how the keypad's buttons are mounted, and the methodology of how the device recognizes which alphanumeric characters or symbols have been selected.

 

  • Membrane keypads do not isolate characters on individual keys, but instead locate characters on the top layer of a three-layer membrane. The characters are printed onto a flexible polymer film that covers the entire keyboard, upon which a soft rubber dome is produced. To select a key, the dome is depressed through perforations in the middle layer to contact the bottom membrane layer, where a short circuit is completed and registered by the device and associated controllers or hardware. These keypads are inexpensive and resistant to inadvertent debris, liquids, or shock, but are quick to degrade with frequent use and often fail before one million keystrokes. It is possible to improve the tactile and auditory feedback of the keypad by utilizing plastic keytops on the top membrane, which is known as an indirect, full-travel keypad.

  • Dome-switch keyboards place electrical switches underneath a membrane of rubber or silicone. The membrane uses metal domes coated with nickel, silver, or gold, or polyurethane domes coated with graphite. When the key is pressed it completes the circuit to register the keystroke. Sometimes keys are mounted on capacitive switches or PCBs. This is the most common type of keypad. Metal domes provide positive tactile and auditory feedback; polyurethane domes are quieter but with less feedback.

Selecting dome-switch keypads

Image credit: Global Sources

  • Scissor-switch keypads have character keys that are attached to the keyboard by a single-stage pantograph mechanism. Rubber domes and a membrane still underlie the keypad, but a keystroke requires less travel and the keypad height is shorter than many other operation types. This type is quiet, with good tactile feedback, but is somewhat more expensive than other keypad types. These types of keypads are difficult to clean, but also less likely to trap dust or debris beneath the keys.

Selecting scissor-type keypads

Image credit: Capacity Keyboard

  • Capacitive-switch keypads have character keys with a flat foam element that is coated with aluminum. Upon depression, the aluminum clings to the underlying PCB to create a series circuit of two capacitors between contact pads, thereby creating a recognizable drop in capacitive resistance. Frequently, the keys do not need a full depression, meaning input can be completed rapidly.

Selecting capacitive-switch keypads

Image credit: Overclock

  • Mechanical keypads utilize a compression spring contained within a plunger mechanism underneath each key. The key depression completes a circuit to signify each key. These keys have both aural and tactile feedback, but are comparatively loud. Keys return to position quickly, and the tactility of keys can be varied. Mechanical keypads are relatively expensive. 

Selecting mechanical key switches

Image credit: Deskthority

  • Buckling-spring keypads are similar to mechanical keypads because they also rely on a spring to provide a return force and key tactility. However, the deflection of the spring is not linear, but parabolic. In its deflection it actuates a small hammer on a pivot, which strikes an electrical contact, be it membrane sheet or capacitive contact. These keypads are highly tactile, but also loud and expensive.  

Selecting buckling-spring key

Image credit: Deskthority

  • Hall effect keypads use magnets and Hall effect sensors to register key depressions. Key deflection moves and accompanying magnet which is detected by a solid-state sensor. These types of keyboards are extremely reliable to several million keystrokes, and are used in critical applications such as on airplanes or in nuclear plants. These types of keypads can be made 100% waterproof and are exceptionally resistant to debris contamination, but are also quite expensive.

Images credits: Sweet et al

 

Mounting and Sizes

 

Most commonly, keypads are integrated into other equipment or devices for access control and data input. They may be hard- or soft-linked to computers, logic controllers, or circuits. As such, it is important to place keypads in an ergonomic and location according to the application specifications.

 

5 x4 keypadThere are four standard keypad sizes:

 

  • 1 x 4. Such keypads typically utilize custom symbols, numerals 1-4, or four separate alphabet letters to designate input.

  • 3 x 4. This is a common type of keypad found on telephones, which typically utilizes all ten single-digit numerals, as well as the number sign (#) and asterisk (*).

  • 4 x 4. Often found on calculators, this keypad features all ten single-digit numerals, as well as various mathematical functions.

  • 5 x 4. This type of keypad has characters and symbols that are typically specified by the end-user according to the application's input needs.

Users who require mounting styles or keypads which may require a different layout matrix should consult a keypad service.

 

Keypad Characters

 

The most common characters placed on keypad buttons include single-digit numerals--thereby allowing an endless permutation of number strings--and the alphabet of the environment's predominant language. Symbols and words may be used to represent specific functions on a key pad as well. Since keypads do not offer the input versatility of an industrial keyboard, buttons are sometimes programmed with alternate meanings. 

 

Specifications

 

Electrical switch specifications for standard keypads include:

 

  • Maximum current rating: The maximum nominal, or name plate current capacity of a device.

  • Maximum alternating current (AC) voltage rating: The maximum AC voltage capacity of a device.

  • Maximum direct current (DC) current rating: The maximum DC voltage capacity of a device.

Standard keypads with X-Y outputs are matrix-style devices. Devices with a single pole or common bus output require the same number of pins as buttons.

 

Features

 

  • Selecting keypad blindersIndustrial keypads are often backlit and include light-emitting diodes (LED) to indicate input recognition, process status, system functions, machine interlocks, and alarm conditions.

  • Embossed switches have graphics or alphanumerical characters that are raised from the switch surface.

  • Switches, panels and keypads that are designed for outdoor use are water resistant or waterproof and can withstand both ultraviolet (UV) light and variations in ambient temperature.

  • Keypads in sensitive applications may require protection from electromagnetic interference, radio frequency interference, and electrostatic discharge. EMI, RF, and ESD protection ensures the device's operation is not compromised by other electrical fields or stray charges.

  • Vandal protection prevents unauthorized individuals from servicing, operating, or hacking the keypad.

  • Keypad blinders prevent nearby individuals from observing the user's input.

  • Covers are an easy way of safeguarding keypads susceptible to debris, liquids, and impacts.

Standards

 

The accompanying standards may be useful when considering industrial keypads, as well as their implementation.

 

- ATIS 0700703  Letter allocation on keypads

- CSA ISO/IEC 9995 Keyboard layouts for text and offices (includes keypads)

- BS DD ENV 13093 Interface requirements for keypads on public transportation systems

- DS/EN 1332-3 Identification card systems and keypads

 

Applications

 

Common applications for industrial keypads include automating manufacturing and industrial equipment, security access, point-of-sale and banking applications, telecommunications, vehicular controls, and display controls.

 

Resources

 

Ergo Canada — Mechanical Keyswitches, Membrane Keyswitches, Scissor-Switch Membrane Keyswitches

 

Wikipeda — Membrane keyboard, Keyboard technology

 

Make Use Of — How Does a Mechanical Keyboard Work?

 

Images Credits

Storm Interface | Geek Alerts