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HUMAN
MACHINE INTERFACE
Human machine interfaces (HMI) are operator interface
terminals. Using HMI, users can interact in order to control machines.
Some human machine interfaces include knobs, levers, and
controls. Others provide programmable function keys or a full key pad.
For example there can be an interface to control the
operation of a pump from remote location.
Devices that include a processor or interface to personal
computers (PCs) are also available. Many human machine interfaces include
alphanumeric or graphic displays. For ease of use, these displays are often backlit
or use standard messages.
When selecting human machine interfaces, important
considerations include devices supported and devices controlled.
Device dimensions, operating temperature, operating
humidity, and vibration and shock ratings are other important factors.
Many human machine interfaces include flat panel displays
(FPDs) that use liquid crystal display (LCD) or gas plasma technologies.
In LCDs, an electric current passes through a liquid crystal
solution that is trapped between two sheets of polarizing material. The
crystals align themselves so that light cannot pass, producing an image on the
screen. LCDs can be monochrome or color. Color displays can use a passive
matrix or an active matrix. Passive matrix displays contain a grid of
horizontal and vertical wires with an LCD element at each intersection. In
active matrix displays, each pixel has a transistor that is switched directly
on or off, improving response times. Unlike LCDs, gas plasma displays consist of
an array of pixels, each of which contains red, blue, and green sub pixels. In
the plasma state, gas reacts with the sub pixels to display the appropriate
color.
Flat
panel displays are very thin displays, commonly used for portable computers.
Technologies
used for flat panel displays include Liquid Crystal Display (LCD) and gas
Universal
serial bus (USB) is a 4-wire, 12-Mbps serial bus for low-to-medium speed
peripheral device connections to personal computers (PC), including keyboards,
mice, modems, printers, joysticks Monitouch Connectable Device list
Monitouch
connects to over 1,000 devices, and supports over 200 serial drivers, over 20
Ethernet drivers and 8 field bus options.