B&R Automation PC 620, User Manual

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Appendix A • Glossary
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559 Automation PC 620 with 945GME N270 CPU board User's Manual V 1.10
Jitter
Jitter is a term that describes time deviations of cyclic events. If, for example, an event should
take place every 200ìs and it actually occurs every 198 to 203ìs, then the jitter is 5ìs. Jitter has
many causes. It originates in the components and transfer media of networks because of noise,
crosstalk, electromagnetic interference and many other random occurrences. In automation
technology, jitter is a measure of the quality of synchronization and timing.
Jumper
A small plug or wire link for adapting the hardware configuration used to connect the different
points of an electronic circuit.
LCD
An abbreviation for " L iquid C rystal D isplay". A display type, based on liquid crystals that have a
polarized molecular structure and are enclosed between two transparent electrodes as a thin
layer. If an electrical field is applied to the electrodes, the molecules align themselves with the
field and form crystalline arrangements that polarize the light passing through. A polarization
filter, which is arranged using lamellar electrodes, blocks the polarized light. In this way, a cell
(pixel) containing liquid crystals can be switched on using electrode gates, thus coloring this pixel
black. Some LCD displays have an electroluminescent plate behind the LCD screen for lighting.
Other types of LCD displays can use color.
LED
An abbreviation for " L ight E mitting D iode". A semiconductor diode which converts electrical
energy into light. LEDs work on the principle of electroluminescence. They are highly efficient
because they do not produce much heat in spite of the amount of light they emit. For example,
"operational status indicators" on floppy disk drives are LEDs.
LPT
Logical device name for line printers. In MS-DOS, names are reserved for up to three parallel
printer ports with the names LPT1, LPT2 and LPT3. The first parallel port (LPT1) is usually
identical to the primary parallel output device PRN (in MS-DOS the logical device name for the
printer). The abbreviation LPT stands for "Line Printer Terminal".
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