Page 148 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Advantages of Multiplexing:
If no multiplexing is used between the users at two different sites that are distance apart, then separate
communication lines would be required

This may not only be costly but may also become difficult to manage. If multiplexing is used then, only one line
is required. This leads to the reduction in the line cost and also it would be easier to keep track of one line than
several lines.

LCD has lots of applications, but digital panel meter is the most common application of LCD. DPM is a measuring
instrument, which uses LCD to display results.
Digital Panel Meter (DPM):

A panel meter is an instrument that receives information from an input signal and then measures and displays
the information in a digital or analog format. It is usually mounted inside an instrument panel. It often indica
temperature, but may also reflect speed, pressure current, and many other variables.
The most common type of panel meter accepts a single input for display, although multiple channel devices
are also available. The units are also available with large displays for visibility. Analog panel meters used to be
common, they have been replaced in most circumstances by the more accurate and functional digital meter.
A digital panel meter is used to measure and display all types of processes and electrical variables, fr voltage
monitoring to current, flow, speed, and more has a bright LED display that presents information in alphanumerical
format with little or no ambiguity.
Many digital panel meters can accept multiple inputs have adjustable or bar graph displays that allow users
also have totalizing, recording, conditioning, or other easily switch between these inputs. Digital displays mar
functional capabilities.

In addition to being significantly more accurate, a digital panel meter generally has more available features than
an analog meter. It can be selected with alarm options along with set point controls that allow users to establish
control limits, as well as ON/OFF controls that can activate or deactivate a process unit. Many digital panel meters
can be connected to a computer to transfer data, and some have ethernet capabilities that allow them to connect
to a LAN or the internet.
Liquid Crystal Display (LCD)
LCD means Liquid Crystal Display. It is a combination of two states of matter, the solid and the liquid. LCD uses
liquid crystal to produce a visible image. Liquid crystal displays are super-thin technology display screens that are
generally used in TVs, cell phones, laptop/computer screen, etc. LCD’s technologies allow displays to be much
thinner when compared to Cathode Ray Tube (CRT) technology.

LCD is composed of several layers which includes two polarized panel filters and electrodes.
LCD is either made up of an active-matrix display grid or a passive display grid. The LCD has a unique advantage
of having low power consumption than the LEDs or CRTs.
Principle of LCD:

The screen works on the principle of blocking light under than emitting light. LCD requires back light they do not
emit light by them.
Construction of LCD:

We need two polarized glass pieces filter in making liquid crystal. The glass which does not have a polarized
surface of it, must be rubbed with a special polymer which will create microscopic grooves on the surface of the
polarized glass filter. The grooves must be in the same direction as the polarized film. Now, add a coating of
pneumatic liquid phase crystal on one of the polarised filters of the polarized glass.
The microscopic channel causes the first layer molecule to to align with filter orientation. When the right angle
ppears at the first layer piece, we should add a second piece of glass with the polarized film. The first filter will be
actually polarized as the light strikes it at the starting stage.

Thus, light travels through each layer and is guided to the next with the help of molecules. The molecule tends to
change its its plane of vibration of the light in order to match their angle.

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CITS : E & H - Electronics Mechanic - Lesson 77 - 83