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Design And Construction Of Ac Voltmeter Using Computer Interface
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i. Passing Ac through D’ Arsonval Meter
This causes useless flutter
of the needle. In order to use a Dc style, meter such as C’ arsenal
design the alternating current must be rectified into Dc. This is most
easily accomplished through the use of devices called Diodes we will see
diodes used in a circuit that demonstrates, the creation of harmonic
frequencies from a distorted (or rectified) sine wave. Another strategy
for a practical ac meter movement is to redesign the movement without
the inherent polarity sensitivity of the Dc types. This means that the
use of permanent magnet should be avoided.
ii. Iron Vane Electromechanically Meter Movement
Electrostatic
attraction between two metals plates separated by air gap is
alternative mechanism for generating a needle –movement force
proportional to applied voltage. This works just as well for Ac as it
does in dc or probably poorly. The force involved is small much smaller
than the magnetic attraction is small much smaller than the magnetic
attraction between an energized coil and iron vane and as such these
“electrostatics meter movement tends to be fragile and easily disturbed
by physical movement.
With some the advantages and disadvantages of
these meters movement technologies having been discussed already, there
is nether factor crucially important to be designer and user of ac
metering instrument to be aware of. This is the issues of Rms
measurement. As we already know, Ac measurements are often cast in a
scale of Dc power equivalent called RMSCRoot- Mean –Squired for the sake
of meaningful comparism with Dc and with other Ac waveforms of varying
shape. None of the meter movement technologies boyar discussed in gently
measures RMS value of an Ac quantity. Meter movement relying on the
motion of mechanical needle (“rectified D’ Arson Val, Iron-vane and
Electrostatic) all tend to mechanically average the instantaneous values
into an overall average value for the waveform. This average value is
not necessarily the same as RMS, although many times it is mistaken as
such. Average and RMS seems to be the kind of measurement most people
are interested in obtaining with an instrument and electromechanical
meter movement naturally deliver average measurement rather than RMS,
what are Ac meter designers to do? Cheat of course! Typically the
assumption is made that the wave form shape to be measured is going to
be sine and then the meter movement scale is altered by the appropriate
multiplication factor. For sine waves we see that RMS is equal to 0.77
times the peak value while average is 0.637 times the Reek, so we can
divide one figure by the other to obtain an average to RMS conversion
factor of 1.109.
=> 0.707 =1.1099
0.637
With square waves,
the RMS and Average value are identical! An Ac meter calibrated to
accurately read RMS voltage or current on a pure sine wave will not give
the proper the proper value while indicating the magnitude of anything
other than a perfect sine wave. This includes triangle waves, square
waves, or kind of distorted sine wave. With harmonics becoming an ever-
present phenomenon in large Ac power systems,. This matter of accurate
RMS measurement is no small matter.
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ABSRACT - [ Total Page(s): 1 ]Voltage is a fundamental quantity that is important in every phase of electrical engineering from power system to voltage inside VLSI chips. Of The need to measure the output voltage of a supply is very important meanwhile, The voltmeter is an instrument for measuring voltage, it could be digital or Direct voltage, meanwhile, the rectification process of the alternating voltage using diode, make, it more possible for ac voltages to be measured.However, the need for modernization makes it necessa ... Continue reading---
