Tuesday, 11 December 2012

Introduction to Digital voltmeter


Digital voltmeter

At present, We known that in technology and science a new innovation  digital signal conversion technique come in place of use of analog signal,so we achieved the fast data transmission , noise less communication between two long distance places, fast speed of
 data measurement, high accuracy and precision in field of measurement instruments medical science, internet etc.  in over world.

If we taught about voltmeter for measurement of voltage, the digital voltmeter is better in place of analog type voltmeter.

This type of voltmeter is converting the analog into digital signal.
It is display the voltage as discrete numerical instead of pointer deflection on Screen of digital display.

This is also referred as DVM. (Digital voltmeter)
It is use to measure ac and dc voltage and also to measure the resistance etc.

In this, reduces the human error reading as misreading of scale, parallax errors.

It can made with the help of analog to digital converter, signal processing elements,
Data transmission elements  and  digital display elements

Convert analog input to digital through Analog to digital converter.

Output of A/D converter is decoded using by signal processing element to drive the seven segment display.

And the data from decoder is transmitting to display through data transmission elements as counter, latch as per requirement.

The digital display element shows the result in digital form.


Thursday, 1 November 2012

Spectrum Analyzer :Introduction,types of spectrum analyzers, Application

           Spectrum Analyzer :
A spectrum analyzer provides a calibrated graphical display on its CRT, 
with frequency on the horizontal axis and amplitude (voltage) on
 the vertical axis.

(The most common way of observing signals is to display them on an oscilloscope with time as the
X-axis (i.e.between amplitude of the signal and time). This is the time domain. It is also useful to display signals in the frequency domain. The providing this frequency domain view is the spectrum analyzer.)

Displayed as vertical lines against these coordinates are sinusoidal components of which the
input signal is composed. The height represents the absolute magnitude, and the horizontal
location represents the frequency.

These instruments provide a display of the frequency spectrum a given frequency band.
Spectrum analyzers use either parallel filter bank or a swept frequency technique.
In a parallel filter in a parallel filter bank analyzer, The frequency range is covered by a series of
filters whose central frequencies and bandwidth are so selected that they overlap each others, as
shown in fig


Typically, an audio analyzer has 32 of these filters, each covering one third of an octave.
For wide band narrow resolution analysis, particularly at RF or microwave signals, the swept
Technique is preferred.


As per reference  to the block diagram of fig.,

 The saw tooth generator provides the saw tooth voltage ,which drives the horizontal axis
 element of the scope and this saw tooth voltage is the frequency controlled element of
 the voltage tuned oscillator.
 As the oscillator sweeps from fmin to fmax of its frequency band at a linear recurring rate,
 it beats with the frequency component of  the input signal and produce an IF, whenever
 a frequency component is met during its sweep.

The frequency component and voltage tuned oscillator frequency beats together to produce a
difference frequency, i.e. The IF corresponding to the component is amplified and detected if
necessary and then applied to the vertical plates of the CRO, producing a display between of amplitude and  frequency.

The spectrum produced if the input wave is a single toned A.M .
One of the principal applications of spectrum analyzers has been in the study of the
 RF spectrum produced in microwave instruments.

 In a microwave instrument, the horizontal axis can display
as a wide a range as 2 - 3 GHz for a broad survey and as narrow as 30 kHz, for a highly
magnified view of any small portion of the spectrum. Signals at microwave frequency 
separated by only a few KHz can be seen individually.
The frequency range covered by this instrument is from I MHz to 40 GHz, 
The basic block diagram is of a spectrum analyzer covering the range 500 kHz to 1 GHz, 
which is representative of a super heterodyne type

The input signal is fed into a mixer which is driven by a local oscillator. This oscillator is
linearly tunable electrically over the range 2 - 3 GHz. 

The mixer provides two signals at its output that are proportional in amplitude to the
 input signal but of frequencies which are the sum and difference of the input signal 
and local oscillator frequency.

The IF amplifier is tuned to a narrow band around 2 GH4 since the local oscillator is 
tuned over the range of 2 - 3 GHz, only inputs that are separated from the local oscillator 
frequency by 2GHz will be converted to IF frequency band, pass through the IF frequency 
amplifier, get rectified and produce a vertical deflection on the CRT.

From this, it is observed that as the saw tooth signal sweeps, the local oscillator 
also sweeps linearly from 2 - 3 GHz. The tuning of the spectrum analyzer is a
 swept receiver, which sweeps linearly from 0 to 1 GHz. 

The saw tooth scanning signal is also applied to the horizontal plates of
the CRT to form the frequency axis. (The spectrum analyzer is also sensitive to
 signals from 4 - 5 GHz referred to as the image frequency of the super heterodyne. 
A low pass filter with a cutoff frequency above I GHz at the input suppresses
 these spurious signals.)

The two types of spectrum analyzers are,

1. Fliter Bank Spectrum analyzer.
2. Super hetero dyne Spectrum analyzer.
1. Filter Bank Spectrum analyzer

2. Super hetero dyne Spectrum analyzer

The modern spectrum analyzers use a narrow band super heterodyne receiver. 
Super heterodyne is nothing but mixing of frequencies in the super above
 audio range. 
The functional block diagram of super heterodyne spectrum analyzer or RF 
spectrum analyzer as shown in the Figure 

The RF input to be analyzed is applied to the input attenuator. After attenuating,
 the signal is fed to low pass filter.
The low pass filter suppresses high frequency components and allows low frequency
 components to pass through it. The output of the low pass filter is given to the mixer,
 where this signal is fixed with the signal coming from voltage controlled or 
voltage tuned oscillator. 

This oscillator is tuned over 2 to 3 GHz range. The output of the mixer includes 
two signals whose amplitudes.are proportional to the input signal but their frequencies 
are the sum and  difference of the input signal and the frequency of the local oscillator. 

Since the frequency range of the oscillator is tuned over 2 to 3 GHz, the IF amplifier is
 tuned to a narrow band of frequencies of about 2 GHz.

Therefore only those signals which are separated from the oscillator frequency by
 2 GHz are converted to Intermediate Frequency (IF) band. This IF signal is amplified by
 IF amplifier and then rectified by the detector. After completing amplification and rectification the signal is applied to vertical plates of CRO to produce a vertical deflection on the CRT screen. 
Thus,  when the saw tooth signal sweeps, the oscillator also sweeps linearly from minimum to
 maximum frequency range i.e., from 2 to 3 GHz. 

Here the saw tooth signal is applied not only to the oscillator (to tune the oscillator)
 but also to the horizontal plates of the CRO to get the frequencyaxis or
 horizontal deflection on the CRT screen. On the CRT screen the vertical axis is 
calibrated in amplitude and the horizontal axis is calibrated in frequency.
These Spectrum analyzers are widely used in the field of,
1. Bio medicals

Saturday, 27 October 2012

Signal Analyzers

Signal Analyzers

 The analysis of any electrical signals  are used in many places as laboratories,         industries, research  and development area etc.
for analysis of its many different instruments can use as,  
- Wave analyzer,
- Harmonic analyzer,
- Spectrum analyzer and Network  analyzer.

 - All analyzers, measure the frequency properties of the signals,and for measurement of its use a different techniques.

 Wave analyzer:

- A Wave analyzer The instrument that used to measure the amplitude of each harmonic or fundamental individually is called as the Wave analyzer

wave analyzers are used in the low RF range.
It is simplest form of analysis in the frequency domain, it can be done with a set tuned filters and a voltmeter.

Distortion analyzers :

A Distortion analyzers measures the total harmonic distortion content is in input signal with indicating he amplitude and frequency of components.
Distortion analyzer operate over range of 5 HZ to 1 MHz.

Network analyzer:
- A Network analyzer is a instrument that used to measure the S-parameters of a network.

Spectrum analyzer:

- A spectrum analyzer,The instrument which graphically presents an energy distribution of the signal as a function of frequency on the C.R.O. is called Spectrum Analyzer.

This study gives us information about the,
  (i) Band width
 (ii) The types of modulation
 (iii) Spurious signal generation
 (iv) Modulation index
 (v) Attenuation
 (vi) The component levels.

Friday, 7 September 2012

Electrostatics Focusing in CRT


 Electrostatic focusing system in CRT :

In Electrostatic Focusing ,Electrostatic lens consists of three anodes, with the middle anode at a lower potential than the other two electrodes.An electrostatic focusing system is shown in figure.
In figure two anodes and its electrostatic lines and equipotential surfaces are shown. 

Potential difference is kept between these two electrodes so that an electric field is generated between them. Spreading of electric field is caused because of repulsion between electric lines. 
If equipotential lines are drawn, as shown in figure, they would bulge at the centre of the two anodes.  as  know that electrons move in a direction opposite to that of electric field lines and equal-potential surfaces are perpendicular to the electric field lines so force on the electron is exerted in the direction normal to the equipotential surface

As shown in figure,Electrons entering at the center line of the two anodes experience no force but electrons displaced from the center line experience a force normal to the direction of equi-potential surface and deflect. 

 An equi-potential surface is shown, in which an electron with velocity V1 and at an angle θ. to the normal of equi-potential surface enters and experiences a force in a direction normal to the equi-potential surface. Thus the velocity of the electron increases to V2. This force on the electron is exerted in the direction normal to equi-potential surface so only the normal component of electron velocity V1N increases to V2N and the tangential component of velocity V1T remains the same.

V1T = V1 sin θ1,
                                      V2T = V2 sin θ2

                                But V1T = V2T
V1 sin θ1 = V2 sin θ2
            V2/V1 = sin θ1 / sin θ2

Equipotential surface acts as a concave lens in geometrical optics. That is why, this focusing system is name an electrostatic lens. 
Now if we go back and refer figure, 

it can be seen that because of middle anode to a lower potential, electron beam coming from the cathode and passing through the first concave electrostatic lens tends
 to become more aligned with the axis of CRT and when 
it enters at the second concave electrostatic lens, 
formed between two anodes at different potentials, it 
is focused at the phosphor screen. 
 Focal length of the electrostatic lens can lie adjusted
by varying potential of middle anode with respect 
too ther two anodes.

Thus very precisely,electron beam can be made to focus at 
  the screen .

                                                                         ..............Read more.........http://ei-notes.blogspot.in/

Thursday, 6 September 2012

Questions and Answers on electronics/instrumentation/Quiz on computer

  Questions and Answers on /Quiz on computer:

1-  This type of monitor is common on desktop computers. It looks much like a standard television.
 Ans- cathode-ray tube
2-  LCD monitors often have a smaller __________ than CRT monitors
 Ans-viewing angle
3-  The __________ monitor is similar to the LCD monitor, but has a phosphorescent film between the layers
Ans- ELD(Electro luminescent displays)
4-  Monitors use various intensities of __________ colors to generate the rainbow
5-  The most complicated part of your computer’s sound system is the __________
 Ans-sound card
6-  The __________ contains speakers and a microphone on a headband
Ans- headset
7-  Newer projectors utilize __________ to achieve clearer and brighter images.     
 Ans-digital light processing
8-  To minimize eyestrain, you should adjust your monitor 
      to a __________     degree angle.
9-  Which of the following measures the speed of dot-matrix printers?
10- In a laser printer, the __________ transfers the image to the paper.
   Ans- drum