Here you will get ebooks as per university syllabus

1. EDUCATION HOLE PRESENTS
ELECTRONICS ENGINEERING
Unit-IV

2. Digital Voltmeter..................................................................................................................... 2
Introduction..........................................................................................................................................................2
RAMP Techniques.................................................................................................................................................3
Digital Multimeters ..........................................................................................................................4
Oscilloscope.....................................................................................................................................5
Introduction......................................................................................................................................................5
Basic Principle..................................................................................................................................5
Learning the oscilloscope (also scopemeter or scope).........................................................................................5
Y Axis - Vertical - Voltage V...................................................................................................................................5
X Axis - Horizontal - Time Base..............................................................................................................................6
Working Principle..................................................................................................................................................6
Trigger Modes...................................................................................................................................................8
CRT.......................................................................................................................................... 8
VERTICAL AMPLIFIER SECTION..............................................................................................................................8
HORIZONTAL-SWEEP SECTION..............................................................................................................................9
Block Diagram of Oscilloscope..........................................................................................................9
Simple CRO .................................................................................................................................... 10
Measurement of voltage................................................................................................................ 11
Current phase and frequency using CRO......................................................................................... 12
Digital Voltmeter
Introduction
A digital voltmeter, or DVM, is used to take highly accurate voltage measurements. These
instruments measure the electrical potential difference between two conductors in a circuit. They
are electric voltmeters and the preferred standard, as they offer several benefits over their analog
counterparts. Voltmeters are used to measure the gain or loss of voltage between two points in a
circuit. The leads are connected in parallel on each side of the circuit being tested. The positive
terminal of the meter should be connected closest to the power supply, and the negative terminal
should be connected after the circuit being tested. The analog dial or digital display will exhibit
the voltage measurement. A digital voltmeter typically consists of an analog to digital converter

3. (A/D) with a digital display. The analog signal is converted into a digital code proportionate to
the magnitude of the signal. Voltages from picovolts to megavolts are measurable, though the
scale usually graduates in millivolts, volts, or kilovolts. Frequencies between zero and several
megahertz may also be measured.
RAMP Techniques
The operating principle of a ramp type digital voltmeter is to measure the time that a linear ramp
voltage takes to change from level of input voltage to zero voltage (or vice versa).
• This time interval is measured with an electronic time interval counter and the count is
displayed as a number of digits on electronic indicating tubes of the output readout of the
voltmeter.
• The conversion of a voltage value of a time interval is shown in the timing diagram of Fig.
At the start of measurement a ramp voltage is initiated.
• A negative going ramp is shown in Fig. but a positive going ramp may also be used.
• The ramp voltage value is continuously compared with the voltage being measured (unknown
voltage).
• At the instant the value of ramp voltage is equal to that of unknown voltage.
• The ramp voltage continues to decrease till it reaches ground level (zero voltage).
• At this instant another comparator called ground comparator generates. a pulse and closes the
gate.
• The time elapsed between opening and closing of the gate is t as indicated in Fig.
• During this time interval pulses from a clock pulse generator pass through the gate and are
counted and displayed.
• The decimal number as indicated by the readout is a measure of the value of input voltage.
• The sample rate multivibrator determines the rate at which the measurement cycles are
initiated.
• The sample rate circuit provides an initiating pulse for the ramp generator to start its next
ramp voltage.

4. • At the same time it sends a pulse to the counters which set all of them to 0.
• This momentarily removes the digital display of the readout.
Digital Multimeters
A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic
measuring instrument that combines several measurement functions in one unit. A typical
multimeter would include basic features such as the ability to measure voltage, current, and
resistance. As the circuits in embedded system designs become more sophisticated and demand
tighter tolerances, you must measure different parameters with a high degree of accuracy to
validate your design.
With a Tektronix digital multimeter you can make voltage, current, resistance, frequency, period,
capacitance and temperature measurements with confidence. You can also monitor and record
measurements over time or environmental ranges and view statistical values to see how your
circuit's performance is changing. And, dedicated front-panel buttons provide fast access to
frequently used functions and parameters, reducing set up time. Each Tektronix digital
multimeter provides the feature-rich tools and precision you need for your most demanding
measurements.
Analog multimeters use a microammeter whose pointer moves over a scale calibrated for all the
different measurements that can be made. Digital multimeters (DMM, DVOM) display the
measured value in numerals, and may also display a bar of a length proportional to the quantity

5. being measured. Digital multimeters are now far more common than analog ones, but analog
multimeters are still preferable in some cases, for example when monitoring a rapidly-varying
value. A multimeter can be a hand-held device useful for basic fault finding and field service
work, or a bench instrument which can measure to a very high degree of accuracy. They can be
used to troubleshoot electrical problems in a wide array of industrial and household devices such
as electronic equipment, motor controls, domestic appliances, power supplies, and wiring
systems.
Oscilloscope
Introduction
An oscilloscope, previously called an oscillograph, and informally known as a scope, CRO (for
cathode-ray oscilloscope), or DSO (for the more modern digital storage oscilloscope), is a type
of electronic test instrument that allows observation of constantly varying signal voltages,
usually as a two-dimensional plot of one or more signals as a function of time. Non-electrical
signals (such as sound or vibration) can be converted to voltages and displayed.
Oscilloscopes are used to observe the change of an electrical signal over time, such that voltage
and time describe a shape which is continuously graphed against a calibrated scale. The observed
waveform can be analyzed for such properties as amplitude, frequency, rise time, time interval,
distortion and others. Modern digital instruments may calculate and display these properties
directly. Originally, calculation of these values required manually measuring the waveform
against the scales built into the screen of the instrument.
Basic Principle
Learning the oscilloscope (also scopemeter or scope)
This short and simple reading allows the understanding of basic working concepts and the
possible uses of a scopemeter. It is not depending on performances and cost of the instrument.
Indeed the oscilloscope is used to observe slow speed signals, like pulses generated from cardiac
heartbeat, or fast and irregular signals of electronic equipments like radio and microprocessor
circuits.
Y Axis - Vertical - Voltage V
There is at least one input channel for the Voltage signal V to be shown, about the two channels
(or dual trace) we will speak later. This signal passes through an adjustable gain amplifier and
the selection knob sets the amplitude value for each Y division. So setting 2 V/Div means that
the maximum watching amplitude of the input signal is 16V (2V multiplied by 8 vertical
divisions) or referring to center (zero) is 8V positive and 8V negative.

6. X Axis - Horizontal - Time Base
This axis too has a selection knob to set the temporal base or how long is a division. For example
setting 10ms/Div means that to trace the whole X axis it spends 0.1 seconds (10 ms multiplied by
10 divisions = 100 ms). We will call scan everyone of this sweeps.
Working Principle
An electronic beam light up a dot on the screen. Where the dot is depends on the two deflection
systems, horizontal and vertical. The vertical axis is driven by the input signal while the
horizontal one by the internal time base. Without input signal the dot moves from left to right
tracing a flatten horizontal line.
Now suppose to apply at the vertical input a 10Vpp (peak to peak) triangular wave signal with
25Hz of repetition frequency. That means 25 cycles per second so a period is:
1/25 = 0,04 seconds = 40ms.
Setting the gain to 5V/Div and the time base to
10ms/Div what is traced at every scan on the
time axis appears as depicts this picture:
There is shown a 2 divisions height signal
repeated every 4 divisions on X axis.
Now if I switch the gain, consequently changes the
vertically filled divisions (Y axis). Switching
instead the time base, changes of course the
occupied horizontal divisions (X axis). So we
realize that every signal with any frequency,
voltage and shape can be shown graphically by the
oscilloscope just setting it up properly. Within of course max and min limits reported on
selectors.
Trigger
It is necessary to emphasize that every scan on the X axis draws a new trace and the time base
knob defines the trace's lenght of time, 0.1 seconds in our example. At this point we have to
understand when a scan begins, or best, what starts it. The trigger perform just that function. We
call trigger the event that starts each single scan.
This fundamental section allows two settings:
• Selecting the edge between positive and negative.

7. • Presetting the trigger voltage level in continuous range (through analog potentiometer),
not by predefined steps.
Practically the above settings define that the trigger event (beginnig of scan) happens when the
input signal crosses the trigger level in one of the two possible ways, rising for the positive edge
and falling for the negative one.
The example trace in previous picture starts at zero voltage level (center of Y axis) hence the
trigger level was preset around zero Volt while the selected edge was negative. At the end of
scan (end tracing on X axis) the electronic beam is turned off and brought back to the left of the
screen (starting point). Then it waits a new trigger event.
With this system happens that, for constantly repeated waves, an identical trigger event restarts a
new scan that retrace exactly the previous shape. In that condition the input signal is triggered
(locked or coupled or hooked up) so we can see a stable waveform on the grid. Without trigger
instead the input signal is shifting on the X axis.
Let us make clearer this concept with a picture. Supposing to have a continuous saw tooth wave
the scopemeter shows just the fraction fitted in one scan. The beam at end of scan switches off
and go back to the left. This operation spends a fixed time known as "HOLD-OFF" time (H). If
now begins a new scan, the new starting point is different from the previous one, please see this
picture:
Here is therefore what is shown without trigger,
our input signal running sliding on temporal axis.

8. Open animated example (new window)
Animated example (same window)
Trigger Modes
All oscilloscopes have at least 3 basic trigger modes:
• SINGLE - In this one shot mode, the scan starts only once at first trigger event. After
that, it must be manually re-enabled by a push-button to wait for another start event. So in
single mode a trace is drawn just once at first trigger event and the lenght of time scan
depends on time base preset.
• NORMAL - A scan restarts only on trigger event. At the end of scan the beam go to the
starting point (left of screen) to wait for next event. Hence in normal mode, when trigger
events lack there is not any trace.
• AUTO - Automatic, the scan restarts automatically at each end of scan also without
trigger event, so a trace is always shown without input signal too. When the input signal
is small, such to not generate a trigger event, it is however shown even if sliding as above
described.
Moreover, on some oscilloscopes there is a special trigger section. It may allows a delay from
trigger event rather than widen the time base into a scan part. Since that section is specific and
change model by model it must be seen case by case. Here let us remain on basic use.
CRT
(CATHODE-RAY TUBE)
Power and Scale Illumination: Turns instrument on and controls illumination of the graticule.
Focus: Focus the spot or trace on the screen.
Intensity: Regulates the brightness of the spot or trace.
VERTICAL AMPLIFIER SECTION
Position: Controls vertical positioning of oscilloscope display.

9. Sensitivity: Selects the sensitivity of the vertical amplifier in calibrated steps.
Variable Sensitivity: Provides a continuous range of sensitivities between the calibrated steps.
Normally the sensitivity is calibrated only when the variable knob is in the fully clockwise
position.
AC-DC-GND: Selects desired coupling (ac or dc) for incoming signal applied to vertical
amplifier, or grounds the amplifier input. Selecting dc couples the input directly to the amplifier;
selecting ac send the signal through a capacitor before going to the amplifier thus blocking any
constant component.
HORIZONTAL-SWEEP SECTION
Sweep time/cm: Selects desired sweep rate from calibrated steps or admits external signal to
horizontal amplifier.
Sweep time/cm Variable: Provides continuously variable sweep rates. Calibrated position is
fully clockwise.
Position: Controls horizontal position of trace on screen.
Horizontal Variable: Controls the attenuation (reduction) of signal applied to horizontal aplifier
through Ext. Horiz. connector
Block Diagram of Oscilloscope

10. Simple CRO
The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides accurate
time and aplitude measurements of voltage signals over a wide range of frequencies. Its
reliability, stability, and ease of operation make it suitable as a general purpose laboratory
instrument. The heart of the CRO is a cathode-ray tube shown schematically in Fig. 1.

11. The cathode ray is a beam of electrons which are emitted by the heated cathode (negative
electrode) and accelerated toward the fluorescent screen. The assembly of the cathode, intensity
grid, focus grid, and accelerating anode (positive electrode) is called an electron gun. Its purpose
is to generate the electron beam and control its intensity and focus. Between the electron gun and
the fluorescent screen are two pair of metal plates - one oriented to provide horizontal deflection
of the beam and one pair oriented ot give vertical deflection to the beam. These plates are thus
referred to as the horizontal and vertical deflection plates. The combination of these two
deflections allows the beam to reach any portion of the fluorescent screen. Wherever the electron
beam hits the screen, the phosphor is excited and light is emitted from that point. This coversion
of electron energy into light allows us to write with points or lines of light on an otherwise
darkened screen.
In the most common use of the oscilloscope the signal to be studied is first amplified and then
applied to the vertical (deflection) plates to deflect the beam vertically and at the same time a
voltage that increases linearly with time is applied to the horizontal (deflection) plates thus
causing the beam to be deflected horizontally at a uniform (constant> rate. The signal applied to
the verical plates is thus displayed on the screen as a function of time. The horizontal axis serves
as a uniform time scale.
Measurement of voltage
Cathode Ray Oscilloscope can be used for the measurement of voltage of any electrical
specification as the deflection of the electrostatic beam is directly proportional to the deflection
plate voltage.
For measurement of the direct voltage, firstly the spot is centered on the screen without applying
any voltage signal to the deflection plates. Then direct voltage to be measured is applied between
a pair of deflection plates and the deflection of the spot is observed on the screen. The magnitude
of the deflection multiplied by the deflection factor gives the value of the direct voltage applied.
Usually the screen is calibrated for fixed operating condition, so by reading the scale, voltage can
be measured directly by the CRO. In case of measurement of alternating voltage of sinusoidal
wave-form, it is applied between a pair of deflection plates and the length of the straight line is
measured. Knowing the deflection sensitivity, the peak to peak value of applied ac voltage can
be determined. The rms value of ac voltage applied will be equal to this peak value divided by
2√2 for sinusoidal wave-form. For measurement of current, the current under measurement is
passed through a known non-inductive resistance and the voltage drop across it is measured by
CRO, as mentioned above. The current can be determined simply by dividing the voltage drop
measured by the value of non-inductive resistance. When the current to be measured is of very
small magnitude, the voltage drop across non-inductive resistance (small value) is usually
amplified by a calibrated amplifier.

12. Current phase and frequency using CRO
The frequency of a signal is measured using oscilloscope in two methods. They are,
1. Using calibrated oscilloscope
2. Using uncelebrated oscilloscope.
Measurement of Frequency using Calibrated Oscilloscope
It is the indirect method of measurement of frequency. In this method, the frequency of unknown
signal is measured by measuring its time period.
Initially, the unknown frequency signal is applied to the vertical inputs of the CRO. Now the
horizontal sweep is turned ON and the display appealing on the screen is adjusted by varying
different control knobs provided on the front panel of CRO, till the signal is suitably displayed
on the screen. After obtaining the display of good deflection, count the number of horizontal
division for a complete cycle. From the counted horizontal divisions, the time period is computed
as,
T=m*n
Where
m=Number of division in one complete cycle
n=Setting of time base =Time/Division
From the measured time period of the signal, the unknown frequency is calculated as,
f =1/T