2. BASIC ELECTRONICS
COURSE OBJECTIVES:
1.To understand the characteristics of diodes and transistor
configurations.
2.To understand the design concepts of biasing of BJT and FET.
3.To understand the design concepts of feedback amplifiers and
oscillators.
4. To study the design concepts of OP Amp and data converters
MATRUSRI
ENGINEERING COLLEGE
3. BASIC ELECTRONICS
MATRUSRI
ENGINEERING COLLEGE
COURSE OUTCOMES:
On successful completion of this course, the students will be able to:
1.Study and analyse the rectifier and regulator circuits.
2.Study and analyse the performance of BJTs, FETs on the basis of their
operation and working.
3.Ability to analyse and design oscillator circuits.
4.Ability to analyse different logic gates and multivibrator circuits.
5.Ability to analyze different data acquisition systems.
4. UNIT-V
MATRUSRI
ENGINEERING COLLEGE
Data Acquisition systems: Construction and operation of transducers-
strain gauge LVDT, Thermo couple , Instrumentation systems.
Data Converters:R-2R Ladder DAC, Successive approximation and Flash
ADC.
OUTCOMES:
Ability to analyze different data acquisition systems.
Ability to design & analyze ADC / DAC converters
5. MATRUSRI
ENGINEERING COLLEGE
OUTCOMES:
Ability to analyze different data acquisition systems-strain
gauge LVDT, Thermo couple , Instrumentation systems.
MODULE-I
MATRUSRI
ENGINEERING COLLEGE
CONTENTS:
Data Acquisition systems: Construction and operation of transducers
strain gauge
LVDT
Thermo couple
Instrumentation systems.
6. MATRUSRI
ENGINEERING COLLEGE
Transducer
• A device which converts a physical quantity into the proportional
electrical signal is called a transducer.
• The electrical signal produced may be a voltage, current or frequency. A
transducer uses many effects to produce such conversion.
• The process of transforming signal from one form to other is called
transduction.
• The transduction element transforms the output of the sensor to an
electrical output.
Sensing
element
Transduction
element
Non-electrical
Quantity
Sensor –Response Electrical
Signal
7. MATRUSRI
ENGINEERING COLLEGE
Components of Transducer
Sensing Element
The physical quantity or its rate of change is sensed and responded to by
this part of the transistor.
Transduction Element
The output of the sensing element is passed on to the transduction
element. This element is responsible for converting the non-electrical
signal into its proportional electrical signal.
8. MATRUSRI
ENGINEERING COLLEGE
Classification of Transducers
The transducers can be classified broadly
On the basis of transduction form used
As primary and secondary transducers
As active and passive transducers
As transducers and inverse transducers.
10. MATRUSRI
ENGINEERING COLLEGE
Inductance Transducers
Magnetic circuit transducer
Reluctance pickup
Differential transformer
Eddy current gage
Magnetostriction gauge
Voltage and current Transducers
Hall effect pickup
Ionization chamber
Photoemissive cell
Photomultiplier tube
11. MATRUSRI
ENGINEERING COLLEGE
Self-Generating Transducers (No External Power) – Active Transducers
They do not require an external power, and produce an analog voltage or
current when stimulated by some physical form of energy.
Thermocouple and thermopile
Moving-coil generator
Photovoltaic cell
Primary Transducers and Secondary Transducers
Analog Transducers
Digital Transducers
Inverse Transducers
12. MATRUSRI
ENGINEERING COLLEGE
Strain Gauge
Applications:
used for measurement of force, torque, pressure, acceleration
principle of operation :
when strain is applied to a thin metallic wire, its dimension changes, thus
changing the resistance of the wire.
Gage Factor:
The Gage Factor of metallic strain gages varies in the range 1.8 to 2.6.
The commercially available strain gages have certain fixed resistance
values, such as, 120Ω, 350 Ω, 1000 Ω, etc.
13. MATRUSRI
ENGINEERING COLLEGE
Metallic Strain Gage
Two types: unbonded and bonded.
The unbonded strain gage is normally used for measuring strain (or
displacement) between a fixed and a moving structure by fixing four
metallic wires in such a way, so that two are in compression and two
are in tension
bonded strain gage, the element is fixed on a backing material, which
is permanently fixed over a structure, whose strain has to be
measured, with adhesive.
unbonded and bonded strain gage
14. MATRUSRI
ENGINEERING COLLEGE
Semiconductor type Strain Gage
Semiconductor type strain gage is made of a thin wire of silicon,
typically 0.005 inch to 0.0005 inch, and length 0.05 inch to 0.5 inch.
Two types: p-type and n-type.
In the former the resistance increases with positive strain, while, in the
later the resistance decreases with temperature.
15. MATRUSRI
ENGINEERING COLLEGE
Linear variable differential transformer (LVDT)
When an externally applied force moves the core to the left-hand
position, more magnetic flux links the left-hand coil than the right hand
coil. The emf induced in the left-hand coil, ES1’ is therefore larger than
the induced emf of the right-hand coil, Es2‘.
The magnitude of the output voltage is then equal to the difference
between the two secondary voltages and it is in phase with the voltage
of the left-handcoil.
16. MATRUSRI
ENGINEERING COLLEGE
Construction of LVDT
The transformer consists of a primary winding P and two
secondary winding S1 and S2 wound on a cylindrical former.
Both the secondary windings have equal number of turns and are
identically placed on the either side of primary winding.
The primary winding is connected to an AC source which
produces a flux in the air gap and voltages are induced in
secondary windings.
A movable soft iron core is placed inside the former and
displacement to be measured is connected to the iron core.
The LVDT is placed inside a stainless steel housing because it will
provide electrostatic and electromagnetic shielding.
The both the secondary windings are connected in such a way
that resulted output is the difference of the voltages of two
windings.
17. MATRUSRI
ENGINEERING COLLEGE
Principle of Operation
As the primary is connected to an AC source so alternating current and
voltages are produced in the secondary of the LVDT.
The output in secondary S1 is e1 and in the secondary S2 is e2.
So the differential output is, eout = e1 - e2 This equation explains the
principle of Operation of LVDT.
18. MATRUSRI
ENGINEERING COLLEGE
Working
CASE I :
When the core is at null position (for no displacement) When the core is at null position then the flux
linking with both the secondary windings is equal so the induced emf is equal in both the windings.
So for no displacement the value of output eout is zero as e1 and e2 both are equal. So it shows that no
displacement took place.
CASE II:
When the core is moved to upward of null position (For displacement to the upward of reference
point) In the this case the flux linking with secondary winding S1 is more as compared to flux linking
with S2. Due to this e1 will be more as that of e2. Due to this output voltage eout is positive.
CASE III:
When the core is moved to downward of Null position (for displacement to the downward of
reference point) In this case magnitude of e2 will be more as that of e1. Due to this output eout will be
negative and shows the output to downward of reference point.
Output VS Core Displacement:
19. MATRUSRI
ENGINEERING COLLEGE
Advantages:
High Range
No Frictional Losses
High Input and High Sensitivity
Low Hysteresis
Low Power Consumption
Direct Conversion to Electrical Signals
Disadvantages:
LVDT is sensitive to stray magnetic fields so they always require a
setup to protect them from stray magnetic fields.
They are affected by vibrations and temperature.
Advantages & Disadvantages of LVDT
20. MATRUSRI
ENGINEERING COLLEGE
Applications of LVDT
Used in applications where displacements ranging from fraction of mm
to few cm are to be measured.
The LVDT acting as a primary Transducer converts the displacement to
electrical signal directly.
They can also acts as the secondary transducers.
E.g. the Bourbon tube which acts as a primary transducer and covert
pressure into linear displacement.then LVDT coverts this displacement into
electrical signal which after calibration gives the ideas of the pressure of
fluid.
21. MATRUSRI
ENGINEERING COLLEGE
Thermocouples
Thermocouple consists of two different metals which are placed in
contact with each other.
First part is called the heater element because when the current will
flow through this, a heat is produced and thus the temperature will
increased at the junction.
At this junction an emf is produced which is approximately proportional
to the temperature difference of hot and cold junctions.
22. MATRUSRI
ENGINEERING COLLEGE
The emf produced is a DC voltage which is directly proportional to
root mean square value of electric current.
A permanent magnet moving coil instrument is connected with the
second part to read the current passing through the heater.
Disadvantages of Thermocouple Type Instruments
The over load capacity of thermocouple type of instrument is small,
even fuse is not able to the heater wire because heater wire may
burn out before the fuse blows out.
23. MATRUSRI
ENGINEERING COLLEGE
Advantages of Thermocouple Type Instruments
• The Thermocouple type of instruments accurately indicates the root
mean square value of current and voltages irrespective of the
waveform.
• Thermocouple type of instruments give very accurate reading even at
high frequency, thus these types of instruments are completely free
from frequency errors.
• The measurement of quantity under these instruments is not affected
by stray magnetic fields.
• These instruments are known for their high sensitivity.
• Usually for measuring the low value of current bridge type of
arrangement is used i.e. ranging from 0.5 Amperes to 20 Amperes
while for measuring the higher value of current heater element is
required to retain accuracy.
24. MATRUSRI
ENGINEERING COLLEGE
Instrumentation systems
An instrumentation system obtains data about a physical system either
for the purpose of collecting information about that physical system or
for the feedback control of the physical system .
Block diagram of a typical instrumentation system with several different
output devices
25. MATRUSRI
ENGINEERING COLLEGE
Any instrumentation system must include an input transducer (sensor), such
as a strain gauge, whose response to a particular stimulus can be measured
electrically.
The other component that is generally present in modern instrumentation
systems is a digital processor, such as a computer or a micro-controller.
These programmable components have the flexibility to be used for a
variety of functions.
The most important function that they perform is to convert data into
information.
In the simplest situation the processing required to extract information may
only involve converting an input signal by a scale factor so that the final
result is in conventional units.
The signal from a transducer is usually analogue in nature, ie. it is
continuously varying and can take any value (within an allowed range).
26. MATRUSRI
ENGINEERING COLLEGE
This continuous analogue data has to be converted to a digital format
prior to being transferred to the digital processor.
Any instrumentation system must therefore include an analogue-to-
digital (A/D) converter (ADC for short) to convert an analogue signal
into a digital format.
A typical ADC will be an existing component that has been designed to
convert an analogue input voltage, typically with a range of a few volts,
into a digital word, which usually contains 8 or more bits.
However, the output from a typical transducer, such as a strain- gauge,
might have an amplitude of less than 10 mV.
This transducer output signal must therefore be amplified in an analogue
signal conditioning circuit before it can be converted into a digital word.
27. MATRUSRI
ENGINEERING COLLEGE
OUTCOMES:
Ability to analyze different data converters.
MODULE-II
MATRUSRI
ENGINEERING COLLEGE
CONTENTS:
Data Converters
R-2R Ladder DAC
Successive approximation
Flash ADC.
28. Data Converter Integrated Circuits
• The transducer circuit will gives an analog signal.
• This signal is transmitted through the LPF circuit to avoid higher components, and
then the signal is sampled at twice the frequency of the signal to avoid the
overlapping.
• The output of the sampling circuit is applied to A/D converter where the samples are
converted into binary data i.e. 0’s and 1’s.
• Like this the analog data converted into digital data.
• The digital data is again reconverted back into analog by doing exact opposite
operation of first half of the diagram.
• Then the output of the D/A convertor is transmitted through the smoothing filter to
avoid the ripples
29. What is a DAC?
A digital to analog converter (DAC) converts a digital signal to an analog
voltage or current output.
Types of DACs
• Binary Weighted Resistor
• R-2R Ladder
Binary Weighted Resistor
• Utilizes a summing op-amp circuit.
• Weighted resistors are used to
distinguish each bit from the most
significant to the least significant.
• Transistors are used to switch
between Vref and ground (bit high or
low).
-
+
R
2R
4R
2nR
Rf
Vout
I
Vref
30. Voltages V1 through Vn are either Vref if corresponding bit is high or ground if
corresponding bit is low
V1 is most significant bit
Vn is least significant bit
R
V
R
V
R
V
R
V
R
IR
V 1
-
n
n
3
2
1
f
f
out
2
4
2
Advantages
• Simple Construction/Analysis
• Fast Conversion
Disadvantages
• Requires large range of resistors (2000:1 for 12-bit DAC) with
necessary high precision for low resistors
• Requires low switch resistances in transistors Can be
expensive.Therefore, usually limited to 8-bit resolution.
31. R-2R Ladder
Vref V2
V1 V3
Vout
2
2
3
2
1
V
V
R
R
R
V
1
2
2
1
V
V
ref
1
2
1
V
V
IR
V
out
R
V
b
R
V
b
R
V
b
R
V
b
R
V
16
8
4
2
ref
0
ref
1
ref
2
ref
3
out
i
n
i
i
n
b
V
V
2
1
1
ref
out
32. Advantages
Only two resistor values (R and 2R)
Does not require high precision resistors
Disadvantage
Lower conversion speed than binary weighted DAC
Specifications of DACs
•Resolution
•Speed
•Linearity
•Settling Time
•Reference Voltages
•Errors
33. Different Types Of ADC’s
• It provides the function just opposite to that of a DAC. It accepts an
analog input voltage Va and produces an output binary word d1, d2,
d3….dn. Where d1 is the most significant bit and dn is the least
significant bit.
• ADCs are broadly classified into two groups according to their
conversion techniques
Direct type
Integrating type
Direct type ADCs compares a given analog signal with the internally
generated equivalent signal. This group includes
Flash (Comparator) type converter
Successive approximation type convertor
Counter type
Servo or Tracking type
Integrated type ADCs perform conversion in an indirect manner by first
changing the analog input signal to linear function of time or frequency and
then to a digital code.
34. Flash (Comparator) Type Converter:
• R is a stable reference voltage provided
by a precision voltage regulator as part
of the converter circuit.
• As the analog input voltage exceeds
the reference voltage at each
comparator, the comparator outputs will
sequentially saturate to a high state.
• The priority encoder generates a binary
number based on the highest-order
active input, ignoring all other active
inputs.
35. Counter Type A/D Converter
• counter is reset to zero count by reset
pulse.
• After releasing the reset pulse the clock
pulses are counted by the binary
counter.
• These pulses go through the AND gate
which is enabled by the voltage
comparator high output.
• The number of pulses counted increase
with time.
• The analog output Vd of DAC is
compared to the analog input inputVa by
the comparator.
• If Va>Vd the output of the comparator
becomes high and the AND gate is
enabled to allow the transmission of the
clock pulses to the counter.
• When Va<Vd the output of the
comparator becomes low and the AND
gate is disabled. This stops the counting
we can get the digital data.
36. Servo Tracking A/D Converter :
• An improved version of counting ADC is the
tracking or servo converter.
• The circuit consists of an up/down counter
with the comparator controlling the direction
of the count.
• The analog output of the DAC is Vd and is
compared with the analog input Va.
• If the input Va is greater than the DAC
output signal, the output of the comparator
goes high and the counter is caused to
count up.
• The DAC output increases with each
incoming clock pulse when it becomes more
than Va the counter reverses the direction
and counts down.
37. Successive-Approximation ADC:
The successive approximation analog to
digital converter circuit typically consists of
• A sample and hold circuit to acquire the
input voltage (Vin).
• An analog voltage comparator that
compares Vin to the output of the
internal DAC and outputs the result of
the comparison to the successive
approximation register (SAR).
• A successive approximation register sub
circuit designed to supply an
approximate digital code of Vin to the
internal DAC.
• An internal reference DAC that supplies
the comparator with an analog voltage
equivalent of the digital code output of
the SAR for comparison with Vin.
38. • The successive approximation register is initialized so that the most
significant bit (MSB) is equal to a digital 1.
• This code is fed into the DAC, which then supplies the analog
equivalent of this digital code (Vref/2) into the comparator circuit for
comparison with the sampled input voltage.
• If this analog voltage exceeds Vin the comparator causes the SAR to
reset this bit; otherwise, the bit is left a 1.
• Then the next bit is set to 1 and the same test is done, continuing
this binary search until every bit in the SAR has been tested.
• The resulting code is the digital approximation of the sampled input
voltage and is finally output by the DAC at the end of the conversion
(EOC).
39. Dual-Slope ADC • An integrating ADC (also dual-slope
ADC) applies the unknown input voltage
to the input of an integrator and allows
the voltage to ramp for a fixed time
period (the run-up period).
• Then a known reference voltage of
opposite polarity is applied to the
integrator and is allowed to ramp until
the integrator output returns to zero (the
run-down period).
• The input voltage is computed as a
function of the reference voltage, the
constant run-up time period, and the
measured run-down time period.
• The run-down time measurement is usually made in units of the
converter's clock, so longer integration times allow for higher resolutions.
• Converters of this type (or variations on the concept) are used in most
digital voltmeters for their linearity and flexibility.
41. MATRUSRI
ENGINEERING COLLEGE
Short Answer Questions
1. What is an instrumentation amplifier?
2. Define gauge factor in strain gauges. What are types of
strain gauges?
3. Explain the limitations of LVDT.
4. What is a transducer?
Long Answer Questions
1. Explain working of LVDT. Derive gauge factor?
2. What are the different types of transducers used for the
measurement of temperature? Explain the principle of any of
these.
3. Explain working of Thermocouple?
42. MATRUSRI
ENGINEERING COLLEGE
Long Answer Questions
Explain working of LVDT. Derive gauge factor?
What are the different types of transducers used for the
measurement of temperature? Explain the principle of any of
these.
