digital measurement

1. A
Presentation on
UNIT 1: Digital Measurement
-Digital Ohm Meter &
Capacitance Meter
Under the Course
Advances in Electrical Engineering
By
Miss. Jyoti Mohan Kharade
(Research Scholar)
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2. 2
Principle of Resistance Measurement:
The foundation of resistance
measurement, Ohm’s Law
For most applications you can use a basic
Ohm’s Law equation of I = V/R

3. 3
Sr.
no
Low Resistance
(<1 Ω)
Medium Resistance
(1Ω – 100kΩ)
High Resistance
(>100kΩ)
1 Kelvin’s Double
Bridge Method
Ammeter-Voltmeter
Method
Loss of Charge
Method
2 Potentiometer
Method
Wheatstone Bridge
Method
Megger
3 Ducter Ohmmeter Substitution Method Megohm bridge
Method
4 Carey- Foster Bridge
Method
Direct Deflection
Method
5 Ohmmeter Method
Some Resistance Measurement techniques:

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A. Digital Ohmmeter:
These are also known as digital multimeter for
resistance measurement
Measures current and voltage in an electronic
circuit. This meter is easy to read when
compared with the analog one.
Measures the resistance in micro ohm, ohms,
kilo-ohms, and mega ohms in a digital display.
Source: Digital micro ohmmeter
Tinsley Precision instruments

5. 5
Construction & Working:
Digital resistance meter is instrument which measure electrical
resistance. They use solid-state components and display values
digitally. Resistance, which is measured in ohms, is the
opposition to the flow of electric current of a conductor.
Fig. 1 Digital resistance meter

6. 6
Specifications:
Digital resistance meters typically display between three and seven
digits along with a leading number such as 0 or 1.
Some digital resistance meters allow users to adjust the sampling rate
or provide internal memory. Others include an auto-ranging feature
that automatically adjusts the measurement range.
Output options include general-purpose interface bus (GPIB), binary
coded decimal (BCD), and digital-to-analog (DA). RS232 is a standard
communication protocol for serial ports.

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Applications:
 Interface to computers and include integral monitoring
software for applications such as data acquisition.
 Programmable digital resistance meters allow users to set
values that trigger monitoring routines.
 Some digital resistance meters are used to monitor devices
such as resistance temperature detectors (RTDs). Others are used
to monitor electronic components such as transistors or diodes.

8. B. Digital Capacitance Meter:
 It was discovered by the scientist Ewald Georg von Kleist in
1745 and independently by the Dutch physicist Pieter van
Musschenbroek at about the same time, while in the process of
investigating electrostatic phenomena.
 There are different type of capacitance meters are available
which allows to measure the capacitance directly between 0.1
Pico farad and 20 microfarads.
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9. Capacitance Meter Definition:
The capacitance meter is one type of
electronic test instrument used for
measuring the capacitor in farads. There are
several methods to measure the
capacitance but the most accurate method
is the bridge method.
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Source: Nut Volts, Robert Reed

10. 10
 Schering Bridge for Capacitance Measurement:
 The Schering bridge is one type of AC bridge, which is used
to measure the unknown capacitance, relative permeability,
dissipation factor, and dielectric loss of a capacitor.
The main objective of this bridge is to find capacitance value.
 The main apparatus required for connection are trainer kit,
decade capacitance box, multimeter, CRO, and patch chords.

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Fig. 2 Schering bridge
Let, Z1, Z2,Z3 and Z4 are the impedances of arms DA, AB, CD and BC
respectively. The values of these impedances will be

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Substitute these impedance values in
the following balancing condition of
AC bridge.
By comparing the respective real &
imaginary terms of above equation,
we will get
By substituting the values
of R1,R2 and C3 in Eq. 1, we will get
the value of capacitor, C4. Similarly, by
substituting the values
of R2,C1 and C3 in Eq. 2, we will get
the value of resistor, R4.
… (1)
…. (2)
Z1/Z2 =Z3/Z4

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Advantages of Schering Bridge
 Compared to other bridges, the cost of this bridge is less
 The balanced equation can be obtained is independent of
frequency.
 At low voltages, it can measure small capacitors
Disadvantages of Schering Bridge
 There is difficulty in obtaining balance as C3 appears in
both equations.

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Fig. 3: Capacitance meter.
The phase difference between V
and VCx measured by the digital
phase meter is
𝜙 = tan-1 𝜔CxR = tan -1𝛼
Where 𝛼 = 𝜔CxR. Here, the phase
reading is not directly proportional
to the unknown capacitance Cx.
Simplified method:

15. Capacitance Meter Working Principle
Fig.4. Block diagram of Capacitance meter
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16. •Linear Capacitance Meter Circuit using 555 IC
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Fig. 5. Capacitance meter using Timer 555 IC
Cycle length of the square wave which is formed by 555 timers can be
calculated using the formula:
T =0.7 X Cx X (Resistor between pin 7 & 8 +2 X Resistor between pin 7 & 6)

17. • Features of digital capacitance meter:
The features of digital capacitance meter are
• Easy to read the measuring values
• High accuracy
• Under the strong magnetic field also the measurements are
possible
• Highly reliable
• Highly durable
• Lightweight
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18. • Digital Capacitance Meter Specifications
Display: LCD
Range: The range of the digital meter is from 0.1 PF to 20 mF
Battery: 9 volts and the battery life of the alkaline battery is
approximately 200hrs and zinc-carbon battery life is approx. 100hrs
Operating temperature: The operating temperature of the digital
CM is 0 degree C to 40 degree C.
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19. • Advantages
• Hardware requirements are less in Arduino based
capacitance meters
• Simple construction
• Small in size
• Less weight
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20. • Maintenance of the Capacitance Meter
• The meter should keep away from water and dust
• Don’t use the meters at high temperatures
• Don’t use the meters at strong magnetic places
• Don’t use the liquids or detergents to wipe the meters
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21. THANK YOU…
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References:
1) Digital Measurement Techniques, T. S. Rathore, Narosa Publishing
House
2) A Course in Electronic Measurements and Instrumentation, A.K.
Sawhney, Dhanpat Rai & Co. (P) Limited