• A multimeter consists of voltmeter, current meter and Ohm meter
• Current drawn by an electronic circuit is in the order of mill amperes. We can measure this using multimeter
• The supply voltage to DC motor is around 240 V, we can measure this voltage by using a multimeter
• We can do continue test of motor winding by using a multimeter

Multimeter:

• A multimeter is an electronic instrument. It is mainly used to measure the three basic electrical characteristics of voltage, current, and resistance.
• It can also be used to test continuity between two points in an electrical circuit.
• The multimeters can not be used to measure electrical quantities such as frequency, charge, etc.
• The multimeter has multi functionalities like, it acts like ammeter, voltmeter, and ohmmeter.
• It is a handheld device with a positive and negative indicator needle over a numeric LCD digital display.
• Multimeters can be used for testing batteries, household wiring, electric motors, and power supplies.

• The power factor meter measures the power factor of a transmission system.
• The power factor meter determines the types of load using on the line, and it also calculates the losses occur on it.
• The meter has one fixed coil which acts as a current coil. This coil is split into two parts and carry the current under test.
• The meter has two identical pressure coils A and B. Both the coils are pivoted on the spindle.
• The pressure coil A has no inductive resistance connected in series with the circuit, and the coil B has highly inductive coil connected in series with the circuit.
• The current in the coil A is in phase with the circuit while the current in the coil B lag by the voltage nearly equal to 90°.
• The meter has two deflecting torque one acting on the coil A, and the other is on coil B. The windings are so arranged that they are opposite in directions. The pointer is in equilibrium when the torques are equal.

Concept:

When two sinusoidal signals of the same frequency and magnitude are applied two both pairs of deflecting plates of CRO, the Lissajous pattern changes with the change of phase difference between signals applied to the CRO

When 0 < ϕ < 90o or 270o < ϕ < 360o 

The Lissajous pattern is of the shape of an Ellipse having a major axis passing through the origin from the first quadrant to the third quadrant.

 When 90o < ø < 180o or 180o < ø < 270o

The Lissajous Pattern is of the shape of an Ellipse having a major axis passing through the origin from the second quadrant to the fourth quadrant.

Explanation:
The Lissajous pattern on the screen of a CRO is an ellipse with a major axis in quadrant 1 and quadrant 3.

Note:

Cathode-Ray Oscilloscope (CRO):

CRO is a very fast X-Y plotter that shows the input signal versus another signal or versus time.

Applications:

The CROs are used to analyze the waveforms, transient, phenomena, and other time-varying quantities from a very low-frequency range to the radio frequencies.

Time Base Generator:

• It generates an output voltage or current waveform, which varies linearly with time.
• The horizontal velocity of a time base generator must be constant.
• The displayed signal should be varied with time.
• It makes the signal to sweep the beam horizontally across the screen.
• Then the displayed signal varies linearly with time.
• Hence the voltage is called Sweep Voltage.
• The Time Base Generators are called Sweep Circuits.

The time base signal in CRO is a Sawtooth signal.

Applications:

Time Base Generators are used in

• CRO
• Televisions
• RADAR displays
• Precise time measurement systems
• Time modulation, etc.

Important points:

• In CRO, the timebase signal is applied to X-plates in the X-Y mode operation only.
• In y-t mode operation, the Timebase signal is not connected.

Aquadag: 

• The bombarding electrons, striking the screen, release secondary emission electrons
• These secondary electrons are collected by an aqueous solution of graphite called Aquadag which is connected to the second anode
• It is the conductive coating on the screen
• Collection of secondary electrons is necessary to keep the CRT screen in a state of electrical equilibrium

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

• For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
• Count the number of cuts made by both lines
• The unknown to known frequency ratio can be measured as follows.

\(\dfrac{{{f_v}}}{{{f_h}}} = \dfrac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

Vertical cuts (nv) = 2

Horizontal cuts (nh) = 8

The frequency ratio of the vertical signal to the horizontal signal is

\(\dfrac{{{f_V}}}{{{f_H}}} = \dfrac{{{n_h}}}{{{n_v}}} = \dfrac{8}{2} = \dfrac{4}{1}\)

Concept:

Deflection sensitivity: The deflection sensitivity of a cathode ray tube is defined as the deflection of the screen per unit deflection voltage.

Deflection sensitivity, \(S = \frac{D}{{{E_d}}} = \frac{{L{l_d}}}{{2d{E_a}}}m/V\)

Where D = deflection of an electron beam on the screen in the Y direction in m

E_d = potential between deflecting plates in V

L = distance between the screen and the center of the deflecting plates in m

l_d = length of the deflecting plates in m

d = distance between deflecting plates in m

E_a = accelerating voltage in V

Deflection factor: Deflection factor of a CRT is defined as the reciprocal of sensitivity.

Deflection factor \(G = \frac{1}{S} = \frac{{2d{E_a}}}{{L{l_d}}}V/m\)

Application:

A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, i.e.

Transducers can be classified into the following types:

• Active or Passive Transducers
• Analog or Digital Transducers

Analog transducers:

• These transducers convert the input quantity into an analog output which is a continuous function of time
• Thus, a strain gauge, an L.V.D.T., a thermocouple or a thermistor may be called as Analog Transducers as they give an output which is a continuous function of time

Digital Transducers:

• These transducers convert the input quantity into an electrical output which is in the form of pulses and its, output is represented by 0 and 1

Pyrometer:

• Pyrometer, the device for measuring relatively high temperatures, such as are encountered in furnaces. Most pyrometers work by measuring radiation from the body whose temperature is to be measured.
• Radiation devices have the advantage of not having to touch the material being measured.
• Radiation Pyrometers are used to measure the temperature of red hot metals up to 3000°C.

1. LVDT:

A linear variable differential transformer (LVDT) is an electro-mechanical device used to convert small mechanical displacements (of the order of a few millimetres or fractions of a millimetre) into amplified electrical signals.

2. ​Strain Guage:

Strain Gauge is a passive transducer that converts a mechanical displacement into the change in resistance (R), inductance (L), or capacitance (C).

A piezoelectric transducer is used for measuring non-electrical quantities such as vibration, acceleration, pressure, and the intensity of sound.

3. Piezoelectric accelerometer:

• It is a sensor that is used to measure acceleration by using the piezoelectric crystal.
• Piezoelectric accelerometer generates a voltage based on acceleration applied.
• It consists of piezoelectric crystal which is supported by mass-spring dampers etc.