1) An electrical tachometer measures angular velocity using electrical transducers instead of mechanical components, providing advantages like fast response, no inertia effects, and less power loss. 2) An eddy current tachometer works by inducing eddy currents in an aluminum cup using a rotating permanent magnet, creating torque that is proportional to rotational speed. 3) The torque causes deflection of the cup and pointer against a spring, with the pointer position on a calibrated scale indicating shaft speed. Eddy current tachometers can measure speeds up to 12,000 rpm and are used in automobile speedometers and modified versions in locomotives.

1. Shri S’ad Vidhya Mandal Institute Of
Technology
Presented by
Sojitra Samarth 150450119161
Presentation on Electrical tachometer

2. Tachometer:-It is an instrument used for measurement of angular velocity of shaft either
by registering the total number of revolutions during the period of contact, or by
indicating direct the number of revolutions per minute.
Electrical tachometer
The mechanical tachometers impose a load on the shafts to which they are connected.
Hence it absorbs power. Therefore, it can not be used for applications involving small
powers.
On account of inertia of mechanical parts, the mechanical tachometers are not able to
follow the sudden variations in the speed. Hence it indicate only the average speed over
the particular interval of time.
Therefore mechanical tachometers cannot be used in applications where instantaneous
indication of speed is desired.
The electrical tachometers are preferred over mechanical tachometer for all
applications, these tachometers offer all advantages associated with electrical
transducers like no inertia effect, fast response, less power loss of machine whose speed
to be measured.

3. Electric
tachometer
Eddy current
Tachogenerators
D.C tachometer
A.C tachometer

4. Eddy current or drag cup tachometer
 Eddy current tachometer works on the principle that when the permanent magnet
(attached with rotating shaft) rotates in a drag cup or disc hold close to the magnet, the
eddy current is induced which produces a torque in the drag cup.
 This torque that tends to turn cup against spring.
 This deflection is proportional to the emf, induced and hence proportional to speed of
shaft. '
 Eddy current tachometer consists of a
permanent magnet which coupled to the
machine shaft whose speed to be
measured as shown in Fig.
 The magnet rotates within an
aluminium cup, to which a pointer is
fixed through spiral spring.

5.  The spring provides the necessary torque to the aluminium cup.
 When the permanent magnet rotates along with shaft, the eddy current
induced in the cup, which causes the torque or drag.
 This drag or torque that tends to turn the cup against Spiral Spring. The
deflection of cup is indicated by pointer which represents the speed of
shaft on calibrated scale.
 This type of tachometer measure speed upto 12000 rpm.

6. Advantages :
(1) It has a linear relationship between output and rotational speed.
(2) It is rugged and inexpensive.
(3) It requires less maintenance.
(4) It gives ripple free output.
Disadvantages :
(1) These tachometer are hard to calibrate.
(2) At high speed, it has a non-linear relationship between speed and output.
Applications :
(1) Automobile speedometer works base on this principle.
(2) Locomotive speed is measured by this tachometer after some modifications.