Torque
Measurement
Presented By
Abdalkareem Abdelwase
Amin Kamal Ahmed
Ayoub Eltoum Ayoub
Mohamed Zuhair Mohamed
/ 074045
/ 074019
/ 054027
/ 064064
Introduction
lever
folcrum
Introduction (cont.)
• Motion in which an entire object
moves is called translation.
• Motion in which an object spins
is called rotation.
• An object can both rotate and
translate.
Torque
 A torque is an action
resulting from a force that
causes objects to rotate.
 Torque is not the same
thing as force.
 Torque is created by force,
but torque also depends on
the point of application and A door pushed at its handle will easily turn
the direction of the force. and open, but a door pushed near its hinges
will not move as easily.
Torque (cont.)
• The point or line about which an
object turns is its center of rotation.
• A force applied far from the center
of rotation produces a greater
torque than a force applied close to
the center of rotation.
• Doorknobs are positioned far from
the hinges to provide the greatest
amount of torque for a given force.
Torque (cont.)
• Torque is created when the line
of action of a force does not
pass through the center of
rotation.
• The line of action is an
imaginary line that follows the
direction of a force and passes
though its point of application.
Torque (cont.)
• To get the maximum torque,
the force should be applied in
a direction that creates the
greatest lever arm.
• The lever arm is the
perpendicular distance
between the line of action of
the force and the center of
rotation
The torque created by force
• The torque created by a force is equal to the lever
arm length times the magnitude of the force.
• Torque is usually represented by the lower case
Greek letter “tau,” t.
• When calculating torque, if the line of action passes
through the center of rotation, the lever arm is zero,
and so is the torque, no matter how large a force is
applied.
Calculating Torque
Lever arm length (m)
Torque (N.m)
t=rxF
Force (N)
Calculating Torque (cont.)
• If more than one torque acts on
an object, the torques are
combined to determine the net
torque.
• If the torques make an object spin
in the same direction, clockwise
or counterclockwise, they are
added together.
Why do we need
to measure
torque ?
 Measurement of applied torque is of fundamental
importance in a rotating shaft.
 It will ensure that the design of the rotating
element is adequate to prevent failure under shear
stress.
 Torque measurement is necessary to know the
power transmitted by the rotating shafts
How to measure the
Torque?
Four methods for
measuring the torque !
 Measuring the reaction force in cradled
shaft bearing.
 Measuring ‘prony brake’ method.
 Measurement of induced strain.
 Optical torque measurement.
Measuring the reaction force
in cradled shaft bearing.
the reaction force in cradled shaft bearing cont…
The torque transmission through a shaft contains both
power
Source and absorber power .
The torque is measured by cradled either the power
source or the Power absorber end of the shaft bearing
and then measuring the reaction force(F) and the arm
length(L).
Then T(torque) = F.L
2- prony brake method :
If the measured force in the spring balance is Fsb.
Then the effective force Feff
exerted by the rope on the shaft is given by:
Feff = mg- Fsb
If the radius of the shaft is Rsh and that of the rope is
Rro then the effective radius

Reff = Rsh+Rro
 Rsh≡radius of shaft
Rro ≡radius of rope
Prony brake method:
Finally the torque in this method will
given by:
T= Feff . Reff
Optical torque
measurement
Optical torque measurement cont…
• Optical techniques for torque measurement
have become available recently with the
development of laser diodes and fiber-optic
light transmission systems.
Optical torque measurement cont…
The advantages:
 Their small physical size.
The cost of such instruments is relatively low.
 The most effective way and more accurate
than previous methods.
 The optical torque sensor is a non-contact
sensor
Optical torque measurement cont…
The disadvantages:
 It requires slightly more sophisticated
processing electronics.
It requires an air gap with a clear optical
path.
Measuring the Strain Produced in a
Rotating Shaft due to applied Torque
 This method basically depends on the strain gauges,
so let us take a look at what do we mean by a strain
gauge??!!
Here we GO!!
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
 A strain gauge is a small electrical element printed on a non-conductive
substrate.
 The pattern of the element is arranged so that if the gauge is stretched (or
compressed) in one direction (along operating axis of the gauge), the
resistance of the element increases (or decreases) in relation to that
stretch.
 A stretch in which it is perpendicular to the axis of the strain gauge has
little effect on the resistance of the element.
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
If a gauge is bonded to the shaft, with its axis aligned with the
direction in which the shaft material stretches when a torque
is applied, the strain gauge will also stretch and therefore the
element will increase in resistance.
If a gauge is bonded to the shaft, with its axis aligned with the
direction in which the shaft material compresses when a
torque is applied, the strain gauge will also compress and
therefore the element will decrease in resistance.
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
In the Torque transducer, strain gauges making up four
resistive elements are bonded to the shaft. Two elements are
aligned with the direction of Tension (stretch). The remaining
two are aligned with the direction of Compression.
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
The four resistive elements are electrically connected in a
‘Wheatstone Bridge’ configuration.
The Wheatstone Bridge configuration is appropriate for
measurement of the small resistance changes produced in the
strain gauges, as the combination increases and decreases in
resistance it produces a change in output voltage.
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
Now let’s Go ahead with the
Method!!
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
 It is the most common method used for torque measurement.
 It doesn’t disturb the measured system by introducing friction
torque the same way as do the last two methods described.
 That’s because it converts torque into an electrical signal.
Electrical signal is preferred over the mechanical signal
because of:
1) It can be transmitted over a long distance.
2) It can be digitized & displayed.
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
It consists of:
1.Mechanical System (shaft).
2.Sensors (strain gauges).
Measuring the Strain Produced in a Rotating
Shaft due to applied Torque (cont’d)
The four strain gauges are mounted on two perpendicular 45°
helixes.
The strain gauges 1 and 3 are mounted on the right hand helix
and these are under elongation.
The strain gauges 2 and 4 are mounted on the left hand helix
and these are under compression.
References
 Measurement & Instrumentation
Principles by Alan.S.Morris.
 Measurement , Instrumentation and
Sensors Handbook.
 www.scribd.com and other internet
Resources.
Special Thanks To
Professor: Alok Barua,
Department of
Electrical Enginnering,
Indian Institute of
Technology, (IIT)
Kharagpur.
Thank You!!