sme1912 week 3 linear n force
TRANSCRIPT
-
7/28/2019 SME1912 Week 3 Linear n Force
1/56
SME1912
EXPERIMENTAL
TECHNIQUES
Chapter 3 Part 1
Measurement of Linear Dimensions
& Forces
-
7/28/2019 SME1912 Week 3 Linear n Force
2/56
WHAT WILL BE
DELIVERED?
Methods of measurement for
1. Linear dimensions,
2. Mass, weight and forces,
3. Pressure and
4. Temperature
-
7/28/2019 SME1912 Week 3 Linear n Force
3/56
WHAT SHOULD STUDENTLEARN?
a. concept,
b. design,
c. application andd. limitation
of various apparatus for the measurement forlinear dimensions, forces, pressure and
temperature
-
7/28/2019 SME1912 Week 3 Linear n Force
4/56
PART 1
MEASUREMENT OFLINEAR DIMENSIONS
-
7/28/2019 SME1912 Week 3 Linear n Force
5/56
DEFINITION
What is linear?
-
7/28/2019 SME1912 Week 3 Linear n Force
6/56
UNITS OF MEASUREMENTOF LINEAR DIMENSION?
Meter
Foot
Metric system
-
7/28/2019 SME1912 Week 3 Linear n Force
7/56
TOOLS TO MEASURELINEAR DIMENSIONS
Ruler Caliper
Vernier calipers Screw gauges
Dial gauges
-
7/28/2019 SME1912 Week 3 Linear n Force
8/56
RULERS
Normal - straight Folding ruler
-
7/28/2019 SME1912 Week 3 Linear n Force
9/56
ACCURACY OF RULER
-
7/28/2019 SME1912 Week 3 Linear n Force
10/56
CALIPERS
outside caliper inside caliper
Used together with rulers
-
7/28/2019 SME1912 Week 3 Linear n Force
11/56
INTERESTING USE OF ACALIPER
-
7/28/2019 SME1912 Week 3 Linear n Force
12/56
VERNIER CALIPERS
-
7/28/2019 SME1912 Week 3 Linear n Force
13/56
Digital vernier caliper
-
7/28/2019 SME1912 Week 3 Linear n Force
14/56
Measuringoutside diameter
Measuring inside
diameter
Measuring depth
-
7/28/2019 SME1912 Week 3 Linear n Force
15/56
HOW TO READ A VERNIER
-
7/28/2019 SME1912 Week 3 Linear n Force
16/56
HOW TO READ A VERNIER
-
7/28/2019 SME1912 Week 3 Linear n Force
17/56
HOW TO READ A VERNIER
Scale reading = 3.70cm
Vernier reading = (0.1/10) x 4 = 0.04
Caliper reading = 3.74cm
-
7/28/2019 SME1912 Week 3 Linear n Force
18/56
SCREW GAUGE
-
7/28/2019 SME1912 Week 3 Linear n Force
19/56
HOW TO READ SCREW
GAUGES
Main scale = 3.00mmThimble reading = (0.5/50)x46 = 0.46
Gauge reading = 3.46
0.5
-
7/28/2019 SME1912 Week 3 Linear n Force
20/56
DIAL GAUGES(for thickness)
-
7/28/2019 SME1912 Week 3 Linear n Force
21/56
IMPORTANT NOTES
For small displacement Mechanism based on plunger and rack and
pinion system
-
7/28/2019 SME1912 Week 3 Linear n Force
22/56
THICKNESS GAUGES
RANGE & ACCURACY
-
7/28/2019 SME1912 Week 3 Linear n Force
23/56
PART 2
MEASUREMENT OF MASS,WEIGHT & FORCES
-
7/28/2019 SME1912 Week 3 Linear n Force
24/56
What is the concept of mass, weight and force
THE CONCEPT OF MASS &FORCE
-
7/28/2019 SME1912 Week 3 Linear n Force
25/56
Mass defined
Mass (symbolized m) is a dimensionless quantity
representing the amount of matter in a particle or
object.
Mass is measured by determining the extent to which a
particle or object resists a change in its direction or
speed when a force is applied. Isaac Newton statedThe standard unit of mass in the International System
(SI) is the kilogram (kg).
-
7/28/2019 SME1912 Week 3 Linear n Force
26/56
EQUIPMENT TO MEASURE
MASS
-
7/28/2019 SME1912 Week 3 Linear n Force
27/56
EQUIPMENT TO MEASURE
MASS
-
7/28/2019 SME1912 Week 3 Linear n Force
28/56
-
7/28/2019 SME1912 Week 3 Linear n Force
29/56
Precision balances
-
7/28/2019 SME1912 Week 3 Linear n Force
30/56
Mass Measurement PrincipleIn its conventional form, this
class of measuringinstrument compares the
sample, placed in a weighing
pan (weighing basin) and
suspended from one end of a
beam with a standard mass or
combination of standard
masses in a scale pan (scale
basin) suspended from the
other end
-
7/28/2019 SME1912 Week 3 Linear n Force
31/56
To weigh an object in the measuring pan, standard
weights are added to the scale pan until the beam isin equilibrium as closely as possible. Then a slider
weight usually present is moved along a scale on or
parallel to the beam (and attached to it) until finebalance is achieved. The slider position gives a fine
correction to the mass value
Standard weight
Slider weight
-
7/28/2019 SME1912 Week 3 Linear n Force
32/56
The arm from which the object to be weighed (the load) is hung is
short and is located close to the pivot point. The other arm is longer,
is graduated and incorporates a counterweight which can be moved
along the arm until the two arms are balanced about the pivot, atwhich time the weight of the load is indicated by the position of the
counterweight
Steelyard Balance
The steelyard comprises a balance
beam which is suspended from a
pivot (or fulcrum) which is very
close to one end of the beam. The
two parts of the beam which flank
the pivot are the arms.
-
7/28/2019 SME1912 Week 3 Linear n Force
33/56
Special notesPrecise measurements are achieved by
ensuring that the fulcrum of the beam is friction-free (a knife edge is the traditional solution),
by attaching a pointer to the beam which amplifiesany deviation from a balance position; and finally
by using the lever principle, which allowsfractional weights to be applied by movement of asmall weight along the measuring arm of the beam
allowing for the buoyancy in air, whose effectdepends on the densities of the weights and thesample.
-
7/28/2019 SME1912 Week 3 Linear n Force
34/56
Weight & Force defined
Weight (symbolized w) is a quantity representingthe force exerted on a particle or object by anacceleration field, particularly the gravitationalfield of the Earth at the surface. In the
International System of Units (SI), weight can beexpressed in terms of the force, in newtons,exerted on a mass in a gravitational field.
The weight of an object is the force of gravity onthe object and may be defined as the mass timesthe acceleration of gravity, w = mg.
-
7/28/2019 SME1912 Week 3 Linear n Force
35/56
use a spring with a known spring constant
(Hooke's law) and measure the
displacement of the spring to produce anestimate of the gravitational force applied
by the object.
typically measure force
cannot be used for commercial
applications unless their springs aretemperature compensated or used at a
fairly constant temperature
Spring Scale/Balance
-
7/28/2019 SME1912 Week 3 Linear n Force
36/56
A proving ring consists
of an elastic ring inwhich the deflection ofthe ring when loaded
along a diameter ismeasured by means of amicrometer screw and a
vibrating reed.
The Proving Ring
-
7/28/2019 SME1912 Week 3 Linear n Force
37/56
The proving ringconsists of two main
elements, the ringitself and thediameter-measuringsystem,
Forces are applied tothe ring through theexternal bosses.
The resulting change
in diameter, referredto as the deflection ofthe ring, is measuredwith a micrometerscrew and thevibrating reedmounteddiametrically withinthe ring.
-
7/28/2019 SME1912 Week 3 Linear n Force
38/56
Force TransducerA device that provides an output quantity having a
determined relationship to the force
some materials change their electrical resistance
when mechanically deformed and can thus be
used as force transducers provided there is a
means available to measure the resistance
change
-
7/28/2019 SME1912 Week 3 Linear n Force
39/56
Strain Gauges For Force
Transducers
gluing such a component to the side of the metal
block in the above example effectively scales-down
the 'squeezing' force applied to it - allowing it to
survive much higher forces
-
7/28/2019 SME1912 Week 3 Linear n Force
40/56
A load cell is an electronic device (transducer) that is
used to convert a force into an electrical signal.
It happens in two stages; (1)mechanical force is sensed
is using a strain gauge, (2) the strain gauge converts the
deformation (strain) to electrical signals.A load cell consists 1 - 4 strain gauges in a wheatstone
bridge configuration, The output of the transducer is
plugged into an algorithm to calculate the force appliedto the transducer.
Load Cells
-
7/28/2019 SME1912 Week 3 Linear n Force
41/56
-
7/28/2019 SME1912 Week 3 Linear n Force
42/56
Torque Measurement
Torque is measured by either sensing theactual shaft deflection caused by a twistingforce, or by detecting the effects of thisdeflection. The surface of a shaft under torquewill experience compression and tension, asshown.
-
7/28/2019 SME1912 Week 3 Linear n Force
43/56
Torque Measurement By
Strain Gauges
To measure torque, strain gage elements usuallyare mounted in pairs on the shaft, one gaugemeasuring the increase in length (in the direction inwhich the surface is under tension), the other
measuring the decrease in length in the otherdirection.
-
7/28/2019 SME1912 Week 3 Linear n Force
44/56
Excitation voltage for the strain gage is
inductively coupled, and the strain gageoutput is converted to a modulated pulsefrequency. Maximum speed of such anarrangement is 15,000 rpm.
The torquesensor can beconnected toits power
source andsignalconditioningelectronics via
a slip ring
-
7/28/2019 SME1912 Week 3 Linear n Force
45/56
Proximity and displacement sensors also candetect torque by measuring the angulardisplacement between a shaft's two ends. Byfixing two identical toothed wheels to the
shaft at some distance apart, the angulardisplacement caused by the torque can bemeasured. Proximity sensors or photocellslocated at each toothed wheel produce
output voltages whose phase differenceincreases as the torque twists the shaft
Torque Measurement By
Angular Displacement
-
7/28/2019 SME1912 Week 3 Linear n Force
46/56
DYNAMOMETERS TOMEASURE ENGINE POWER
Consists of an absorption unit, plus a means to measure
torque and rotational speed. It has some type of rotor in a
housing. The rotor is coupled to the engine under test and is
free to rotate. Some means is provided to develop a braking
torque between dynamometer's rotor and housing. The
means for developing torque can be frictional, hydraulic,
electromagnetic etc. according to the type of
absorption/driver unit
-
7/28/2019 SME1912 Week 3 Linear n Force
47/56
Dynamometer Setup
-
7/28/2019 SME1912 Week 3 Linear n Force
48/56
Types of Dynamometers
Absorption Driving
Transmission
-
7/28/2019 SME1912 Week 3 Linear n Force
49/56
Absorption Dynamometer
Absorption dynamometers produce the torque that they
measure by creating a constant restraint to the turning of ashaft by either mechanical friction, fluid friction, or
electromagnetic induction. A Prony brake develops
mechanical friction on the periphery of a rotating pulleyby means of brake blocks that are squeezed against the
wheel by tightening the bolts...
-
7/28/2019 SME1912 Week 3 Linear n Force
50/56
The Prony Brake
-
7/28/2019 SME1912 Week 3 Linear n Force
51/56
Driving Dynamometer
A dynamometer can also be used to determine the torque
and power required to operate a driven machine such as apump. In that case, a motoringordrivingdynamometer is
used
-
7/28/2019 SME1912 Week 3 Linear n Force
52/56
Transmission Dynamometer
A dynamometer in which power is measured, without
being absorbed or used up, during transmission
The transmission dynamometer transmits the force
while measuring the elastic twist of the output shaft.
Also called torsion meter as it measure the torque on a
shaft, and hence the horse power of an engine, esp. of a
marine engine of high power, by measuring the amount of
twist of a given length of the shaft
-
7/28/2019 SME1912 Week 3 Linear n Force
53/56
Types of AbsorptionDynamometers
Mechanical Electrical
Hydraulic
-
7/28/2019 SME1912 Week 3 Linear n Force
54/56
mg
BHP = Tx = Tx2N
but T = mgL
BHP = mgLx2N
L
Mechanical Absorption Dyno. -The Prony Brake
Electrical Dynamometer
-
7/28/2019 SME1912 Week 3 Linear n Force
55/56
Electrical Dynamometer
-
7/28/2019 SME1912 Week 3 Linear n Force
56/56
Hydraulic/water Brake Dyno.The housing
attempts to
rotate inresponse to the
torque
produced but
is restrained by
the scale or
torque
metering cellwhich
measures the
torque.