Sensors (Potentiometer and Strain Gauge)

A brief about Potentiometer and Strain Gauge Sensor.

2. SENSOR VS ACTUATOR
Sensor
Non Electrical IN
(Quantity)
Electrical OUT
(Signal)
Actuator
Electrical IN
(Signal)
Non Electrical OUT
(Quantity)
Source : P.P.L. Regtien(Auth.) -Sensors for Mechatronics(2012)

3. SENSORS CLASSIFICATION
1.Displacement, Position & Proximity
2.Velocity and Motion
3. Force
4.Fluid Pressure
5.Liquid Flow
6.Liquid Level
7.Temperature

4. Measures the length of the straight line
between two defined points.
Measures the change of position relative to a
reference point.
Measures the co-ordinates of a specified point
of an object in a specified reference system.
•Determines the sign (positive or negative) of the
linear distance between an object point and a
fixed reference point; also called a switch.
•A contact-free displacement or distance sensor for
short distances (down to zero)
DISTANCE SENSOR
DISPLACEMENT SENSOR
POSITION SENSOR
PROXIMITY SENSOR
Source : P.P.L. Regtien(Auth.) -Sensors for Mechatronics(2012)

5. DISPLACEMENT SENSORS
1. Potentiometer Sensor
2. Strain Gauge Element
3. Capacitive element based Sensor
4. Linear Variable Differential Transformer (LVDT)

6. POSITION & PROXIMITY SENSORS
1. Eddy current proximity sensor
2. Inductive proximity switch
3. Optical Encoder
4. Pneumatic Sensor
5. Proximity Switch
6. Hall effect sensor

7. 1. POTENTIOMETER SENSOR
Principle:Conversion of mechanical
displacement into an electrical signal.

8. 1. POTENTIOMETER SENSOR
Mathematical Expression :
??????
??????=????????????
�
But ??????=
????????????
??????�+??????�
,
Therefore ??????
0=
??????????????????�
??????�+??????�
As we know that ??????=
????????????
�
, where ρ is electrical
resistivity, L is length of resistor and A is area of
cross section
??????
??????=
??????
????????????
�
??????
�+??????
�

9. 1. POTENTIOMETER SENSOR
Applications:
•Controlsystemswithafeedbackloop
•Machine-toolcontrols,Elevators,Liquid-level
assemblies,Forklifttrucks,Automobile
throttlecontrols
•Controlofinjectionmouldingmachines,
Woodworkingmachinery,Printing,Spraying,
Robotics.
Source : NPTEL (Mechanical –Mechatronics and Manufacturing Automation)

10. 2. STRAIN GAUGE ELEMENT
Thestraininanelementisaratioofchangeinlengthinthedirection
ofappliedloadtotheoriginallengthofanelement.
i.e.ThestrainchangestheresistanceRoftheelement.

11. 2. STRAIN GAUGE ELEMENT
MathematicalExpression:
Δ??????
??????
????????????⇒
Δ??????
??????
=????????????
whereGistheconstantofproportionalityandis
calledasgaugefactor.
Thischangeinresistancecanbedetectedbya
usingaWheatstone’sresistancebridge.
Inthebalancedbridgewecanhavearelation,
??????
2
??????
1
=
??????
??????
??????
3
where??????
??????isresistanceofstraingaugeelement,
??????
2isbalancing/adjustableresistor,??????
1and??????
3are
knownconstantvalueresistors.

12. 2. STRAIN GAUGE ELEMENT
Applications:
•Experimentalstressanalysisanddiagnosisonmachines
andfailureanalysis.
•Multi-axialstressfatiguetesting,residualstressand
vibrationmeasurement,torquemeasurement,bending
anddeflectionmeasurement,compressionandtension
measurementandstrainmeasurement.
•Assensorsformachinetoolsandsafetyinautomotive.
Source : NPTEL (Mechanical –Mechatronics and Manufacturing Automation)

13. REFERENCES
1.NPTEL –Mechanical –Mechatronics and Manufacturing
Automation
2.P.P.L. Regtien(Auth.) -Sensors for Mechatronics(2012)
3.W. Bolton (Auth.) -Mechatronics Electronic control systems in
mechanical and electric engineering