This document discusses sensors and actuators, providing classifications of common sensors. It focuses on displacement, position, and proximity sensors, describing four main types: potentiometer sensors, strain gauge sensors, capacitive sensors, and linear variable differential transformers (LVDTs). For each sensor type, it provides the underlying measurement principle, relevant mathematical expressions, and examples of applications. The document is intended as a reference for mechatronics and manufacturing automation.

2. SENSOR VS ACTUATOR
SensorNon Electrical IN
(Quantity)
Electrical OUT
(Signal)
ActuatorElectrical 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 :
𝑉𝑂 = 𝐼𝑅 𝐴
But 𝐼 =
𝑉𝑠
𝑅 𝐴+𝑅 𝐵
,
Therefore 𝑉0 =
𝑉𝑠 𝑅 𝐴
𝑅 𝐴+𝑅 𝐵
As we know that 𝑅 =
𝜌𝐿
𝐴
, where ρ is electrical
resistivity, L is length of resistor and A is area of
cross section
𝑉𝑂 =
𝑉𝑠 𝐿 𝐴
𝐿 𝐴 + 𝐿 𝐵

9. 1. POTENTIOMETER SENSOR
Applications:
• Control systems with a feedback loop
• Machine-tool controls, Elevators, Liquid-level
assemblies, Forklift trucks, Automobile
throttle controls
• Control of injection moulding machines,
Woodworking machinery, Printing, Spraying,
Robotics.
Source : NPTEL (Mechanical – Mechatronics and Manufacturing Automation)

10. 2. STRAIN GAUGE ELEMENT
The strain in an element is a ratio of change in length in the direction
of applied load to the original length of an element.
i.e. The strain changes the resistance R of the element.

11. 2. STRAIN GAUGE ELEMENT
Mathematical Expression :
Δ𝑅
𝑅
𝛼 𝜀 ⇒
Δ𝑅
𝑅
= 𝐺 𝜀
where G is the constant of proportionality and is
called as gauge factor.
This change in resistance can be detected by a
using a Wheatstone’s resistance bridge.
In the balanced bridge we can have a relation,
𝑅2
𝑅1
=
𝑅 𝑥
𝑅3
where 𝑅 𝑥 is resistance of strain gauge element,
𝑅2 is balancing/adjustable resistor, 𝑅1 and 𝑅3 are
known constant value resistors.

12. 2. STRAIN GAUGE ELEMENT
Applications:
• Experimental stress analysis and diagnosis on machines
and failure analysis.
• Multi-axial stress fatigue testing, residual stress and
vibration measurement, torque measurement, bending
and deflection measurement, compression and tension
measurement and strain measurement.
• As sensors for machine tools and safety in automotive.
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