URDANETA CITY UNIVERSITY

COLLEGE OF ENGINEERING AND ARCHITECTURE

1st Semester A.Y. 2024-2025

INDUSTRIAL ELECTRONICS
Written Report
FORCE AND STRAIN TRANSDUCER

Members:
Sharia Kim Mejia
Kyle Christian Maines
Jeaneia Pearl Mamaril

ENGR. DINMAR LINWEL R. CABURAL, ECT

Instructor

Introduction
A sensor is an object whose purpose is to detect events or changes in its environment, and
then provide a corresponding output. Sensors typically use electrical or optical signals as
output.

Force Gauge
A force gauge is a small measuring instrument used to measure the force during a push or
pull test.
There are two kinds of force gauges:
-Digital Force Gauge
-Mechanical force gauges

Digital Force Gauges

• Piezoelectric Sensor
• Strain Gauge Sensor

Piezoelectric Sensor
History: Piezoelectric effect was first proven in 1880 by the French Physicist brothers
Pierre and Jacques Curie .
In the 1950s manufacturers begin to use the piezoelectric effect.

Mechanism 1/2
The charges in a piezoelectric crystal are exactly balanced The effects of the charges exactly
cancel out, leaving no net charge on the crystal faces.

Mechanism 2/2
If crystal squeezed, the charges are forced to be out of balance
By squeezing the crystal, a voltage is produced across its opposite faces-
and that's piezoelectric effect.
Applications:
Industrial and aerospace: Used in medical devices like nebulizers, infusion pumps,
and ultrasound equipment.
Automotive: Used in automotive systems to monitor vehicle safety and performance
Consumer electronics: Used in smartphones, tablets, and gaming controllers to detect
touch and pressure.
Structural health monitoring: Used to monitor the structural health of airplanes,
buildings, and bridges.
Industrial equipment: Used to detect force, strain, motion, and other variables in
harsh environments.
Defense applications: Used in guidance systems, depth sounders, and sonar
equipment.

Strain Gauge Sensor

History: Invented by Edward E. Simmons and Arthur C. in 1938

• A strain gauge is a device used to measure strain on an object

• Strain can be related to stress force
• As the foil is subjected to force, the resistance of the foil changes in a defined way.

Mechanism 1/3
Initial State:
• No extension
 • Resistance zero
• No compression

Mechanism 2/3
If a strip of conductive metal is stretched, it will result in an increase of electrical resistance.

Mechanism 3/3
If a strip of conductive metal is broaden and shorten, it will result in a
decrease of electrical resistance

Application:
Aerospace: Measuring stress and strain in aircraft during flight, including wings, control
surfaces, and engine racks
Rail: Monitoring stress and strain on railway lines
Civil engineering: Measuring stress in structural components of bridges and buildings
Load cells: Measuring strain and stress to determine weight and quantities
Circuit boards: Measuring stress on electric circuit boards and other confined spaces
Medical devices: Measuring blood pressure, used in dialysis machines, syringe pumps,
and force feedback crutches
Rotating equipment: Measuring torque applied by motors, turbines, and engines
Materials testing: Used in materials testing
Construction: Used in construction
Robotics: Used in robotics
Architectural engineering: Used in architectural engineering

Mechanical force gauges

• Spring scale
•Strain Transducer

Spring scale
History: The first spring balance was made around 1770 by Richard Salter of Bilston.
In 1838 they obtained the spring balance patent.

Definition
• A spring scale is a type of weighing scale
• It consists of:
• Spring fixed at one end
• Hook to attach an object at the other
• The scale markings are equally spaced
•Spring balances come in different sizes
• Small scales that measure newton will have a less firm spring
• Larger ones that measure tens, hundreds or thousands of newton or even more depending
on the scale of newton used.

Mechanism
• Measure only weight
• A spring scale will only read correctly in a frame of reference
• It works by Hooke's Law

Applications:
Weighing heavy loads
Measuring force
Laboratory experiments
Determining the weight of catches
Weighing ingredients
Bathroom scales
Strain Transducer
A strain gauge is an example of passive transducer that converts a mechanical displacement
into a change of resistance

Structure
•The majority of strain gauges are foil types, available in a wide choice of shapes and sizes
to suit a variety of applications.
•They consist of a pattern of resistive foil which is mountedon a backing material.

Working
The strain gauge is connected into a Wheatstone Bridge circuit. The change in resistance is
proportional to applied strain and is measured with Wheatstone bridge.

Working
The sensitivity of a strain gauge is described in terms of a characteristic called the gauge
factor, defined as unit change in resistance per unit change in length, or

Gauge factor is related to Poisson's ratio u by,

TYPES
Based on principle of working for
•Mechanical
•Electrical
•Piezoelectric

MECHANICAL STRAIN GAUGE

It is made up of two separate plastic layers. The bottom layer has a ruled scale on it and the
top layer has a red arrow or pointer. One layer is glued to one side of the crack and one layer
to the other. As the crack opens, the layers slide very slowly past one another and the pointer
moves over the scale. The red crosshairs move on the scale as the crack widens.
Application:
Quality control: Used to evaluate the strength, hardness, and durability of materials
R&D: Used to verify the safety and operability of products and parts
Compliance: Used to ensure compliance with industry standards
Friction testing: Used to measure friction
Door opening: Used to test how much force is required to open a door
Wire strength: Used to test the strength of wire

ELECTRICAL STRAIN GAUGE

• When an electrical wire is stretched within the limits of its elasticity such that it does not
break or permanently deform, it will become narrower and longer, changes that increase its
electrical resistance end-to-end.
• Strain can be inferred by measuring change in resistance.

Application: Commonly used in structural health monitoring, load cells, and mechanical
testing. They measure the deformation of materials under stress.

PIEZOELECTRIC STRAIN GAUGE

Piezoelectric generate electric voltage when strain is applied over it. Strain can be calculated
from voltage. Piezoelectric strain gauges are the most sensitive and reliable devices.

Application: Used in dynamic measurements such as vibration analysis and impact

testing. They convert mechanical stress into electrical charge, making them suitable for high-
frequency applications.

Based on mounting:
•Bonded strain gauge
•Unbonded strain gauge

BONDED STRAIN GAUGE

A bonded strain-gage element, consisting of a metallic wire, etched foil, vacuum-deposited
film, or semiconductor bar, is cemented to the strained surface.
Application: Typically employed in situations where accurate and stable measurements
are needed. They are bonded to the surface of the material being tested, making them ideal
for structural testing and research.

UNBONDED STRAIN GAUGE

The unbonded strain gage consists of a wire stretched between two points in an insulating
medium such as air. One end of the wire is fixed and the other end is attached to a movable
element.

Application: Used for measuring large deformations and in applications where the gauge
cannot be attached directly to the material. Common in experimental mechanics and non-
destructive testing.

Based on construction :
•Foil strain gauge
•Semiconductor strain gauge
•Photoelectric Strain gauge

FOIL STRAIN GAUGE

The foil strain gage has metal foil photo-etched in a grid pattern on the electric insulator of
the thin resin and gage leads attached.

Application: Widely used in both laboratory and industrial settings. They offer high
accuracy and stability, making them suitable for load cells, pressure transducers, and torque
measurements.

SEMICONDUCTOR STRAIN GAUGE

For measurements of small strain, semiconductor strain gauges, so called piezoresistors, are
often preferred over foil gauges. Semiconductor strain gauges depend on the piezoresistive
effects of silicon or germanium and measure the change in resistance with stress as opposed
to strain.

Application: Used in high-sensitivity applications due to their greater gauge factor

compared to metallic gauges. Commonly found in microelectronics, sensor applications, and
advanced materials testing.

PHOTOELECTRIC STRAIN GAUGE

The photoelectric gauge uses a light beam, two fine gratings, and a photocell detector to
generate an electrical current that is proportional to strain. The gage length of these devices
can be as short as 1/16 inch, but they are costly and delicate.

Application: Utilized in applications where non-contact measurement is crucial, such as

in rotating machinery or delicate structures. They measure strain by detecting changes in
light patterns.