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# “What is a strain gauge? Explanation of Purpose, Principle of Measurement, Merits, Calculation Formula and Examples of Use

## What is a strain gauge?

### What is a strain?

Strain is a measure of how much an object's shape or volume is displaced when a force is applied to it.

### Strain gauge’s Principle and Mechanism of Measurement with Strain gauges

This section describes the measurement principle and mechanism of strain gauges, which measure strain, in comparison with a tool used for similar applications, the pressure measurement film.

#### What is a strain gauge?

Strain gauges were created by utilizing the principle of strain.

When a certain force is applied to a metal to make it expand or contract, the electrical resistance changes accordingly.
The strain gauge measures the amount of strain by reading this electrical resistance and amplifying it to an electrical output.

What is pressure measurement film “Prescale”

Pressure measurement film is a film used to measure the load per unit area when force is applied to an object.
Fujifilm offers these films under the name of "Prescale”.

Prescale, sometimes called as “pressure indicating film”, “pressure inspecting film” or “pressure paper”, is a film that enables visualization and quantification of pressure on a surface.

Surface pressure can be easily measured simply by inserting the film between the desired areas.

### Purpose and Role of Strain gauges

Strain gauges are installed in Load Cells and other load measuring instruments.
The role of a strain gauge is to measure force by installing a strain gauge on a component called a "strain generator," which generates strain due to force, measuring the degree of strain and converting it into an electrical signal.

Load cells in which these strain gauges are used are often used together with “Prescale," a film that measures pressure.

Load Cells using strain gauges can be used to measure the load value applied to an object, while Prescale measures surface pressure

Measure the load value (point) applied to an object

Pressure Measurement Film

Measure the surface pressure applied to an object

### Strain gauge Calculation Formula

Strain can be obtained by the following formula.

ΔR (resistance change) ÷ R (original resistance) = K (gauge factor, proportionality constant) × ε (strain)

## Strain gauge Applications

Here are some examples of using load cells with strain gauges.

E.g. Dry film lamination adhesion process in substrate manufacturing

Check load values at both ends of the roller

#### Prescale

Insert Prescale between rollers and visually or quantitatively check pressure values, roller tilt, wattage, roller condition, etc. based on coloration.

Good

Uniform pressure is applied by the rollers.

Poor

Rollers hit each other strongly in some parts or rollers are scratched.

E.g. Stacking process in substrates or multilayer ceramic devices manufacturing

Check the load value of the shaft of a lamination press.

#### Prescale

Insert Prescale between the lamination press and the component to visually or quantitatively check for fragmentation, distribution, foreign matter, etc. on the press surface based on the coloring condition.

Good

Pressure is evenly applied by the mold.

Poor

Mold is hitting one side, weak hit in the center

### Contact condition

E.g. Crimping process with wafer bonding equipment in semiconductor manufacturing

Check the load value at the axis of the crimping jig

#### Prescale

Place Prescale between the material to be crimped and the jig, and visually or quantitatively check the parallelism of the jig, pressure irregularity, load value, etc. based on the coloration.

Good

Pressure is evenly applied.

Poor

Pressure is unevenly applied

E.g. Sealing process of outer packaging materials or activation process in lithium-ion battery manufacturing

Check load values at heat seal bar or a jig

#### Prescale

Visually or quantitatively check the parallelism of bars and jigs, pressure distribution, load values, etc., by placing a Prescale between the sealing bar and the sealing member or between the fixing jig and the pressurizing member.

Good

Horizontal parallelism is being achieved, and pressure is being applied evenly.

Poor

No parallelism, uneven pressure

## Prescale to solve strain gauge problems

### Strain gauge problems

A load cell equipped with a strain gauge can measure the force applied to that one point (one-dimensional), but it cannot see the pressure applied to a surface (two-dimensional).

If the pressure value on a surface is not controlled, it is not possible to grasp the inclination of the equipment or the overall trend, which may lead to product defects.

This is where the pressure measurement film "Prescale" comes in.

What is pressure measurement film “Prescale”

Prescale, sometimes called as “pressure indicating film”, “pressure inspecting film” or “pressure paper”, is a film that enables visualization and quantification of pressure on a surface.
Surface pressure can be easily measured simply by inserting the film between the desired areas.