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.
Advantages of strain gauges
Load Cells using strain gauges can be used to measure the load value applied to an object, while Prescale measures surface pressure
Load Cells (strain gauges)
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.
Roller (nip) load value
E.g. Dry film lamination adhesion process in substrate manufacturing
Load Cell
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.
Load value at stacking
E.g. Stacking process in substrates or multilayer ceramic devices manufacturing
Load Cell
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
Load Cell
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
Load Cell
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.
How to use
How to visually check pressure distribution with Prescale.
1
Cut the Prescale or Prescale Sheets into the shapes needed for measurement.
2
Insert the Prescale between the surfaces to be measured and apply pressure.
3
Remove the Prescale
4
You can now see the pressure and its distribution.
Quantification of pressure is also possible by utilizing dedicated tools, “FUJIFILM Prescale Mobile”!
Fujifilm has been supporting customers in various industries through pressure measurement since 1977, when the Prescale was launched.
If you have any questions, please feel free to contact us.
Free samples of various films are available from our official website.