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Measurement FundamentalsWhat are Displacement Sensors (Displacement Gauges) and Dimension Measurement Systems?

What are Displacement Sensors (Displacement Gauges)?

A displacement sensor (displacement gauge) is used to measure travel range between where an object is and a reference position. Displacement sensors can be used for dimension measurement to determine an object's height, thickness, and width in addition to travel range. Selecting the most appropriate equipment according to the application, required accuracy, and usage environment is necessary. Measurements with displacement sensors can be classified into two large categories: non-contact measurement using light or magnetic fields / sound waves, or contact measurement performed in direct contact with the target.

The principles and features for each method are as follows.

Item Non-contact type Contact type
Optical type Eddy current type Ultrasonic type Laser focus method
Detection targets Most targets Metal Most targets Most targets Solid
Measurement distance Normal Short Long Short Short
Accuracy High High Low High High
Response speed Fast Fast Slow Normal Slow
Dust, water, oil, etc. Normal Strong Normal Normal Strong
Measurement surface Small Normal Large Small Small

Various Applications

Displacement sensors (displacement gauges) are used for a wide range of purposes. Below are a few examples.

Intent Example
Thickness Measuring whether the thickness of rolled steel sheets is uniform, whether the thickness of laminated glass is within the standards, etc.
Height and step Measuring whether the height of aligned PCBs is uniform, and whether unusual steps on chips assembled on the PCBs are present.
Outer diameter Measuring the outer diameter of mass-produced cylindrical components to determine whether the components are acceptable or not.
Warpage and Flatness Measuring whether a glass substrate is warped, whether a polished metal component is flat, etc.
Stroke and positioning Measuring the stroke amount of a camera module, whether the target has arrived in the correct position within the processing equipment, etc.
3D Shape In addition to checking components for warpage, measuring for warpage in all directions on a flat surface rather than just one line.

Reflective Models

Photoelectric/proximity switch Displacement sensor
Present Not present Small Large Far Close

Thrubeam Model

Photoelectric/proximity switch Displacement sensor
Present Not present Small Large Placed in centre Placed near top

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