How do I perform a gloss measurement with a gloss sensor?

The operation of gloss sensors and associated software.

Image of the GLOSS-15-16 from Sensor Instruments

Gloss sensors perform a gloss measurement on a certain surface. How can the measured glossiness be expressed? With the gloss factor. With the help of a gloss factor it is possible to monitor the quality of a product. For example: the gloss factor of stainless steel, copper or aluminium but also that of laminate, veneer layers or sheets tells something about the roughness of the surface. This makes an after-processing of the materials unnecessary because the product will already fit the necessary specifications. The spray quality can be monitored by measuring the gloss of a layer of paint; the so-called orange peel will have a lower gloss factor as a result of this.

When the gloss factor is measured on multiple positions, it is possible to determine whether the quality of the product is distributed equally. This prevents production errors, saves paint or material and elevates production efficiency.

Multiple sensors in order to measure gloss on multiple spots

How does a gloss measurement or gloss inspection work?

The gloss of a product, is an apparent trait. Specifically when the surface of the material is so smooth that the relief is smaller than the wavelength of visible light. Also known as GLOSS effect. The rule of thumb for gloss measurement is: angle of incidence = angle of reflection. A greater angle α indicates that the surface reflects worse. For the gloss measurement it is important that the angle of incidence is standardized. Standards are 20°, 60°, 75° and 85°.

Angle of incidence of 20°

Angle of incidence of 60° and 75°

Angle of incidence at 85°

This angle of incidence is used frequently for the measurement of high glossy materials, such as aluminium, copper, stainless steel, plastic foil or glass plates. These materials have a different type of reflection, compared to matte surfaces. Thus it requires another angle. 

A gloss measurement with a 20° angle of incidence.

These are the most frequently used angles of incidence. Almost all materials can be measured for gloss from glossy to light matte. Specifically, the paper industry makes use of the sensor. When the gloss has to be measured conform the TAPPI norms the angle of incidence of 75° has to be used.

A gloss measurement with a 60° angle of incidence.

This angle of incidence is used frequently for the measurement of high flossy materials, such as aluminium, copper, stainless steel, plastic foil or glass plates. The glass processing industry and metal industry work with materials that make it hard to shine the sensor light directly on them.

A gloss measurement with a 85° angle of incidence

How do gloss sensors work?

By installing a GLOSS sensor in the production line, the quality of the product can be measured. But how exactly does this sensor work?

The GLOSS sensor is basically a light source (transmitter) of white LED light. Which is sent to the material at a specific angle. The reflection is received in the receiver. By using a beam splitter, part of the emitted light is received by a reference receiver. This is then compared to the value that the actual receiver gets. The gloss value is determined on the basis of these.

Processing gloss inspection data with software

The gloss sensor can easily be configured. For this, the Scope software from Sensor Instruments is provided. You can also use your own software and read the data output directly. The included software displays the most important parameters, like the value of the reference receiver and of the receiver for direct reflection. In addition, parameters for a trigger can be set in your process. If other gloss sensors are used which have to be compared, it is possible to calibrate the sensors mutually.

A screen display of the software that is used for a gloss measurement.

Handheld vs. inline gloss sensors

In the market there are different types of sensors for performing gloss measurements or inspections. One of the fundamental differences is the method of use. A well-known example is the handheld gloss sensor. This is a handheld device with which an operator or quality officer can inspect or measure a material for its gloss factor. The disadvantage that comes with these sensors is the fact that it is only usable before or after the processing of the material.

This is where inline gloss sensors are the better choice. These sensors not only function standalone but also before, during and after the processing of the material.

But this is not the only advantage that inline gloss sensors have with which they prevail over their handheld counterparts. Examples are:

  • Insusceptibility to external light sources and a non-contact measurement or inspection;
  • Multiple outputs, analog as well as digital;
  • Support for multiple serial interfaces: RS232, USB and Ethernet;
  • The internal light source can be adjusted to the surface for an optimal measurement or inspection.

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