Factors to consider when selecting non-contact colour measurement sensors

There are several key factors that need to be considered before purchasing or specifying a non-contact sensor, including accuracy, the type of surface or object being measured, environmental conditions and mechanical set up, says Stephen Smith, Product Sales Engineer at Micro-Epsilon UK.


How accurate does the sensor need to be? Is it the absolute colour that you need to measure or just colour detection. For measuring absolute colour, the sensor accuracy (measured in Delta E) will need to be high, in the range 0 to 1.0 ΔE. If you are unsure of the accuracy, speak to the sensor supplier for advice and guidance.

What object or material do you need to measure?

For non-contact colour sensors, the ideal surface in terms of sensor performance and accuracy is a flat, smooth one, where the same optics can be used. However, textured or structured surfaces can also be measured accurately by changing the measuring head on the sensor and/or the light source. In addition, multiple sensors can be used to measure at different measuring points on the sample and then averaging these values.

Curved surfaces or samples can also cause problems for colour sensors. On a curved surface, the light from the light source is reflected back to the receiver differently compared to a flat surface. If the sensor controller is not set up to deal with this, the accuracy of the sensor will suffer. For a sensor to perform accurately, the measurement opening has to be fully covered and, as a general rule, the curved radius of the sample should be less than 10 times the diameter of the measurement field.

Even transparent or translucent objects can be measured using a non-contact colour sensor.

Environmental conditions

If the colour sensor becomes too hot, its accuracy may suffer, i.e. the Delta E value of the sensor will change as the temperature increases. Therefore, look for a supplier that states clearly on the sensor datasheet how the accuracy of the sensor changes with temperature. Dirt, dust and oil will affect the accuracy of colour measurements. Non-contact colour sensors are more sensitive to contaminants in the measuring gap.

Mechanical set up, filters and lenses, connectivity/networking, adaptive learning also so need to be considered before purchasing non-contacts colour sensor…

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