Why applications need a full spectrum of color sensors

How to choose microprocessor-equipped sensors, monochrome sensors, contrast sensors and fast color sensors.

By Mike Bacidore, editor in chief

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Sensing color can open up several options for machine builders, but making the choice isn’t a black-and-white decision.

This panel of automation suppliers explains the need for speed and the advantages of a microprocessor-equipped sensor, as well as when monochrome sensors or contrast sensors are appropriate.

Meet the panel

CD 1508 Greg Trainor

Greg Trainor, sensors & safety North American business unit manager, Datalogic

CD 1508 Steve Nylund

Steve Nylund, president, Delta Computer Systems

CD 1508 Tim Kelley

Tim Kelley, vice president, U.S. sales, Tri-Tronics

CD1508 Luis Torralva

Luis Torralva, North American marketing manager, Telemecanique Sensors

CD 1508 Ryan Hinrichsen

Ryan Hinrichsen, applications engineer, Banner Engineering

CD 1508 Jack Moermond

Jack Moermond, marketing manager, object detection sensors, Balluff

CD 1508 Felicia Shu

Felicia Shu, design specialist, Teledyne Dalsa

What sorts of speeds can be expected from color sensors, and is there a need for greater speed?

 

Nylund: Color sensors typically have a response time of 1 millisecond or slower. This is adequate for most applications. If the application calls for detecting a single color at high speeds, then contrast sensors, which typically operate about 10 times as fast, may provide a solution.

Kelley: Some color sensors can process for sortation of different hues as fast as 90 microseconds. Others are much slower. If the sensing application is to determine precise color hue or intensity/shade, then the sensor requires more processing time and can slow the inspection time down to as much as 1 millisecond or more. Time in the inspection/verification process is always increasing. Throughput in production is the overriding cost factor, and precision of delivered quality product is a constant customer requirement.

Torralva: We can find color mark readers as the most standard application on bagging or labeling machines. Speeds can go from 2.5 m/s to 10 m/s for a 1 mm wide mark, but of course machines are improving their speeds and customers are looking more and more for faster sensors. Color sensors will need more time for processing and identify the color, so speeds are much lower.

Also read: Can automation industries simplify color sensing?

Hinrichsen: True color sensors are typically used to detect color marks on a moving web. As the marks get smaller and the speed of the web gets faster, there is always a need for faster responding color sensors.

Moermond: Response time, which is the time it takes to switch the output once the object has been detected, for color sensors can be as fast as 300 µs. Switching frequencies can be as fast as 2,000 Hz. There will always be a need for greater speeds as cycle times are being increased to meet production demands and machine speeds.

Trainor: Industrial photoelectric color sensors offer speeds with response times measured in microseconds. For example Datalogic’s S65-V series color sensor has a response time of 340 microseconds. With an increased emphasis on throughput in all sectors of manufacturing, sensor speeds will have to keep pace and provide even faster response times.

Many color sensors now can include a microprocessor. What sorts of advantages does that enable?

 

Moermond: Microprocessors in color sensors allow configuring of the sensor outputs based on a particular color needing to be evaluated with configuration software. Additionally, some color sensors are now able to reside directly on I/O networks that allow them to provide diagnostics to the main controller. Also, the controller can provide parameterization of the sensors in the event a sensor is replaced or during recipe changes. In the past color sensors usually could be taught to detect three colors maximum. With the color sensors that reside on networks, as many as 256 colors can be detected by one sensor. Some sensors can communicate via RS-232 or other serial networks providing more data than just discrete on-off outputs.

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