Functionality and Technology of Differential, Contrast and Color Sensors

Color Sensors

The sensor works on a three-stage principle; It emits red, green and blue colors and then measures the proportions of the three colors reflected by the object.

The color of an object is programmed with the Teach-in procedure. If the sensor recognizes this color again during operation, it activates the corresponding output. Optional tolerances allow it to detect large or small color differences.

Features and Benefits

  • Simple usage:Four different colors can be programmed with three buttons.
  • The subtlest color transition:One of five tolerance stages can be selected for each color.
  • Short response time:High detection rates can be achieved with a response time of 0.34 ms.
  • Sync entry:It enables controlled color measurement.
  • External Teach-in input:It allows full remote control of all Teach-in functions via serial data transfer. An RS 232 interface transducer with galvanic isolation is available as an accessory.

Assembly and Adjustment

The color sensor is as simple to use as diffuse sensors. Only the following points should be noted:

  • For shiny objects, tilt the sensor approximately 15°.
  • If you want to detect very subtle color differences, a detection distance of 40 mm must be observed.

Diffuse Contrast Sensors

Diffuse contrast sensors can detect the subtlest contrast differences. Contrasts are created by bright and dark areas on surfaces (for example, a dark mark on a bright primary color) or by structures on the surface (for example, a weld seam).

Diffuse contrast sensors are based on the principle of intensity difference with a small clearly defined light spot. At the ideal working distance, the sensor is optimized to detect the subtlest differences in contrast almost independently of small changes in distance.

Features and Benefits

  • White Light Sensor:The narrow white light line enables precise detection of color marks.
  • Laser Sensors:Thanks to the focused beam, even the smallest edges up to 0.1 mm high can be detected.
  • Fast Response Time:Very short response times of up to 50 μs enable “real-time” recording of signals and increase process accuracy.
  • Sensor with Analog Signal:It allows importing desired nominal values and detecting deviations from them.

Assembly and Adjustment

The sensor should generally be mounted at an angle of 5° to 20° to the object surface, especially when scanning glossy material. When scanning edges, grooves or recesses, the sensor must be aligned with the light beam so that direct reflection can be detected.

Difference Sensors

Difference sensors offer new perspectives in the field of sensing. Patented functions offer innovative solutions such as detecting objects, monitoring tolerances or comparing object sizes and positions. Objects are detected precisely with a thin laser beam and sensors with low color sensitivity. Five different sensors are available with five different functions:

  • Step analysis
  • Window analysis
  • Tolerance analysis
  • Min./max. analysis
  • 2-point comparison

Features and Benefits

Difference Sensors with Step Analysis

In step analysis, objects are detected based on height differences and reported as a digital output signal. The sensor evaluates the positive or negative height difference within a certain time window (max. 5 ms). If the height difference is more than 50% of the taught value, an impulse of at least 10 ms is given at the output. If the value is less than 50%, the sensor turns OFF. If the height differences within the time window are less than 50% of the taught value (for example, fluctuation in the conveyor belt), the sensor remains in the OFF state.

Advantages:

  • The step/edge at which objects are detected is adjustable (minimum object height 0.2 mm)
  • Defined output pulse of 10 ms (can also be read by a normal PLC)
  • Detection of objects on a fluctuating conveyor belt
  • Detection of steps or edges
  • Positioning objects with an edge regardless of distance

Difference Sensors with Min/Max Analysis

In min/max analysis, objects are inspected and tracked based on the scanned contour or shape. Scanning of objects is activated by an external control signal. At the end of the detection sequence, the measured values ​​are evaluated and the difference between the minimum and maximum values ​​is determined. If the difference exceeds the nominal difference previously taught to the sensor, this is signaled as an ON signal. This signal remains active until a new detection sequence is initiated. When this starts, the output turns OFF. If the difference is less than the nominal difference, the output remains OFF.

Advantages:

  • The difference is perceived regardless of distance
  • Start and stop of the measuring cycle can be determined independently
  • Rolling or knocking control of wheels or discs can be done regardless of distance
  • Deformation of plastic parts can be controlled after cooling

Difference Sensors with Tolerance Analysis

The dimensional tolerance of objects can be determined by tolerance analysis. In continuous detection of object distances, it checks whether all measured values ​​are within the specified maximum and minimum tolerances. If in range, an ON signal is given at the output. When the distance remains within the tolerance range, the sensor remains OFF.

Advantages:

  • Sensor in caliper form
  • Simple distance tracking (pass/fail information)
  • Tolerance range and nominal distance can be taught separately
  • Material thickness control after roller mill and extruders

Difference Sensors with Window Analysis

With window analysis, objects can be classified by a specific switching window. For this purpose, the switching window is determined with upper and lower limits by a simple teach-in procedure. If the object is outside the specified limits, this is reported on the switching output.

Advantages:

  • Foreground and background suppression in a single sensor
  • Positions can be taught individually
  • Obstructive objects in front and behind can be suppressed
  • Objects can be detected on a segmented conveyor belt

2-Point Comparative Difference Sensors

In 2-point comparison, two perceived distances at specific times are measured and compared. Time selection is made using the synchronization signal. The first distance is measured on the rising edge of the signal, the second distance is measured on the falling edge of the signal. After the second distance is measured, the sensor evaluates the difference between the two distances and if this difference exceeds the pre-taught maximum allowable deviation, the output turns ON.

Advantages:

  • Object heights can be compared regardless of distance
  • Deviation teachable (min. 0.3 mm)
  • Measurement time can be determined individually with an external signal
  • Control of the pressing depth of the pins
  • Comparison of distance/height of objects with reference value

Assembly and Adjustment

  • Direct reflection from shiny or reflective objects should not fall on the receiver. This can be prevented by slightly tilting the sensor.
  • For optimum measurement results, the sensor should be mounted at right angles to the direction of movement of the object.