Sourcing flexible sensors for varying automation demands

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By eeNews Europe

On top of this, there are the choices to be made on interfacing to other systems, as well as how the environment where the sensor is to be used will impact housing choice.

Many situations simply require the detection of an object, for example on a conveyor belt, table or transport trolley. However, it may not be possible to fit a reflector to use in conjunction with a retro-reflective sensor, or the receiving end of a through beam sensor. If the object to be detected lies in front of an interfering background, a diffuse sensor with background suppression could be the answer.

For situations where a through beam sensor is impractical (R), the diffuse sensor with background suppression (L) might make suitable alternative.

Such sensors use the principle of triangulation to measure the light intensity reflected by the desired target as well as the distance is it away. The minimum size of the object is then defined by the dimensions of the light beam being used. The distance to the object is configured by set screw, although some more advanced solutions have a “Teach-in” method that can be used. Featuring a red light emitter, this visible light source makes it simple to adjust, even in conjunction with small objects. Laser-based sensors are capable of detecting objects with a size of just 0.1mm, while pinpoint diode-based sensors have a 2mm diameter spot of light at their focus. Their design is such that the object being detected can vary in both colour and material without detriment to the detection capability, while objects moving in the background do not trigger unwanted detection.

A prime example of a robust, IP67 rated solution, is the FHDK 14P5104 Series of photoelectric sensors from Baumer. These are packaged inside a 14.8×43 mm housing, are available with a wired interface, M8 or M12 4-pin fitting, and feature a sensing distance Tw of 30 to 500mm. They are also electrically robust, with both short circuit and reverse polarity protection, with a PNP output supporting < 100mA output current for both light and dark operate function. The front optics are made from PMMA and the integrated electronics uses a flashing yellow LED to indicate both issues with alignment or a soiled lens.

Some visual detection solutions require a more accurate assessment of the object being detected. This could be to determine whether a label has been fitted correctly, or if the product is undamaged. Industrial vision systems based upon an IP-based networked camera together with an industrial PC is one approach. However, a solution dedicated to the task can be more appropriate. With the continuous growth in processing performance and memory, vision systems are now available with competent vision recognition performance packed into a standard video camera housing.

One such solution is the ZFV machine vision systems from Omron. These ultra-high-speed CCD cameras can be mounted in a fixed position or integrated onto a robot arm system. Depending on application, the camera line-up supports a sensing area from 5×4.6mm, up to 50x46mm. Each camera features its own light source in the form of eight red LEDs, providing a pulsed light, and the housing is IP65 rated.

The cameras are used in combination with an Amplifier Unit. Once trained, the system is then capable of providing a positive recognition response within 4 to 15ms, depending on the type of image being recognised. The Amplifier Units can also be gang mounted. This allows the use of two or more cameras to analyse adjacent objects, such as an integrated circuit, checking orientation of the product, or that bottles with their barcodes are correctly positioned. As the Amplifier Unit is only IP20 rated, it must be appropriately mounted. Successful recognition can trigger an NPN or PNP output, while images can additionally be logged to a memory card.

The ZFS Series from Omron is a complete vision system capable of detecting correct orientation and position of objects.

Sensing of liquids in tanks and pipes brings its own set of challenges. Some liquids foam up, while others, with lower viscosity, have a tendency to cling to surfaces. This can cause issues in sensing quality. The CleverLevel LBFH series from Baumer are compact level switches that integrate a bright LED, visible around 360°, to indicate the sensor status. Available in an IP69K housing, they are suitable for food and beverage, pharmaceutical and chemical applications. Based upon a capacitive resonant circuit measurement technique, they make use of frequency changes that occur in the presence of the material being detected.

The LBFH series of level sensors from Baumer work on the principle of a resonant capacitive circuit.

The sensors can also be configured to have different switching windows, distinguishing between oil, water, foam and liquids. They are also capable of protecting from empty pipes and tanks, detecting pasty media and solid-bulk materials such as flour or plastic granulate. For the most demanding foaming or adhering materials, Baumer also provide their FlexProgrammer 9701. This programming tool can be linked to a PC via its USB interface. In collaboration with the user-friendly software, various help menus help to configure the sensor to meet the application’s demands. Measured data can also be visualised, enabling further parameter adjustment, such as time constants on damping functions and inverting the switching output logic.In some environments, the object to be detected cannot be reliably detected due to variations in the object’s colour, or due to the material it is made of. There are also challenges in detecting transparent materials, such as plastic films and glass bottles. In such situations, ultrasound sensors, either in through-beam or reflective form, are an ideal candidate. One candidate here is the UB800 series from Pepperl+Fuchs, a single head system in a short, 40mm design.

The sensors are capable of detecting items in the 50 to 800mm range, with a dead band between 0 and 50mm. They provide immediate indication of their status, with a green indicator showing the sensor is powered, while yellow indicates that an object is in the evaluation range. A TEACH-IN input provides a simple method for configuring the upper and lower limits of the evaluation range. The sensor provides a 20mA output for a detected object, 4mA when no object is presence, and a ramped change as objects move between the limits. The sensor is built into an IP67 rated casing.

A diffuse mode ultrasound sensor can be configured to detect an object at a specified distance.

As Industry 4.0 and more digitalisation drives more internetworked automated manufacturing systems, more and more sensors will be required to develop these platforms. With enormous variety in materials, liquids and objects being sensed, it is a challenge to determine precisely which sensor best meets the needs of the application. Suppliers are providing a wide range of solutions, with more features integrated into them. Highly visible indicators provide visual feedback on whether power has been applied, and whether an object has been detected. They are also increasingly configurable, from high-end, camera-based vision systems, down to the relatively simple distance and liquid detection sensors. Regardless of what is to be detected, it is highly likely that there is a sensing solution that matches the task’s needs.

About the author:

Peteris Sprogis is Regional Sales Manager of Technical Components at Distrelec –


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