Photoelectric Sensors These "Eyes" Miss Nothing

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Contrinex not only manufactures exceptionally small optical sensors but has also developed a groundbreaking technology for detecting transparent objects. The company's sensor solutions enable the industry to significantly optimize their processes.

Optical sensors are now ubiquitous in automation technology: they count glass bottles on conveyor belts, detect the position of circuit boards in soldering systems, or monitor the temperature in jam production. Since the objects to be detected often vary greatly and move very quickly, the requirements for the sensors used are high. They must not only reliably differentiate between light and dark surfaces but also cover large detection areas.

Inductive and capacitive sensors are not suitable for these applications, as they only detect objects made of specific materials or are easily affected. Optical sensors, therefore, provide the most reliable detection of objects with differently structured and colored surfaces.

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The reason for the extremely high accuracy of optical sensors lies in their functionality: An emitting diode (LED) emits a beam of pulsed light that strikes the object to be detected. This beam is partially interrupted and partially reflected. Depending on the type of optical sensor used, either the interruption of the beam or the light reflected by the object is evaluated.

Top Performance in the Smallest Space

The sensor specialist Contrinex manufactures a wide portfolio of optical sensors with extensive detection ranges, including reflective photoelectric sensors, through-beam sensors, diffuse sensors with and without background suppression, and sensors with analog output. The product range also includes sensor technologies and sizes that are exclusively available from Contrinex, such as the TRU-C23 sensors for detecting transparent objects and the world's smallest optical sensors.

The photoelectric miniature sensors are particularly suitable for applications with very limited installation space. A good example is intelligent conveyor belts in packaging machines. Here, photoelectric sensors such as the LTI-D04MA-NSK-403 type with a diameter of only 0.16 inches are used. The sensors detect passing plastic trays from below and stop them so that the respective batch can be scanned and recorded.

Different Technologies for Different Objects

Since the trays to be detected are made of dark plastic, the user chose the infrared version of the sensors. With an infrared measuring beam, unlike with a laser or a standard LED, dark objects can be detected as they emit significantly more heat than light objects. This heat is then detected by the sensor and converted into a switching signal. The functional principle of diffuse sensors or laser LEDs, on the other hand, is different: they detect objects based on the reflection of an emitted LED beam. However, since dark objects hardly reflect light, these technologies were not suitable for detecting the plastic trays.

The LTI-D04MA-NSK-403 can detect objects at a distance between 0 inches and 0.47 inches (infrared LED 880 nm) and operates in ambient temperatures ranging from -13 to 149 °F. With a response time of ≤ 500 ms and a switching frequency of <1 kHz (normal mode), the sensor reliably detects even very fast-moving objects. For applications where the background should not be detected by the sensor, Contrinex also offers a teach-in variant (IO-Link or wire-teach), allowing the desired distance to be set precisely.

Reliably Detect Transparent Objects

Another unique feature of the Swiss sensor specialist is its TRU-C23 sensors for detecting transparent objects (detection range: 147 inches). The sensors are based on patented UV technology that leverages the properties of translucent materials.

Unlike light of other wavelengths, polarized UV light is largely absorbed even by transparent objects. For this reason, the threshold at which the sensors should switch can be set very easily by the user. Neither the thickness nor the shape of the object to be detected has any influence on the measurement result. At the heart of the TRU-C23 sensors are an LED that emits polarized UV light and a UV reflector. This allows the sensors to detect even the thinnest transparent objects.

Thicker transparent objects can be reliably detected with the C23 Transparent Standard sensor. It emits polarized red light and detects objects at distances of up to 197 inches. The C23 Transparent Standard sensors are equipped with a pinpoint LED, allowing them to completely suppress the background.

New Optics Provide Even Higher Accuracy

Contrinex continuously optimizes its photoelectric sensors. Since the latest redesign, a combination of PBT/PMMA is used instead of sapphire. As a result, the beam of infrared, laser, and pinpoint LEDs is even more focused and can now detect even the smallest objects. For easy handling, the optical miniature sensors are also available in a red light version: here, the light spot is visible and can therefore be aligned to the objects to be detected with minimal effort.

For detecting the smallest black objects against a bright background, Contrinex offers reflective sensors with background suppression. These feature a patented dual-optic system with an exceptionally large adjustment range of 1 to 20 inches and exhibit no black-and-white shift.

Contrinex uses a special autocollimation optics system in its reflective photoelectric sensors and TRU-C23 sensors. This prevents the creation of a blind zone near the sensor where objects cannot be detected. The autocollimation optics are characterized by identical optical axes for the transmitting and receiving channels. To achieve this, the light is deflected using a semi-transparent mirror.

ASIC Processes Sensor Signals

The signal processing of Contrinex's photoelectric sensors is performed on a highly complex application-specific chip (ASIC) developed in-house. All optical sensors in the C23, C55, and M18 series also feature an IO-Link interface, making them ready for intelligent Smart Factory applications. IO-Link not only enables continuous monitoring of process data but also allows for constant monitoring of the sensor status, sensitivity adjustment, and verification of the sensor ID. This ensures that the correct sensor is in the right location.

Both calibration and installation of Contrinex's optical sensors are straightforward. Since most series are calibrated through ASIC parameterization, minimal effort is required. This type of calibration also ensures high measurement accuracy and low unit variation. The sensors are also very easy to integrate into applications, as they can be mounted in any position. This applies to all designs, but especially to the miniaturized models. Thanks to the IO-Link interface, it is even possible to adjust the sensors while they are installed.

Dipl.-Ing. Norbert Matthes is Technical Sales Manager at Contrinex Sensor GmbH

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