New cost-effective weld-immune inductive proximity sensors from Contrinex slash down-time in welding cells

An automated automotive chassis-welding line is a spectacular sight as transfer robots move large, often complex parts from one assembly station to the next, whilst numerous welding robots swoop into position and fuse components together with perfect synchronisation.

To ensure complete safety and little or no human intervention, an array of sensors and safety devices protect people, equipment, and workpieces effectively, reliably and almost invisibly.

Engineers require presence-and position sensors that perform reliably in a harsh environment with minimal maintenance over extended periods of operation. For tasks such as these, industrial designers specify inductive sensors –often referred to as inductive proximity switches –which are ideally suited for some of the most challenging applications and environments; over time, they have become some of the basic building blocks for automation engineers.

The inductive sensor is acknowledged as a robust, reliable and affordable solution for detecting metallic objects. In welding applications, the build-up of weld spatter is common (and may cause false triggers), while the very strong magnetic fields created by high welding currents cause non-robust sensors to malfunction or fail prematurely. In extreme cases, precautionary maintenance measures include daily replacement of inadequately protected sensors and cables, simply to avoid costly unplanned downtime.

To overcome these challenges, Swiss manufacturer Contrinex, a recognised technology leader in the innovative development of inductive sensors, has introduced its Weld-Immune range –these are devices that are reliably immune to welding fields and that do not detect welding debris and spatter as false targets. Weld Immune sensors are also available with the exclusive ACTIVSTONE coating, preventing the rapid build-up of high-temperature spatter on the sensing face.

Conventional inductive sensors fail in welding fields

Conventional inductive-sensor technology relies on an LC oscillator that generates a high-frequency magnetic field adjacent to the coil of the inductor; the physical arrangement of the components ensures that the magnetic field emerges at the sensing face of the device. When a metallic object (the target) enters the magnetic field, eddy currents are induced in the target, absorbing energy from the oscillator, and decreasing the amplitude of the oscillation (the Eddy Current Killed Oscillator, or “ECKO” principle).

A trigger circuit within the sensor electronics evaluates the degree of damping and switches the output state of the sensor when a pre-determined threshold is reached. In a common welding application, inductive proximity sensors confirm the position of parts to be welded or ensure that powered welding clamps are closed correctly. They are often within a few centimetres of the field source –typically a welding cable carrying currents, which may reach 15kA –and this tends to be the case whether the process requires a continuous weld or a short duration, high-energy pulse.

Most automated welding processes fall into one of two categories: ‘traditional’ 50Hz mains-powered welding, or the more recent (and more efficient) 1kHz medium-frequency (MF) welding. In each case, the welding currents create electromagnetic fields of the corresponding frequency generating an extreme electromagnetic-interference (EMI) challenge for electronic devices operating around the welding areas. Square-wave field strengths can reach 40 millitesla (mT) for the 50Hz technology and 200mT for MF welding processes. These fields are strong enough to cause non-robust inductive sensors to malfunction owing to their interaction with the oscillator’s field; in particularly challenging situations, permanent damage to discrete components of the sensor electronics may occur. Contrinex inductive proximity sensors were the first to benefit from the advantages of an ASIC design, and will resist such environments, while the newly launched Weld-Immune range is guaranteed to function flawlessly in these extreme electromagnetic fields.

Weld-field immunity

Weld-field immunity in inductive sensors is a further step forward, using Condet technology from Contrinex, developed to revolutionise the inductive sensor world. While these sensors embody inductive technology, the coil, which generates the magnetic field is not part of the oscillator circuit. Instead, an on-board pulse generator causes periodic, short-duration transmitter current pulses to flow through the coil, generating an alternating sensing field with a square waveform (see the below figure). This field induces a voltage in the target, which, in turn, generates a current flow in it.

When the transmitter current pulse is switched off, the current in the target dies away, causing a voltage to be induced in the transmitting coil. This voltage generates the signal required, and is, in principle, independent of the energy loss in the sensing field. This technology allows the sensor, including its sensing face, to be fully encapsulated in a one-piece protective housing, machined from V2A/AISI 303 stainless steel –with the added benefit of extended sensing distances (up to 40mm). The sensing circuit also performs equally well with steel and aluminium targets; no reduction factor is required. The high-performance Series 700 Extreme range, resistant to shock, was the foundation for the new Weld-Immune range. Indeed, by tuning its Condet principle to the weld-field-specific EMI environment, Contrinex was able to achieve weld-field immunity not only for the 40mTfields of historic 50Hz welding machines, but also the much stronger fields created by modern 15kA MF welding equipment.

Weld spatter immunity

Condet oscillator-free technology already allows Weld-Immune sensors to ignore small debris and slag that accumulate on the sensing face over time. However, weld spatter accumulation is also a problem as it hinders the correct orientation of the sensor and can create a protruding layer that collides with the target object. Contrinex sensors can benefit from an ACTIVSTONE coating that, thanks to its ceramic composition, creates a non-stick surface where spatter can’t accumulate. Additionally, and unlike other industry coatings, ACTIVSTONE resists high temperatures over long periods of operation and withstands frequent aggressive cleaning with wire brushes and dry ice. Unsurprisingly, with attention to detail at the core of Contrinex Swiss quality, the Weld Immune range has been validated under the most extreme conditions in both laboratory and automotive field-testing.

Complete range and accessories

Conscious of the continually evolving challenge presented by welding applications, in July 2021 Contrinex released a brand-new line of cost-effective Weld Immune sensors in the form of the Series 600 increased distance family with a PEEK sensing face, covering a new range of applications. Finally, Contrinex provides a full range of accessories that match the quality and robustness of its Weld-Immune sensors; purpose-designed mounting brackets allow fast and precise sensor installation, while high-temperature PUR cables with optional additional protective tubes resist weld spatter. The days of the consumable sensor and sacrificial cables are over; engineers now design new welding lines with durable, high-quality fit-and-forget products, allowing dramatic savings of time and money, while virtually eliminating waste.

PRODUCT ADVANTAGES

🔨Robust & reliable in demanding conditions, 🔧Highly Reliable with Long Service Life, 📏Long sensing ranges, 💎Ceramic ACTIVSTONE coating option, 🎛️IO-Link – Ideal for Industry 4

PLUS Automation aims to help you #MakeSenseofSensors, helping solve applications, improve machine performance and reliability, and reduce costs using Contrinex’s exceptional Inductive🧲, Photoelectric🔦, Ultrasonic🦇, RFID📻 & Machine Safety👷 sensors.

Read more at www.Weld.PLUSAx.co.uk, or Click to download Contrinex’s Weld-immune Inductive flyer, or Click to download Contrinex’s Product Overview brochure to find out more.

Read more automotive applications at www.Auto.PLUSAx.co.uk

Find more information and read other application examples at www.PLUSAx.co.uk or call me on 07910 156 470 to discuss how to #MakeSenseofSensors.