SENSORS
3D image of welding process
Building inweld-immunity A
New cost-effective weld-immune inductive proximity sensors from Contrinex slash down time in welding cells
n automated chassis-welding line in the automotive sector, running at full speed,
is a spectacular sight – transfer robots move large, complex parts from one assembly station to the next, while multiple welding robots swoop into position and fuse components together with perfect synchronisation. It’s all done in complete safety and with
little or no human intervention, thanks to an array of sensors and safety devices that protect people, equipment, and workpieces – effectively, reliably and almost invisibly. Engineers require presence- and position- sensors that perform reliably in the harsh
Sensor face with/without coating 38 SEPTEMBER 2021 | ELECTRONICS TODAY
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, 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
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