Welding sensor shows its mettle

A sensor, particularly suited to harsh applications, uses new technology to sense at a distance

Problem: Welding bays can be quite unpleasant places to work. Automated welding cells, by their very nature, demand automation hardware which is robust enough to handle the environment but still accurate enough to deliver the required levels of tolerance. Standard sensors are up to the job in the early stages but they do not last forever as the elements found in these types of environments eventually get the better of them. Even those covered with Teflon will soon have their efficiency impaired as collision and abrasion damage takes its toll and weld spatter inexorably burns its way through the covering. If you take into account the demands of an automotive plant then downtime is something that cannot be tolerated due to the high costs involved and the disruption it can cause to the factory flow. Solution: Contrinex has developed a sensing concept which, thanks to its method of operation, allows the sensor body to be made from a single piece of stainless steel. The sensors are also able to sense over distances far greater than their proprietary peers, even when measuring non-ferrous metals. The Condet technology used in the sensor works in principle like a transformer. A single coil behind the sensing face acts as the primary coil and transmits a current pulse creating a magnetic field in front of the sensor. As in the case of a secondary coil, a voltage is induced in the conducting target, provoking a current flow. When the transmitter current pulse is abruptly turned off the object becomes the primary coil. As its induced current fades away it induces a voltage in the coil within the sensor which has now taken on the role of a secondary coil. This reversed induced voltage is then evaluated by the device. This technology gives it a sensing distance up to three times that of conventional products so greater clearances can be used – minimising the risk of collision damage. Applications: To showcase how rugged the Series 700 sensor is, the company has mounted on in the face of a hammer which is then used to drive nails into apiece of wood. After thousands of hits the face shows sign of ‘battle fatigue’ but the sensing element within is still working perfectly. It has seen action in many different applications some where it has replaced other sensors which would only last a month or so. One company tells us: “As required by our customer, we check our welds every half hour by hammering into a weld three times to make sure it doesn’t break. Sometimes, we hit the sensor by mistake but even that does not damage it.” Although the sensors in this application cost 20% more than the previous models being used, eight moths later none of them needed replacing so the cost benefits are self evident. MF