The inductive proximity sensor has been at the forefront of factory automation giving reliable switching and feedback on plant and machinery for 50 years. PACE explains.
The story behind the humble proximity sensor is extraordinary. The initial quest was to find a replacement to the mechanical limit switch that was good for the times but unreliable and prone to breakage and lost production. The inception of the proximity switch – being solid state and non-contact – was a giant leap forward in industrial automation which in reality, should not be overlooked.
Since this time, the growth of the product line from ifm has been big. Body sizes and styles changed depending on a customer’s requirements. There needed to be a new and innovative range of sensors and sensor technology. They increased in size to get greater sensing ranges in heavy industrial environments, such as detection of large carts in brick making, plants for manufacturing of vehicles, harsh mining applications and the list goes on. There were also needs from industry for tiny proximity sensors as small as 3mm in diameter for robotics, CNC, surgical and the like. But, there were also requirements in harsher industries such as dairies and food and beverage manufacturing.
Extreme wash-down with caustic substances and a high resistance to heat while being hit with the high pressure of a gurney, meant more was required from this sensor than ever before, so more research and development was required. Requests came in from truck manufacturers, trains and rail line switching junctions, tram, plane loaders, mine processing, mine excavators – the requirements were vast. If there was a need to see a position of a door, vice, rubbish bin flap, public toilet doors – the inductive proximity sensor was there.
The timeline of the proximity sensor is amazing from a cylindrical housing as small as 3mm up to a 164mm in diameter with a 120mm sensing range. There is also a family of rectangular proximity sensors down to new flat pack design for those tight spaces, which has a sensing range of 8mm.
The range of body types are quite extensive. For example, full metal stainless-steel bodies with high wash-down with IP68/69K for all food pharmaceutical manufacturing. Special sensors for welding applications have been developed, which have a non-stick coating that is designed for installations around spot welders that throw weld spatter all over the sensor and whatever doesn’t just fall off, can be easily and safely brushed away with a wire brush with no damage to the sensor. There are also sensors specifically for trucks and the ever-expanding requirements of the mobile vehicle industry. Then there are those made for rubbish trucks, elevated work platforms, mining trucks, excavators, fork lifts, concrete pumpers, bulldozers, public transport such as buses, trains, trams etc.
Most of these environments are extreme and need specific design characteristics to survive road conditions, high and low temperatures and humidity. With Australian weather conditions being extreme, ifm sensors must survive and be suitable to the conditions that are presented to them. There was a new requirement, valve actuator feedback for open and closed positioning due to the constant breakdown of mechanical micro switches. So the dual-head proximity sensor was designed with a large acceptance from all industries that needed this critical information sent back to the control system. Now these sensors have evolved to give 0.1° feedback accuracy to know if the valve is stuck, closes too slowly, or doesn’t close due to a failing seal. Special sensors, (now seen as standard) to detect all metals at the same range no matter if it’s mild steel, stainless steel, brass etc were introduced to the market from ifm. There are also a few specialist type proximity sensors for use in safety door applications and hazardous area zones that are intrinsically safe.
Kplus sensors, one sensing range for all metals
Inductive Kplus sensors have the same sensing range for all metal types. So they are suited for the detection of aluminium where conventional sensors show a reduced sensing range. High switching frequencies allow the monitoring of fast-moving targets up to 2000Hz. The resistant of a stainless-steel housing is also suited for applications with continuous contact with oils and coolants. The temperature range, as well as the high protection ratings, allows universal use of the new sensors.
Switching technology
Now to the actual switching technology. Initially, the sensor was only designed to switch on and off. There was a higher level of requirement from industry for continuous feedback with an analogue signal that was a leap forward in technology. With an IO-Link-enabled proximity sensor, users could imagine that number of areas where it could be utilised. One sensor for NO/NC, PNP/ NPN, protection rating of IP 65/ IP 66/IP 67/IP 68 /IP 69K and users could decide where the sensor actually switches within the sensing zone. This allowed for continuous feedback over a known network such as EtherNet/IP, EtherCAT, Profinet and Modbus TCP.
The basics of the binary connection of inductive sensors had only been rated for pure switching information, IO-Link could even transfer distance information without loss of the data through interference or analogue-to-digital conversion loses. This allowed the user to monitor the process continuously and react to deviations caused by wear over time. The new inductive ifm sensors with IO-Link could be integrated into almost any individual application. Inductive sensors with IO-Link interface measure the distance to the target permanently and transfer it to the controller and the ERP system via the ifm IO-Link master. Now that all this data has been collected, the user could do whatever they want.
The new inductive ifm sensors with IO-Link could be integrated into almost any individual application. Plant and machine efficiencies could be largely improved. Downtime was slashed and production increased. With the ever- increasing competition to a business owner’s product in the market place, these improvements on machine efficiencies and production increases were imperative.
These are some of the most important pieces of the automation puzzle that are often overlooked and at times, ignored. This is why it is important that when looking for sensors you get the right type for the right job.