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Try to imagine a manufacturing process without sensors, it'd be a complete disaster.
Today we demand more measurement, tracking, monitoring and communication within industry applications than ever before, and to boot we want the information now. Smart manufacturing relies ultimately on the data picked up on field devices being sent back to the controller within milliseconds, but this data is only as good as the sensor can allow. Make bad sensor choices and the whole process will become less efficient, more costly and unreliable.
Industrial proximity sensors - part 1
Other than limit switches most proximity sensors are non-contact. But where to start, inductive, capacitive, photo-electric, ultrasonic or vision sensors and more, so much choice.
In this first article we are going to focus on the simple but highly effective and probably the most commonly used proximity sensor in industry, the inductive proximity sensor. Ultimately the inductive sensor is a real solution provider on an industrial scale and is used in millions of processes world-wide. Next time you visit the car wash or say an amusement park, see how many you can spot.
SICK IME inductive sensor in action
Working on the induced magnetic field principle Inductive Proximity Sensors are devices that detect the presence or absence of metallic objects.
From the oscillator circuit an electro-magnetic field is created, the coil radiates this around the sensor tip thus producing the sensing field.
Once a metal object enters the sensing field, eddy currents are induced within the metal surface. This changes the reluctance of the magnetic field, as the object moves closer to sensor face more energy is taken from the oscillator circuit, thus dampening the amplitude of oscillation until ultimately oscillation will stall. Hence the name Eddy Current Killed Oscillator, (ECKO principle).
Basic components of Inductive Sensor
NB: Eddy currents are reverse currents that have been induced on the surface of metal conductors by a changing magnetic field.
Changing state of an Inductive Sensor
The metal object causes the oscillation amplitude to decrease the closer it moves to the sensor tip, and conversely as the metal object moves away from the sensor tip the oscillation amplitude returns to normal level. This is how proximity sensors change state.
The distance at which the oscillator will stall can be predetermined. When this condition occurs the trigger circuit changes the state of the output circuit.
The output circuit of inductive sensors can be interfaced with PLC inputs, relays, control valves, sounders and beacons to name a few examples. This is where the sensor interacts with the control circuits and provides real time monitoring of the process
Inductive sensor benefits
- Extremely robust they withstand shocks and vibrations
- Suitable for harsh industrial environments,
- High operating temperature range -50°C to 200°C
- Not effected by water, oil, dirt, or non-metallic particles
- Not effected by target surface or colour
- High IP ratings typically IP69K
- Quality control monitoring
Inductive proximity sensors are used in many industrial processes, including food & beverage (stainless steel versions), oil & gas (ATEX & IECEx approved version) and particularly, where shocks, vibrations, dust and dirt are present.
Sensing distance and reduction factors.
The sensing distance of an inductive sensor is dependent on the shape, size and which material is being sensed. A reduction factor is applied for different metal types so it's important that this is taken in to account. The table below shows the reduction factor referenced to iron.
NB: Sensing distance will be different for ferrous and non-ferrous metal objects, unless the sensors are Factor 1, like the Turck NI30U, then all metals will be sensed at the same distance. Double distance sensing
A real solution provider over many applications are the popular E2A and E2B ranges from Omron, which are suited to automotive manufacturing, packaging machines, conveyors, commercial vehicles and much more.
The benefit is their double distance sensing range, this protects against damage from moving objects and with the increased sensing range allows for selection of smaller sensors therefore saving space and cost on machine builds.
E2A & E2B - with increased sensing range
Block Sensor or Limit Switch
Inductive proximity sensors come in many sizes but the form is usually cylindrical or block. The function is the same for both it's more a consideration of design.
Block style sensors are now being manufactured to the same footprint as their limit switch counterparts for example check out the Varikont NBB15-U1-A2-V1.
Varikont Inductive Proximity Sensors, extreme environments
As an inductive sensor is basically a solid state device the operational life is far superior to that of the mechanical limit switch. Another key thing to take into account is the application, as mentioned before inductive sensors are extremely robust. Whether you are considering new build or overhaul, switching to inductive sensors is certainly worth serious consideration. Be cautious and don't rush in, limit switches are extremely efficient in the correct environment and application.
So much choice With lots of choice on market at the moment, for a dependable rugged sensor consider the RS Pro barrel range. With stainless steel housing and factor 1 built-in, it's a great robust product. Also if your working with senors a handy little product to have around is the RS Pro sensor checker, ideal for you pocket or tool bag.
If it's big brands you are looking for then simply click the links below and choose inductive sensors.
In future posts we will look at amongst other things;
Capacitive, photoelectric and ultrasonic sensing applications
The rise of vision sensors
IoT and sensing technologies