Proximity sensor / switch: Electronic devices using different technologies to detect a movement or presence of material within its designed range.

A sensor consist of distinct sections:

1. A sensing head, (This normally determines the type of sensor)

2. Converter/ transducer) / amplifier

3. Output(s).

Various technologies for section can be used in as many different types of sensors.

Generally there are no moving parts within a proximity switch and if a solid state type is selected

it has unlimited lifespan and requires no maintenance whatsoever. But of greater importance, espacially in manudfatcturing processors is the operating time...they are super fast...even microseconds can be achieved.

Important fundamentals:

Namur sensor: This refers to the 2 wire technology where the sensor uses the "leakage" (off/on state) current through the load to power the electronics of the sensor. The device resistance changes with activation of the sensing field. Essentially it is a sensor with no output amplifier and they can be designed around any sensing technology:- Inductive, capacitive, magnetic, photo electric etc..      

Namur sensors works with specific controllers(amplifiers) only and cannot work with normal loads such as relays. To give an idea of how specific the criteria is: For N/C, when not activated, the circuit mA is >2-3mA (Normal closed condition), the normal open condition <1mA. Usually normal closed but one can get normal open versions.

Namur sensors comes into its own in intrinsic safe environments (explosive environments) where the amount of energy available in the different EX zones are explicitly defined by law.

In this case the namur sensor would then be wired through the INTRINSIC SAFETY BARRIER/ I.S BARRIER/ GALVANIC ISOLATION BARRIER into then into its amplifier.

Rating definitions:

Standardised sensing plate:

The plate by which a inductive sensor gets measured against as defined by the European standard EN60947-5-2. The plate is square and has a thickness of 1 mm and made of steel (Fe360).

Its use allows the comparison of the values of sensing distance (see table). The measuring method is defined by the european standard EN60947-5-2. The normalized plate is square and has a thickness of 1 mm, the material of this plate must be steel (Fe360). Other materials mean that different intervention distances are obtained. The length of the sides of the plate must correspond to the diameter of a circle that is the active surface of the sensor. A larger plate does not result in an increase in the nominal intervention distance, however a reduction in the plate reduces the intervention distance.

Nominal sensing distance / NOMINAL INTERVENTION DISTANCE Sn: The nominal distance is defined as the switching value where variations due to changes in temperature and voltage are taken into account.

The guaranteed distance at which the switch will operate within the limits of the temperature and voltage variations.

Real sensing distance - Sr: REAL INTERVENTION DISTANCE Sr: This is the distance measured according to the EN standard at nominal temperature and voltage: 0,9Sn ≤Sr ≤1,1Sn.

Intervention distance - Su:

This is the distance measured according to the EN standard at a specified temperature and voltage between the allowed limits 0,9Sr ≤Su ≤1,1Sr.

Connections:

An unwritten rule (or maybe not) across the world is the color wires.

Brown = Positive / live supply.

Blue = Negative/ground/ neutral.

Black = Normal open output.

White = Normal closed output.   

NPN transistor or

Inductive sensor:

Applying a frequency to a coil creates a magnetic field around it.

Mount such a coil in a housing, then when a metallic object enters, the magnetic field is modified. This field modification is amplified to switch an output stage e.g. relay, transistor(for DC) or triac(for AC).

The type of material (steel, aluminium, copper, brass etc.) has a higher/lower effect on the field.

By applying a voltage to the oscillator coil an alternating inductive field is created in front of the active surface of the unit.

When a metallic object (steel, aluminium, copper, brass etc.) enters this field from any direction and the state of the oscillator is modified until the threshold of the trigger is inverted this induces a change in the final stage and the subsequent command of an external load. The intervention distance depends on the type of metal and as described earlier, in the reduction factors. All the sensors are protected against inversion of polarity and electrical disturbances of inductive sources and can be supplied with short circuit protection in the D.C. version. The main advantages offered by proximity sensors in relation to normal limit switches are mainly unlimited duration as they have no moving parts (wheels, springs etc.) lack of maintenance requirement and elimination of possible false contacts due to contact movement.

Capacitive sensor:

These detectors also have an oscillator but they monitor the dielectric of air, and whenever it is different it knows there is something different in the field.

To phrase it a bit more technically correct is to say:  When an ac signal is applied to 2 plates with a dielectric medium between the plates, it forms a capacitance circuit. The value of capacitance is determined by size/types of plates, type of dielectric medium, distance between the plates and so forth. For capacitive sensors this medium is air and any change within this field is amplified.  

It is for this reason capacitive sensors are said to be able to sense any material and even works through glass and other mediums, if set correctly.

Photo electric sensors:

Light beams (optical)...that is what makes these tick. This includes Infrared, laser light beams.

Different solutions dependant on range required

PS: The noted ranges is from what I am aware of.

What's up with the nice sci-fi name ULTRASONIC?

I guess those in the know wanted us to know that the transmitted beam is at a high frequency. Many say it refers to any frequency higher then our normal hearing frequency which is about 20kHz

This transmitted sound waves gets reflected back from the measured object is then managed and monitored and from this we can decipher how far the object is from the sensor head.

Its so good we can even tell it what to do between two points in its range.

Only thing I must mention here is this: There are models with a dead band in front of the head...so the object must be farther then this distance.

This technology is generally  unaffected by environmental factors smoke, smog, dust, colours.

Can even detect oil, water ...and if can do that it can do just about anything!  

Guess where it will not work so well...sound absorbing materials like foam...sound proofing materials will kill it!

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When not to use ultrasonic sensors? (Microdetectors) -ultrasonics

The functioning principle of the ultrasonic sensors is based on the emission of a sound impulse and on the measurement of the time elapsing from the emission to the reception of the echo signal reflected by the object of which you want to detect the presence or the dimensions. Since the transmission mean is the air, any kind of disturb influencing the air column, can cause problems to the measurement. Pneumatic valves outlets, high temperature objects or anything producing whirling air motions could make the measurement ineffective.

The ultrasonic beam is very well reflected by almost all materials (metal, wood, plastic, glass, liquid, etc.) whether they

Serie SU-UHZ-TU - SU-UHZ-TU Series 3 series SU-UHZ-TU - SU-UHZ-TU series

are coloured, transparent or bright.

A decline in performance is possible in case of sound-absorbent materials (that absorb the ultrasonic beam) or objects having reclined surfaces with respect to the sensor axis (that deflect the ultrasonic beam far from the receiver).

In the direct or retro reflective models, the same ultrasonic capacity is used both to emit and receive the ultrasonic

beam. During the emission, the reception is disabled and, during the short time necessary for the commutation of the emission to the reception function, the echo signal cannot be received. As a result, there is an area nearby the reflection sensor in which the object detection is not possible.

In the retro-reflective models, any kind surface that is flat and orthogonal to the sensor axis can be used as reflector (you can use also a fixed part o the device). Therefore, any object passing between sensor and reflector can be detected.

In the direct reflection models, the detection happens when the object is in front of the sensor and, it will therefore be necessary to check that eventual backgrounds are not detected. If this is the case, it will be necessary to adjust sensitivity through the trimmer or teach-in key (for the models where such a function is foreseen).