Sensing techniques of distance

Abstract:

The ultimate goal when an automaton system is constructed is to be optimized and to be compliant with all specifications.

To fulfill the wants typically you’ll pay several hours simply to type associate degreed determine the sensors that will be the most effective for associate degree application like detection and following an object. During this article, we have a tendency to explore all sensing element sorts that used for Distance measuring and following further as options and therefore the sorts of applications wherever they will be used.

Introduction

Sensors are the most important component in any device’s system. The function of sensor is to get the Ore data from the physical measurement and then create electrical signal and send it as input to the signal conditional circuits.

Distance sensors are used for various applications that require the distance quantity to make the appropriate actuator.

Types of Distance Sensor

Proximity sensors:

Divided into two types:

• Capacitive Sensor: builds his work on the generation of an electric field changes when approaching an electrically insulating body so called capacitive proximity switches

• Inductive Sensor: based his work on generating a magnetic field changes when a metal object such as the approach is called convergence keys inductive.

Key features convergent:

• Have no moving parts

• old is not affected by the number of operating times and the separation at a rate not operating

• Do not affected by moisture or oil and dust

• Have a very quick response when a foreign body such as the approach which reduces power transit and sense of distance ranging from 0 mm to 40 mm

Inductive proximity sensor:

This sensor is one of the most important sensors used in industrial processes such as production lines and conveyor belts, packaging and packaging, and many others

And here in this report I explain how it works and how well mounted and connected to a private engineers and maintenance of automatic control and also the architects of the electric distribution

Use: uses the inductive proximity sensor in determining the mineral material as it approached him a specific distance

Of the most important features that affected a small degree of moisture and dust, oil and which exist in abundance in factories

Figure (1) show Inductive sensor’s parts :

Figure (1) : Inductive sensor’s parts

Figure(2) is an Image explain his work on the conduct of a special production line

Figure(2) :Inductive sensor application

The idea of his work:

The idea is very simply rely on the work of this sensor ECKO any principle of Eddy Current Killed Oscillator

It’s Inside installation is shown in Figure(3):

Figure(3): Inside installation of Inductive sensor

Explaining the internal structure of the inductive proximity sensor:

The sensor generates a magnetic field a certain worth, and the approach of the metal material of the sensor is generated by Injectors eddy current and creates a lost energy, and therefore less magnetic field and the value here comes the role of the trigger circuit, which is observing the change in the field of value and you change the setting points emerging from the sensor

And the points are either Normally opened and when the sensor work of changing to a closed

Or point be in the original closed (Normally closed) and when the sensor work of changing to open

And there are some sensors by more than one point closed and the other open

To find out all kinds of points possible presence on the sensor came out, see this explanation: all kinds of access points used in electrical control

How to choose the sensor Convergent:

It depends on several factors, the most important

1. Sensing distance: and is the maximum distance of any sensor work then the maximum distance can then sense of mineral material and this distance varies depending mainly on the sensor’s diameter.

The sensor’s diameter has increased its own sense of distance

2- Response time: and this is an important criterion which determines how long it takes the sensor points in the switch and put it at the presence of metal close to him

This time is very important, especially in applications where the material is moving very quickly

3. Power Supply: who will be sensor must determine its value and its kind DC or AC

And there are sensors operate at more than the value and type of voltage

4. The temperature of the place where sensor will be placed there as an example, where are some sensors bear up to 60 ° C and another bear up to 90 degrees (of course, be more expensive)

5. knowing the IP code :that is special to the sensor which illustrates the degree of protection of sensor moisture and dust

6. Knowing the global standard which governing the sensor specifications and including NEC or IEC or NEMA or CENELEC

7. kind :shielded or unshielded

Meaning of shielded: that the sensor’s body, especially near its surface area is covered with a thin layer of metal

And the importance of the type shielded magnetic field concentration on the surface of sensor, leading to increased accuracy

Either type unshielded do not contain this metal layer

Figure(4) shows the difference:

Figure(4): difference between shielded & unshielded types

Note very important: when the sensor mounted on the surface of the metal if it is shielded type is mounted so that it applies to the sensor surface of the metal surface subject him if he kind of unshielded be installed so that the surface of sensor specific distance rises from the surface of the metal

Also note: The sense of distance in the case of larger kind of sense of distance in case of unshielded shielded (and therefore when diameter of sensor equals in both types)

How to connect inductive proximity sensor:

First: if it came out a sensor two wires are connected only by the power source and the other party to load, which will control its sensor then connected the load with the other side of the voltage source as Figure(5):

Figure(5)

Second: If the sensor came with three parties and there is two types:

PNP type: which contains the transistors of the kind PNP

NPN type: which contains the transistors of the kind NPN

And with the two types .. often be three parties colors are:

– Brown Wire: and be connected voltage anode to the source (usually the source DC)

– Blue color Wire: it is plugged voltage negative terminal of the source

– Black color Wire: and is the control wire and it is connected to load which be controlled (and it is often be contactor filament) and plug the other end of load in different file types (and the following picture in Figure(6)shows the difference)

Figure(6)

Note When install more than sensor to the metal surface must take into account the existence of a certain distance between each sensor and another so as not to interfere generated magnetic fields of both, and this distance clear of two types of the corresponding Figure above

Capacitive proximity sensor

is a sensor senses the approaching metals or non-metals such as paper, glass, and also if he senses fluid on the approach of a substance from a specific distance .. It switches his connected points

various Photo forms of capacitive sensors in Figure(7)

Figure(7): capacitive sensors

Composition and how it works:

The idea that his work on the generation of an electric field of electric field and when any body is located (metal, liquid or Non-metal material) causes increased capacitance in the oscillator circuit

look at Figure (8):

Figure (8): Composition of capacitive sensor

Here comes the role of the trigger circuit where the observation of this increase in capacity whereupon the oscillator to change the status output points

And this point are normally opened then change it to the closed

Or this point are normally closed then change it to open

And possible that there are two points then change both

Note: There are two types of sensor output and two PNP and NPN

Information: out sensor that one end only with the parties to turn it on

– Type PNP (the most common), the output constant voltage positive and is connected to load, which will be control by the sensor (such as contactor or Relays or input points of PLC and others) and the other end of load takes voltage negative (of course, the same value as the sensor output)

– Type NPN be output ongoing voltage negative and it is connected to load, which will control its sensor (such as Contactor or Relays or input points of PLC and others) and the other side of the load takes a positive voltage.

How to choose the capacitive proximity sensor:

There are some factors to be taken into consideration most important:

1. Sensing distance: and is the maximum distance can sensor which sense rule and alter the status of his points and depends on several factors :

– Diameter of sensor: larger the diameter sensor increased sense of its own

– a distance of material and size of the type: The greater the volume of material. . increased the sense of distance and the type of material is also very important in determining the sense of distance as we know where each item is fixed to isolate a specific dielectric constant and the more this constant sense of distance has increased .. if increased by the purchase of sensor material must determine which will sense it and what your dielectric constant by

2. Determine the response time :which is the time it takes to change the sensor points put on the approach of a substance from the scope of his work and that time is very important in fast applications (such as the conduct of the production line)

3. voltage source working on the sensor type (DC or AC) and DC often have and also to determine its value and its frequency if AC

4. Sensor type :shielded or unshielded

The Similarity between capacitive sensor & inductive sensor in that both can be no shielded or unshielded

shielded type: Containing this kind on a high metal layer covers part responsible for the generation of electric field and called the probe where it acts on the electric field concentration on the face of the sensor contrast of material to be disclosed

And the biggest advantage of this type that can be put on any metal surface without fear of the impact of the metal surface to detect material process

Note composition in Figure(8):

Figure(8): composition of shielded type capacitive sensor

Either unshielded type: do not contain the metal layer shall be electric field is the center of the face of the sensor contrast with the material that wanted to expos so usually are the so-called compensation probe, which works to increase the efficiency of the sensor in detecting material

See INSTALLATION:

Figure(9): composition of Unshielded type capacitive sensor

Note .. the distance of sensor in the unshielded type larger than the distance of sensor of the shielded type and when equal diameter sensor and also match the size and type of material required by the sense of

Note very important mechanism for the sensor work of capacitive capacitive sensor:

Material must be a constant sense of their own insulation be greater than the dielectric constant topic by material

A process which uses a capacitive proximity sensor applications:

1. Determine the height of fluid within the vessel, as Figure(10)

Figure(10): determine the height of fluid using capacitive sensor

2. Identification of the inside of an explosive product on the conduct of a special production line as Figure(11)

Figure(11): capacitive sensor in production line application

Ultrasonic Sensor

First: the working principle of ultrasonic sensors:

Ultrasonic sensors uses power converter for sending and receiving high-frequency audio signals applications. When cutting the target sound wave will be reflected to the key and thus activated or canceled to activate the output.

Figure(12): Ultrasonic sensors

• Piezo-electric disk:

Piezo-electric disc which is from ceramic is proved on the surface of the sensor, this disk can sends and receives high-frequency pulses, applied high-frequency signal on this disk voltage and that makes the disc vibrate in the same frequency and the disk thus generate sound waves in the same frequency.

When sending impulses collide body reflective sound will be formed steel caused by the collision sensor which measures how long it takes the sound to rebound from the goal.

When a particular object enters the extent of the sensor output will change his condition and while leaving the body’s term lender for sensor output will return to its original state.

Figure(13): Piezo-electric disk

The impulses sent is in fact a collection of thirty impulses of 200µV and echo is usually the area of the Micro Volt.

Figure(14): Echo pulses of Ultrasonic

• Blind spot:

Blind spot is positioned directly in front of the sensor and depending on sensor to the type of the region ranging from the 80 ÷ 6 Cm.

If a target is positioned in this region then that will generate unstable output.

Figure(14):Blind spot of Ultrasonic

• Determine Range:

The length of time between sending and receiving the signal is directly proportional to the distance between the target and sensor.

Field of work is adjusted according to the currently placed in the target area of the sensor work, if the upper limit can be modified in all sensors while the adjustment of the minimum available in some species only.

Crossing any target, that increases beyond the minimum to the sensor work will not cause a change in the output state and This is known as the principle of neutralizing background.

In some sensors forming the so-called field of prevention (blocking) this area is positioned between the minimum field of sensor work, and blind zone.

The presence of target or object in this region prevents sensor to identify or sensing over objects in the workplace.

Figure(15): Determine Range

• Radiation pattern:

The radiation is sensor to X-model ultrasound consists of a component (cone) which is basic and other components nearby.

The main cone angle of approximately 5 degrees.

Figure(16): Radiation pattern of Ultrasonic

• Free Zones:

Must be maintained free zones or free on sensor not to hinder Send side components, and the following example will show the required free zone in different situations:

1- Case of sensors in parallel:

In the first example is positioned two sensors in the same field of work in parallel and perpendicular on the sound beam, if the distance between the sensor determined on the basis “for the field sensing For example, if the field work or sensing for both sensor equals 6Cm should be apart by 15 Cm at least .

Figure(16): Case of sensors in parallel:

2- Mutual interference:

This situation occurs when sensor is located close to each other and be objective positiones “to reflect the sensor reference to the other, in this case, the distance between sensor (X) is determined experimentally.”

Figure(17): Mutual interference:

3-Sensors opposite case:

In this case the two sensors are positioned in opposite direction and working in the same field of work, in this case must be maintained smaller distance between sensors so do not get overlap between sensors.

Figure(18): sensors opposite case

• Dealing with irregular surfaces:

Existance of a sensor to sense the body with a smooth surface as walls or machines with a smooth surface requires free space is less than required sensing objects with irregular surfaces .

Figure(19): Dealing with irregular surfaces

• Angular Positioned:

The positioning target angle when entering the workplace must be estimated at ± 3º taken into account that the corner of maximum allowable deflection body

Figure(20): Angular Positioned:

If the deviation of the body is greater than 3º angle will be the body reflects the wave of the sensor away from him and therefore will not receive any sensor resonance.

Figure(21): deviation of the body

• Fluids and coarse granular materials:

The liquids such as water, for example, should not exceed deviation angle 3º As for the coarse-grained materials, for example, it could take a deflection angle of up to 45º, because the sound will be reflected in a broad field for these materials.

Figure(22): Fluids and coarse granular materials

• Neutralize unwanted obstacles:

The body is placed close to the sensor will make the sensor work is stable as previously stated.

It can neutralize such objects through the use of barrier problem of sound-absorbing materials, rock wool provider aperture to allow access to the acoustic waves.

This process will limit the display beam transmitter and thus inhibit impulses from the collision objects crippling.

Figure(23): Neutralize unwanted obstacles

Second: Work patterns of Ultrasonic Sensors:

Sensors can be used ultrasound to operate in different modes, including:

spread pattern, the Reflection pattern and Access pattern.

1 – Spread pattern:

This pattern is a standard pattern in which they operate most of the sensors.

The goal in any area of the sensor work of the move will lead to a change in the output state of the sensor and that this pattern is similar to the sensors convergence.

Figure(24) : Spread pattern

2- Reflection pattern:

In this mode it uses a reflector seated in the field of work set to a sensor area and is working to adjust the reflector.

The impulses backfire on the inverter back to the sensor and when cut a target radiation from the sensor will block the radiation from the sensor and therefore will do the sensor came out, usually used this style in applications where the goal is to be an object absorbing sound.

Figure(25) : Reflection pattern

3- Access pattern ((Breakthrough)):

The sensing system in this pattern consists of a transmitter that sends sound waves and a receiver cut in the case of radiation between the transmitter and receiver to change the output status.

Figure(26): Access pattern ((Breakthrough))

Third: Surrounding effects:

The speed of sound influenced by the physical properties of air and this in turn will affect the sensor work.

Table(1) show the influence of the Physical property on Ultrasonic Sensors:

Physical property Influence

Heat The speed of sound change by 17 %/ ºK

Most sensors can be calibrated to compensate for this effect.

Pressure The change in atmospheric pressure by ± 5% causes change the speed of sound by ± 0.6%.

Decreasing the speed of sound by 3.6% between sea level and altitude 3 km above sea level.

It must adjust the sensor to get the field work required.

Dislocations Sensors do not operate in a vacuum.

Humidity The speed of sound increases with humidity and this gives the impression that sensor objects closer than it is the truth.

Air stream For airflow speeds:

50 km/h has no effect.

50-100 Km/h can not predict the sensor job.

100 Km/h >does not receive any sensitive resonance.

Surrounding gases Sensors designed to operate in the field of natural atmosphere.

In the case of sensor work in a different area around the perimeter as an example the problem of the gas carbon monoxide wrong measurements will produce.

Different weather Rain and snow natural profusely does not affect the operation of sensor and must be maintained on the surface of the sensor is to be dry.

Dust The dusty environment will cut down the field sensor sensitivity by 25-30%.

Table(1): Surrounding effects on Ultrasonic Sensors

Fourth: sensors families ultrasound of the company: Simens

Family includes sensors, ultrasonic sensors from Simens company of type:

1-Thru-Bean

2- Compact Range [M18, Compact Range 0, I, II and III]

3- Modular Range II

Figure(27): sensors families ultrasound of the Simens company

1-Thru-beam:

The sensor of this type consists of a sender and receiver where the sender sends reciprocating package tight and when the body is positioned between the sender and the receiver will break the beam, which in turn causes the output state change.

Work voltage for this sensor or Nominal voltage of 20 – 30 Volt and has a chapter link frequency of 200 Hz is sensor when working in the field of 40 Cm between sender and receiver.

Figure(28): Thru-beam

2 -Thru-beam Receiver:

There are two types of receptors for these sensors is used both types PNP transistors, providing the first type of contactless NO and NC in the second contactless narrated.

Figure(29): Thru-beam Receiver

The sensitivity and frequency of transmission of the sensor itself Thru-beam is determined by the electrode X1 in the receiver connection.

Table(2): Comparison between Thru-beam Receiver sensors

The smaller-sized objects can not detect it follows the distance between the transmitter and receiver If the distance between the transmitter and receiver less than 40 cm and was vacuum Minimum allowable between my body k consecutive equal to 3 cm can then fumbling for the bodies of a width of 2 cm or more.

If the distance between the less sensitive it can allow an interval between objects of up to 1 mm.

When working in the field of maximum sensitivity of the sensor, then sensor senses objects in larger than 4 cm purpose .

3 -Compact Range 0:

Sensors are available from this type built within the sender of sensor or separate transmitter and are usually in contact with open or closed out naturally or Analog.

These sensors form a parallel rectangles with dimensions (88 * 65 * 30 mm) and the nominal voltage of these sensors ranges (18-35 Volt Dc) and can run loads of up to (100 mAmp)

Figure(30): Compact Range 0:

Depending on the type of sensor, the scope of work ranges from:

From 6 to 30 cm in the case of a separate transmitter

From 20-100 cm in the case of built-in transmitter.

frequency (of Connecting-Disconnecting) ranges between 5 to 8 Hz

These sensors have put out the remote areas where the property is adjusted by sensing the field rheostat.

Passing a target within the scope of the sensor work out the exact area will not be sensor to the sensor him.

Figure(31): scope of work ranges of Compact Range 0

4 – Compact Range 1:

These sensors are available in contact either NO or NC in contact may also be available with both sensor. These sensors form a cylindrical (M 30 * 150 mm) are available, including several models of each provider separately sender or ROM.

The field of action of 20-30 Volt DC loads and can run up to 200mAmp

Figure(32): Compact Range 1

Depending on the type of sensor, the field of sensing be:

[6-30 CM], [20 – 130 Cm], [40 -300 Cm], [60 – 600 Cm]

frequency (of Connecting-Disconnecting) ranges between 1 – 8 Hz and this type of sensors has put out the remote areas and areas near feature also any that could be in this sensor adjust the field of higher labor and lower by two variable resistors though goals passage outside the controlled area will not affect the sensor work.

Figure(33): Compact Range 1 Sensing ranges

• Son Prog:

The sensors that have been mentioned so far are either not subject to pressure or can be manually adjusted by variable resistors.

The Son Prog Semens is a program of the company is used to adjust the sensors of the type:

Compact range II, Compact range III, Compact M 18,

Table(3): Adjustment of siemens ultrasonic sensors

Using the Son Prog sensors adjusted individually in order to operate in a particular application.

It is connected between the suitability of the sensor and circuit Rs232 port on your computer and can use Son Prog set the following parameters:

• beginning and end of the field sensing.

• Bata knots.

• the beginning and end of the analogue field came out.

• Determine the end of the blind zone

• Adjust petitions NO / NC.

• Activating adjustment by variable resistors or canceled.

These settings can be stored or retrieved when needed, for example when replacing the sensor can easily be applied to old settings on the new sensor.

5 – Compact range II

These sensors are similar in shape sensors of the type Compact range I shall be the difference between the two types is that the sensors of the type Compact I are calibration manually using Bernam SonProg available these sensors in contact NC or NO Oopkla two petitions in Al-Kharj.

Figure(34): Compact Range II

A cylindrical shape (150 * M30 mm) and are available in different models each with a built-in or a separate transmitter and can run loads up to 300 mA and voltage (20 – 30 Volt DC) can be synchronized sensors from Compact2 type to prevent interference when using a number of sensors small spaces comma in them.

According to the sensor type ranging field of allergy:

[6-30Cm], [20-130Cm], [40 – 300 cm], [60-600 cm]

Separation rate – arrived ranges from 1 – 8 Hz and is fitted with feature suppressions distant and near.

6 – Compact Range II Analog Version:

Analog type sensor is available for Compact range 2 where analogue measurements for this sensor is converted to digital pulses and then can counter the plc-type logo that is after these pulses to calculate the desired measurement.

For example, if you adjust the sensor so that every 50 beats per second is equivalent to 50 cm it can be for a device the plc that the distance measuring accurately shows by counting the pulses.

Figure(35): Compact Range II Analog Version

7 – Compact range III

These sensors can be calibrated manually or by SonProg program, as in the case of Compact 2 and some of which is in contact open or closed or two similar outputs ranges of (0 – 20 mAmp) or (0 – 10 Volt Dc)

Sensor works hard 20 – 30 Volt Dc and operating loads 300 mAmp can synchronize these sensors to prevent interference when using multiple sensors and spaces close to each other, in addition owns this sensor calculation property and this property is used for sensing liquid level, for example, where it can be changes in measurement resulting occur on the surface of the liquid where the vibration compensation or reduce the impact of these changes this property.

Depending on the type of sensor range lies sensing:

6-30 cm, 20 – 120 cm, 40 – 300 cm, 60 – 600 cm, 80 – 1000 cm

Separation rate – arrived ranges from 0.5 – 5 Hz

This type Provider feature near and distant suppression.

8 – Compact range M 18:

The small size of this sensor (M18 * 101 mm) makes it suitable for applications where small distances.

Figure(36): Compact range M 18

These sensors are available in contact open or closed output of natural or Analog

4 – 20 m Amp, 0 – 20 m Amp, 0 – 10 Volt Dc

The sensor works on the voltage 20 – 30 Volt Dc feeds loads up

mAmp 100, depending on the type of sensor range lies sensing 5 – 30 cm

15 – 100 cm and frequency Sal- chapter 4 – 5 Hz and in feature-term suppression.

Figure(37):Ranges of Compact range M 18:

Fifth: Calculation of distance:

Distance from Object=(Speed of Sound × Time Passed )/2

the speed of sound is 343.2 m/s in air

Infrared Sensor:

This sensor can determine the distance of 10-80 cm.

Working principle :

Figure(38): Working principle of Infrared Sensor

It’s work is very simple sense of where the sender Tx send the Infrared and in the event of a collision with an object or barrier before them and they will bounce back to the receiver in the sensor Rx.

Light rebound depends on the body depending on the nature of the material Collide by these rays and reflective ratio is different from the material for other “white reflection coefficient reflective ratio has a significant greater than 90% and the color black has little reflection coefficient”

Calculate the distance:

Major problem in this sensor is to measure accurately the distance, if that has to do with this sensor non-linear so we can not find a clear formula or an easy way to find the relationship between distance and voltage output V0.

Figure(39): output voltage vs distance in Infrared Sensor

Also there is another inverse relationship between distance and voltages, and its linear relationship significantly. As in Figure(40):

Figure(40): inverse relationship between distance and voltages in Infrared

How can we derive the equation from curves?

Using propensity law and create a linear equation from two known points

we can find a tendency if we know two points in drawing, given to the relationship:

Slope = Y2-Y1 / X2-X1

And linear equation law gives the relationship

Y-Y1=Slope(X-X1)

Of compensation in equations using a colon (0.14,2.98) and (0.016,0.5) Inclination Slope it was 19:53, and the final equation join the inverse of distance with voltage:

distance =X=0.05Y – 0.013

Where x expresses the inverted distance and y expresses the voltage output.

Of course the bad in this sensor that the distance is less than 6 cm can not accurately read and may give false readings if the body in front of him, which is less than 6 cm.

Conclusion & Recommendation:

Ultrasonic distance sensors was very easy to use and it has an acceptable accuracy.

Infrared is cheap nowadays and non-contact sensor also it meets our demand in project

At the end, and after these properties of different techniques of measuring the distance, I recommend to use the Ultrasonic Sensor and the Infrared Sensor.

References

[1] Buck, N.L. & Aherin, R.A. 1991. Human presence detection by a capacitive proximity sensor., 55–60.

[2] Jacob Fraden,Springer Science & Business Media, 29 Apr 2006 – Technology & Engineering

[3] http://www.societyofrobots.com/member_tutorials/book/export/html/71

[4] JohnWilson .Sensor Technology Handbook

[5] Professor Ludwik Finkelstoin .Measurment Science for Engineers.2012

Source: Essay UK - http://www.essay.uk.com/essays/engineering/sensing-techniques-distance/


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