Radio Communication

Sound and radio waves are different phenomena. Sound consists of pressure variations in matter, such as air or water. Sound will not travel through a vacuum. Radio waves, like visible light, infrared, ultraviolet, X-rays and gamma rays, are electromagnetic waves that do travel through a vacuum. When
you turn on a radio you hear sounds because the transmitter at the radio station has converted the sound waves into electromagnetic waves, which are then encoded onto an electromagnetic wave in the radio frequency range (generally in the range of 500-1600 kHz for AM stations, or 86-107 MHz for FM stations). Radio electromagnetic waves are used because they can travel very large distances through the atmosphere without being greatly attenuated due to scattering or absorption. Your radio receives the radio waves, decodes this information, and uses a speaker to change it back into a sound wave. An animated illustration of this process is given below (mouse-over the images for animations).

• A sound wave is produced with a frequency of 5 Hz - 20 kHz.                                                                                                    
• The sound wave is equivalent to a pressure wave traveling through the air.

• A microphone converts the sound wave into an electrical signal.

•    The electrical wave traveling through the microphone wire is analogous to the original sound wave. 
• The electrical wave is used to encode or modulate a high-frequency "carrier" radio wave. The carrier wave itself does not include any of the sound information until it has been modulated.
• The carrier wave can either be amplitude modulated by the electrical signal, or frequency modulated.
• 
• The signal is transmitted by a radio broadcast tower.
• 
• Your radio contains an antennato detect the transmitted signal, a tuner to pick out the desired frequency, a demodulator to extract the original sound wave from the transmitted signal, and an amplifier which sends the signal to the speakers. The speakers convert the electrical signal into physical vibrations (sound).

HOW METAL DETECTOR WORKS

Transmitter

Inside the metal detector's loop there is a coil of wire called the transmit coil. Electronic current is driven through the coil to create an electromagnetic field. The direction of the current flow is reversed several thousand times every second; the transmit frequency "operating frequency" refers to the number of times per second that the current flow goes from clockwise to counterclockwise and back to clockwise again.

When the current flows in a given direction, a magnetic field is produced whose polarity  points into the ground; when the current flow is reversed, the field's polarity points out of the ground. Any metallic object which happens to be nearby will have a flow of current induced inside of it by the influence of the changing magnetic field, in much the same way that an electric generator produces electricity by moving a coil of wire inside a fixed magnetic field. This current flow inside a metal object in turn produces its own magnetic field, with a polarity that tends to be pointed opposite to the transmit field.

Receiver

A second coil of wire inside the loop, the receive coil, is arranged so that nearly all of the current that would ordinarily flow in it due to the influence of the transmitted field is cancelled out. Therefore, the field produced by the currents flowing in the nearby metal object will cause currents to flow in the receive coil which may be amplified and processed by the metal detector's electronics without being swamped by currents resulting from the much stronger transmitted field.
The resulting received signal will usually appear delayed when compared to the transmitted signal. This delay is due to the tendency of conductors to impede the flow of current (resistance) and to impede changes in the flow of current (inductance). We call this apparent delay "phase shift". The largest phase shift will occur for metal objects which are primarily inductive; large, thick objects made from excellent conductors like gold, silver, and copper. Smaller phase shifts are typical for objects which are primarily resistive; smaller, thinner objects, or those composed of less conductive materials.

Position Sensors

Position Sensors

In this tutorial we will look at a variety of devices which are classed as Input Devices and are therefore called "Sensors" and in particular those sensors which are Positional in nature which means that they are re
ferenced either to or from some fixed point or position. As their name implies, these types of sensors provide a "position" feedback.

One method of determining a position, is to use either "distance", which could be the distance between two points such as the distance travelled or moved away from some fixed point, or by "rotation" (angular movement). For example, the rotation of a robots wheel to determine its distance travelled along the ground. Either way, Position Sensors can detect the movement of an object in a straight line usingLinear Sensors or by its angular movement using Rotational Sensors.

The Potentiometer.

The most commonly used of all the "Position Sensors", is the potentiometer because it is an inexpensive and easy to use position sensor. It has a wiper contact linked to a mechanical shaft that can be either angular (rotational) or linear (slider type) in its movement, and which causes the resistance value between the wiper/slider and the two end connections to change giving an electrical signal output that has a proportional relationship between the actual wiper position on the resistive track and its resistance value. In other words, resistance is proportional to position.

Potentiometer

Potentiometers come in a wide range of designs and sizes such as the commonly available round rotational type or the longer and flat linear slider types. When used as a positional sensor the moveable object is connected directly to the shaft or slider of the potentiometer and a DC reference voltage is applied across the two outer fixed connections forming the resistive element. The output voltage signal is taken from the wiper terminal of the sliding contact as shown below.

this configuration produces a potential or voltage divider type circuit output which is proportional to the shaft position. Then for example, if you apply a voltage of say 10v across the resistive element of the potentiometer the maximum output voltage would be equal to the supply voltage at 10 volts, with the minimum output voltage equal to 0 volts. Then the potentiometer wiper will vary the output signal from 0 to 10 volts, with 5 volts indicating that the wiper or slider is at its half-way or centre position.

Potentiometer Construction

The output signal (Vout) from the potentiometer is taken from the centre wiper connection as it moves along the resistive track, and is proportional to the angular position of the shaft.

Example of a simple Positional Sensing Circuit

While resistive potentiometer position sensors have many advantages: low cost, low tech, easy to use etc, as a position sensor they also have many disadvantages: wear due to moving parts, low accuracy, low repeatability, and limited frequency response.

But there is one main disadvantage of using the potentiometer as a positional sensor. The range of movement of its wiper or slider (and hence the output signal obtained) is limited to the physical size of the potentiometer being used. For example a single turn rotational potentiometer generally only has a fixed electrical rotation between about 240 to 330^o however, multi-turn pots of up to 3600^o of electrical rotation are also available. Most types of potentiometers use carbon film for their resistive track, but these types are electrically noisy (the crackle on a radio volume control), and also have a short mechanical life.

Wire-wound pots also known as rheostats, in the form of either a straight wire or wound coil resistive wire can also be used, but wire wound pots suffer from resolution problems as their wiper jumps from one wire segment to the next producing a logarithmic (LOG) output resulting in errors in the output signal. These too suffer from electrical noise.

For high precision low noise applications conductive plastic resistance element type polymer film or cermet type potentiometers are now available. These pots have a smooth low friction electrically linear (LIN) resistive track giving them a low noise, long life and excellent resolution and are available as both multi-turn and single turn devices. Typical applications for this type of high accuracy position sensor is in computer game joysticks, steering wheels, industrial and robot applications.

Inductive Position Sensors.

Linear Variable Differential Transformer

One type of positional sensor that does not suffer from mechanical wear problems is the "Linear Variable Differential Transformer" or LVDT for short. This is an inductive type position sensor which works on the same principle as the AC transformer that is used to measure movement. It is a very accurate device for measuring linear displacement and whose output is proportional to the position of its moveable core.

It basically consists of three coils wound on a hollow tube former, one forming the primary coil and the other two coils forming identical secondaries connected electrically together in series but 180^o out of phase either side of the primary coil. A moveable soft iron ferromagnetic core (sometimes called an "armature") which is connected to the object being measured, slides or moves up and down inside the tube. A small AC reference voltage called the "excitation signal" (2 - 20V rms, 2 - 20kHz) is applied to the primary winding which inturn induces an EMF signal into the two adjacent secondary windings (transformer principles).

If the soft iron magnetic core armature is exactly in the centre of the tube and the windings, "null position", the two induced emf's in the two secondary windings cancel each other out as they are 180^oout of phase, so the resultant output voltage is zero. As the core is displaced slightly to one side or the other from this null or zero position, the induced voltage in one of the secondaries will be become greater than that of the other secondary and an output will be produced.

The polarity of the output signal depends upon the direction and displacement of the moving core. The greater the movement of the soft iron core from its central null position the greater will be the resulting output signal. The result is a differential voltage output which varies linearly with the cores position. Therefore, the output signal has both an amplitude that is a linear function of the cores displacement and a polarity that indicates direction of movement.

The phase of the output signal can be compared to the primary coil excitation phase enabling suitable electronic circuits such as the AD592 LVDT Sensor Amplifier to know which half of the coil the magnetic core is in and thereby know the direction of travel.

The Linear Variable Differential Transformer

When the armature is moved from one end to the other through the centre position the output voltages changes from maximum to zero and back to maximum again but in the process changes its phase angle by 180 deg's. This enables the LVDT to produce an output AC signal whose magnitude represents the amount of movement from the centre position and whose phase angle represents the direction of movement of the core.

A typical application of a linear variable differential transformer (LDVT) sensor would be as a pressure transducer, were the pressure being measured pushes against a diaphragm to produce a force. The force is then converted into a readable voltage signal by the sensor.

Advantages of the linear variable differential transformer, or LVDT compared to a resistive potentiometer are that its linearity, that is its voltage output to displacement is excellent, very good accuracy, good resolution, high sensitivity as well as frictionless operation. They are also sealed for use in hostile environments.

Inductive Proximity Sensors.

Another type of inductive sensor in common use is the Inductive Proximity Sensor also called an Eddy current sensor. While they do not actually measure displacement or angular rotation they are mainly used to detect the presence of an object in front of them or within a close proximity, hence the name proximity sensors.

Proximity sensors, are non-contact devices that use a magnetic field for detection with the simplest magnetic sensor being the reed switch. In an inductive sensor, a coil is wound around an iron core within an electromagnetic field to form an inductive loop.

When a ferromagnetic material is placed within the eddy current field generated around the inductive sensor, such as a ferromagnetic metal plate or metal screw, the inductance of the coil changes significantly. The proximity sensors detection circuit detects this change producing an output voltage. Therefore, inductive proximity sensors operate under the electrical principle of Faraday's Law of inductance.

Inductive Proximity Sensors

An inductive proximity sensor has four main components; The oscillator which produces the electromagnetic field, the coil which generates the magnetic field, the detection circuit which detects any change in the field when an object enters it and the output circuit which produces the output signal, either with normally closed (NC) or normally open (NO) contacts. Inductive proximity sensors allow for the detection of metallic objects in front of the sensor head without any physical contact of the object itself being detected. This makes them ideal for use in dirty or wet environments. The "sensing" range of proximity sensors is very small, typically 0.1mm to 12mm.

Proximity Sensor

As well as industrial applications, inductive proximity sensors are also used to control the changing of traffic lights at junctions and cross roads. Rectangular inductive loops of wire are buried into the tarmac road surface and when a car or other road vehicle passes over the loop, the metallic body of the vehicle changes the loops inductance and activates the sensor thereby alerting the traffic lights controller that there is a vehicle waiting.

One main disadvantage of these types of sensors is that they are "Omni-directional", that is they will sense a metallic object either above, below or to the side of it. Also, they do not detect non-metallic objects althoughCapacitive Proximity Sensors and Ultrasonic Proximity Sensors are available. Other commonly available magnetic position sensor include: reed switches, hall effect sensors and variable reluctance sensors.

Rotary Encoders.

Rotary Encoders resemble potentiometers mentioned earlier but are non-contact optical devices used for converting the angular position of a rotating shaft into an analogue or digital data code. In other words, they convert mechanical movement into an electrical signal (preferably digital).

All optical encoders work on the same basic principle. Light from an LED or infra-red light source is passed through a rotating high-resolution encoded disk that contains the required code patterns, either binary, grey code or BCD. Photo detectors scan the disk as it rotates and an electronic circuit processes the information into a digital form as a stream of binary output pulses that are fed to counters or controllers which determine the actual angular position of the shaft.

There are two basic types of rotary optical encoders, Incremental Encoders and Absolute Position Encoders.

Incremental Encoder

Encoder Disk

Incremental Encoders, also known as quadrature encoders or relative rotary encoder, are the simplest of the two position sensors. Their output is a series of square wave pulses generated by a photocell arrangement as the coded disk, with evenly spaced transparent and dark lines called segments on its surface, moves or rotates past the light source. The encoder produces a stream of square wave pulses which, when counted, indicates the angular position of the rotating shaft.

Incremental encoders have two separate outputs called "quadrature outputs". These two outputs are displaced at 90^oout of phase from each other with the direction of rotation of the shaft being determined from the output sequence.

The number of transparent and dark segments or slots on the disk determines the resolution of the device and increasing the number of lines in the pattern increases the resolution per degree of rotation. Typical encoded discs have a resolution of up to 256 pulses or 8-bits per rotation.

The simplest incremental encoder is called a tachometer. It has one single square wave output and is often used in unidirectional applications where basic position or speed information only is required. The "Quadrature" or "Sine wave" encoder is the more common and has two output square waves commonly called channel A and channel B. This device uses two photo detectors, slightly offset from each other by 90^o thereby producing two separate sine and cosine output signals.

Simple Incremental Encoder

By using the Arc Tangent mathematical function the angle of the shaft in radians can be calculated. Generally, the optical disk used in rotary position encoders is circular, then the resolution of the output will be given as: θ = 360/n, where n equals the number of segments on coded disk. Then for example, the number of segments required to give an incremental encoder a resolution of 1^o will be: 1^o = 360/n, therefore, n = 360 windows, etc. Also the direction of rotation is determined by noting which channel produces an output first, either channel A or channel B giving two directions of rotation, A leads B or B leads A. This arrangement is shown below.

Incremental Encoder Output

One main disadvantage of incremental encoders when used as a position sensor, is that they require external counters to determine the absolute angle of the shaft within a given rotation. If the power is momentarily shut off, or if the encoder misses a pulse due to noise or a dirty disc, the resulting angular information will produce an error. One way of overcoming this disadvantage is to use absolute position encoders.

Absolute Position Encoder

Absolute Position Encoders are more complex than quadrature encoders. They provide a unique output code for every single position of rotation indicating both position and direction. Their coded disk consists of multiple concentric "tracks" of light and dark segments. Each track is independent with its own photo detector to simultaneously read a unique coded position value for each angle of movement. The number of tracks on the disk corresponds to the binary "bit"-resolution of the encoder so a 12-bit absolute encoder would have 12 tracks and the same coded value only appears once per revolution.

4-bit Binary Coded Disc

One main advantage of an absolute encoder is its non-volatile memory which retains the exact position of the encoder without the need to return to a "home" position if the power fails. Most rotary encoders are defined as "single-turn" devices, but absolute multi-turn devices are available, which obtain feedback over several revolutions by adding extra code disks.

Typical application of absolute position encoders are in computer hard drives and CD/DVD drives were the absolute position of the drives read/write heads are monitored or in printers/plotters to accurately position the printing heads over the paper.

Ultrasonic level measurement

Liquid Level Sensors

Non-contact ultrasonic level measurement is ideal for simple standard applications, both for liquids and for solids.

Measuring principle of ultrasonic level measurement

The ultrasonic sensor emits ultrasonic pulses in the direction of the medium, which then reflects them back.
The elapsed time from emission to reception of the signals is proportional to the level in the tank.

The advantages of ultrasonic level measurement

The non-contact measurement with ultrasonic sensors is independent of product properties and provides for maintenance-free operation.

VEGASON 61

Application area

The VEGASON 61 is an ultrasonic sensor for continuous level measurement of liquids or bulk solids. Typical applications are the measurement of liquids in storage tanks or open basins. The sensor is also suitable for the detection of bulk solids in small vessels or open containers. The non-contact measuring principle is independent of product features and allows a setup without medium.

Advantages

• Non-contact measurement
• Reliable measurement independent of product features
• Price-favourable solution for simple applications

Technical data

Measuring range

in liquids: 0.25 … 5 m
in bulk solids: 0.25 … 2 m

Process fitting

thread G1½, 1½ NPT

Process temperature

-40 … +80 °C

Process pressure

-0,2 … +2 bar
(-20 … +200 kPa)

Accuracy

+/- 10 mm

SIL qualification

optionally up to SIL2

VEGASON 62

Application area

The VEGASON 62 is an ultrasonic sensor for continuous level measurement of liquids and bulk solids. Typical applications are the measurement of liquids in storage vessels or open basins. The sensor is also suitable for the detection of bulk solids in small vessels or silos. Application areas can be found in all industries. The non-contact measuring principle is unaffected by product features and allows a setup without medium.

Advantages

• Non-contact measurement
• Reliable measurement independent of product features
• Price-favourable solution for simple applications

Technical data

Measuring range

in liquids: 0.4 … 8 m
in bulk solids: 0.4 … 3.5 m

Process fitting

thread G2, 2 NPT

Process temperature

-40 … +80 °C

Process pressure

-0,2 … +2 bar(-20 … +200 kPa)

Accuracy

+/- 10 mm

SIL qualification

optionally up to SIL2

VEGASON 63

Application area

The VEGASON 63 is an ultrasonic sensor for continuous level measurement of liquids and bulk solids. Typical applications are the measurement of liquids in storage tanks and open basins. The sensor is suitable for continuous level measurement of bulk solids in small up to average-size vessels. The non-contact measuring principle is independent of product features and allows a setup without medium.

Advantages

• Non-contact measurement
• Reliable measurement, independent of product features
• Proven measurement technology for standard applications

Technical data

Measuring range

in liquids: 0.6 … 15 m
in bulk solids: 0.6 … 7 m

Process fitting

compression flange DN 100
mounting strap

Process temperature

-40 … +80 °C

Process pressure

-0,2 … +1 bar
(-20 … +100 kPa)

Accuracy

+/- 10 mm

SIL qualification

optionally up to SIL2

Basic Info About SIM Card

A smart SIM card is a small piece of technology with many big uses. Whether boosting cell phone memory or allowing secure mobile bank transactions, these small chips are a popular component in many industries. Lightweight construction and massive memory capacities help them edge out traditional smart card technology. 

A traditional SIM card is a small card with an embedded microchip that allows it to process data. Sim cards
are constructed of PVC plastic, and many feature a hologram for authentication purposes. Each card has unique smart card encryption in order to provide security. A smart SIM card provides the same features but has a larger capacity for memory and speed than a traditional SIM card. These most commonly are found within cell phones but are becoming more popular in identification and credit cards.
A cell phone is the most likely place to find a smart SIM card, which typically is the size of a postage stamp and located securely behind the battery. The GSM phone has been utilizing this technology more than other phones, and it provides an instant boost in performance to any model holding it. Most smart cards come with about 65 kilobytes of memory, nearly double other SIM cards. The card also has the capacity for storing up to 250 phone numbers, compared to most SIM cards' bank of 100. The encryption option also allows for storing passwords and user IDs securely. 

A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that securely stores the International Mobile Subscriber Identity (IMSI) and the related key used to identify and authenticate subscribers on mobile telephony devices ,such as mobile phones and computers.

It  is also a portable memory chip used mostly in cell phones that operate on the Global System for Mobile Communications (GSM) network. These cards hold the personal information of the account holder, including his or her phone number, address book, text messages, and other data. When a user wants to change phones, he or she can usually easily remove the card from one handset and insert it into another. SIM cards are convenient and popular with many users, and are a key part of developing cell phone technology.

Sim Cards are of four (4) Types. Named as Below H1, H2, H3, H4
H1= You Will Get Normal Network On This Sim
H2= You Will Get Better Network On This Sim, Means Strong
H3= You Will Get More Better Network On This Sim, Means Stronger
H4= Normal, Better, More Better Is Nothing In Front OF This Sim.
Basically H4 Sim giving for Corporate Sim, Army Peoples etc. The Company doesn’t Provide H4 Sim To all User,because this Sim eat More bandwidth. For knowing Which Type of  Sim is using Just Check Its Back Side and will Get the Sim No. and the Sim Type.

SIM cards are made in three different sizes to accommodate different devices. Most phones use mini-SIM or micro-SIM cards, which are quite small — the mini is 25 mm by 15 mm , and the micro is 15 mm by 12 mm.Full-sized cards are much larger, 85.6 mm by 53.98 mm , and are too big for most phones. All cards are only 0.76 mm thick, and the microchip contacts are in the same arrangement. This means that, with the proper adapter, the smaller cards can be used in devices designed for larger ones.

A SIM card offers security for both the user’s data and his or her calls. The cards can be locked, meaning that only someone who has the correct personal identification number (PIN) can use the card. If the phone is stolen, the thief cannot use a locked SIM or get any information off of it without the PIN.