Summer Training Report

On

Passenger Boarding Bridges Operation

Submitted to

Department of Electronics & communication Engineering

TERII

(Technology Education & Research Integrated Institution)

By:

Rajdeep Majumdar

ECE 5thSemester.

Acknowledgement

It is a great pleasure to present this summer training report as a partial fulfilment of the B. Tech course to the department of electronics and communication at TERII, after completing a prosperous tenure of six weeks of training at the Indira Gandhi International Airport for passenger boarding bridges operation.

Where we installed and fabricated the electronic circuits of the passenger boarding bridges which are manuvered automatically by user terminals situated inside the airport terminal.

Thanks to our division incharge Mr Papni and the company ICS we were able to learn all about passenger boarding bridges operation.

Preface

Life is a long journey, wherein each one of us crosses number of

milestones. Every stoppage teaches us a lot. I, being the student of B.

Tech, learnt a plethora of things and was being bombarded with lots of

learning, events, projects, and seminar .

The partial 2-years of the B. Tech course helped in lots of learning.

Such has been the presentations and projects which enhanced our learning

by adding on to our world of knowledge. And summer training is one of the

part to enhance our skills.

It was a life time experience for which I thank to all the staff members of

ICS, my parents, faculty members, administration of TERII, affiliated to

Kurukshetra University.

Declaration

I Rajdeep Majumdar Roll no. 3508149 of 5th semester, B. Tech electronics and communication engineering, hereby assure that the information provided in this summer training report is appropriate to the best of my knowledge.

Rajdeep Majumdar

Roll no. 3508149

5th Semester, ECE.

Index

1. Introduction

2. History

3. Reason for the introduction of Aerobridges

4. Types of Aerobridges

5. Construction of Aerobridges

6. Loading of the Aerobridge

7. The Engineer’s role

8. Electronics used

a. 8 bit Infineon microcontroller

i. Interrupts

ii. Programs

iii. Other microcontroller features

iv. Volumes

b. 40 A Solid State Relay

i. Solid state contactor

c. Capacitive proximity sensors

i. Capacitive displacement sensor

d. Motor controller

i. Applications

ii. Types of motor controllers

9. Future designs

10.Conclusion.

Company profile

The company ICS was established on 1994 by Mr. K.K. Aggarwal when he came to the decision of leading a company for the projects which were becoming quite familiar at the time. Now the company has many branches of electronics, projects, etc. It now has its own division of LED display boards manufacturing company along with undertaken projects like aerobridge construction, display modules for various kinds of display units, etc.

Now the company has almost 5% shares in the state project undertaking at new delhi, one of them is the aerobridge construction. And it has gained a ISO 9000:2000 certification over the past years due to which its value has increased several times since the early years of starting.

At the present moment the son of the owner is partially handling the companies and overseeing most of the work going on at the different working sites. Son of Mr. K.K. Aggarwal is Mr. Rajat Aggarwal. The project of aerobridge operation is managed by the project manager Mr. Sahil Anand.

Introduction

A passenger boarding bridge also known as aerobridge is a new generation pathway for bridging the

gaping distance between the airport terminal and the aeroplane which has been docked at the

terminal. The aerobridge is mainly used for passenger embarkment and disembarkment in the

aeroplane with complete comfort of the passengers. Since the starting of commercial commuting by

the airways using aeroplanes aerobridges are used as the aeroplanes have a definite height which far

surpasses a human’s height. Hence to reach the aircraft comfortably aerobridges are used. At earlier

time of aviation history there were stairs which were manuvered using ground personnel who were

incharge. Later since the stairs were heavy and time consuming to manuver, so they were integrated

with diesel trucks for easy and fast manuverablity. This consumed less time for embarkment and

disembarkment of passengers on the aircraft. The aerobridges also offer all weather protection for the

passengers during boarding operations. This causes efficient operation in rainy, summer seasons.

History

Boarding aircraft dated back to 1900 when Wilbur Wright built his first glider where he climbed into

his seat in the glider. As technology advanced allowing aircraft to carry small number of passengers

due to its size, boarding was done via stairs which were part of the aircraft door. This was possible as

aircraft were generally lower in height, thus allowing the stairs to be fitted on the door. This method

of boarding is still used today on small regional aircraft such as the Canadair CL-600-2C10 Regional

Jet CRJ-700. This aircraft uses stairs on the front left door to embark and disembark passengers and

crews. As this method is very much restricted to being used on small aircraft with a low height, larger

aircraft required a different method of loading.

This was overcome by using external stairs to connect from the aircraft door to the ground. This

method can be used on virtually all commercial passenger/ cargo aircraft.

Originally, these stairs were made of mild construction steel or aluminum and are manually moved

by ground staff. These fixed units maybe easily moved by ground staff when serving small aircraft

such as the Boeing 737s. However, problems arise when serving larger aircraft and at larger airports.

For serving larger aircraft, the stair unit would be larger thus creating problems for ground staff to

move the unit as they could reach over 5 meters in height. Also, at large busy airports, it would be

virtually impossible to move these stair units around the airport manually. This problem was solved

by simply building the stairs above a truck which would simply drive the stairs to the aircraft. This

allowed transportation of large stairs and also moving it at a quicker speed with easy manuverablity.

But after 1970s to save time and providing more comfort to the passengers the aircrafts were parked near the terminals and the gap between the aircraft and the terminal was bridged by mechanical construction of tunnel pathways through which the passengers would embark and disembark in any seasonal condition.

Reason for the introduction of Aerobridges

The main reason for introducing the aerobridge is mainly for passenger comfort. However, it was

only possible with the advancement in technology in the 1970s where manufacturers were able meet

the mechanical requirements for the operation of the aerobridge. Also, the box girder bridge

construction contributed to the development of the aerobridge as the aerobridge is of a box girder

construction. There was not much influence on the material side as aluminum and mild construction

steel were available before the time aerobridge was introduced.

Considering the social side for introducing the aerobridge, one of the main reasons was to serve

disabled passengers without great difficulties. Their immobility may prevent them from using stairs,

thus creating a problem as they may need crews to carry them onto the aircraft and will also likely to

slow the boarding process. If the boarding process took longer than expected, the flight may miss

their time slot for take-off and clearance thus causing delays. Another problem the aerobridge solved

was sheltering passenger from the weather. At stormy, rainy weathers, passengers are likely to get

wet while walking to the stairs. Even once on the stairs which provides an overhead covering, they

may get wet due to the uncovered sides. The aerobridge provided a shelter for passengers as the

aerobridge is in the form of a tunnel where it shields the weather from the passengers inside. Also the

aerobridge is connected to the terminal building which means that passengers need not to walk

outdoor to board the aircraft, as the aerobridge is of a box girder construction, passengers walk inside

the tunnel of the aerobridge. This method of boarding and disembarking will save a considerable

amount of time which is to the advantage of the airline as the turnaround time for the aircraft is

shorter thus allowing the airline to maximize the usage of each aircraft.

Since the introduction of the first aerobridge, there were several improvements made to aerobridges.

As mentioned in the previous section, one of the earliest types is made of aluminum which is not

corrugated (Pedestal Bridge). Although it is light in weight but aluminum would limit its strength

considerably. Problem arises when using aluminum since it burns easily and quickly thus may not be

manufactured nowadays as it would not meet the safety requirements.

The improved type of aerobridge manufactured and used nowadays is made out of mild construction

steel which is corrugated (Apron Dive Bridge). This provides extra strength and with its coating of

fire resistant paint, it can withstand fire for up to 45 minutes which meets the fire safety standard

(NFPA-417). The newest type of material used on aerobridge is glass as its side panels. This uses the

construction of trusses to support the bridge and is also preferred as glass will not corrode.

The earlier types of aerobridges have fixed supports at both ends which limited its movements thus

restricting the number of different types of aircraft the bridge may serve. As mechanics improved,

aerobridges were constructed to having a pivot support at the end closest to the terminal and a roller

support at the end closest to the aircraft which allowed the aerobridge to serve a wider range of

aircraft. The roller support is created by installing wheels on the end closest to the aircraft which

maybe driven changing the position of the aerobridge.

Types of Aerobridges

There are two major types of aerobridges. One uses fixed supports at both end of the bridge (Pedestal Bridge) while the other type have a pivot support at the end closest to the terminal and a roller support at the end closest to the aircraft. (Apron Drive Bridge)

The Pedestal bridge have fixed supports at both the terminal end and at the aircraft end and may only serve a limited range of aircraft as different types of aircraft have different door height in relations to the ground and any aerobridges may not create a slope greater than 8.33% for passenger comfort. The fixed support also requires the aircraft to be stopped at a near exact position to the cab. The Pedestal Bridge is suitable and useful at terminals which serve a large number of same types of aircraft such as T2 and T3 of the Sydney Airport as these domestic terminals handle a large number of Boeing 737s, therefore several gates maybe designated to serve the particular type of aircraft. Using the pedestal bridges are also advantageous when only a limited types of aircraft use the gate as there are less number of serviceable parts in the pedestal bridge comparing to the apron drive bridge. This would minimize the chance of failure. This is attractive to airport operators as reliability is very important because failures causing the gate to be out of use will lead to delays and inconvenience of passengers.

However, when a range of aircraft are to use the same gate, the Apron Drive Passenger Boarding Bridge (PBB) is more suitable as it may serve a large variety of aircraft since it is capable to move to a range of position. The PBB has a pivot support at the terminal end and a roller support at the aircraft end. This allows the PBB to swing a total of 175 degrees (87 degrees both clockwise and counterclockwise) and also have the ability to extend out a greater length allowing serving a wide range of aircraft. As noted above, any aerobridge may not generate a slope greater than 8.33% as it may create problems for passengers boarding the aircraft Therefore, for the PBB to serve in the same gate both large aircraft such as the Boeing 747-400 and small aircraft such as the Boeing 737s, which has a door height difference of over 2 meters, the rotunda at the terminal end is positioned at the average height of the minimum and maximum door height of the aircraft which its designated to handle. Then since the tunnels maybe extended or contracted as the tunnel section comprises of two or three different size tunnels which is fitted inside each other, this may compensate for the slope the PBB will create to meet the height requirement. i.e. as the slope is the gradient of the PBB and has the formula of rise over run, therefore for the same value of rise, increasing the value of run will make the slope gentler while with the same value of rise in a short run distance, the slope will be a lot more sharp thus causing passenger discomfort. Thus the PBB can serve a wider variety of aircraft as the roller support allows the PBB to be extended and contracted. In practice, using the PBB for a larger aircraft will result in less of the tunnel being extended out as larger aircraft have a taller door height while smaller aircraft uses a

greater length of the tunnel as they have a lower door height and the extended tunnel compensate the change in height.

The pivot support is suitable in the PBB as it allows the PBB to swing to its desired position to meet the door position of the aircraft since the aircraft may not stop at exactly where the tunnel of the PBB has been pre-positioned. In fact, the rotunda at the aircraft end provides another pivot support for the cab which rotates about the rotunda. This pivot point will allow further adjustments to position the cab to meet the aircraft door.

Construction of Aerobridge

The method of construction of the aerobridge is the box girder construction as the aerobridge is essentially a tunnel in the shape of a rectangle prism. The aerobridge uses the box girder construction as this construction provides a rigid structure which is strong in strength including torsional strength as the box type construction can withstand twisting force (torque) to a large extent. Ability to withstand torque is imperative as airports are often located in open areas or adjacent to waterfronts which are susceptible to strong wind, thus the bridge need to withstand such twisting force. Another reason for using the box girder construction is that passengers can walk through the box which shields the weather from them.

The aerobridge sits on two supports which are the footing of the bridge. These footings can either be both fixed supports or pivot support along with a roller support. Fixed supports are bolted into the high strength concrete ground of the airport apron. This is done by using large size nuts and bolts to fix the position of the metal support (footing) to the ground. Another method for settling the supports into the concrete ground is to embed the support into the ground by pouring concrete around the support.

Pivot supports are joined to the ground by using nuts and bolts identical to the fix supports. This is possible as the pivot point is well above the ground up at where the rotunda is.

The roller support is not fixed to the ground but the wheels of the support are in contact, thus the aerobridge maybe moved.

The construction method to make the aerobridge is by joining the corrugated mild construction steel sheets together to provide the box type tunnel. This joining is done by the method of welding. The welding must comply with the American Welding Society (AWS) standard. The type of welding is fusion welding which provides great strength. This allows the metal sheets to join together to create the tunnels of the bridge.

In the aerobridges with fix supports, the tunnel is fixed onto the supports by means of nuts and bolts to hold the two members together.

The rotunda is fixed on either the pivot support by using nuts and bolts to hold the two components together. It also uses ball bearings for the rotational function. The tunnel also uses ball bearings internally to connect to the rotundas on both ends for its rotational purpose.

The roller support is fixed to the tunnel by means of nuts and bolts. The vertical movements of the roller support are possible as the columns connected to the tunnel are joined into another column of support which is in contact to the wheels. The vertical movement uses a system of two re-circulating ball bearing screw assemblies moving the column up and down one part of the column system is screwed to the tunnel. The vertical movement speed can reach up to 1097mm per minute. The wheel unit of the roller support is also fixed to the other member by means of nuts and bolts. The horizontal movement uses an electro-mechanical drive system to move outwards with the aid of ball bearings inside the tunnels.

All the metal components of the aerobridge are Commercial Blast cleaned then painted with Sherwin Williams High Build Epoxy Primer paint as the base coat and the finishing coat is Sherwin Williams Polane Polyurethane topcoat. The blast cleaning will ensure excess material and intruding materials be cleaned away to minimize chance of corrosion and the painting will prevent corrosion by the weather. The painting also will make the metal fire resistance for 45 minutes to meet the fire safety standards.

Loading of the Aerobridge

Since the main purpose of the aerobridge is to provide a passage way for passengers to board and disembark from the aircraft with their hand carry baggage, the maximum loading will not be too great. The maximum loading is very much depended on the length of the aerobridge as the cross sectional length is all standard. Maximum loading shall only be estimated for the Apron Drive Passenger Boarding Bridge as this is the main type of aerobridge used nowadays. There are two types of Apron Drive PBB used in Sydney Airport at the moment, the two tunnel model and the three tunnel model. The difference between the two types is the number of tunnels which the tunnel section is comprised of. Three tunnels will result in conserving space when the PBB is fully retracted but fully extended length are not depending on the number of tunnels.

According to the Airport Equipment Ltd/ Jetway Systems General Specification, the maximum live load for the PBB is 195kg/m2. Calculating this figure with the different models of PBB available, the shortest PBB (Max. operating length of 12.497m) can withstand a load of 3460.4193kg equivalent to 46 average adults of 75kg each or 42 average adults with carry on baggage of 7kg each. The longest PBB (Max. operating length of 42.673m) can carry a maximum load of 11816.1537kg equivalent to 157 average adults or 144 average adults with carry on baggage of 7kg each.

The PPB need to also withstand a wind load of 122kg/m2 (145hm/hr) when unused and an operational wind load of 61kg/m2 (97hm/hr).

A roof load of 122kg/m2 is also required when technicians and engineers are required to work on the roof.

The base of the tunnels comprise of corrugated ASTM-A36 medium carbon construction steel to withstand this load along with a centre beam running perpendicular to the corrugated patterns.

The Engineer’s Role

To design and manufacture an aerobridge, several types of engineers need to cooperate together so that the final product maybe manufactured. Different types of engineers include Electronics engineers, Electrical Engineers, Material Engineers and Mechanical Engineers.

Electronics engineers have the role of installing, maintenance and troubleshooting of the sensors, controller units of the drive motors which are connected to the control panel situated inside the airport terminal, as well as they have the role of installing the solid state auxiliary power units and the ground power units which are needed for the powering up of the aircraft when it is docked at the terminal while its own power generator engine is turned off.

Electrical engineers have the role to connect electrical power from the ground source to the aerobridge so that electrical power can provide lighting inside the aerobridge through fluorescent light tubes and also controlling the aerobridge maybe possible as the aerobridge is driven by a joystick which connects to the computer that requires electricity to run on. Electrical power is also required for outside flood lights on the aerobridge while operating at night or at adverse weather so that the aerobridge maybe seen at a distance. The electrical engineer also needed to design an electrical system which is well protected from the weather and from people passing through the aerobridge for safety requirements. To solve this problem, all the electrical cables and other operation related cables are located underneath the tunnel which has limited shelter from the weather and cannot be reached by passengers. Since the horizontal drive of the aerobridge uses an electro-mechanical drive system, electrical power is also required for this purpose.

Material engineers have the role to choose the correct materials to be used in the construction of the aerobridge. Choosing the correct material is imperative as the material is needed to withstand the expect load and work under a range of different weather conditions. The material engineer also needs to select materials that will be reliable and be used for a long period of time without the need of constant maintenance and repairs.

Mechanical engineers are required to design an efficient way to operate (move) the aerobridge for its usage. This includes making the aerobridge move outwards/inwards, upwards/downwards and also swing to meet the aircraft door. The mechanical engineers need to find the way to operate without the excessive use of power and resources.

Thus designing and manufacturing an aerobridge is a big project requiring various types of engineers from different fields to work as a team to design and manufacture an aerobridge that is widely used nowadays.

Electronics used

Although aerobridges are basically are tunnels used for boarding purposes, but due to the technological advancements and increased passenger comfort integrated circuits are used for the synchronisation of the aerobridge with the aeroplane. Apart from these there is a power unit known as the auxiliary power unit which is active when the plane is docked at the terminal, since the plane when docked its power generators are turned off for refuelling and other operations. The following main electronics components were used on which I worked on integrating them and troubleshooting them:

1. 8-bit Infineon Microcontroller.

2. 40 Amp Solid state relay.

3. Capacitive displacement proximity sensor.

4. Motor controller

8-bit Infineon Microcontroller

A microcontroller can be considered a self-contained system with a processor, memory and peripherals and can be used as an embedded system. The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. In this case the control of the lift and drop of the aerobridge through the sensor input.

While some embedded systems are very sophisticated, many have minimal requirements for memory and program length, with no operating system, and low software complexity. Typical input and output devices include switches, relays, solenoids, LEDs, small or custom LCD displays, radio frequency devices, and sensors for data such as temperature, humidity, light level etc.

Embedded systems usually have no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer, and may lack human interaction devices of any kind.

Interrupts

Microcontrollers must provide real time (predictable, though not necessarily fast) response to events in the embedded system they are controlling. When certain events occur, an interrupt system can signal the processor to suspend processing the current instruction sequence and to begin an interrupt service routine (ISR, or "interrupt handler").

The ISR will perform any processing required based on the source of the interrupt before returning to the original instruction sequence. Possible interrupt sources are device dependent, and often include events such as an internal timer overflow, completing an analogue to digital conversion, a logic level change on an input such as from a button being pressed, and data received on a communication link.

Where power consumption is important as in battery operated devices, interrupts may also wake a microcontroller from a low power sleep state where the processor is halted until required to do something by a peripheral event.

Programs

Microcontroller programs must fit in the available on-chip program memory, since it would be costly to provide a system with external, expandable, memory. Compilers and assemblers are used to convert high-level language and assembler language codes into a compact machine code for storage in the microcontroller's memory.

Depending on the device, the program memory may be permanent, read-only memory that can only be programmed at the factory, or program memory may be field-alterable flash or erasable read-only memory.

Other microcontroller features

Microcontrollers usually contain from several to dozens of general purpose input/output pins (GPIO). GPIO pins are software configurable to either an input or an output state. When GPIO pins are configured to an input state, they are often used to read sensors or external signals. Configured to the output state, GPIO pins can drive external devices such as LEDs or motors.

Many embedded systems need to read sensors that produce analogue signals. This is the purpose of the analogue to digital converter (ADC). Since processors are built to interpret and process digital data, i.e. 1s and 0s, they are not able to do anything with the analogue signals that may be sent to it by a device. So the analogue to digital converter is used to convert the incoming data into a form that the processor can recognize. A less common feature on some microcontrollers is a digital to analogue (DAC) that allows the processor to output analogue signals or voltage levels.

In addition to the converters, many embedded microprocessors include a variety of timers as well. One of the most common types of timers is the programmable interval timer (PIT). A PIT may either count down from some value to zero, or up to the capacity of the count register, overflowing to zero. Once it reaches zero, it sends an interrupt to the processor indicating that it has finished counting. This is useful for devices such as thermostats, which periodically test the temperature around them to see if they need to turn the air conditioner on, the heater on, etc.

A micro-controller is a single integrated circuit, commonly with the following features:

Central processing unit - ranging from small and simple 4-bit processors to complex 32- or 64-bit processors

discrete input and output bits, allowing control or detection of the logic state of an individual package pin

serial input/output such as serial ports.

other serial communication interfaces like serial peripheral interfaces and control area network for system interconnect

peripherals such as timers, event counters, PWM generators, and watchdog

volatile memory (RAM) for data storage

many include analog-to-digital converters

in-circuit programming and debugging support

This integration drastically reduces the number of chips and the amount of wiring and circuit board space that would be needed to produce equivalent systems using separate chips. Furthermore, and on low pin count devices in particular, each pin may interface to several internal peripherals, with the pin function selected by software. This allows a part to be used in a wider variety of applications than if pins had dedicated functions. Micro-controllers have proved to be highly popular in embedded systems since their introduction in the 1970s.

Some microcontrollers use a Harvard architecture separate memory buses for instructions and data, allowing accesses to take place concurrently. Where Harvard architecture is used, instruction words for the processor may be a different bit size than the length of internal memory and registers; for example: 12-bit instructions used with 8-bit data registers.

The decision of which peripheral to integrate is often difficult. The microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall lower system cost. Manufacturers have to balance the need to minimize the chip size against additional functionality.

Microcontroller architectures vary widely. Some designs include general-purpose microprocessor cores, with one or more ROM, RAM, or I/O functions integrated onto the package. Other designs are purpose built for control applications. A micro-controller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact. For example, a general purpose processor might require several instructions to test a bit in a register and branch if the bit is set, where a micro-controller could have a single instruction to provide that commonly-required function.

Microcontrollers typically do not have a math co processor, so floating point arithmetic is performed by software.

Volumes

About 55% of all CPUs sold in the world are 8-bit microcontrollers and microprocessors. According to Semico, over four billion 8-bit microcontrollers were sold in 2006.

A typical home in a developed country is likely to have only four general-purpose microprocessors but around three dozen microcontrollers. A typical mid-range automobile has as many as 30 or more microcontrollers. They can also be found in many electrical devices such as washing machines, microwave ovens, and telephones.

Manufacturers have often produced special versions of their microcontrollers in order to help the hardware and software development of the target system. Originally these included EPROM versions that have a "window" on the top of the device through which program memory can be erased by ultraviolet light, ready for reprogramming after a programming ("burn") and test cycle. Since 1998, EPROM versions are rare and have been replaced by EEPROM and flash, which are easier to use (can be erased electronically) and cheaper to manufacture.

Other versions may be available where the ROM is accessed as an external device rather than as internal memory, however these are becoming increasingly rare due to the widespread availability of cheap microcontroller programmers.

The use of field-programmable devices on a microcontroller may allow field update of the firmware or permit late factory revisions to products that have been assembled but not yet shipped. Programmable memory also reduces the lead time required for deployment of a new product.

Where hundreds of thousands of identical devices are required, using parts programmed at the time of manufacture can be an economical option. These "mask programmed" parts have the program laid down in the same way as the logic of the chip, at the same time.

Programming environments

Microcontrollers were originally programmed only in assembly languages, but various high level programming languages are now also in common use to target microcontrollers. These languages are either designed specially for the purpose, or versions of general purpose languages such as the C programming language. Compilers for general purpose languages will typically have some restrictions as well as enhancements to better support the unique characteristics of microcontrollers. Some microcontrollers have environments to aid developing certain types of applications. Microcontroller vendors often make tools freely available to make it easier to adopt their hardware.

Many microcontrollers are so quirky that they effectively require their own non-standard dialects of C, such as SDCC for 8051, which prevent using standard tools (such as code libraries or static analysis tools) even for code unrelated to hardware features. Interpreters are often used to hide such low level quirks.

Simulators are available for some microcontrollers, such as in Microchip's MPLAB environment. These allow a developer to analyze what the behaviour of the microcontroller and their program should be if they were using the actual part. A simulator will show the internal processor state and also that of the outputs, as well as allowing input signals to be generated. While on the one hand most simulators will be limited from being unable to simulate much other hardware in a system, they can exercise conditions that may otherwise be hard to reproduce at will in the physical implementation, and can be the quickest way to debug and analyze problems.

Recent microcontrollers are often integrated with on-chip debug circuitry that when accessed by an in-circuit emulator via JTAG, allow debugging of the firmware with a debugger.

And many others, some of which are used in very narrow range of applications or are more like applications processors than microcontrollers. The microcontroller market is extremely fragmented, with numerous vendors, technologies, and markets. Note that many vendors sell (or have sold) multiple architectures.

Interrupt latency

In contrast to general-purpose computers, microcontrollers used in embedded systems often seek to optimize interrupt latency over instruction throughput. Issues include both reducing the latency, and making it be more predictable (to support real-time control).

When an electronic device causes an interrupt, the intermediate results (registers) have to be saved before the software responsible for handling the interrupt can run. They must also be restored after that software is finished. If there are more registers, this saving and restoring process takes more time, increasing the latency. Ways to reduce such context/restore latency include having relatively few registers in their central processing units (undesirable because it slows down most non-interrupt processing substantially), or at least having the hardware not save them all (this fails if the software then needs to compensate by saving the rest "manually"). Another technique involves spending silicon gates on "shadow registers": one or more duplicate registers used only by the interrupt software, perhaps supporting a dedicated stack.

Other factors affecting interrupt latency include:

Cycles needed to complete current CPU activities. To minimize those costs, microcontrollers tend to have short pipelines (often three instructions or less), small write buffers, and ensure that longer instructions are continuable or restartable. RISC design principles ensure that most instructions take the same number of cycles, helping avoid the need for most such continuation/restart logic.

The length of any critical section that needs to be interrupted. Entry to a critical section restricts concurrent data structure access. When a data structure must be accessed by an interrupt handler, the critical section must block that interrupt. Accordingly, interrupt latency is increased by however long that interrupt is blocked. When there are hard external constraints on system latency, developers often need tools to measure interrupt latencies and track down which critical sections cause slowdowns.

o One common technique just blocks all interrupts for the duration of the critical section. This is easy to implement, but sometimes critical sections get uncomfortably long.

o A more complex technique just blocks the interrupts that may trigger access to that data structure. This often based on interrupt priorities, which tend to not

correspond well to the relevant system data structures. Accordingly, this technique is used mostly in very constrained environments.

Interrupt nesting. Some microcontrollers allow higher priority interrupts to interrupt lower priority ones. This allows software to manage latency by giving time-critical interrupts higher priority (and thus lower and more predictable latency) than less-critical ones.

Trigger rate. When interrupts occur back-to-back, microcontrollers may avoid an extra context save/restore cycle by a form of tail call optimization.

Lower end microcontrollers tend to support fewer interrupt latency controls than higher end ones.

Specifications:

Manufacturer: Infineon Microprocessors Ltd.

Operating Temperature: 0 to 110 degree centigrade

Grade: Commercial

Architecture: Harvard

Maximum pins: 40

Bit width: 8 bits.

40 Amp solid state relay

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

SPST – Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.

SPDT – Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

DPST – Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. The poles may be Form A or Form B (or one of each).

DPDT – Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100 to 1,200 amperes, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients.

Solid state contactor relay

A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controllers (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

Specifications:

Manufacturer: Tesla Electronics limited

Grade: Military

Operating Temperature: -20 to 90 degree centigrade

Voltage rating: 440 volts AC

Voltage rating for the activation of relay: 48 volts DC

Maximum current capacity: 40 amps

Maximum current absorbed: 0.25 amps

Internal resistance: 245 ohms.

Capacitive displacement proximity sensor

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor requires a metal target.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

Proximity sensors are also used in machine vibration monitoring to measure the variation in distance between a shaft and its support bearing. This is common in large steam turbines, compressors, and motors that use sleeve-type bearings.

A proximity sensor adjusted to a very short range is often used as a touch switch.

A proximity sensor is divided in two halves and if the two halves move away from each other, then a signal is activated.

A proximity sensor can be used in windows, and when the window opens an alarm is activated.

Capacitive displacement sensor

Capacitive displacement sensors “are non-contact devices capable of high-resolution measurement of the position and/or change of position of any conductive target”. They are also able to measure the thickness or density of non-conductive materials. Capacitive displacement sensors are used in a wide variety of applications including semiconductor processing, assembly of precision equipment such as disk drives, precision thickness measurements, machine tool metrology and assembly line testing. These types of sensors can be found in machining and manufacturing facilities around the world.

To sense the displacement by the capacitive sensor the basic capacitance equation is used:

Where C is the capacitance, ε0 is the permittivity of free space constant, K is the dielectric constant of the material in the gap, A is the area of the plates, and d is the distance between the plates. A capacitive sensing system uses a similar model, but in place of one of the conductive plates, is the sensor, and in place of the other, is the conductive target to be measured. Since the area of the probe and target remain constant, and the dielectric of the material in the gap (usually air) also remains constant, "any change in capacitance is a result of a change in the distance between the probe and the target." Therefore, the equation above can simplified to:

Where α indicates a proportional relationship. Due to this proportional relationship, a capacitive sensing system is able to measure changes in capacitance and translate these changes into distance measurements.

The capacitive sensor senses the level of the aeroplane since it is set on suspensions which compress and decompress upon boarding procedure which can damage the door since it directly lies inside the aerobridge as it is opened outside. Whenever the level of the aeroplane drops or lifts from the safety limits the microcontroller senses the displacement through the capacitive sensor and sends the signal to the motor controller and then this motor controller controls the life and drop of the aerobridge.

Specifications:

Manufacturers: Jet Semiconductors LTD.

Grade: Military

Operating temperature: -20 to 80 degree Centigrade

Accuracy: 96%

Effective sensing distance: 40 mm

Operating voltage: 5 volts

Current rating: 2mA

Motor controller

A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motors. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.

Motor controllers can be of different types but here only solid state motor controller is used since there is a need of interfacing between the microcontrollers.

Applications

Every electric motor has to have some sort of controller. The motor controller will have differing features and complexity depending on the task that the motor will be performing.

The simplest case is a switch to connect a motor to a power source, such as in small appliances or power tools. The switch may be manually operated or may be a relay or contactor connected to some form of sensor to automatically start and stop the motor. The switch may have several positions to select different connections of the motor. This may allow reduced-voltage starting of the motor, reversing control or selection of multiple speeds. Overload and overcurrent protection may be omitted in very small motor controllers, which rely on the supplying circuit to have overcurrent protection. Small motors may have built-in overload devices to automatically open the circuit on overload. Larger motors have a protective overload relay or temperature sensing relay included in the controller and fuses or circuit breakers for overcurrent protection. An automatic motor controller may also include limit switches or other devices to protect the driven machinery.

More complex motor controllers may be used to accurately control the speed and torque of the connected motor (or motors) and may be part of closed loop control systems for precise positioning of a driven machine. For example, a numerically controlled lathe will accurately position the cutting tool according to a preprogrammed profile and compensate for varying load conditions and perturbing forces to maintain tool position.

Types of motor controllers

Motor controllers can be manually, remotely or automatically operated. They may include only the means for starting and stopping the motor or they may include other functions.

An electric motor controller can be classified by the type of motor it is to drive such as permanent magnet, servo, series, separately excited, and alternating current.

A motor controller is connected to a power source such as a battery pack or power supply, and control circuitry in the form of analog or digital input signals.

Specifications of the motor controller:

Voltage rating for the controller: 48 volts DC

Amperage rating for the controller: 2 amps

Voltage rating for the motor: 440 volts AC three phase

Maximum amperage rating: 125 amperes

Operating temperature: -10 to 80 degree Centigrade

Tolerance: 10%

Inductance: 0.65 Henry

Future Designs

Although the Apron Drive PBB is sufficient for today’s aviation industry, improvements are being continuously thought of to minimize aircraft turn around time thus maximizing the usage of each single aircraft. This resulted in busy airports having 2 separate apron drive PBBs at each gate so that passengers may board and deplane the aircraft at a much quicker rate. The best example is at Hong Kong Chek Lap Kok International airport where there are 2 independent apron drive PBBs serving each gate so that First and Business class passengers may board the aircraft using one PBB while Economy class passengers board via the other PBB. Although this will not save too much time during the boarding process as passengers are restricted to which PBB they may used, but having 2 PBBs can save a considerable amount of time for when passengers deplane on arrival. Once the First and Business class passengers have deplaned via their designated PBB, the remaining Economy class passengers may also use the First and Business class passenger’s PBB to deplane thus saving time. This concept is imperative for larger planes as there could well be over 350 passengers on the plane at one time thus will take some time to board and deplane all passengers. Especially when the Airbus A380-800 comes into service in 2006, dual PBB must be used as this aircraft is capable of carrying 550 passengers.

Another improvement on existing apron drive PBB is the Glass Boarding Bridge where the side panels of the tunnels are made of glass. The main reason for this improvement is for

consumer’s requirement as it provides passenger with a clear view of the apron prior boarding their aircraft.

Conclusion

The aerobridge itself is a wonderful product as it has a long history as of the aeroplane itself. This training taught us a lot about the aerobridge itself and its components. With this we also learnt little about the other engineering trades like mechanical engineering, electrical engineering, etc. And cooperating with them as this was a combined project.

The aerobridge is quite complex in the making since it has so many intricate detailed components which are crucial for the stable operation of the aerobridge in the future. These types of projects bring all kinds of persons with different expertise together to make a new product which is marvellous in every aspect. This project trains us about knowledge and information of the project itself, but at the same time it teaches us about group cooperation along with various precious skills which are crucial for our future when we would be leading a team of fine trainees.