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Group Members:Nur Mustakim Bin Jalil

Wan Ameerul Izwan Bin NordinRozzaireen Bin Ishak

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You are maintenance team in your factory which assignedwith a special task to investigate a faulty pneumaticcylinder in a assembly line. During inspection is was learntthat the faulty part was the sensor for the piston position

detection. The cylinder is made of aluminum casing wall.

The task of your team is to rectify the faulty sensor. Inorder to accomplish this, your team need to identify thetype of sensor, the operating principal of the sensor and

also the sensor characteristic and parameters. You have topresent your solution to the plant manager by emphasizingthe sensor switching behavior and justify why it is the bestsolution for this problem.

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Magnetic cylinder sensors are used to detect the position ofpistons in pneumatic cylinders. They are attached directly tothe cylinder body and operate according to the same

principle as for magnetic proximity sensors. They detect aring magnet in the piston through the housing wallmade of non-magnetizable material (aluminium, brass,stainless steel).

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Traverse distances Response sensitivity Actuating speed

The traversedistances isbetween 5 and 20mm, depending onthe cylinder'sconstruction (wall

thickness, diameter,and magneticinduction). Thetypical hysteresis is1mm and remainsconstant.

The magneticinduction ofpneumatic cylinders isbetween 5 and 25mTesla. A responsesensitivity of

3mTesla is enough toensure signaltriggering.Thesensitivity of 3mT is aguide value whichdepunds on the designof the cylinder.

The short responsetimes of thesensors allowactuating speeds ofup to 5 m/s.

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H ave many type of magnetic sensor. But wechoose only 3 magnetic sensor.

1. H all-Effect sensor2. GMR sensor3. REED switch sensor

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H all-Effect sensors are solid-state electronicdevices.

In operation, a steady dc current passes throughthe thin H all-Effect chip.

The sensor output switches on when thegenerated voltage reaches the comparatorsthreshold.

H all-Effect sensors are electronic devices, theyhave no moving parts. Unlike a reed switch,

their response time does not depend onmagnetic forces overcoming mechanical inertia. Inexpensive H all-Effect sensors can switch twice

because they detect both poles of the magnet,not just one or the other.

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The most up-to-date magnetic field sensingtechnology is called giant magnetoresistiveor GMR. GMR sensors have a more robust

reaction to the presence of a magnetic field,at least 10%.

GMR sensors can be packaged in muchsmaller housings for short-stroke cylinders,

extremely small-bore cylinders, or miniaturepneumatic grippers.

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The simplest magnetic-field sensor is a reed switch. Itcontains two ferromagnetic nickel and iron reed elementsin an evacuated, hermetically sealed glass tube tominimize contact arcing. When an axially aligned magnet

approaches the switch, its magnetic force closes thereeds. The magnet typically generates at least a 50 Gaussforce to overcome the return force or spring memory ofthe reed elements.

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P ull In (PI) is the point where the reed switchcontacts close.

D rop out (DO) is the point where the reed switchcontacts open.

Most companies measure the reed switch in AmpereTurns (AT). Universally milliTesla (mT) is a moregenerally accepted magnetic measurementunit. MEDER electronic is the first and onlymanufacturer to convert over to mT, but continues toreference AT.

Pull-in and Drop-out are the points referred to whenthe contacts close and open. AT or mT indicate therelative magnetic strength at these opening andclosing points. Also, its very convenient to specifythe closure and opening points in distance for specificapplications.

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Reed switches are the least expensiveand simplest type of magnetic fieldsensors. Magnets on the pistonsactivate the reed switches when theyare in close proximity.

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The reason why we choose a Reed switchsensor because :

1. Its can be function at both of AC and DCelectrical load.

2. Reed switches installed in high shock andvibration applications.

3. Reed switches are the least inexpensive andsimplest type of magnetic field sensors.