CHAPTER 5 - BRIDGE MEASURING CIRCUIT

BRIDGE MEASURING CIRCUIT

     A bridge circuit is a type of electrical circuit in which two circuit branches (usually in parallel with each other) are "bridged" by a third branch connected between the first two branches at some intermediate point along them. The bridge was originally developed for laboratory measurement purposes and one of the intermediate bridging points is often adjustable when so used. Bridge circuits now find many applications, both linear and non-linear, including in instrumentation, filtering and power conversion.

     The best-known bridge circuit, the Wheatstone bridge, was invented by Samuel Hunter Christie and popularized by Charles Wheatstone, and is used for measuring resistance. It is constructed from four resistors, two of known values R1 and R3 (see diagram), one whose resistance is to be determined Rx, and one which is variable and calibrated R2. Two opposite vertices are connected to a source of electric current, such as a battery, and a galvanometer is connected across the other two vertices. The variable resistor is adjusted until the galvanometer reads zero. It is then known that the ratio between the variable resistor and its neighbor R1 is equal to the ratio between the unknown resistor and its neighbor R3, which enables the value of the unknown resistor to be calculated.

     The Wheatstone bridge has also been generalized to measure impedance in AC circuits, and to measure resistance, inductance, capacitance, and dissipation factor separately. Various arrangements are known as the Wien bridge, Maxwell Bridge and Heaviside bridge. All are based on the same principle, which is to compare the output of two potentiometers sharing a common source.

     The Wheatstone bridge (or resistance bridge) circuit can be used in a number of applications and today, with modern Operational Amplifiers. We also can use the Wheatstone Bridge Circuit to interface various transducers and sensors to these amplifier circuits.

     The Wheatstone Bridge circuit is nothing more than two simple series-parallel arrangements of resistors connected between a voltage supply terminal and ground producing zero voltage difference when the two parallel resistor legs are balanced. A Wheatstone bridge circuit has two input terminals and two output terminals consisting of four resistors configured in a diamond-like arrangement as shown.

     In power supply design, a bridge circuit or bridge rectifier is an arrangement of diodes or similar devices used to rectify an electric current, i.e. to convert it from an unknown or alternating polarity to a direct current of known polarity.

     In some motor controllers, a H-bridge is used to control the direction the motor turns.


References:

Young, Hugh D. Just the FACTS101.

http://dbpedia.org/describe/?url=http%3A%2F%2Fdbpedia.org%2Fresource%2FBridge_circuit&graph=http%3A%2F%2Fdbpedia.org 24 April 2014

CHAPTER 4 - MECHANICALLY OPERATED SWITCH

MECHANICALLY OPERATED SWITCH

This is switch with the momentary type, a force has to be applied to change the switch from ON to OFF (or OFF to ON). When the force is removed, the switch immediately returns to its original position. Or lets say that mechanically operated switch is one that is controlled automatically by factors such as pressure, position, and temperature.

·         Limit switch is a very common industrial control device which are designed to operate only when predetermined limit is reached and they are usually actuated by contact with an object as cam.

·         Microswitch is a snap-acting switch housed in small enclosure. In a snap-acting switch, as in a toggle switch, the actual switching of the circuit takes place at a fixed speed no matter how quickly or slowly the activating mechanism moves

·         Temperature switches (thermostats) are used to sense temperature changes. Although there are many type available, they are actuated by some specific environmental temperature change. It open or closed when designated temperature is reached.

·         Pressure switches are used to control the pressure of liquid and gases. Again, it will open or close (actuate) until designated pressure is reached. Pressure switches are pneumatically (air) operated switches. Generally a bellows or diaphragm presses up against a small microswitch and causes it to open or close.

·         Level switches are used to sense the height of a liquid. The raising or lowering of a float, which is mechanically attach to the level switch, trips the level switch. The level switches itself is used to control motor-driven pump that empty or fill tanks. Level switches are also used to open or close piping solenoid valves to control fluids.

References:

Petruzella, Frank. 1996. Industrial Electronics. Mc-Graw Hill. Singapore

CHAPTER 3 - TRANSFORMER

INTRODUCTION OF TRANSFORMER

A transformer is a static device used to transfer energy from one ac circuit to another. This transfer of energy may involve an increase or decrease in voltage, but the frequency will be the same on both circuit. When the transformation takes place with an increase on voltage, it called a step-up transformer, and step-down transformer for vice versa.

Without transformer the widespread distribution of electrical power would be impractical.   Transformer makes it possible to generate power at a convenient voltage for long distance transmission, and then step down for practical distribution.

Basic transformer consist of two windings/coil wound around on an iron core. The principle of transformer’s operation is based on mutual induction which occurs when the magnetic field surrounding one conductor cuts across another conductor, inducing a voltage on it. This effect may be increased by forming the conduction into coils and winding them on a common magnetic core.

When the primary coil of transformer is connected to an alternating voltage, there will be a current in primary coil called the exciting current which will set u an alternating flux that links the turns and induced voltage in both windings.

Function of transformer:

· The function of a transformer is to increase voltage prior to sending electricity over long distances through wires. They also function to decrease the voltage of electronic products to a level that is appropriate for the voltage circuits contained in the product.

· The function of a transformer is to move electricity currents between circuits within an electrical system. This is done via inductive electrical conductors.

      A transformer is a very common magnetic structure found in many everyday applications. AC circuits are very commonly connected to each other by means of transformers.
      A transformer couples two circuits magnetically rather than through any direct connection. It is used to raise or lower voltage and current between one circuit and the other, and plays a major role in almost all AC circuits.

Application Example: Transformers are a necessary part of all power supplies.

Application Example: Electric power systems

    Transformers find many applications in electric power distribution where they are employed for increasing or decreasing voltage levels.

References:

          Petruzella, Frank. 1996. Industrial Electronics. Mc-Graw Hill. Singapore

vlab.ee.nus.edu.sg.Transformer. http://vlab.ee.nus.edu.sg/~bmchen/courses/EG1108_Transformers.pdf 20 April 2014

CHAPTER 2 - LADDER DIAGRAM

Ladder (or line or elementary) diagram is a schematic representation of an electrical circuit and it is not a physical representation. It is an important concept not only at electro-pneumatic systems, but also at PLC. Each ladder diagram is constructed from input switches and out relays that lies between the positive and negative power lines. The order of elements in a ladder diagram, shown as below:

As shown by the figure, the positive power line of the supply is on the extreme left of the ladder. While the negative line of the supply (ground here) is on the extreme right. Between the power lines come the inputs and outputs. Each line the ladder is called a "rung". Each rung may contain only one output unless the outputs are in parallel.

Outputs in a ladder diagram are always at the right just before the negative line of the power supply. Mainly we want the current to flow from the positive line to the negative line through the output in order for it to be actuated. Outputs in ladder diagrams are mainly relays in operation.

As an introduction to ladder diagrams, consider the simple wiring diagram for an electrical circuit in Figure 11.1a. The diagram shows the circuit for switching on or off an electric motor. We can redraw this diagram in a different way, using two vertical lines to represent the input power rails and stringing the rest of the circuit between them. Figure 11.1b shows the result. Both circuits have the switch in series with the motor and supplied with electrical power when the switch is closed. The circuit shown in Figure 11.1b is termed a ladder diagram.

    

References:

Petruzella, Frank. 1996. Industrial Electronics. Mc-Graw Hill. Singapore

Maxfield, Clive. FPGAs: World Class Designs: World Class Designs. http://books.google.co.id/books?id=kQuOKBSOz5QC&pg=PA455&lpg=PA455&dq=IEI&redir_esc=y#v=onepage&q&f=false 20 April 2014

Laboratory, Automation. Electro-Pneumatic Circuits. http://www.msalah.com/PCL/Session%202.pdf 20 April 2014

CHAPTER1 - SAFETY IN THE WORKPLACE, FIRE PREVENTION

CH.1 SAFETY IN WORKPLACE – FIRE PREVENTION

     Fire can create huge destructions in the workplace. If it’s not too bad, it causes minor injuries or none at all. If it’s a major one, it results in serious injuries and even fatalities.

     In reality, it’s impossible to completely get rid of fire hazards in your worksite. But that’s not to say that you can’t do a number of things to control these hazards.


Workplace Fire Facts

     Major causes of fires in office buildings:

Arson
     Pay close attention to security measures. Keep doors and windows locked after business hours. Keep areas around the building - especially alleys and loading docks - well lit and clear of combustibles.
     Pay attention to housekeeping within the building as well.

Smoking Materials
     In areas where smoking is allowed, use large, non-tip ashtrays and make sure everything in them is cold before they are emptied. Be sure that no one leaves smoldering cigarettes on furniture or in a wastebasket.

Wiring & Appliances
     Designate an employee to turn off or unplug all appliances - including coffee makers- at the end of each working day. Do not overload outlets, and make sure to replace any broken or cracked electrical cords.


General Safety Measures

     The following are general safety measures in establishing and maintaining fire protection in the workplace:

· Never pile or lay material in a way that it covers or blocks access to firefighting equipment.
· Make sure to use only approved containers for the separation and disposal of combustible refuse. Remember to always replace the lid.
· Never store flammable materials within 10 feet of a building or other structure.
· Stack and pile all materials in orderly and stable piles.
· Never let unnecessary combustible materials get accumulated in any part of your work area.
· Make a periodic clean-up of entire work site and keep grass and weeds under control.
· Regularly dispose of combustible debris and scrap from your work area.
· Use only approved containers and tanks for storage, handling, and transport of combustible and flammable liquid.
· Always perform evaluation procedures before performing operations that present fire hazards like welding.


Fire Response Plans

     Become familiar with your facility’s fire and life safety systems. Know which of the following your building has, as well as their location and use:
· Manual pull alarms
· Fire extinguishers
· Smoke detectors
· Fire alarm monitoring service
· Exit doors & stairwells
· Voice alarm
· Sprinklers
· Fire doors

Common fire and life safety hazards to watch for in the workplace:
· Missing or broken fire safety equipment
· Accumulated trash
· Open fire doors
· Burned out exit lights
· Blocked stairways

Here are guidelines you must follow in using fire equipment:
· Inspect and maintain firefighting equipment regularly.
· Place an adequate number of firefighting equipment in plain view in your work areas. When appropriate, label the location of each one and make sure it is properly rated.
· Provide employees with proper training in fire prevention and protection.
· Prohibit smoking at or around work areas where fire hazards are present. Put up signs, saying NO SMOKING or OPEN FLAMES.
· Configure an alarm system that consists of both visual and audible signals (bells, sirens, whistles, blinking lights).
· Post reporting instructions and local Fire Department codes on info boards, common areas, and areas near the phone


Have a fire emergency plan.
     It’s nothing difficult, just a well thought out plan that takes into consideration the unique features of each building and its occupants. This plan should be in writing, and easily available to all employees. This includes those who work weekends and off-shifts. The plan should be kept current through periodic updating.


References:

Safetyservicescompany. 2012. FIRE PREVENTION IN YOUR WORKPLACE: GETTING BETTER FIRE SAFETY MEASURES. http://www.safetyservicescompany.com/topic/training/fire-prevention-in-your-workplace-getting-better-fire-safety-measures/. 20 April 2014

Seattle, WA. Workplace Fire Safety. http://www.seattle.gov/fire/pubed/business/Workplace%20Fire%20Safety.pdf , 20 April 2014

MAGNETIC CONTACTOR - INDUSTRIAL ELECTRONIC ASSIGNMENT

http://www.youtube.com/watch?v=Q7RdtqY6hCg

CHAPTER 5 - TRIAC

TRIAC’s Introduction

TRIAC or known as Bidirectional Triode Thyristor, electric current can flow in both directions when triggered (turned on). Triggered by a TRIAC can give positive or negative voltage to the gate electrode. Once triggered, it will continue to send components to lower the current flowing from the flow cell, for example at the end of the half cycle of alternating current. TRIAC operation is very similar to the SCR. The difference is when the SCR is connected to the ac circuit, the output voltage is rectified into direct current, while a TRIAC is designed to deliver on the second mid of the output waveform. Therefore, the output of the TRIAC is alternating current, not direct current. TRIAC created to provide a way for enhanced control of ac power

The TRIAC is a semiconductor component that is composed of four layers of structured PNPN diode with three pn junction. TRIAC has three electrodes, namely: gate, MT1, MT2.

If we want to use in the manufacture of devices or TRIAC electronic control systems, there are several things which need attention in choosing TRIAC as follows.

•             Forward and reverse breakover voltage

•             Maximum current (IT max)

•             The minimum cell current (Ih min)

•             Voltage and gate trigger current required

•             Switching speed

•             The maximum voltage dV / dt

•             TRIAC blocking voltage (VDRM)

Symbol and Shape of TRIAC

TRIAC will be connected (on) when it was in the quadrant I that small positive currents passing through the terminal gate to MT1, and MTT2 has higher polarity than MT1. When the TRIAC gate circuit is connected and uncontrolled, then the TRIAC still connected as long as the polarity of MT2 remains higher than MT1 and current flows greater than the current cell (holding current / ick) and TRIAC will also connect when the negative current TRIAC passing through the terminal gate to MT1 and MT1 higher polarity of MT2, and the TRIAC will remain connected even if the circuit does not hold the gate polarity control during higher MT1 MT2. In addition to giving triggering through the gate terminals, TRIAC can also be made connected (on) by providing a high voltage that exceeds the breakover voltage of the MT1 and MT2 of the terminal, but this way is not allowed because it can cause the TRIAC will be damaged. At the time of the TRIAC is connected (on) the forward voltage drop between terminals MT1 and MT2 is very small ranging from 0.5 volts to 2 volts.

TRIAC’s Characteristic curves

In the lighting circuit, current changes in incandescent bulbs will change the amount of light emitted by the lamp. Thus, it can be used as a controller TRIAC light overcast condition. At the same motor circuit, the current changes will alter the speed of the motor.