P1 Semester Report Sample 1 Page 2
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3. BASIC HAND SKILLS
Crimping tools were used to crimp different types of cables used in industry; like a BNC crimper which is used to crimp an RJ59 cable (coaxial cable). An RJ45 crimper is used to crimp CAT5 cable (network cable).
SOME TOOLS USED
- Screw drivers
- Adjustable spanners
- Long nose pliers
- Side cutter
- Cable striper
- BNC (RJ 59) crimper
- RJ 45 crimper
- Soldering iron
- Drilling machine
- Spirit level
For electrical work, wires are usually soldered to printed circuit boards, other wires, or small terminals. A low-power iron (15-30 Watts) is suitable for this work. Higher power is used for non-electrical metal-work.
Some soldering irons have interchangeable tips for different types of work.
Pyramid tips with a triangular flat face are useful for soldering sheet metal. Fine round or chisel tips are typically used for electronics work. When not in use, soldering irons are often placed in stands to keep them away from flammable materials. Such a stand often also comes with a sponge and flux pot for cleaning the tip.
Some soldering irons for continuous and professional use come as part of a soldering station, which allows the exact temperature of the tip to be adjusted, kept constant, and displayed. A new tip needs to be coated, heated, and then covered with solder before its first use. This procedure is called “tinning”. The tinning forms a liquid layer which facilitates the transfer of heat to the work piece. A dirty tip does not transfer heat well. The tip needs to be kept coated with a shiny layer of solder by occasional wiping and applying solder directly to the tip.
For best results, particularly in electrical work where good electrical contact is required, the iron should be used to heat the work piece, and solder applied to it: this helps to prevent “cold joints”, where hot solder is applied by the iron to a relatively cold target, shrouding it in solder to look like a good joint, but without wetting it properly, and without forming a good connection. Some electrical solder contains flux cores (the purpose of the flux is to clean the oxides off the metals to permit a good joint). If the solder is applied to the iron first then the flux is rapidly burnt off and cannot serve its purpose on the joint.
The most advanced soldering irons are digital and control temperature via a microprocessor in the station that monitors a thermocouple inside the tip, increasing or decreasing the power on the tip based on the selected temperature.
When two cables have to be joined, the junction must be covered with a heat shrinkable tube to isolate the junction.
. 4. TEST EQUIPMENT
Different types of instruments were used for different type of job.
A multimeter is used to measure voltages and current in a circuit. It is also used to measure resistances frequencies and continuity. When one cable has to be traced among a bunch of cables, the cable can be shorted at one end, and measure continuity between the cables to find the one with continuity. Voltage must be measured on power supply to check the amount of voltage drop in a circuit.
An oscilloscope is an instrument used to measure voltage and frequency in a circuit.
oscilloscope can measure a DC signal and an AC signal with frequency from 1Hz up to 20MHz. An oscilloscope has to be calibrated before measurement can be taken. An oscilloscope displays graphically the magnitude and shape of a signal in a circuit and gives the accurate frequency of the signal. An oscilloscope can be used where a weak signal has to be monitored in fault finding, like in CCTV system. Network cable tester A network cable tester is used to measure continuity of a network cable (CAT5) and to check if it was correctly crimped.
A test monitor is used in CCTV system to see if the correct picture signal is produced by the cameras. It is also used to focus cameras.
5. ELECTRICAL AND ELECTRONIC COMPONENTS
5.1. ELECTRICAL COMPONENTS USED
Relays come in many different types, depending on operating voltages and supported current. A relay is a controlled magnetic switch with usually normally open (NO), normally closed (NC) and common(C) terminals. The coil of a relay is supplied with low a voltage (usually 12VDC) but can switch high power devices on its contact.
Fig 5.1. A relay
A transformer is composed of two windings, a primary and secondary on a soft metal core. Depending on the ratio of winding between the primary and secondary, the input voltage can be stepped up or down. In electronic circuits, transformers are used mainly in power supply to step down the main voltage to a lower operating voltage of the circuit. The input voltage, output voltage, maximum output current and the power of the transformer are usually written on the transformer.
A fuse is a thin wire of low melting metal used in a circuit as a protection device. In case of high current drawn from the circuit or a short circuit, the fuse will melt, and thus protecting the rest. The maximum current is written on the fuse.
5.2. ELECTRONIC COMPONENTS USED
Resistor is widely used in all electronic devices for voltage or current division or reduction and transistor’s biasing. Resistors are also used in access control to terminate a line, monitoring if the line is not being tampered.The value of a resistor is written on the resistor in a colour code.
Fig 5.2. Resistors
Resistors can be fixed or variable (potentiometer).
There are many different types of capacitors depending on usage. There are electrolytic capacitors with values ranging from 0.1μF to a few thousand micro farad. The capacitance and polarity of electrolytic capacitors is written on the body of the capacitor. There are also non polarized ceramic, polyester, metal film Capacitor. On these capacitors, the capacitance is written in the form of color code or a number code.
Fig 5.3. A capacitor
An inductor is a coil wound on metal core or having air as core. Inductors together with capacitors are used in resonance circuit, oscillators and power supplies
Fig 5.4. An inductor
A diode is semi-conductor device that conducts current only in one direction. Rectifier diodes come in different shape depending on the power of the diode and are used in power supplies to change AC voltage to DC. Signal diodes, schottky, varicap and variable diodes are small and are used in logic and oscillating circuits. An identifying number is written on the body of the diode like 1N4007 which helps to find characteristic of that diode in a data sheet. An LED is used in display systems and as indicators.
Fig 5.5 A diode
A transistor is a semi-conductor device used to amplify the signal in the circuit. There are many types of transistors and they come in different shape from small cap like to large metallic power transistor with heat sink connection. The types of transistors include: Bipolar transistors (NPN and PNP), Metal Oxide Semiconductor Field Effect Transistor (Channel N and P) and Photo transistors. An identifying number is written on the body of the transistor like 2N2222 which helps to find characteristic of that transistor in a data sheet.
Fig 5.6 Transistors