LABORATORY EQUIPMENT MAINTENANCE VSC Unit I

THE PPT DESCRIBES THE UNIT I OF THE VOCATIONAL SKILL COURSE OFFERED BY UNIVERSITY OF MUMBAI FOR THE FIRST YEAR UNDERGRADUATE STUDENTS. IT DISCUSSED THE TESTING OF PASSIVE AND ACTIVE COMPONENTS LIKE RESISTORS, DIODES, INDUCTORS, TRANSISTORS ETC. IT ALSO DISCUSSES TESTING OF COMPONENTS USING MULTIMETER

1. FYBSC Physics (Vocational Skill Course ) Course code: USPHPVSC1 Title: - Laboratory Equipment Maintenance Asst. Prof. Dr. Vikas V. Deshmane

2. Unit-I (7 Hours) Testing of Passive Electronic Components using Digital Multimeter (DMM) Passive components - resistors, capacitors, inductors, failures in fixed resistors, testing of resistors, variable resistors, variable resistor as potentiometer, measuring resistors using color codes. Testing of various types of capacitors & inductors.

3. The key difference between active and passive components Electronic components are categorized as active or passive depending on the functions they are able to perform. In a nutshell, active components can, generally speaking, inject power into a circuit and are capable of electrically controlling and amplifying the flow of electrical current, whereas passive components cannot. Unlike active components, passive components either consume or store energy. A simple way to test whether a component is active or not is to measure the difference be-tween its input and output signals. If there is a decline in power, the component is passive. If the signal is amplified, it is active.

4. Passive components and their functions Passive components can influence the flow of electricity running through them. For example, they can resist its flow, store energy for later use, or produce inductance. However, they cannot control or amplify electricity themselves. The most common components and their functions: Resistor :  Resists the flow of electrical current in a circuit; used to lower voltage Capacitor :  Stores electrical energy electrostatically in an electric field (known as ‘charging’), and can release it later when needed Inductor :  Stores electrical energy in a magnetic field; allows direct current (DC) to flow through it, but not alternating current (AC) Transducer :  Converts an input signal from one type of energy into another type; sensors are a type of transducer that convert physical action/input into an electrical signal

5. Active components and their functions Active components require a source of energy, typically in the form of a  direct current , in order to perform their specific function. They are able to manipulate the flow of electricity in some way. Most active components consist of semiconductor devices, such as  diodes , transistors and  integrated circuits . Transistor :  Mostly used for amplifying electrical signals or as switching devices Diode:  Permits electricity to flow in one direction only Integrated circuit (chips or microchips):  multiple complex circuits on a circuit board; used to perform all kinds of tasks; still considered a component despite consisting of many other components Display devices  such as LCD, LED and CRT displays Power sources  such as batteries and other sources of alternating current (AC) or direct current (DC)

6. Resistance is a property that describes how a material or component resists the flow of electrical current. It is the ratio of voltage (V) applied across a component to the current (I) passing through it and is expressed as R = V/I.   Factors Affecting Resistance: Material:  Different materials have different electrical resistivity, which influence their resistance. For example, metals like copper have low resistivity, making them good conductors, while insulators have high resistivity. Length:  The longer a wire or component, the more resistance it typically has. Cross-Sectional Area:  A wider cross-sectional area generally results in less resistance. Temperature:  Resistance can change with temperature. Some materials, like conductors, generally have increasing resistance with temperature, while semiconductors may decrease in resistance with higher temperatures. RESISTANCE

7. MEASURING RESISTANCE Turn a circuit off before measuring resistance. If any voltage is present, the value of resistance will be incorrect. In most cases you cannot measure a component while it is in-circuit. This is because the meter is actually measuring a voltage across a component and calling it a "resistance ." The voltage comes from the battery inside the meter. If any other voltage is present, the meter will produce a false reading. If you are measuring the resistance of a component while still "in circuit," (with the power off) the reading will be lower than the true reading. RESISTANCE

8. CREATING ANY VALUE OF RESISTANCE Any value of resistance can be created by connecting two resistors in PARALLEL or SERIES . TWO EQUAL-VALUE RESISTORS IN SERIES Two equal-value resistors IN SERIES creates a value of DOUBLE. You simply ADD the values . RESISTANCE TWO EQUAL-VALUE RESISTORS IN PARALLEL Two equal-value resistors IN PARALLEL creates a value of HALF. Three equal-value resistors in parallel is equal to one-third the value.

9. A "BURNT" RESISTOR - normally and technically called a " burnt-out“ resistor . The resistance of a "burnt" resistor can sometimes be determined by scraping away the outer coating - if the resistor has a spiral of resistance-material. RESISTANCE Note the spirals of conductive carbon . The number of spirals has nothing to with the resistance. It is the amount of carbon particles in the "track" that determines the resistance . It is also the thickness and width of the track that determines the resistance. And then it is the overall size of the resistor that determines the wattage. And then the size of the leads, the closeness to the PCB and the size of the lands that eventually determines how hot the resistor will get.

10. POTENTIOMETER WORKING PRINCIPLE The basic principle of the potentiometer is that the potential drop across any section of the wire will be directly proportional to the length of the wire, provided the wire is of a uniform cross-sectional area and a uniform current flows through the wire.

11. POTENTIOMETER VS RHEOSTAT The most basic explanation of the difference between these two devices is that a potentiometer is a three terminal device used for voltage control. A rheostat is a two terminal device used for current control. However, by simply leaving one leg of a potentiometer unconnected, it is possible to use potentiometers as rheostats .

12. Types of Potentiometer Although the basic working principle and construction of all potentiometers are the same, they differ based on the geometry of moving terminals. Most of the potentiometers have a wiper that rotates on an arc-shaped resistive material. Nonetheless, in some other types of potentiometers, the wiper slides linearly on a straight resistive strip. Based on the concept of the resistive strip, the potentiometers are of two types: Rotary and Linear. Rotary Potentiometer: This sort of pot has a wiper that rotates across two terminals for varying the resistance of the potentiometer. Depending upon the number of times one can turn or rotate the wiper, rotary potentiometers can be classified in the below categories: Single Turn: The wiper takes only a single turn and often rotates just 3/4th of the complete turn.  Multi-Turn: These potentiometers can make multiple rotations such as 5, 10, or more.  Concentric Pot: Here, two pots are adjusted together by using concentric shafts. Servo Pot: This is a motorized pot used to adjust or control a servo motor automatically.   Linear Potentiometer: Also known as slider, fader, or slide pot, these are potentiometers in which the wiper slides on a straight resistive strip. These can further be classified in the following categories: Slide Pot: Slide potentiometers are the high-quality pots mostly made from conductive plastics. Dual Slide Pot: This sort of pot is the calibration of two slide pots in parallel.  Multi-Turn Pot: This type of potentiometer is constructed by using a spindle, which actuates the slider.  Motorized Fader: The resistance and movement of the wiper in this pot are controlled by a motor.

13. Applications of Potentiometer A potentiometer operates as a voltage divider and, therefore, has numerous applications. Some of the applications of pots are as follows:  Audio Control: Both rotary and linear Potentiometers are used to control audio devices for changing and controlling the loudness and other audio-related signals.  Television: In televisions, the pots are used to control the brightness, colour , and contrast of the picture.  Motion Control: Pots are also used as servomechanisms, the position feedback devices used to create a closed-loop control.   Transducers: Due to the aspect of giving large output signals, pots find applications in designing displacement transducers.

14. TESTING POTENTIOMETERS (variable resistors) To check the value of a variable resistor, it should be removed from circuit or at least 2 legs should be removed. A Rheostat is a variable resistor using only one end and the middle connected to a circuit. The resistance between the two outside pins is the value marked on the component and the center leg will change from nearly zero to the full resistance as the shaft is rotated. "Pots" generally suffer from "crackle" when turned and this can be fixed by spraying up the shaft and into the pot via the shaft with a tube fixed to a can of " spray lubricant“ ( contact cleaner). "Pre-set pots" and "trim pots" are miniature versions of a potentiometer and they are all tested the same . The photo shows a pot, two mini pots and 3 mini trim pots. POTENTIOMETER

15. Unlike the battery, a capacitor is a circuit component that temporarily stores electrical energy through distributing charged particles on (generally two) plates to create a potential difference. A capacitor can take a shorter time than a battery to charge up and it can release all the energy very quickly. CAPACITOR

16. CAPACITOR A capacitor is a device that is used to store charges in an electrical circuit. A capacitor works on the principle that the capacitance of a conductor increases appreciably when an earthed conductor is brought near it. Hence, a capacitor has two plates separated by a distance having equal and opposite charges. The space between the conductors may be filled by vacuum or with an insulating material known as a dielectric. The ability of the capacitor to store charges is known as capacitance. Equation of capacitance is given by, 𝑞=𝐶𝑉[𝑞=𝑐ℎ𝑎𝑟𝑔𝑒,𝐶=𝑐𝑎𝑝𝑎𝑐𝑖tan𝑐𝑒,𝑉=𝑣𝑜𝑙𝑡𝑎𝑔𝑒]

17. CAPACITOR WORKING Consider the following circuit, which shows the working principle of a parallel plate capacitor with a dielectric between them. Apply the voltage V as shown in the circuit, with plate 1 being positive and plate 2 being negative. An electric field appears across the capacitor. When the voltage is supplied to these plates, plate 1 will carry a positive charge from the battery, and plate 2 will carry a negative charge from the battery. The voltage is supplied for a period of time, during which time the capacitor is charged to its maximum holding charge, and this period is referred to as the capacitor's charging time. After a period of time, when the capacitor has reached its full charging capacity, we will turn off the electricity to the capacitor. The two plates have a negative and positive charge for a period of time. As a result, the capacitor serves as a source of electricity. If these plates are connected to a load, current flows from plate 1 to plate 2 until all charges on both plates have been dissipated. The time it takes for the capacitor to discharge is referred to as the dissipation time.

18. CAPACITOR VALUES

19. CAPACITORS IN SERIES AND PARALLEL COMBINATION

20. Traditional Basic Capacitor Testing Method Disconnect the capacitor from its circuit. Check the capacitance value on the capacitor's exterior. Select a capacitance setting on your multimeter. Connect the multimeter with the capacitor terminals. Compare the multimeter reading with the capacitance value. CAPACITOR TESTING

21. CAPACITOR TESTING Checking a Capacitor using Multimeter without Capacitance Setting Most of the low end and cheap Digital Multimeters do not include Capacitance Meter or Capacitance Settings. Even with these Multimeters , we can test a Capacitor . Remove the Capacitor from the circuit or board and make sure it is completely discharged. Set the Multimeter to measure resistance i.e., set the knob to Ohm or Resistance Settings. If there are multiple ranges of resistance measurement (on a manual multimeter), select a higher range (often 20 KΩ to 200 KΩ). Connect the multimeter probes to the leads of the capacitor (red to positive and black to negative in case of polarized capacitors). The Digital Multimeter will show a reading of resistance on the display and soon it will display the resistance of an open circuit (infinity). Note down the reading that was displayed for that short period. Disconnect the capacitor from the multimeter and repeat the test several times. Every attempt of the test should show similar result on the display for a good capacitor. If there is no change in the resistance in the further tests, the capacitor is dead. This method of testing the capacitor might not be accurate but can differentiate between a good and bad capacitors. This method also doesn’t give the capacitance of the capacitor .

22. Inductors are measured with an INDUCTANCE METER but the value of some inductors is very small and some Inductance Meters do not give an accurate reading . The solution is to measure a larger inductor and note the reading. Now put the two inductors in SERIES and the values ADD UP - just like resistors in SERIES. This way you can measure very small inductors. MEASURING AND TESTING INDUCTOR

23. V=L di/ dt This states that the voltage across an inductor is proportional to the current through the inductor's rate of change. The energy stored by an inductor.  

24. Coils , inductors, chokes and yokes are just coils (turns) of wire. The wire may be wrapped around a core made of iron or ferrite. It is labeled "L" on a circuit board. You can test this component for continuity between the ends of the winding and also make sure there is no continuity between the winding and the core. It is important to understand the turns are insulated but a slight fracture in the insulation can cause two turns to touch each other and this is called a "SHORTED TURN“. When this happens, the inductor allows the circuit to draw MORE CURRENT. This causes the fuse to "blow .“ It might look like a very simple component, but it can operate in a very complex way. The quickest way to check an inductor is to replace it, but if you want to measure the inductance , you can use an INDUCTANCE METER. You can then compare the inductance with a known good component. An inductor with a shorted turn will have a very low or zero inductance, however you may not be able to detect the fault when it is not working in a circuit as the fault may be created by a high voltage generated between two of the turns . INDUCTOR TESTING