FAMILIARIZATION AND APPLICATION OF TESTING INSTRUMENTS AND COMMONLY USED TOOLS
a) MULTIMETERS
The Multimeters are the general purpose meters which can be used to measure
i) Voltage – ac and dc
ii) Current – ac and dc
iii) Resistance
Switches on the meter are used to select both the function and the range of the meter. Make sure that the meter is adjusted to the correct function and initially set the meter to a less sensitive range than is needed. (Note all meters are not provided with auto range and over load cut out)
Before measuring the resistance, check the meter at zero resistance by shorting the two leads and when the instrument is not in use, always return the selection knob to to the normal “off” position to avoid draining the battery.
Digital Multimeters have better accuracy and resolution. They usually have auto ranging, and auto zero facilities, which means the user need only to set the function switch and get the reading. The digital multimeter converts an input signal into equivalent digital display. The signal input might be a dc voltage, an ac voltage, a resistance or an ac or dc current. Advanced meters will also have facilities to measure capacitance and frequency.
b) OSCILLOSCOPE
Oscilloscope is the most versatile of the test instruments. It can be used for waveform analysis, signal frequency measurement, peak to peak voltage measurement and the most importantly for signal tracing. The heart of an oscilloscope is the cathode ray tube (CRT).
The working of a CRT depends upon generation of electrons by a heated cathode, focusing it to a thin beam and making it to travel towards positively charged anode. The electron strikes on a glass screen, coated with phosphor which gives off light, making spot on the screen. The brightness of the spot can be controlled and so its position. The spot can be deflected to any part of the screen by applying a varying electric field to the deflection plates – four of them arranged in pairs, called X-plates and Y-plates. The Y-plates deflect the spot vertically up or down, while the X-plate move it from side to side.
Thus, an oscilloscope can be routinely used to
i) Display the waveforms
ii) Measure its frequency
iii) Measure its peak to peak amplitude.
To use the oscilloscope, carefully observe all the controls on the front panel. The essential controls are Intensity or Brightness control, Focus control, X and Y position control and Trigger control.
Before using the instrument, make sure the following setting: Intensity control fully anticlockwise Trigger control to Auto 2 Vertical and horizontal position controls to midway round Volts/cm control to highest value of the range Time/cm control to 1ms/cm or its nearest value Triggering is probably the most complicated function performed by the scope. To create a stable image of a repetitive waveform, the scope must „trigger‟ its display at a particular voltage, known as the trigger „threshold‟. The display is synchronized whenever the input signal crosses that voltage, so that many images of the signal occurring one after another can be superimposed in the same place on the screen. The level knob sets the threshold voltage for triggering. You can select whether triggering occurs when the threshold voltage is crossed from below („rising-edge‟ triggering) or from above („falling-edge‟ triggering) using the trigger control knobs and switches. You can also select the signal source for the triggering circuitry to be channel 1, channel 2, an external trigger signal, or the 240 V AC power line.
For voltage measurement, count the number of centimeters on the vertical scale from negative peak to the positive peak and then multiply this number by the settings of the volts per centimeter switch. For example, if the volts/cm switch is set to 5V/cm, and the waveform measures 4.8 cm from peak to peak, the waveform voltage is 4.8 x 5 = 24.0 V peak to peak.
AIM
To familiarize
with different instruments used in electronic laboratories and study the its
functions and familiarize the commonly used tools.
EQUIPMENTS
REQUIRED
Multimeters, DC
power supply,Function Generator and oscilloscope and Commonly used tools.
THEORY
1.
MEASURING
INSTRUMENTS
a) MULTIMETERS
The Multimeters are the general purpose meters which can be used to measure
i) Voltage – ac and dc
ii) Current – ac and dc
iii) Resistance
Switches on the meter are used to select both the function and the range of the meter. Make sure that the meter is adjusted to the correct function and initially set the meter to a less sensitive range than is needed. (Note all meters are not provided with auto range and over load cut out)
Before measuring the resistance, check the meter at zero resistance by shorting the two leads and when the instrument is not in use, always return the selection knob to to the normal “off” position to avoid draining the battery.
Digital Multimeters have better accuracy and resolution. They usually have auto ranging, and auto zero facilities, which means the user need only to set the function switch and get the reading. The digital multimeter converts an input signal into equivalent digital display. The signal input might be a dc voltage, an ac voltage, a resistance or an ac or dc current. Advanced meters will also have facilities to measure capacitance and frequency.
b) OSCILLOSCOPE
Oscilloscope is the most versatile of the test instruments. It can be used for waveform analysis, signal frequency measurement, peak to peak voltage measurement and the most importantly for signal tracing. The heart of an oscilloscope is the cathode ray tube (CRT).
The working of a CRT depends upon generation of electrons by a heated cathode, focusing it to a thin beam and making it to travel towards positively charged anode. The electron strikes on a glass screen, coated with phosphor which gives off light, making spot on the screen. The brightness of the spot can be controlled and so its position. The spot can be deflected to any part of the screen by applying a varying electric field to the deflection plates – four of them arranged in pairs, called X-plates and Y-plates. The Y-plates deflect the spot vertically up or down, while the X-plate move it from side to side.
Thus, an oscilloscope can be routinely used to
i) Display the waveforms
ii) Measure its frequency
iii) Measure its peak to peak amplitude.
To use the oscilloscope, carefully observe all the controls on the front panel. The essential controls are Intensity or Brightness control, Focus control, X and Y position control and Trigger control.
Before using the instrument, make sure the following setting: Intensity control fully anticlockwise Trigger control to Auto 2 Vertical and horizontal position controls to midway round Volts/cm control to highest value of the range Time/cm control to 1ms/cm or its nearest value Triggering is probably the most complicated function performed by the scope. To create a stable image of a repetitive waveform, the scope must „trigger‟ its display at a particular voltage, known as the trigger „threshold‟. The display is synchronized whenever the input signal crosses that voltage, so that many images of the signal occurring one after another can be superimposed in the same place on the screen. The level knob sets the threshold voltage for triggering. You can select whether triggering occurs when the threshold voltage is crossed from below („rising-edge‟ triggering) or from above („falling-edge‟ triggering) using the trigger control knobs and switches. You can also select the signal source for the triggering circuitry to be channel 1, channel 2, an external trigger signal, or the 240 V AC power line.
For voltage measurement, count the number of centimeters on the vertical scale from negative peak to the positive peak and then multiply this number by the settings of the volts per centimeter switch. For example, if the volts/cm switch is set to 5V/cm, and the waveform measures 4.8 cm from peak to peak, the waveform voltage is 4.8 x 5 = 24.0 V peak to peak.
For frequency measurement, the method is to measure the time period of one complete cycle on the screen i.e. the horizontal distance between two identical points on the neighboring waves. This distance multiplied by the setting of time/cm switch to calculate the period of one cycle. The reciprocal of this time is the frequency of the waveform. For example, if the peaks of the waveform are 5 cm apart and time/cm switch is set to 200 ms/cm, the time of one cycle is 5 x 200ms = 1 s and the frequency is 1Hz.
c) FUNCTION GENERATOR
A function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine, square, triangular and sawtooth shapes
d) POWER SUPPLY
Almost all electronic circuits need a DC bias voltage. DC power sources are mainly categorized into; fixed and variable DC power sources. Some DC sources provide only positive voltages while some others provide both positive and negative. DC source which provide positive and negative voltages are called dual power sources. Certain integrated circuits and discrete circuits needed dual power sources. Operator can vary the DC voltage output from the variable DC sources using coarse and fine knobs provided. Most of the DC power sources are either 0-30V variable or +/- 15V fixed
2. COMMONLY USED TOOLS
a) SOLDERING ION
To make good connection you have to heat the junction somewhat above the melting temperature of solder this is the job of the soldering iron. • Soldering iron comes in different sizes. • It is rated in terms of wattage (5W to 100W). • Thicker connection such as connectors requires more heat from soldering iron so we need higher wattage soldering iron. • Lighter connections like IC pins requires less heat so requires only less wattage irons
b) De Soldering Pump
The usual way is to use a desoldering pump which works like a small spring-loaded pump, only in reverse (More demanding users using CMOS devices might need a pump which is ESD safe.) A spring-loaded plunger is released at the push of a button and the molten solder is then drawn up into the pump. It may take one or two attempts to clean up a joint this way, but a small desoldering pump is an invaluable tool especially for PCB work
c) PLIERS
COMBINATION PLIER
Combination pliers are a type of pliers used by electricians and other tradesmen primarily for gripping, twisting, bending and cutting wire and cable. Linemen's pliers owe their effectiveness to their plier design, which multiplies force through leverage. Lineman's pliers have a gripping joint at their snub nose and cutting edge in their craw. Some versions include either an additional gripping or crimping device at the crux of the handle side of the pliers' joint
NEEDLE NOSE PLIERS
Needle-nose pliers (also known as pointy-nose pliers, long-nose pliers, pinch-nose pliers or snipe-nose pliers) are both cutting and holding.
d) WIRE STRIPPER
A wire stripper is a small, hand-held device used to strip the electrical insulation from electric wires.
e) SCREW DRIVER
Screwdriver is a tool, manual or powered, for turning (driving or removing) screws. A typical simple screwdriver has a handle and a shaft, and a tip that the user inserts into the screw head to turn it. A screwdriver is classified by its tip, which is shaped to fit the driving surfaces—slots, grooves, recesses, etc.—on the corresponding screw head.
f) TWEEZERS
Tweezers are tools used for picking up objects too small to be easily handled with the human hands. They are probably derived from tongs, pincers, or scissors-like pliers used to grab or hold hot objects since the dawn of recorded history. In a scientific or medical context they are normally referred to as forceps.
Tweezers make use of two third-class levers connected at one fixed end (the fulcrum point of each lever), with the pincers at the others
g) HOT AIR SOLDERING AND DE SOLDERING STATION
The hot-air rework stations with features including mechanical arms, suction pens and wands, and built-in soldering irons. With everything from compact rework centers to deluxe CPU-controlled, ESD-safe SMD hot-air rework stations with sixteen nozzles, you're bound to find the right de-soldering/rework station. Hot-air stations provide tight temperature tolerances and large air flows for removing solder and components from circuit boards. Combination soldering/hot-air rework stations available
RESULT:
The Functions, operations and uses of multimeter, CRO, function generator etc are studied and familiarized the commonly used tools
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