btec nc - electronic measurement and test - electronic measurement and test

Brendan Burr BTEC National Certificate in ElectronicsElectronic Measurement & Test

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Task 11.1a) Digital Multimeter No. – PG 017b) The multimeter has an easy to read LED display, allowing the user to take accurate measurements to 3 decimal places, depending on the setting of the multimeter.The measuring device is easy to hold and is ergonomic to allow easier use.There is a stand on the back of the device to enable the user further ease of reading measurements during testing. There is a small hole on the back allowing the device to also be hung up on a wall.The multimeter has very clear labelling, the colours stand out well and the font is not too small or unclear.The device has a protection pouch that prevents the device from being damaged in the event of a fall.It has a calibration certificate, to allow the user to see if the device may be giving false readings.c) Due to the multimeter being a multi function instrument, it has various settings to meet the users’ requirements.The device can be set to resistance to measure various resistances of resistors of other components, effectively isolating the device to an ohmmeter.The same can be said for the voltage over a component, changing the device to a voltmeter.When measuring the current of the circuit, the multimeter needs to be placed in series with the circuit component. The multimeter will effectively become an ammeter. The device has a fuse, protecting the user in case of excess current.The continuity of a wire or a polarised component can be measured, via the small diode symbol setting. This means you can loom a large amount of cables and still test to find both ends of a wire.The multimeter can also measure the capacitance of a capacitor. This means you could accurately find the time difference in a capacitor and resistor timing circuit.Another function the multimeter has is the capability of determining if a transistor is NPN or PNP type.The frequency can also be measured in hertz.d) Voltage = 0.002 - 600 Ohms = 200 - 20000000 Amps = 0.2 – 10 Farads = 0.000000000002 – 0.000002 HFE = NPN – PNP Hertz = Hi – Lo

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Dimensions= 151 x 70 x 38 mm1.2Farnell 0-30V, 1A Stabilised Power Supply Unita) LT30-1b) The power supply seems ergonomic. It has a handle on the top, to enable ease of use, as well as a place to wrap the mains lead, to prevent tripping when carrying. The knobs on the supply unit have grooves on to improve the grip between the user and the device. This allows for slightly better accuracy as it means the user can easily fine tune the device to meet the voltage or ampere required. The input, output, current constant and earth points are clearly indicated through colour. The input is red, the output is black, the current constant is blue and the earth is green.Red LED’s are used to show current flow.There are two easy to read display screens in analogue that are inaccurate, so a DMM should be used to measure the output voltage.c) DC voltage is connected through + and -.There are two screens that enable the user to compare the current or voltage of two circuits.The voltage can be adjusted using the fine and coarse knobs, allowing the user to quickly and accurately get to the desired voltage or current.There is a switch that can change the meter from voltage to current.The current can be set by the user using the current limiter.d) Screens x 2 = 0 – 30V 0 – 1A. Meter measurement = Volts or Amps.

Signal Generatora) TG 102b) The signal generator has easy to read buttons that are clearly labelled.The main body of the generator is grey made from ABS a type of polymer. This gives the device a light weight feel and durability.The signal generator has a handle that acts as a stand as well giving the user ease of use.The knob to determine the frequency has ridges on to better the user grip on the device.c) The input is through a coaxial lead.The frequency can be changed to sinusoidal, square or triangular waveforms.The multiplier multiplies the frequency which is set in Hertz.The output level is amplitude.d) Multiplier = 1 – 1000000 Hertz.Waveforms = sinusoidal, square and triangular.

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Oscilloscopea) ISR 620b) The oscilloscope has an easy to carry handle, like the others, which makes the device more transportable, as it is quite heavy.The screen is easy to read and is easily adjustable to meet the users requirements.The screen also has a backlight so that if a camera was placed on the front of the oscilloscope the graph will still be displayed clearly.All of the knobs allow the user to easily change all of the dials such as Time(s) and Volts(V). This provides the user with ease when trying to tune the device to find the waveform.c) The device has two inputs, allowing the user to compare two different circuits.The oscilloscope has adjusting knobs for the x and y axis, allowing the waveform to be placed in the middle of the graph.d) Time/Div = 0.0000005 – 2 Seconds Volts/Div = 0.05 – 20 Volts Channel = 2

1.3a) Ohms (Ω)b) Currentc) Voltmeterd) Volts (V)e) Amps (A)f) Counters are used for storing information to count to the next digit.g) Hertz (Hz)h) Seconds (s)i) Voltage (V)j) Time (s)k) F = . 1 .

time F = . 1 .

50 F = 2msOne period of a cycle.l) Waveformsm) Root Mean Square = Peak x 0.707n) The time/volts of one complete waveform.o) Resolution = the amount of pixels or bits of information that can be stored in the one screen.

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Task 2

ELEX 108

j) Record the peak to peak voltage[V p-p] and periodic time T in secs.

V p-p = 0.0006 V

Time = 1 secs

Frequency = 1666.666667 Hz

Controls Item Number

Power 2/3

Intensity 4

Focus 6

Illumination 8

Vertical Mode 14

Ch 1 ↕ Position 9

Ch 1 Volts/Div 12

Ch 1 Variable 13

Ch 1 AC-GND-DC 10

Ch 2 ↕ Position 20

Ch 2 Volts/Div 16

Ch 2 Variable 17

Ch 2 AC-GND-DC 19

Source 26

Coupling 25

Slope 24

Level 22

Hold Off 21

Mode (Sweep) 27

Time/Div 30

Variable 31

↔ Position 32

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Task 3When measuring an unknown value such as voltage, it is best practice to begin the measurements at the highest value for example 600V, even though the voltage might be 0.002V. This is so the measuring device can not be damaged by overloading the system. This lengthens the life of the device and gives a much more accurate reading.As said the measuring device might be damaged by exceeding the test specifications. If this occurs then the device would have to be sent to be repaired and recalibrated, this would take time and money, for simply not starting at the highest measuring specification.When a damaged device is used for measuring a set of test results, anomalies may be present where they wouldn’t normally be, causing an inaccurate range of data.If a current was measured in a microcomputer and the value was measured incorrectly, as the measuring device was faulty, then the whole board, with all of the connected components could be damaged, costing large sums of money.

Task 4a) ResolutionThe resolution on an oscilloscope is the smallest measurable unit, in the case of the ISR 620 time/div dial it is 0.04μs. This is because the smallest time per division is 0.2μs and there are 5 spacers in each division, therefore 0.2 / 5 = 0.04. If this is put in terms of frequency then it calculates as f = 1 / 0.04, therefore f = 25Hz. This is at the absolute boundary as the line appears extremely faint and could be misread. The ISR 620 is stated at 20Hz, therefore for optimum measurements, should be operating at 0.05μs to a minimum graticule.The voltage/div minimum is measured at 1mV.

b) BandwidthBandwidth is the amount of data that can be passed onto the screen. This is important on an oscilloscope as the specification can be as small as 0.0000005 seconds, meaning that the more data available on the screen the more accurate the measurements can be.If, for example, the oscilloscope could transfer more data to the screen, then the time could be even smaller than 0.0000005 seconds, thus creating greater accuracy. The bandwidth is commonly measured as bits per second but it can also be represented as a frequency in Hertz.

c) Sensitivity

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In analogue devices the components inside the device can rub together causing friction and resistance, altering the measured value and the response time. This can cause inaccuracies in reading data as an oscilloscope is measured using time, so if one device isn’t as sensitive as another, the information could be flawed due to the response time of the individual oscilloscope.In digital oscilloscopes the only analogue components are the connections between the circuit and the computer. This can still alter the readings, as the resistivity of the connection could impede the current flow.

d) Input impedanceThe input impedance is used, to prevent the oscilloscope from affecting the circuit which is being measured. If the oscilloscope affected the circuit it can produce false readings, and therefore inaccuracies in the data gathered.

The impedance is measured in ohms, in the oscilloscope used the valueof this is 1MΩ.

e) AccuracyThis is how accurate the oscilloscope actually is, meaning if it states 2 volts then the device is actually oscillating at 2 volts and not 1.8 for example. The tolerances of the components that make the device have a huge part to play in the accuracy. This is because if all of the components had large tolerance levels then the overall tolerance would be very large, creating inaccuracies.

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1MΩR in

DC AC

Oscilloscope


Task 5Colour Bands

Type

Power Rating

(W) 1 2 3 4

Nominal Value

(Ω)%

ToleranceMin

ValueMax

Value

R1

Carbon Film 0.66 Yellow Violet Red Gold 4700 5 4465 4935

R2

Carbon Film 0.66 Brown Black Orange Gold 10000 5 9500 10500

R3

Carbon Film 0.66 Yellow Violet Orange Gold 47000 5 44650 49350

Measured Resistance (Ω)

Measured Voltage (V)

Measured Current (mA)

Calculated Resistance

DMM AVO DMM AVO DMM AVO DMM AVO

R1 4500 4700 9.97 9.7 2.1 2 4748 4850

R2 9700 10000 9.91 10 9.95 9.5 9959 10526

R3 46900 50000 10.01 10 21.2 20 47216 471695.1The results gathered in Task 2 shows the variance of the actual value of resistors. The tolerance band is shown as 5% on the resistors 4th band to indicate how lenient the actual value could be compared to the nominal value. The leniencies are due to the manufacturing processes of the resistor. The make-up of the resistor that was used for Task 2 is shown to the right. It consists of a ceramic core with a carbon film spiralled around the core. Because the carbon and ceramic have lower resistivities than the copper wire, the current is impeded and thus lowers the voltage according to ohms law. It is because the carbon spirals the ceramic that causes slight inaccuracies. The resistances of the component are varied by removing or adding some of the carbon film, this reduces or increases the resistance of the component.It is very difficult to make two resistors exactly the same, which means that the resistances will be different, however small. This problem is heightened because of the component being mass produced, therefore the tolerance is almost always used. This is why the indicated value (or nominal value) is often very different to the measured value, as the nominal value is the preferred value built by the manufacturer.I feel it is because of the inaccurate manufacturing methods that the resistor was always measured at a different value as to what is stated by the nominal value.

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With the oscilloscope experiment I found that by calibrating the oscilloscope using the 2V p-p calibrator signal you can receive a much more accurate waveform from your circuit. This is because the trace is set to the correct point allowing all of the measurements to be taken off of this calibrated mark of 0V.The oscilloscope measurements are also limited by the human eye. The trace can be focused and intensified which increases and decreases the thickness of the trace, which can also thicken the line of the waveform. This means that information can be added by simply playing with these two functions. If the trace was too thick then the oscilloscope may have been calibrated incorrectly.

5.2All of the testing devices are subject to limitations due to their specifications. A digital multimeter for example, can only display the units as a whole number as the number would be rounded up or down to fit the information onto the screen. For example the measurement 25.3526842182611 would be displayed as 25.35, the remaining 0.0026842182611 is disregarded.An analogue multimeter is more accurate as it will display the information without the restrictions of running out of space on the display. The AVO device isn’t restricted, however the human eye is. It is difficult to read the needle on the display as it is often wavering between a value, meaning estimations must be made, creating inaccuracies.The main limitations of an oscilloscope are limited bandwidth and inadequate sensitivity. The low sensitivity can cause a lower response time in the measurement of circuits, this can cause inaccuracies in the data. The limited bandwidth means that the data cannot be displayed on the screen in time as there is too much information.

5.3 I came across a fault whilst measuring the R3 voltage with a digital multimeter. It produced a reading of 10.01 Volts across the resistor which shouldn’t be possible as only 10 volts were put into the circuit. This shows that the DMM needed to be recalibrated to increase its accuracy. A DMM had to be set up to read the voltage input as the analogue display on the power supply was inaccurate, it was actually measuring less than the voltage output, which could have damaged components.When I measured the R3 resistance using an AVO meter, it showed 50000 Ω when the maximum value should be 49350 Ω. This indicates that the resistor is over its tolerance and should be disposed of, however when measuring with a DMM the component measured at 46900 Ω. These two measurements show how the two devices can be extremely different, which can also affect any

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calculated measurements. This is shown with the 10K0 Ω resistor (R2), when using the AVO measurements, I calculated the resistance to be 10526 Ω, which shows that the tolerances have been exceeded. When using the DMM measurements the calculated resistance is 9959 Ω.When calibrating the oscilloscope I was unable to find the trace. I had to adjust the position on the x and y axis, to locate it. I had to also make sure that the sweep was on automatic, as the trace would only oscillate the screen once on single mode, which would make it difficult to catch and line up with the screens graph.

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btec nc - electronic measurement and test - electronic measurement and test

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