A Lab Report On Experiment 17: Experimental Error (Lab Report Sample)

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A Lab Report On Experiment 17 –Experimental Error
Abstract
This lab report covers the concept of errors and two experiments on DC of a common emitter amplifier and amplification of AC signals. The types of errors, their sources, classifications and ways of reducing errors in laboratory experiments are described. The experiments were conducted using SK10 boards and analysis of the results carried out. The certainty of the measured values was calculated and the absolute and relative error calculated too in this report.
Declaration
This laboratory report is my original work, except where due acknowledgement is made in the text, and to the best of my knowledge has not been previously submitted any other institution.
Table of Contents TOC \o "1-3" \h \z \u Abstract PAGEREF _Toc464407602 \h 1Declaration PAGEREF _Toc464407603 \h 11.0 Introduction PAGEREF _Toc464407604 \h 21.1 Objectives of the experiment PAGEREF _Toc464407605 \h 21.2 Theoretical background PAGEREF _Toc464407606 \h 21.3 Ways of reducing errors PAGEREF _Toc464407607 \h 51.3.1 Reducing systematic errors PAGEREF _Toc464407608 \h 51.3.2 Reducing random errors PAGEREF _Toc464407609 \h 62.0 Materials and procedures PAGEREF _Toc464407610 \h 62.1 Apparatus PAGEREF _Toc464407611 \h 62.2 Procedure for using SK10 board PAGEREF _Toc464407612 \h 72.3 The procedure for practical work: part I – DC bias of a common emitter amplifier. PAGEREF _Toc464407613 \h 72.4 Procedure for Practical work: Part II- Amplification of AC signals PAGEREF _Toc464407614 \h 104.0 Discussion and Conclusion PAGEREF _Toc464407615 \h 144.1 Discussion PAGEREF _Toc464407616 \h 144.2 Conclusion PAGEREF _Toc464407617 \h 145.0 Work Cited PAGEREF _Toc464407618 \h 15
1.0 Introduction
1.1 Objectives of the experiment
1 To familiarize with the type of errors, their sources, ways of reducing them, and how to report uncertainty.
2 To be able to build a common emitter amplifier circuit, test its DC bias setting and amplify AC signals.
1.2 Theoretical background
Scientific procedures to test or discovery of something in the laboratory will always involve comparison of measured quantity with predetermined values of similar quantity. The difference between the measured value and the absolute value is called an error. The error may arise from various sources like environmental changes, while performing the experiment, which some are impossible to avoid and can only be minimized by employing refined techniques or improved instruments. The indication of how much error the measurement might contain makes the results of the experiment that involve measurement to be complete. This means that the knowledge of the types of errors, ways of reducing these errors and proper ways of treating data is required in order to obtain estimate of the degree of uncertainty in measurements. An error is therefore, an uncertainty with measurements, which cannot be eliminated but can only be minimized. CITATION Ric11 \l 1033 (Richard S. Figliola)
Errors can be categorized into systematic errors and random errors. Systematic errors describe errors in the output reading of an instrument that are consistently on one side of the correct reading. That is either all the errors are positive or all are negative and they tend to shift the mean of data toward a single direction. Sources of this error include; systematic disturbance during measurement, effect of environment on the instruments (or modifying imputes), bent meter needles, calibration error, drift in instrument features and lastly poor connections practices of the instruments. An error resulting from calibration is always there in an instrument and the value is usually indicated by the manufacturer. CITATION Ala01 \l 1033 (Morris)
On the other hand, random errors are those that fluctuate from one measurement to the next, yielding the results that are distributed about a certain mean value. For example, timing of the oscillation of a pendulum when measuring the period, changes in temperatures and in-line voltages. Sources of this error include; human error, errors resulting from variations in definitions, uncontrollable fluctuations in the inputs conditions in the measurements, electrical noise , lack of precise definition of the quantity being measured and many other unpredicted conditions/ situations. These errors can be minimized by taking several values from the same experiment and find the mean value or by improving the experimental techniques.
Mathematical expression governing this error:
X= ¯x ±Δ x
Where ¯x is the mean, Δx is the uncertainty in the measurement and x is the experimental measurement to be reported. CITATION Dep15 \l 1033 (Electronics)
In an experiment, precision and accuracy are essentials to obtain almost error free data. Accuracy is how close the measured value is to the true value or theoretical value; while precision describe the spread of these measurements when repeated. This means an experiment with high repeatability has high precision, and can result into high accuracy results. The figure1 below illustrates the difference between accuracy and precision.
Figure 1: illustration of accuracy and precision CITATION Dep15 \l 1033 (Electronics)
The numbers that can be read directly from the instrument in addition to the estimated value is a reflection of the precision and is called significant figure. The error usually has one significant value hence no need of expressing it in scientific form. When multiplying or dividing, measurement values, the least significant figures in the measurement will be equal to the number of significant figures in the final answer. On the other hand, when adding or subtracting, the number of the decimals in the measurements is the main factor that determines the number of significant figures of the final answer.
1.3 Ways of reducing errors
It is of paramount important to minimize errors in an experiment for high precision and accuracy. This will make the data acquired more reliable. Several methods have been device to reduce errors depending on the nature or type of the error and their sources.
1.3.1 Reducing systematic errors
* Systematic errors can develop over a period of time due to wear in instrument’s components. Recalibration more often gives a full remedy to calibration error.
* Observing proper measurement practices would aid in reduction of this error
* Use of improved and more intelligent instruments. The equipment should have smallest possible uncertainty.
* Making maximum use of available scale and measuring the sum of known number of items for the small values that are mot up to instrument’s resolution.
1.3.2 Reducing random errors
A random error displaces measurements in an arbitrary direction because of the nature of the sources of this error, which makes it unpredictable and inconsistence. Some of the ways to reduce this error include:
* Minimizing human error by avoiding parallax
* Taking repeated measurements and then finding the mean,
* Careful connection, grounding, reducing of nodes and connector to minimize electrical noise and
* Having consistency in measurement techniques.
In the following section, an experiment were conducted to build an emitter amplifier circuit, test its DC bias setting and amplify its AC signal using SK10 boards. SK10 board is designed for prototyping electric circuit, in which the conductors are arranged in parallel and the electronics can be inserted to make contact with the conductors. The components are connected by use of a short wire.
2.0 Materials and procedures
2.1 Apparatus
1 DC power
2 Function generator
3 Oscilloscope
4 Digital multimeter
5 SK10 bread board
6 Transistors BC109
7 Resistors
8 Capacitors
2.2 Procedure for using SK10 board
* The parallel tracks on the outside of the board was use for power supply
* The wire connecting the power supply to the circuit together were twisted to minimize electrical pickup
* A coloour scheme was used for wiring
* The shortest possible length was always used to connect between components to avoid making big loops
* The integrated circuit was wired around
* The circuit was always built up one section at a time. Then this part was tested to see if it works first before continuing.
2.3 The procedure for practical work: part I – DC bias of a common emitter amplifier.
A basic transistor amplifier known as a common emitter amplifier was built using transistor BC109 as shown in the circuit below
Figure 2: A circuit for pat I CITATION Dep15 \l 1033 (Electronics)
Step 0: oscilloscope calibration
* Channel 1 and channel 2 of the oscilloscope were calibrated. The test waveform was ensured that they appear as expected.
Step 1: power supply connections
* Two long wire, a red and a black, were taken, their ends were striped and were twisted together.
* One end of the red wire was connected to the positive terminal of power supply and the other end of the black wire to the negative supply.
* The other end of each wire was connected to one of the parallel sets of line along the edge of SK10. The red wire was put onto the top line and the black wire onto the bottom line.
* Using the oscilloscope with proper scope probes, the power supply was set to 15 V and this voltage was checked if it was seen along the positive supply rail on the SK10.
Step 2: Base bias
* A note of the percentage and absolute tolerance of all resistors used in the experiment were made using the resistor colour codes. These values were put in the table.
* Resistors R1 and R2 were connected on the figure 2. The top lead of R1 was attached to the positive supply rail with the bottom lead into one of the central conductors of SK10.
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