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THE
LABORATORY REPORT
The
report you turn in after completion of each series of experiments is the main
product of the team’s work which will be used for grading. Therefore you
should devote enough attention to this final but critical step in the laboratory
experience. Writing good technical reports is a valuable skill, which in the
future will help advance you professional career. Start practicing it now.
The purpose of the laboratory
report is to provide information on the measurement procedure, obtained results,
analysis, and interpretation and discussion of these results. The discussion
and conclusions are very important in a report because they show what knowledge
you gained by doing the experiments.
There is no one best format
for all technical reports but there are a few simple rules concerning technical
presentations which should be followed. Adapted to this laboratory they may
be summarized in the following recommended report format:
1.
The Cover Page
should have the names of the team members, and a designation such
as Group 3, if the groups are numbered, section and course numbers
(e.g. ECE 291, Section 003). It should also contain the number and the
title of the experiments, such as "Experiments VII RC circuits; Passive
filters". Cover page should also have the date of the report delivery,
not the due date.
2.
The Introduction
should contain a brief statement in which you state the objectives,
or goals of the experiments. It should also help guide the reader
through the report by stating, for example, that experiments were
done with three different circuits or consisted of two parts etc.
or that additional calculations or data sheets can be found in the
appendix. It is also a good place to state that the experimental results
were as expected or that there were some problems, as explained in
the Conclusions.
You may state what was learned in this set of experiments
3.
The Procedure
describes the experimental setup and how the measurements were made.
Include here circuit schematics with the values of components. Mention
instruments used, their settings and describe any special measurement
procedure that was used.
4.
The Experimental Data section
should be presented clearly with a reference to the procedure the
schematic used in measurements. Tables are often a good way of presenting
results. This section can also include some calculations or data analysis.
For example, in describing the measurements of a frequency distribution,
make a table with frequency in one column and the peak-to-peak voltage
measured with an oscilloscope in another. The third column might contain
the voltage rms values, calculated from the first column, which may
be compared with the data obtained with a voltmeter, listed in fourth
column. Another column may contain values calculated from theory.
In
many student’s reports in the past there was not enough information in this
section. For example, when reporting measurement of an amplifier gain, input and
output voltages were recorded but no information would be given on the frequency
at which the measurements were performed or whether the data were taken with a
voltmeter or an oscilloscope. Remember: giving more information is not a
mistake, less may be.
The best form of presentation
of some of the data is graphical. In engineering presentations a picture
is often worth more than a thousand words. There are some
simple
rules concerning graphs and figures which should always be followed. If there is
more than one figure in the report, the figures should be numbered. Each figure
must have a caption following the number. For example: Fig. 1 Schematic of the
resonance circuit used in experiment 1, or Fig. 3. Dependence of voltage VR on
frequency. All components in the schematics should be labeled with symbols (C1,
R2) or values (10 nF, 100k). If symbols are used, particular values used in
experiments should be listed in the text. All graphs, beside captions, should
have clearly labeled axes. Axes, beside labels, should have scales and units.
For example, in a graph of a diode characteristic, a horizontal axis may be
labeled with a symbol VD and have marks (ticks) indicating voltage scale: 0.1,
0.2, 0.3, etc. with the word "volts" or symbol V written under the
axis. Similarly the vertical axis may have symbol ID, for current, with numbers
and units designated by the symbol mA, for miliamperes. The lack of proper
figure identification and labeling is a very often seen shortcoming in student’s
reports.
5.
The Discussion
is a critical part of the report which testify to the student’s understanding
of the experiments and its purpose. In this part of the report you
should compare the expected outcome of the experiment, such as derived
from theory or computer simulation, with the measured value. Before
you can make such comparison you may have to do some data analysis
or manipulation. The simplest example would be conversion of peak
to peak voltage obtained from an oscilloscope to rms values or conversion
of a waveform period to frequency. When comparing experimental data
with numbers obtained from theory, make very clear which is which.
The best way of analyzing strings of data, such as a frequency distribution,
is to make an appropriate graph on which the theory is represented
by a continuous curve and experimental data by points. In such case
you do not need to join the points with a continuous line; their distance
from the curve will be the measure of agreement of the experiment
and theory. If there is no theoretical curve on the graph, the data
points may be joined by a continuous line which is to represent the
measured function. A caution is advised if there are just a few data
points on the graph. Computers may draw a meaningless zigzag stick
figure through such scattered points. You may do a much better job
by drawing a smooth line between the points by hand, unless you use
software with capabilities of fitting a spline or other function,
based on statistical analysis of the data.
A
critical part of discussion is error analysis. In comparison of theory and
experiment you may not get and usually do not get a perfect agreement. Sometimes
the agreement is poor. It does not necessarily mean that your experiment was a
failure. The results will be accepted, provided that you can account for the
discrepancy. Precision and accuracy of the instruments or your ability to read
the scales may be one limitation. The value of some circuit components may not
be well known and a nominal value given by the manufacturer does not always
correspond to reality. Very often, however, the reason for the difference
between the expected and measured values lies in the experimental procedure or
in not taking into account all factors that enter into analysis. A good example
comes from a student’s report. Low-pass filter characteristic obtained by
measuring voltage across a capacitor did not agree with the theoretical curve.
The measurements appeared to be precise and the scatter of experimental points
was negligible. The instructor pointed out a small value of capacitance, which
students choose for the filter. After some discussion they realized that the
capacitance of the cable connecting the circuit to the meter changed its
characteristics. When this capacitance was taken into account the agreement was
quite good and the report was accepted. The above example shows that data
analysis requires an open mind and a critical approach to your own work and that
routine methods may not be sufficient.
6.
The Conclusions
, should contain several short statement closing a report. They should inform
the reader if the experiments agreed with the theory. If there were differences
between measured and expected results, try to explain possible reasons for
these differences. You may also say what could have been done differently,
how experiments may be improved, or make other comments on the laboratory.
Constructive and original statements are highly valued.
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