Formal Lab Report Info
·
Read the manual
·
Read closely the report production
instructions
·
Decide what can be answered without much
effort
·
Start taking notes
·
Get an understanding of the laboratory
itself
·
Talk to your lab partners
·
Highlight the needs of the report that
will be discovered in the laboratory itself
·
Start assembling the required information
for the specific sections:
Abstract
Nomenclature
Introduction
Lab Observations
Results
Discussion
Conclusion
·
If you do not have all the needed
information – ask questions – see your TA
·
Prepare a rough draft and have X number
of people read it
·
Make changes where they see the need
·
Make decisions on why it is good or poor
communication – change if needed
Suggestions
·
Find readers
·
Read out loud
·
Read to see if it makes sense
·
Read to see if it follows some kind of
order
·
Read to see if it is understandable
·
Read as if your job depended upon it
·
Ask for help when you need it
Read Instructions
Follow Instructions
Ask Questions
Clarify everything
Build a readership
The following items make up the elements that will be evaluated in the
formal reports for ME 451 from the composition side. Teaching assistants will comment on the
inadequate elements, and you will have to address those comments.
Examples of all these items can be found in the lab and in the library
under Craig Gunn's name in the reserved reading.
If you can’t put these numbers at places within your report, then there
are important element missing; and you need to address them.
TITLE PAGE
1.Title of paper
2.Course
3.Date due
4.Section time
5.Name
6.DRAFT OR FINAL COPY
SUMMARY
7.Overview of the lab
8.Why was the lab
performed
9.How was the lab
performed
10. What was discovered,achieved, or
concluded
11. Recommendations
12.Past tense used
13.Reference to experiment not paper
14.No personal reference ( I,We)
15. It is
before the Tale of Contents
TABLE OF CONTENTS
16.All sections represented
17.Abstract and Table of C not listed
18.Lab Observations as a heading
Analysis,equip,procedure,
results - sub headings
19.All columns lined up
MOTIVATION AND OVERVIEW
20.Ample motivation for the experiment stated
20A.yours
20B.Whirlwind's
21.Sufficient information to orient reader to
the substance of experiment
22.Sections to follow mentioned
23.Any terminology that reader will need to
understand the text.
THEORETICAL BACKGROUND
24.Mathematical model used to predict system
behavior presented with ample explanation and lead in
25.equations
numbered
26.punctuation
with equations
(: with follow/s/ing
only)
27.equations
have space
EXPERIMENTAL SETUP AND
PROCEDURE
28.Schematic of equipment used
29.Figures/Tables correct
(Figure 1.
Title)
30.Figures oriented correctly
Clearly labelled and referenced
31.Highlights of equip. used
32.Highlights of the procedure (not specific steps)
RESULTS AND DISCUSSION
33.Data presented with clear indication of what data applies to
34.Reader will understand what this data
refers to
35.Trends in data stated (then to be discussed
in the discussion section)
36.Clear indication of what reader should see
in the data
37.Complete discussion of the results
appears
38.Connection of data and Whirlwind is clearly
stated
39.Comparison to similar experiments is
shown
40.Strong points of study given
41.Weak points of study given
42.Statements are specific
43.Logical progression to support
conclusions that follow
CONCLUSIONS AND
RECOMMENDATIONS
44."The following conclusions are supported by this
study:"
45.Conclusions are numbered
46.Conclusions are concise and highly
specific
47.Vague statements do not exist
48.Conclusions directly flow from
discussion
REFERENCES
49.Initials for first names
50.All information included
51.References #d in text [1]
Comments appear across your papers and
the following give you an idea of what those comments entail. Sometimes our own
writing sounds perfectly appropriate until someone else takes a look. See what
you think.
The
Place jumper between sockets A and B; none
between X and Y
The Women’s Advisory Group is comprised of
representatives from four broad areas:
When you smell an odorless gas, it is probably
carbon monoxide.
I had a great internship with Whirl poop.
Blood
flows down one leg and up the other.
Three kinds of blood vessels are arteries,
vanes, and caterpillars.
To remove dust from the eye, pull the eye down
over the nose.
If we don’t succeed ,
we run the risk of failure.
Poor Wording – etc.
I was recently on a tour of
Mars is essentially in the same orbit....Mars is
somewhat the same distance from the Sun, which is very important. We have seen
pictures where there are canals, we believe, and water. If there is water, that
means there is oxygen. If oxygen, that means we can breathe.
i souport publik edukashun.
The device must be able to withstand a certain
amount of heat
Iraqi Head Seeks Arms
Queen Mary Having Bottom Scraped
Lawmen from
Two Soviet Ships Collide – One Dies
Enraged Cow Injures Farmer with Ax
Man is Fatally Slain
Take a look at thses examples and see if you can
figure why the punctuation is approapriate or not.
In the experiment, the results were conclusive.
I found it easy to examine the magnesium,
cordite and byrillium, and lead.
Mary, Bob and I shared the inheritance.
You were not to be found using the devices, and
I will have to report you for the failure to follow the rules.
The last conclusion was correct; the first was
slightly wrong.
The job was enjoyable; comforting, relaxing, and
worthwhile; and long.
We need to understand the following:
Ethics
Morality
Price
of Lunch
Vacations
We need to understand Ethics, Morality, Price of
Lunch, and Vacations.
I gave you:
money
good
looks
talent
Some suggestions from the reports that have been
turned in over the course of the semesters:
Put the laboratory TA’s name on the memo – he/she gives you the grade and should be recognized.
It’s means it is
Its is
the possessive.
Comma in a series - better to use John, Mary, and Bill – use
comma before and
Do not use commas where the sentence is simply
showing two items connected by and
When you have an adverb at the beginning of the
sentence, place a comma after it to separate it from the
rest of the sentence.
Avoid prepositions
at end of a sentence .
Don’t put a comma
before BUT if no subject and verb follow it.
Use a colon to designate a
list to follow.
When using a sentence that has two independent
clauses connected by a coordinating conjunction use a
comma to show the reader that you have two separate sentence ideas contained in
the one sentence.
SUGGESTION:
DATA – This is a plural
word so requires a plural verb.
##
You can use the present
and the past tenses, but make sure that the reader knows when these things are
happening.
Avoid:
“ “

s
p
e
e
d
action
Figure
1. The Cascading
Harmonics of F=W+2
Figure 1 The
Cascading Harmonics of F=W+2
Figure 1 The
Cascading Harmonics of F=W+2. Applications enhanced by J.Tomlinson, MIT.
Table
1. Number of Trial
Runs in Relation to Temperature
|
|
Trial Runs |
|
|
|
|
Temperature |
|
|
|
|
|
|
|
|
|
|
Notice the
different acceptable formats for the figures.
Figures
designated under the figure. Tables with headings on top.
By Spelling out
and capitalizing Figure and Table, your entire document is uniform.
Consistency is vital in any document that you create.
Paragraphing:
topic sentences
supporting ideas
no more
Transitions:
Word, phrase, sentence, paragraph, or even a
longer passage that ties information together
usually
however
on the other hand
in spite of
moreover
also
as a result of
therefore
for example
next
then
and
but
in the first place
1.
To start out – be mechanical
This concludes the discussion. Next I will tell
about the conclusions. The conclusions are now over.
2.
When done with a first draft read it out loud and look
for places where a good transition would help the text to flow more smoothly.
Remember
– Don’t let your reader get lost. Transitions help the reader to connect
thoughts together. Without the connections, it is easy to lose track of the
message.
Make sure that nouns and pronouns agree with
each other. Also make sure that the reader knows exactly what you are referring
to when you use a pronoun. First paragraph has many unclear pronouns. Paragraph
two is much better.
The magnesium became much lighter after the tube
was filled and greater heat was gained in the process, which it didn’t account
for. It was difficult to handle. This might not have caused any problems, but
it could have created some difficulty in measuring the results, which they were
not accounted for in.
The magnesium became much lighter after the tube
was filled and after greater heat was gained in the process. A
lightness that was not accounted for in the process. The magnesium at
this point in the process was difficult to handle because of its temperature
and its lack of weight. These problems might not have caused any problems, but
they could have created some difficulty in measuring the results, results that
were not accounted for in the original expectations of the experiment.
Notice how the placement of the subject to the verb affects the understanding of the text – if the verb and subject are close, it is easier to understand. If further apart, the meaning is less clear.
The magnesium after filling the tube and gaining
greater heat in the process which was not a bad thing but might have created
some difficulty became much lighter.
The magnesium became much lighter after the tube
was filled and greater heat was gained in the process, which was not a bad
thing but might have created some difficulty
The magnesium became much lighter after the tube
was filled and greater heat was gained in the process. This might not have
caused any problems, but could have created some difficulty in measuring the
results.
While we state and approximate page length, It is
vital that you get your message across and stop. Repetition does not get you a
better grade. A short succinct report speaks volumes.
The experiments were conducted to (don’t mention
anything about people – only the lab) ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________
The laboratories were conducted by using the
following tools, materials, laws, theories
____________________________________________________________________________________________________________________________________________________________________________________________________________________________________
The conclusions drawn from the laboratories were
________________________________________________________________________
________________________________________________________________________
All symbols contained in the equations ( no abbreviations) in alphabetical order
f =
frequency
H(t) = heat in the mixing tank
h = heater core
temperature
T(t) = mixing tank temperature
T =
Time (seconds)
t = V/Q = time constant (sec)
r = density (gm/cc)
In industry, processes often require control of the temperature of a fluid in a holding tank. Therefore, two experiments were performed which investigated the issues related to this control process. The first was a simulation, utilizing Matlab scripts to simulate a physical system; the second was an actual temperature control experiment involving a holding tank of water with hot and cold water inputs. The primary objective of performing this experiment was to gain an understanding of the response of a first-order system. This response was characterized by a time constant and a time delay, which were functions of the system parameters.
Some important background material that may be
of importance to the reader is
__________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________________________________________________________________________________________________
The system’s behavior was predicted (see Analysis) using mathematical models and then tested (see Experimental Procedure) to see how favorably the system’s actual response followed the predicted response (see Results and Discussion). Conclusions based on data acquired are presented along with practical applications for utilizing the lessons learned in the laboratory.
Equipments
and Procedures (don’t COPY lab manual -approximately 2 pages –
A
pump is used to inject water of temperature Tinp into a mixing
tank. The input water’s temperature is
controlled by selecting fluid from tank 1 at T1 or tank 2 at T2. The changing temperature in the mixing tank
is sensed by a thermocouple. If the
temperature in the tank is too high, the high temperature valve is closed (valve
2) and the low temperature valve is opened (valve 1). If the temperature in the tank is too low,
the low temperature valve is closed and the high temperature valve is opened.
And any other equipment or computer programs used
____________________________________________________________________________________________________________________________________________________________________________________________________________________________________
It is perfectly okay to bullet the equipment used and then explain why it was used
· A mixing bowl
· Two ice cubes
· Three tongs
The above list of equipment was used to ……The ice cubes were of particular importance because…..
Results
(approximately 1 page)
It is important to note the following information that can be learned/shown from the data collected in the three experiments _________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
(do not explain
just tell what data were collected)
Table 1. Title


Figure 1. Title
Spend time making sure that yours readers understand what you want them to see. What are the specific things that everyone must be clear on before you present your interpretations of those happenings.
The section should show
a unified set of results that do not come from each experiment but reflect a
total picture of what you have discovered and what you will tell the reader.
Discussion/Interpretations of Results (approximately 1/2 – 1 page)
The time constant of the system was
in agreement with its theoretical calculated value for all the experiments
performed. The same is true for all the
time delays, except the tdly for the long process delay loop. The actual delay time was 25 sec.; the
predicted delay time was 60 sec. ( notice how the results are explained) This is probably due to the fact that the water in the delay tube was
hot water from the previous experiment, not cold water as the equation
assumed. Since the water temperature in
the tube was higher than predicted, its effect on the mixing tank water was
quicker and more profound (Figure 12).
Conclusions
(use 1.2.3.form to indicate your conclusions from the experiments)
The
following conclusions are supported by the results of these experiments:
1.
The time constant of a physical system is independent of the time delay for
said system and vice-versa.
1.
The system should be designed such that the delay time is neither too short nor
too long. Too short, and the valves are
continually being open and shut to regulate temperature. Too long, and the system’s temperature
fluctuates too much to be in equilibrium.
ME
451 : Control Systems
Section
7B
YOUR
NAME
TA’s
NAME
Many industrial processes require the
control of the temperature of a fluid in a holding tank. To gain insight into the actual process of
fluid temperature control, several experiments were performed. Matlab scripts were used to simulate the
response of the physical system used later:
A mixing tank containing water was connected to a cold
water holding tank and a hot water holding tank. Water was pumped from each of these tanks,
and the effects of time delay and the time constant of the response of the
physical control apparatus were examined.
The virtual instrument “Tank Temperature Control” was used to control
the operation of the system which utilized thermocouples to monitor the tank
temperature.
Several important conclusions were supported by the
experiments performed. The time constant
of a system is independent of the time delay, and vice-versa. Also, the system should be designed for a
delay time that is neither too long or too short. With a short time delay, the valves are
continually being opened and closed to regulate temperature. This is known as hunting. Too long, and the tank temperature fluctuates
too much to be in equilibrium. Finally,
the system should utilize valves that can be opened and closed incrementally,
rather than valves which have only 2 states: fully open or fully closed. Multi-stage valves would allow the system
temperature to approach the desired equilibrium point with more precision and
accuracy and reduce the percent overshoot.
Nomenclature
Arabic
Cp = specific heat of water (cal/C*gm)
H(t) = heat in mixing tank
Hinp(t) =
heat added to tank
Hs(t) =
heat spilled from the tank
H(0) = initial heat in
tank
Qinp(t) =
input flow rate (cc/min)
Qs(t) =
spill flow rate (cc/min)
Tinp(t) =
input temperature (C)
T(t) = mixing tank
temperature (C)
V = mixing tank volume (cc)
Greek
t = V/Q = time constant (sec)
r = density (gm/cc)
Contents
Nomenclature…………………………………… 3
Introduction……………………………………... 5
Analysis…………………………………………. 5
Experimental Procedure………………………… 12
Results…………………………………………... 23
Discussion………………………………………. 24
Conclusions………………………………...…… 25
Introduction
In industry, processes often require
control of the temperature of a fluid in a holding tank. Therefore, two experiments were performed which
investigated the issues related to this control process. The first was a simulation, utilizing Matlab
scripts to simulate a physical system; the second was an actual temperature
control experiment involving a holding tank of water with hot and cold water
inputs. The primary objective of
performing this experiment was to gain an understanding of the response of a
first-order system. This response was
characterized by a time constant and a time delay, which were functions of the
system parameters.
The system’s behavior was predicted
(see Analysis) using mathematical models and then tested (see Experimental
Procedure) to see how favorably the system’s actual response followed the
predicted response (see Results and Discussion). Conclusions based on data acquired were
recorded.
A pump is used to inject water of
temperature Tinp into a mixing tank.
The input water’s temperature is controlled by selecting fluid from tank
1 at T1 or tank 2 at T2.
The changing temperature in the mixing tank is sensed by a
thermocouple. If the temperature in the
tank is too high, the high temperature valve is closed (valve 2) and the low
temperature valve is opened (valve 1).
If the temperature in the tank is too low, the low temperature valve is
closed and the high temperature valve is opened.
Figure 1. System
Diagram
The mixing system consisted of the plant (the apparatus
required to perform the operations) and the associated control system. To model the plant, consider the heat in the
mixing tank as a function of time, which was given by
H(t) = H(0) + Hinp(t) + Hs(t)
(1)
The
heat added to the tank from time 0 to time t was
(2)
while
the total heat spilled from the mixing tank was
Hs(t) =
rcpT(t)Qs(t)dt
(3)
where
cp and r
were assumed to be constants.
Substituting eq. (2) and eq. (3)
into eq. (1) gave
H(t) = H(0) + rcpTinp(t)Qinp(t)dt - rcpT(t)Qs(t)dt
(4)
However, since
H(t)
= rcpVT
(5)
we
can rearrange eq. (4) using eq. (5) to get
T(t) = T(0) + 1/V
Tinp(t)Qinp(t)dt - 1/V T(t)Qs(t)dt
(6)
In the experiment performed, as in
normal operating situations, the spill volume equaled the input volume (Qs
= Qinp = Q). Taking the
derivative of eq. (6) with respect to time gave
T(t) = -(Q/V)T(t) + (Q/V)Tinp(t)
(7)
which was the system state equation. Tinp(t)
was the system input and T(t), the mixing tank temperature, was the system
output. The plant transfer function,
which relates output to input, was placed in the “s” domain by taking the
Laplace Transform of eq. (5) and rearranging terms, giving
Output = Transfer Function * Input
or
T(s) = Gp(s)Tinp(s)
where
Gp
= (Q/V)/(s + Q/V)
(8)
There exists two distinctly different
ways of controlling the output of a given plant: open-loop control and
closed-loop feedback control.
An open-loop control system uses the
desired output and the plant model to determine an input function that will
give the desired output. An open-loop
control system assumes the desired output is reached upon execution of the
input (see Figure 2).
Figure 2. An Open-Loop Control
A closed-loop feedback control system monitors the output in
order to make changes to the input. With
the addition of a feedback loop, the output becomes a function of the input
(see Figure 3).
Figure 3. A
Closed-Loop Feedback Control
Once the control system has been selected, the state equation can be solved. The input function can be written as a step function
Tinp(t) = Tinph(t-tdly)
(9)
where
h(t-tdly)
= 1 if t ³ tdly
0 if t
£ tdly
The step function above represents
the on-off condition of the input function and Tinp represents the
magnitude of the input function (either T1, high temperature, or T2,
low temperature). Solving eq. (7), the
state equation, for the above input temperature gives
T(t) = A*exp(-Q/V)t + Tinp
(10)
where
(Q/V) = 1/t and A = (T0 – Tinp)
with T0 as the initial mixing tank temperature.
This is a decaying exponential that
starts at T0 and approaches the input temperature Tinp at
a speed determined by the time constant t. Large values of t yield a system with slow response time while small values
of t yield a system with a quicker response
time (see Figure 4).
Figure
4. Plant Response for a Small and Large Time Constant
The mixing tank temperature is
regulated in iterated steps when implementing a closed-loop feedback control
system. If the mixing tank temperature
is too hot, cold water is added by opening the appropriate valve. If the tank temperature is too cold, hot
water is added. During these operations,
the mixing tank responds according to eq. (8) with initial condition given by
tank temperature at the moment the mixing tank input switches from hot to cold
or cold to hot.
How fast the control can change the
input temperature T0 is determined by the time delay, which is the
time between when the control changes input flow and the time that flow reaches
the mixing tank. Figure 5 shows a
typical response with a time delay. The
figure shows the response of the system for a desired temperature Td
when the tank starts at a temperature of T0. The time from t0 to t2
represents the time high temperature water is withdrawn from the hot water
tank. The system responds after the
delay time, tdly, which equals the time required for hot (or cold)
water to travel from its holding tank through hoses to the mixing tank. The delay is seen in the time difference from
t1 to t0 and t3 to t2. At t1, the system starts
responding according to eq. (10). At t2,
the control measures the mixing tank temperature as too high, and switches from
hot to cold water input. The mixing tank
temperature continues to rise because hot water is still present in the hose
system until enough water has been pumped from the cold water tank to force
cold water into the mixing tank.
Figure
5. System Response
Equipment includes:
·
Matlab scripts to
simulate response of a physical system
·
Physical system seen in
Figure 1
·
Virtual instrument “Tank
Temperature Control”
Simulation
For the simulation part of the experiment, it was assumed that Q = 30 cc/sec and V = 2000 cc. The differential equation governing the system is, therefore
(11)
and
the plant transfer function is
Gp
= [(3/200)/(s + 3/200)]
(12)
(13)
Open-Loop
Mode
Using Matlab commands, a physical
control system was simulated. The flow
rate was set to 30 cc/sec; the mixing tank volume,
2000 cc. A time vector from 0 to 400
seconds was then created.
The first experiment simulated heating a mixing tank from 15 °C to 40 °C
using a hot water input of 40 °C. The result was then plotted (see Figure 6).
Figure 6. System Response for T0 = 15 °C and Tinp = 40 °C
The second experiment simulated cooling the mixing tank from 45 °C to 16 °C
using cold water at 16 °C
as the input. The result was then
plotted (see Figure 7).
Figure 7. System Response for T0 = 45 °C and Tinp = 16 °C
The third experiment simulated heating the mixing tank from 21° C to 45 °C
using 45 °C water as the input. The result is plotted in Figure 8.
Figure 8. System Response for T0 = 21 °C
and Tinp = 45 °C
Using Matlab, a simulation of a
feedback control system was established.
In this simulation, the valve is opened from the cold water tank when
the measured water temperature in the mixing tank goes above the desired
value. Similarly, when the holding tank
temperature is below the desired value, the valve from the hot water tank is
opened.
Using the script “lab2_sim” available in the laboratory, several experiments were performed, keeping t equal to the value set earlier, and setting the hot water tank to a temperature of 45 °C and the cold water tank to 15 °C.
Experiment
4: (see Figure 9)
delay time = 0 sec., initial temperature = 30 °C, desired temperature = 38 °C
Figure 9. System Response for tdly = 0 sec.,
T0 = 30 °C and Tdesired = 38 °C
Experiment 5: (see Figure 10)
delay time = 16 sec., initial temperature = 30 °C, desired temperature = 38 °C
Figure
10. System Response for tdly = 16
sec., T0 = 30 °C,
and Tdesired = 38 °C
Experiment
6: (see Figure 11)
delay time = 32 sec., initial
temperature = 30 °C,
desired temperature = 38 °C
Figure
11. System Response for tdly = 32
sec., T0 = 30 °C,
and Tdesired = 38 °C
The effects of time delay and the
time constant on the response of the water temperature control apparatus were
examined using the system seen in Figure 1 and the Virtual Instrument (VI)
“Water Temperature Control” available on the computers in the laboratory. The lengths of the tubes connecting tanks 1
and 2 to the mixing tank were measured without the process delay loop: L1
= L2 = 1.308 m. The lengths
of the long process delay tubes were then measured: Ldly = 7.84
m. The cross-sectional area of the tubes connecting the holding tanks to the mixing tanks
were also measured: A = 1.572E-4 m2. The volume of the mixing tank up to the
height of the primary overflow tube was also measured: V = 1.966E-3 m3. The flow rates (Q) into the mixing tank were
measured by catching the overflow for 150 seconds, weighing the total amount of
water that overflowed the tank (equal to amount of water which flowed into the
mixing tank), dividing the weight by the density of water (1000 kg/m3),
and finally dividing by the elapsed time (150 sec.): Qavg. = 23.81
cc/sec.
Experiment 7: (see Figure 12)
Tank 1 was filled with cold water
(16 °C) and tank 2 with hot water
(47 °C). The VI was set to manual mode and the mixing
turned off. With the initial mixing tank
temperature, T0, at 26 °C, and a desired temperature of 41 °C, the hot water valve was manually opened. The short process delay was used, so when the
mixing tank reached 41 °C,
the hot water was turned off and the cold water turned on. There was a short time delay, then the water temperature began to steadily decrease. Switching to the long process delay, a new
desired temperature of 24 °C
was established. When the tank
temperature
reached 24 °C,
the cold water was turned off and the hot water turned on. There was a longer delay this time, however, since a longer process delay tube was used.
Figure
12. Manually Controlled
Feedback System. T0 =
26 °C, Tdesired = 41 °C
Experiment 8: (see Figure 13)
The VI was switched to automatic mode and a desired temperature of 32 °C was entered. Using inputs of 16 °C for tank 1 and 44 °C for tank 2, a graph showing the system response was created. Using Matlab once again, the script “wtemp” was run. After inputting the system parameters mentioned above, a graph was created, simulating the response of the physical system. These two graphs were then superimposed for comparison.
Figure 13. Automatic Control Feedback
System. Comparison of Measured
vs. Predicted Values
Figure 14. Determining Steady State
Condition of Response. T0
= 16 °C,
Tinp = 45 °C
Finding the time constant, t,
of the system can be done two ways:
-1- t = V/Q = (2000cc)/(30cc/sec) = 66.7
sec.
-2- Graphically – see Figures 4 and 8: t = time it takes for system to make 63% of the temperature change from T0 to Tinp. t = 65 sec.
The system is deemed having reached its steady state after 98% of the temperature change has occurred. This occurs after approximately 4 time constants. In other words, after 4t seconds, the system is in equilibrium.
Using
the long process delay loop, the time delay and time constant of the system
were determined graphically (see Figure 11).
t
= 66 seconds (t
is the same value for all experiments).
time delay = 32 seconds.
The time delay of the control system was determined by the length of the tube that connected each holding tank to the mixing tank. Longer tube means longer time delay.
The time constant of the control
system was determined by the flow rate (Q) into the mixing tank and the volume
(V) of the mixing tank. large V = large t,
large Q = small t.
For the physical system used, the
flow rate was equal to 23.81 cc/sec. This value was unchanged by the process delay
time. Using the measured values of V and
Q, t
was calculated for the physical system. t = 82.57 sec. The
delay time for the system was calculated using tdly = (A*L)/Q. tdly = 8.64 sec for the short
process delay, tdly = 60.4 sec. for the long process delay.
Using the graph generated from the manual control mode (Figure 12), the time delay and time constants were calculated.
Short process delay loop: t = 86 sec., tdly = 12 sec.
Long process delay loop: t = 88 sec., tdly = 25 sec.
The time constant of the system was
in agreement with its theoretical calculated value for all the experiments
performed. The same is true for all the
time delays, except the tdly for the long process delay loop. The actual delay time was 25 sec.; the
predicted delay time was 60 sec. This is
probably due to the fact that the water in the delay tube was hot water from
the previous experiment, not cold water as the equation assumed. Since the water temperature in the tube was
higher than predicted, its effect on the mixing tank water was quicker and more
profound (Figure 12).
The actual time delay for the short
delay loop was measured as 12 seconds, while the predicted delay time was 8.5
seconds. Figure 13 shows the
discrepancies between these 2 systems.
The system reached steady-state, or
98% of its final value, in 285 seconds (Figure 14). This is approximately equal to 4.2 time
constants. The standard determination
for steady state is after 4t
seconds, where t
is a function of system parameters.
Conclusions
The following conclusions are supported by the results of
these experiments:
1. The time constant of a physical system is independent of the
time delay for said system, and vice-versa.
2. The system should be designed such that the delay time is
neither too short nor too long. Too
short, and the valves are continually being open and shut to regulate
temperature. Too long, and the system’s
temperature fluctuates too much to be in equilibrium.
3. Instead of using valves that have only 2 states, open or
closed, an optimum system would incorporate valves that can be opened and
closed incrementally. This would allow
the system to approach the desired equilibrium point with more precision and
accuracy and reduce the percent overshoot.