Modern Engineering
Laboratories at a Distance
Jim
Henry, Charles Knight
Jim-Henry@utc.edu
and Charles-Knight@utc.edu
Abstract
This paper describes the technical aspects of conducting laboratory
experiments from remote locations. Sixteen laboratory systems are available at
UTC for students to operate remotely via the Internet. Collected data can be
shared with other students via the Web. The laboratory systems described in the
paper could be used by engineering and engineering technology programs in lieu
of or to supplement existing laboratory curriculum content.
Experimental
Setups
The
Table 1. Remotely Operable Mechanical
Engineering Stations
|
1. Kinematics of Motion |
|
2. Linear Vibrations |
|
3. Heat Exchanger |
Access
to these experiments is obtained by clicking on "Mechanical
Engineering" on the above web page. Each of these stations is connected to
a personal computer that serves as the operator's station for control and data
acquisition. Whether the
student-operator is sitting at the computer or is remote is irrelevant as far
as the laboratory equipment is concerned.
The equipment is available for conducting experiments at all hours of
the day and night, every day of the week.
The students perform the complete planning and
conducting of the experiments in all the stations described here.
Figure
1 presents a schematic of the generic setup for these experiments. The computer contains one or more data
acquisition (DAQ) cards that (1) send signals to the laboratory equipment to
control system parameters and (2) receive signals from the sensors or
transmitters for parameters being measured.
Students may operate the equipment while sitting at the computer station
near the equipment or they may operate it remotely via a Web page interface or,
in some cases, a remote program that communicates directly between the remote
and laboratory computers.
For
all laboratory systems at UTC, LabVIEW software and DAQ boards by National
Instruments are used for data acquisition, control and communication. Some of
the systems are "real time" controlled remotely, by either Web page
plug-ins using LabVIEW 6.1's Web serving facility or by separate LabVIEW remote
client programs, or "batch" runs with experiment specifications that
are submitted by users through a Microsoft Internet Information Server.
The
Kinematics of Motion Station is comprised of a single-cylinder gasoline engine
with its cylinder head removed. A
3-phase motor connected to a variable-voltage, variable-frequency drive,
externally drives the crank. The motor
drive receives an analog signal from the DAQ board upon computer command. An LVDT position sensor for both piston and
valve sends an analog signal to the DAQ board.
Figure 2 presents a schematic of this system.
The
user specifies what rotational speed is desired for the crank and whether the
piston or valve motion is to be observed.
The equipment then runs the motor at that speed and collects position
and time data from the appropriate sensor.
LabVIEW then generates the first and second derivative of the position
data and makes graphs of position-vs-time, speed-vs-time and
acceleration-vs-time for either the valve or piston motion. The piston motion
is studied with the crank and connecting rod lengths being determined using the
experimental data and TK Solver or Maple.
A detail study of the experimental valve motion enables the student to
determine the type of cam profile (parabolic, cycloidal, or harmonic) that is
being used in the engine.
The
Linear Vibrations Station consists of an upgraded Sanderson Linear Vibrations
system. It has a mass, spring and damper with a variable speed motor
drive. Electronic sensors were added to
measure position, velocity, and acceleration of the vibrating mass and
displacement position of the base excitation while the variable speed drive is
computer control via a pulse-width modulated DC power supply. Figure 3 presents
a schematic of the vibrations system.
The
user specifies what speed to run the drive motor, ranging from 1 to 5 Hertz,
and the desired length of the experiment, ranging from about
The
Heat Exchanger Station consists of a shell-and-tube heat exchanger. For this station there are two variables
available for user control: one is a variable-voltage, variable-frequency drive
for the 3-phase motor that drives a pump in the hot water loop and the other is
a variable flow control valve in the cold water supply line. The water passes
through a thermostatically controlled electric hot water heater before going to
the heat exchanger. These
actuators receive analog signal from the DAQ board upon computer command. The temperature is measured at four points
(inlet and outlet temperature for both hot and cold flows of the heat
exchanger), and the water flow rate is measured for both hot and cold water
flows. Figure 4 presents a schematic of
the Heat Exchanger Station. In the cold water loop, there are two solenoid
valves in parallel that can be opened and closed on command. These serve to simulate “disturbances” to the
system during normal operations. In Figure 4 the signal output lines from each
of the transmitters to the DAQ card are omitted for clarity and the disturbance valves are not shown.
The heart
of the Temperature Control System is a shell-and-tube heat exchanger. The
system is valved so that the flow can be either counter-current or co-current,
and the hot water can be either on the shell side or the tube side. This allows for a variety of interesting
operating situations to be examined. The temperature system inputs are the
hot-water loop flow variable ranging from 0-100% of full pump output and 0-100%
of the cold-water loop flow CWS valve opening.
Table 2. Remotely Operable
Controls Stations.
|
4. Speed Control Station |
|
5. Voltage Control Station |
|
6. Level Control Station |
|
7. Pressure Control Station |
|
8. Flow Control Station |
|
9. Temperature Control Station |
For each
controls station, students-user can run a variety of experiments. There is a set of "system
identification" experiments and a set of "controller design"
experiments. The system identification
experiments include:
1.
Constant input value
(useful for developing the steady state operating curve),
2.
Step function input (for
obtaining reaction curve, step response data),
3.
Sine function input (for
obtaining frequency response behavior and Bode plots),
4.
Ramp function input,
5.
Pulse function input,
6.
Design-your-own function
input and,
7.
Relay-feedback or
clamped proportional feedback function [17] (recently added).
The
controller design experiments are for testing the tuning of PID controllers.
For
the two simplest stations, Speed Control and Voltage Control, there is one
actuator, a variable-voltage, variable-frequency drive for the 3-phase motor.
This motor drive receives an analog output signal from the DAQ board upon
computer command. For each of these systems,
there is one sensor (speed sensor or voltage sensor) that sends a signal to the
DAQ board. Figure 5 presents a schematic
of the system. These two
"stations" are actually the same system; the user chooses whether the
computer collects speed or voltage data.
These
two systems are essentially, single input, single output systems. The "input" to each system is the
manipulated variable ranging from 0-100% of full motor output. The "output" of each system is the
controlled variable. For speed it is RPM in the range 0-1800 RPM; for voltage
is it DC Volts in the range 0-140 Volts.
For
the Level Control Station also has one actuator, a pulse-width modulated DC
power supply that drives the pump in the system. This power supply receives an analog signal
from the DAQ board upon computer command. In the controlled-level tank, there is a level
transmitter composed of a hydrostatic pressure sensor at the bottom of the
tank. Figure 6 presents a schematic of
the system. Two totally independent
tanks can be used at this station; one has an inside diameter of about 2
inches, the other has an inside diameter of about 6 inches.
The
level system is also essentially, a single input, single output system. The "input" to the system is the
manipulated variable ranging from 0-100% of full pump output. The "output" of the system is the
controlled variable, water level in the range of 0-70 cm.
For
the Flow Control and Pressure Control Stations also each have one actuator, a
variable-voltage, variable-frequency drive for the 3-phase motor. This power
supply receives an analog signal from the DAQ board upon computer command. In the Flow Control Station a MicroMotion
coriolis flow rate sensor is located in one branch of the flow system. Figure 7 presents a schematic of the Flow
Control Station. In the Pressure Control Station, a pressure transmitter is
located at the blower outlet. Figure 8
presents a schematic of the Pressure Control Station.
The
flow system is also essentially, a single input, single output system. The "input" to the system is the
manipulated variable ranging from 0-100% of full pump output. The "output" of the system is the
controlled variable, water level in the range of 0-70 cm. This system has two
"disturbances" that can be activated at the discretion of the
operator by opening two motor-operated valves that bypass water out of the line
that contains the flow transmitter.
The
Pressure Station is also essentially, a single input, single output
system. The "input" to the
system is the manipulated variable ranging from 0-100% of full blower
output. The "output" of the
system is the controlled variable, air pressure in the range of 0-7 cm of H2O.
This system has two "disturbances" that can be activated at the
discretion of the operator by closing two motor-operated dampers that provide a
blockage out of two of the three lines that exhaust the airflow.
The
Temperature Control Station is the same hardware mentioned above as the Heat
Exchanger Station. The temperature system is a multi-input, multi-output
system. The "inputs" to the
system are the manipulated variable ranging from 0-100% of full pump output and
0-100% of the CWS valve opening. The
"outputs" of the system are the controlled variables, and are the
temperatures of the hot water outlet and the cold water outlet. Since the flow
can be either counter-current or co-current, and the hot water can be either on
the shell side or the tube side, a variety of interesting control situations to
be examined.
Table 2. Remotely Operable Chemical
Engineering Stations.
|
10.Packed Column Absorption |
|
11.Distillation |
|
12.Heat Exchanger Station |
|
13.Flow Through Porous Media |
|
14.Batch Dryer |
|
15.Pressure Swing Absorption |
|
16.Gas-Fired Water Heater |
For
the chemical engineering stations, they are mainly "manually"
controlled. Essentially, our students
operate them in manual mode to observe the equipment's typical operating
characteristics. Access to these experiments is obtained by clicking on
"Chemical Engineering" on the above-mentioned web page.
The Packed Column Absorption Station as represented in Figure 9 is a packed column stripper. It is 4 inches diameter and 4 feet tall, packed with 1/4-inch glass rings. At this time, UTC students only study the flow dynamics of the system. The liquid is a (recycled) loop of water. The gas side is compressed air. Under computer control, again either locally or remotely, the water flow rate or airflow rate can be varied. The computer receives signals for the flow rates and the pressure drop across the column. Under remote operation, the flow is restricted so that flooding does not occur. When it is operated locally, the students do have the capacity to operate under flooding conditions.
The
Distillation Column (Figure 10) is a 12-tray, bubble-cap column. The tray
diameter is about 4 inches. The student
is able to control the heat to the reboiler, the reflux ratio and the feed flow
rate. The computer receives signals for
the flows, temperatures and the pressure drop across the column. Under remote operation, flow conditions are
restricted so that flooding does not occur.
When it is operated locally, the students do have the capacity to
operate under flooding conditions.
The
Heat Exchanger Station is the same station that is used for Mechanical
Engineering Station Number 3 described earlier.
For unit operations, the students conduct heat balances and calculate
the heat transfer coefficients.
The
Batch Dryer Station consists of eight trays of sand in a large oven with a
variable temperature control. Each tray is suspended on a load cell that senses
the weight of the tray. The drying
experiment may take as long as 10 to 20 hours.
The students can begin the experiment in the laboratory and monitor the
progress of the experiment remotely.
Plans exist to remotely operate the entire experiment in the near
future.
The
Flow Through Porous Media Station consists of water being pumped through one of
four pipes filled with small glass beads.
The pipes are of two different lengths, 4 feet and 8 feet, and two
different diameters, 1 inch and 2 inches.
The students can specify a pump rate (similar to the Level system
described above) and observe the pressure drop across the porous media path.
The
Pressure Swing Adsorption Station consists of a commercial home oxygen concentrator
that has been extensively instrumented for flow, temperature and
concentration. Remote operation of the
unit is possible. The student can change
the pressure swing cycle time and observe the impact on oxygen production rate
and concentration.
The
Gas Fired Water Heater Station is a domestic gas water heater that is
extensively instrumented for flows and temperatures of the water, combustion
air and flue gas and measuring the flue gas composition. The water flow rate is
controllable by the student. The students can study the effect of combustion
parameters and heat transfer in this system.
For
safety reasons, all these systems are equipped with safety shutdowns and other
safety monitors. The safety shutdown
will turn off all equipment if the controlling computer fails.
On-line
capabilities
Each
of the experimental stations is on-line 24 hours a day, 7 days a week. The students can run the experiments at any
time from any location on the Internet. The
experiment is queued according to a privilege ranking that students are
given. Otherwise, the experiments are
run first come, first served.
The
students design their experiments according to the objectives of the experiment
and submit, via the Internet, a request for the experiment to be run. Networked computers according to the
students’ specified parameters operate the equipment. The computers collect the data and present
the results to the students via the Web.
The data is also saved on the laboratory Web server for later retrieval [15,17].
Team communication
Teamwork
and collaborative learning are important in our lab courses. When a student runs an experiment, he or she
can notify teammates who can observe and/or download the results at another
location.
A Web
"front-end' has been developed to facilitate this team communication. This is a support system for team interaction
associated with laboratory assignments.
Each student has a personalized Web-Lab site that presents links to all
experiments run by the team.
Typical
assignments
We
have found it effective, where possible, to start students out with simpler
experiments and then have them proceed to experiments in which they are observe
more complex phenomena. For example, in Controls, all students in the first
week take data and construct a steady-state operating curve for their
system. In fact, steady-state
performance curves are good starting points for nearly all of the experiments
mentioned here.
Desired
outcomes for laboratory courses
We
have the following as desired learning outcomes for our laboratories:
·
Learn by doing
·
Guided discovery
·
Demonstrate by
experiment the phenomena developed in lecture or textbook
·
Design of experiments
·
Collection of data
·
Analysis of data
·
Presentation of data and
results
All
of these outcomes are possible with the experiment being run remotely.
Student-faculty responses are being collected to provide outcomes assessment
for our students15.
Conclusions
Modern
engineering laboratories can have equipment control and data acquisition by
computers that are controllable via the Internet. All of the desired learning outcomes for
students can be achieved by using remotely controlled equipment. A teamwork supported system integrated with
Internet operated laboratories can be effective in helping students learn.
Acknowledgement
Grateful
acknowledgment is given for the support of the Center for Excellence in
Computer Applications at UTC, the
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Jim Henry
Dr. Henry is a professor
in the area of chemical and environmental engineering at the
Charles Knight
Dr. Knight is a
professor in the area of mechanical engineering at the
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