Prescott, Arizona Campus
Department of Electrical and Computer Engineering
EE 402 Control Systems Laboratory
Fall Semester 2014
Lab Section 51: Thurs 9:10 – 11:50 am
Lab Section 50: Thurs 1:25 – 4:05 p.m.
in KEC 122
Lab Instructor:
Dr. Stephen Bruder
Lab 04
Introduction to the MS 150 Servo System
Date Experiment Performed:
Thursday, October 02, 2014

Instructor’s Comments:
Comment #1

Comment #2
Date Report Submitted:
??, 2014
Group Members:
Student # 1 Name & Email
Student # 2 Name & Email
Grade:
EE 402 Control Systems Lab
Fall 2014
1. GETTING STARTED
Configure your workstation as shown in Figure 1 below. Do NOT turn on the power until the
lab instructor checks your wiring!!! Note that you will be using the voltmeter on the Reduction
Gear Tacho Unit (GT150X) as required. Also, terminal 1 of the servo amp is being driven by the
pot and terminal 2 is grounded.
+15V
- 15V
I/O Signal
Figure 1 MS150 starting configuration

Rotate the pot on the attenuator unit fully counter-clockwise to position “0,” next, adjust the
load unit to position “0” (i.e., no loading), and then turn on the power supply. The motor
should not spin. Slowly rotate the knob on the pot clockwise until the motor just begins to
spin. Record this minimum voltage ( Vmin ).
Vmin  ??? Volts

Carefully increase the pot and confirm that the motor spins faster as you increase the input
voltage and slower as you decrease it.

Set the input to 1 Volt and count the number of rotations of the output pot in a 1-minute
interval. Confirm that 30× this number is about the rpm reading you are reading on the
tachometer. Please record both values.
Measured input voltage = ?? Volts, rotations / min = ??, tach rpm = ??.
Names of Students in the Group
Page 2 of 7
EE 402 Control Systems Lab
Fall 2014
2. MOTOR SPEED AND TORQUE CHARACTERISTICTS
For the next two experiments we will use the starting configuration of Figure 1.
1.1. Motor Speed Characteristics
As we saw in the pre-lab, the motor speed varies approximately linearly with the applied input
voltage. Using the tachometer to measure the motor speed (in rpm) and the voltmeter (also on
the GT150X) to measure the applied input voltage, complete the table below and insert a plot of
the motor speed in rad/s vs input voltage into Figure 3. It is difficult to get exact input voltages
so simply get close to the prescribed levels and record your actual value (e.g., 1.05 V for 1 V).
Vin
Speed
Speed
(Volts)
(rpm)
(rad/s)
Desired
Actual
0.5
1
1.5
2
2.5
Figure 2 Motor speed vs input voltage
See the MS150 Book 1 page 41 for an example of what to expect for this plot.
Figure 3 Plot of motor speed vs input voltage
Estimate of the slope of the plot
Kg 
Names of Students in the Group
speed
 ???? (rad/s)/V
input voltage
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EE 402 Control Systems Lab
Fall 2014
1.2. Motor Torque Characteristics
In this experiment, we will be determining the effect of increasing the load torque on the
motor’s speed for two different fixed input voltages. First, fix the input voltage at 0.5 V and
record the motor’s speed. Set the load unit to “0” (no load) and vary as indicated in Figure 5.
Please try to center the disk in the cavity of the magnet as well as you can.
Figure 4 Load unit unloaded (left), partially loaded (center), and fully loaded (right)
Use the provided approximate “brake scale1” column in order to calculate the load torque at
each brake position. Note that the brake scale is given at 1000 rpm and must be converted based
on your measured speed.
Brake
Position
0
1
2
3
4
5
6
7
8
9
10
Input Voltage = 0.5 V
Load
Motor Speed
Torque
(rpm)
(rad/s)
(Nm)
Input Voltage = 1.0 V
Load
Motor Speed
Torque
(rpm)
(rad/s)
(Nm)
Brake Scale
(Nmm at
1000 rpm)
0
4
12
20
40
56
70
81
110
142
160
Figure 5 Motor speed vs load torque for two different input voltages
Plot both speed (rad/s) vs load torque (Nm) curves together and insert them into Figure 6. See
the MS150 Book 1 page 41 for an example of what to expect for this plot.
1
See MS150 book 1 page 46.
Names of Students in the Group
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EE 402 Control Systems Lab
Fall 2014
Figure 6 Plot of motor speed vs load torque
3. ERROR CHANNEL INVESTIGATION
In this portion of the lab, we will be generating and
calibrating the error signal formed between the Output
V V 
Vout   R f  1  2 
 R1 R2 
Potentiometer (OP150K) & Input Potentiometer
(IP150H) using the Operational Amplifier (OA150A)
as a comparator.
Figure 7 A simple comparator
Recall the operation of an Op. Amp. configured as a comparator (see Figure 7).
1.3. Set the Offset of the Comparator to Zero
Configure your Op Amp unit as shown in Figure 8.
Rotate the feedback selector on the Op. Amp. to the
100 kΩ resistor setting. Apply power (±15V & GND) to the
Op. Amp. Unit (QA150A) and measure the output (terminal
6) voltage with no input connection. Adjust the “Zero Set”
knob to achieve as close to zero volts as you can. This will
Figure 8 Setting the Offset to 0
accomplish the task of setting the comparator offset to zero.
Names of Students in the Group
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EE 402 Control Systems Lab
Fall 2014
1.4. Zeroing the Input and Output Pots
Connect the Power Supply, Op. Amp, Input pot, and Output pot as shown in Figure 9.
You will still need to
power the GT150X
(use it as a voltmeter)
To Voltmeter
Figure 9 Error channel calibration configuration
Be certain to connect the polarity of power to the input pot and output pot as shown (i.e., they
intentionally have opposite polarities).
-
Starting with the input pot, rotate the knob on the front face to set the pot to 0 and
then “adjust” the cursor until the voltage on terminal 3 is zero (ask for help as this may
involve a crescent wrench). Note do NOT rotate this pot beyond ±150 as this will
compromise your calibration!!
-
Transferring attention to the output pot, carefully turn the motor shaft (DO NOT TRY
TO ROTATE THE OUTPUT POT DIRECTLY) so as to rotate the dial on the output
pot to zero. Measure the voltage on terminal 3. If this voltage is not ~0V, rotate the
motor shaft to achieve a voltage of 0 V and record the output pot angle ( 0 =??). This
will be your offset angle for the remainder of the lab. Also, rotate the output pot to
read 0 and record the voltage ( V0 =?? Volts). BE SURE TO SUBTRACT THIS
OFFSET ANGLE FROM ALL OUTPUT POT ANGLES!!!!
Names of Students in the Group
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EE 402 Control Systems Lab
Fall 2014
1.5. Calibrating the Error Factor (Ke)
We now seek to determine the error factor, Ke ,
Input
Angle
+
-
Voltage
Error
Angle
Output
Angle
which has units of volts/degree. With the output

potentiometer at a fixed value, we will vary the input
potentiometer to experimentally determine the error
Figure 10 The error factor (Ke)
factor.
Fill in the table below and plot the error voltage (Op. Amp. output voltage) vs input angle in
deg. Each column of the table corresponds to a different output pot angle.
Input Pot
(Degrees)
Amplifier Output
V0 (Volts)
O/P Pot @ –60
O/P Pot @ –30
O/P Pot @ 0
O/P Pot @ 30
O/P Pot @ 60
–60
–30
0
30
60
Figure 11 Error voltage vs Input pot angle for various output pot angles.
Plot each column of the “Amplifier Output” against the “Input Pot” angle (in deg) all on the
same graph (please include a legend and remember to subtract 0 from the O/P pot angle). Next,
compute the slope of these lines and then the average slope across all of the lines.
Figure 12 Plot of the error voltage vs input angle for multiple output angles
The average slope is the error factor, Ke .
K e  ??? volts/degree
Names of Students in the Group
Page 7 of 7