Updated 5-27-08
Vibrating Table Procedure
The purpose of this experiment is to study the response of a damped system to an
external load. The experimental apparatus, shown in Figure 1 (schematic in Figure
2) can be mathematically modeled as a mass attached to a spring (th e four vertical
leaf springs at the base of the table) and a viscous damper which works as a break
on the system (the oil-filled dashpot on the base of the table). The electric motor
and belt driven wheel are used to apply a sinusoidal force for steady sta te analysis.
Figure 1: Vibrating Table
Transient Response
First, the transient response of the table will be investigated. An impulse force is applied to the table by
hitting it with a hammer and the acceleration of the table will be recorded as a function of time. You will be
able to see the table oscillate until it converges to zero and will determine the values of the damped natural
frequency d and damping coefficient C.
Steady State Response
In the steady state analysis, an oscillatory force will be applied to the same table by attaching a disc to a
motor with a weighted blot mounted eccentrically away from the center of the wheel. This is analogous to
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continuously applying a sinusoidal force on the table and investigating its response. By varying the motor
speed the frequency of the forcing function is varied.
Power
Switch
Speed
Control
Rotating
Mass
Motor
Proximeter
Accelerometer
Oil
Damper
Leaf Springs
Proximeter
Signal Processor
Filter module
Computer
Figure 2: Schematic Diagram of the Vibrating Table Apparatus
Experimental Equipment
Table
 Models a mass attached to a spring and damper
 Four vertical leaf springs attach the table to the base
 Oil-filled dashpot on the base of the table works as a damper
 Mass : 62.72 kg (including the safety cover)
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Figure 3: Vibrating Table Components
Motor
 Used to apply a sinusoidal force for steady state analysis
 Controlled using the blue Motor controller
 Attached to disc with 74.20 g bolt mounted eccentrically 82.6 mm away from the center of the
wheel in order to apply the sinusoidal force
Accelerometer
 Measures the acceleration of the table
 Manufacturer: Analog Devices
 Model: ADXL50EM-1 +4g
Tachometer
 Measures the frequency of the force (or the rate of the rotating wheel)
 Displays the motor revolutions per minute (RPM) on The SPU
Proximeter/Linear Displacement Sensor
 Omega LD701-2/5
 Non-contact transducer that measures distance based on inductive technology
 Located adjacent to a cam mounted on the shaft that drives the wheel and unbalanced mass. As
the shaft rotates the distance between the cam and the proximeter varies and the proximeter gives
a sinusoidal electrical signal which is linearly converted to the angular position of the mass. This can
then be related to the forcing function.
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Signal-processing Unit (SPU)
 Signal-conditioning for the Proximeter and Tachometer
Figure 4: Signal Processing Chassis
Procedure
Set Up
1. The module is located downstairs at lab station 17B. It is best if the module is set up so that the
Vibrating Table is to the right of the cart with the SPU and motor control. The cart should be placed
so that it is at the end of the lab station so the power cords do not have to stretch.
2. Connect the marked, matching cable ends for the accelerometer, tachometer and proximeter
between the vibrating table and the signal processing unit (SPU). Note where the sensors are
mounted on the table.
3. Connect the military connector exiting the SPU to P3B on the lab station base next to the computer
tower. Turn ON the SCXI chassis found directly above the computer tower on the B side of the lab
station.
4. Connect the large black power cable between the motor and the blue switch box. Make sure you
twist the connector to lock it in place.
5. Connect power to the accelerometer. Connect the +5V terminal of the power supply (mounted on
the side of the lab-station panel near the computer monitor) to + XTRA6 terminal on the lab station
panel using a red banana cable and connect the GND of the power supply to -XTRA6 terminal using
the black banana cable.
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CAUTION: ENSURE YOU HAVE NOT REVERSED THE POLARITY BEFORE TURNING THE POWER SUPPLY ON. REVERSING
THE POLARITY WILL DAMAGE THE ACCELEROMETER!
6. Finally, plug the power cable from the motor power switch into circuit #7 (power outlet opposite
the military connector) and the power to the spu into circuit #6 (below circuit #7). IF BOTH PLUGS ARE
PLUGGED INTO THE SAME CIRCUIT , THERE IS A CHANCE OF BLOWING A FUSE OR WORSE !!! Note: both plugs
must use the sockets on the same Labstation in order to use a common ground. Do not turn on the
motor or SPU yet.
7. Turn on the +5V power supply on the side of the breakout panel of the LabStation.
Transient Response
1. Open the Vibrating Table Transient Response.vi, located under Vibrating Table in the Modules
folder on the desktop.
2. Run the VI by clicking on the run arrow on the upper left hand corner of the VI.
3. Begin data acquisition by clicking on “Start Acquisition” and then hitting the SIDE of the table near
the black power cable where it says “hit here” with the rubber mallet. Do not hit the
accelerometer side of the table. If you fail to trigger the VI (within approximately ten seconds)
check that your equipment is set up correctly.
4. A “good” data set center around a constant line, have clear peaks and valleys (no double-peaks and
no clipping) and show a smooth exponential decay. Change the VI settings so that there is enough
data to show the end of the vibration. This will show if there is any offset in the data collection (i.e.
does the vibration center around zero?). .
5. When you produce a “good” set of data, save it and record the sample rate and the number of
samples acquired. It should be noted that you have to hit the “Start Acquisition” button each time
before you hit the table.
6. Repeat this procedure two more times, saving the data each time. You will use this data to estimate
uncertainty in your calculations.
7. Exit the VI.
Steady-State Response
1. Open Vibrating Table Steady State with Lissajous.vi found in the Module Folder on the desktop
under vibrating table.
2. Turn on the SPU by flipping the switch.
3. Turn on the power to the motor by flipping the black circuit breaker to the right of the SPU. A red
light will be illuminated when the power supply is on.
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4. Turn the motor speed knob on the blue controller fully Counter-clock-wise and press the start
button in the upper left corner of the blue motor controller.
5. Run the VI. Note where all the sensors are located and what information they are giving you. The
time-base scope is visible so that you can more easily understand what is happening with the
Lissajous display. The table vibrations are shown in green, and the phase of the forcing function
(the angle of the heavy, off-set mass) is shown in red. Adjust the motor speed until you find the
resonant frequency (how do you tell that you have found the resonant frequency?). Save your data
and record the RPM.
6. To ensure that you have selected an appropriate resonance frequency, take data (as above) for
several motor speeds very close to your suspected resonance and save your data for each trial. Be
sure to record which file corresponds to which motor frequency (RPM).
7. Repeat data collection for at least eight more motor speeds, four below and four above the
resonant frequency in 25 RPM increments. The speeds should be within 100 RPM range of the
resonant frequency. Your goal is to produce data for a system frequency response plot with good
resolution near the resonant frequency. Be sure to record which file corresponds to which motor
frequency (RPM).
8. When finished, press “stop” on the VI and quit LabView. Also, press “stop” on the blue motor
controller and close the VI. Turn off the SPU, motor power circuit breaker, 5 V power supply, and
SCXI chassis. Carefully unplug all cables, return checked out items and clean up.
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