BMM3532
MEASUREMENT & INSTRUMENTATION
EXPERIMENT REPORT ON SENSOR
LECTURER: DR. CHE KU EDDY NIZWAN BIN CHE KU HUSIN
Name
Matric No
SIT KIAN WAI
MA17041
WONG HAN SIONG
MA17158
MOHAMAD ZURAIDEE BIN CHE SUKERI
MA17215
NA JIAN
MA19173
NIE XIAO HAN
MA19174
YAO HAO
MA19175
LAU GUAN HONG
MH17034
Introduction review on the sensor
Generally, vibration systems consist of means for storing potential energy (spring or
elasticity), kinetic energy (mass and inertia) by which energy is gradually lost (damper).
Vibration is divided into two main types which are free vibration and forced vibration. Free
vibration will occur when a mechanical system is set off with an initial input and then allowed
to vibrate freely while forced vibration occurs when a time-varying disturbance (load,
displacement or velocity) is applied to a mechanical system. The disturbance can be a periodic,
steady-state input, a transient input, or a random input. The periodic input may be a harmonic
or a non-harmonic disturbance. If the frequency of excitation coincides with the natural
frequency of the system, the response will be very large. The condition known as resonance,
which is to avoid or prevent failure to the system. The vibration produced by an unbalanced
rotating machine, the oscillations of a tall chimney due to vortex shedding in a steady wind,
and the vertical motion of an automobile on a sinusoidal road surface are examples of
harmonically excited vibration.
Background
2.1 Name and composition
The electric fan is referred to as an electric fan, which is also called a fan. It is a
household appliance that uses a motor to drive the fan blades to rotate to achieve accelerated
air circulation. Widely used in homes, classrooms, offices, shops, hospitals and hotels.
The fan is mainly composed of fan head, blade, net cover and control device. The fan
head includes a motor, a front and rear end cover, and a shaking head blower mechanism.
The main components of electric fans are: AC motors. Its working principle is: the energized
coil rotates under force in a magnetic field. Electrical energy is converted into mechanical
energy. At the same time, because of the coil resistance, a part of the electrical energy is
inevitably converted into thermal energy.
Common household electric fans are essentially axial fans, that is, the direction of the
wind is parallel to the axis of rotation of the fan blades.
2.2 Working principle
The main components of electric fans are: AC motors. Its working principle is: the
energized coil rotates under force in a magnetic field. Electrical energy is converted into
mechanical energy. At the same time, because of the coil resistance, a part of the electrical
energy is inevitably converted into thermal energy. In addition, DC motors, DC brushless
motors and other low-power motors are becoming more and more widely used in small
electric fans.
When the electric fan is working (assuming there is no heat transfer between the room
and the outside world), the temperature in the room not only does not decrease, but increases.
Let's analyze the reason for the temperature rise: When the electric fan is operating, because
there is a current passing through the coil of the electric fan, the wire has resistance, so it will
inevitably generate heat to radiate outward, and the temperature will naturally rise. But why
do people feel cool? Because the human body has a large amount of sweat, when the electric
fan is turned on, the indoor air will flow, so it can promote the rapid evaporation of sweat,
combined with "evaporation needs to absorb a lot of heat", so people will feel cool.
2.3 Cause of vibration
There are many reasons for the fan to generate vibration, and the "eccentricity" of the fan
blade is the main reason for the vibration. The center of gravity of the high-quality fan is on
the axis, which is very stable when running, and the vibration is very small. However, the
inferior fan often has a certain deviation. After the fan is turned, it is equivalent to an
oscillator (an oscillator is an eccentric wheel on the motor shaft). As the use time becomes
longer, the fan bearings gradually wear out, or the fan's heat sink is not installed securely and
loosens Etc. will aggravate the vibration.
Methodology:
Apparatus use:
•
Standing fan
•
Data acquisition module
•
Accelerometers
•
Tachometer
•
Digital signal processing and Display
•
Computer with Virtual Instrument Software (DasyLab)
Setup (hardware) and setting for National Instrument
I.
II.
III.
First, we make sure all the apparatus is connected and functioned well.
We measured the speed of fan by using tachometer.
Then we open the Dasylab software based on the following steps:
1. Open the Measurement & Automation (NI-DAQmx) software.
2. Under ‘My System’, choose ‘Data Neighbourhood’.
3. Then, click ‘Create New’ which you will create a new task for the measurement
setup.
4. Choose ‘NI-DAQmx Task’ to create new task, then click ‘Next’.
5. Then, click at ‘Acquire Signal’, then choose ‘Analog Input’.
6. We use accelerometer as the sensor. So, under the ‘Analog Input’ tree choose
Acceleration’.
7. We choose channel ‘ai0’ since accelerometer is plugged in into channel 0 at the
DAQ, then click ‘Next’.
8. Next, renamed the task and finally click ‘Finish’.
9. Change the sensitivity value and unit for the apparatus use.
10. Change the ‘Acquisition Mode’ to ‘Continuous Sample’.
11. Click ‘Run’ to test the setting and finally click ‘save’ to save the setting
Setup software (DasyLab)
I.
In Dasylab, click on ‘Measurement> Hardware Setup> NI-DAQmx> Synchronization
with MAX configuration’.
II.
Then, under the ‘Measurement’ tab, select ‘Time Bases> All Setting’ to set the value
of block size and sampling rate based on the experiment requirement.
III.
Connect all the modules that is needed to obtain the data of our experiment.
IV.
The Dasylab layout of our experiment is shown below:
-For scalling module, we change the unit conversion to acceleration which is from
g(m/(s*s)
-For the digital filter module, we use low pass with limit frequency 20Hz and filter
order of 8
-For the differentiation/integration module, we change the function to integrate so we
could obtain the velocity graph.
-For the digital meter module, we set the mode to RMS that the value of RMS velocity
can be obtain.
-For the data window module, we change the window type to flatop and the output with
the output block size 8192.
V.
So, our objective is to observed the time domain, frequency domain and velocity time
graph with three different axes (x-axis, y-axis, z-axis).
Result and discussion:
1. Time domain
Amplitude vs Time
Amplitude
20
10
0
0
1
2
3
4
5
-10
-20
Time (s)
Figure 1.1 shows the time domain measured by accelerometer in x-axis within 4 seconds
Amplitude vs Time
Amplitude
10
5
0
0
1
2
3
4
5
-5
-10
Time (s)
Figure 1.2 shows the time domain measured by accelerometer in y-axis within 4 seconds
Amplitude vs Time
6
4
Amplitude
2
0
-2 0
1
2
3
4
5
-4
-6
-8
Time (s)
Figure 1.3 shows the time domain measured by accelerometer in z-axis within 4 seconds
The three figures above show that how the signal change over time. In our experiment, the time
domain (time waveform) above refers to variation of amplitude of signal with time. So, from
the results, we can say that vibration in x-axis has the highest amplitude compare to y and z
axis. Actually, time waveforms show a short time sample of raw vibration, revealing clues to
the condition of machinery not always clear in the frequency spectrum. A method of employing
time waveform vibration signals as a vibration analysis tool is by using FFT.
2. Fast Fourier Transform (FFT)
FFT is defined as an algorithm used to calculate a spectrum from a time waveform. In
other words, it's a calculation intended to break down a signal into all its frequencies.
If you'll recall time domain and frequency domain discussed above, FFT converts a
signal from the time domain into the frequency domain. Fast Fourier transform is most
often used for detecting machine faults like misalignment or unbalance. In our
experiment we also include data window to FFT analysis to get rid all leakage and
scalloping loses.
For x-axis
Acceleration vs Frequency (without data window)
7
Acceleration (m/s^2)
6
5
4
3
2
1
0
-1
0
200
400
600
800
1000
Frequency (s)
Figure 2.1 shows FFT data analysis without windowing
1200
Acceleration vs Frequency (with data window)
9
Acceleration (m/s^2)
8
7
6
5
4
3
2
1
0
-1 0
200
400
600
800
1000
1200
Frequency (s)
Figure 2.2 shows FFT data analysis with windowing
For y axis
Acceleration vs Frequency (without data window)
4
Acceleration (m/s^2)
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
0
200
400
600
800
1000
Frequency (Hz)
Figure 2.3 shows FFT data analysis without windowing
1200
Acceleration vs Frequency (with data window)
5
4.5
Acceleration (m/s^2)
4
3.5
3
2.5
2
1.5
1
0.5
0
-0.5 0
200
400
600
800
1000
1200
Frequency (Hz)
Figure 2.4 shows FFT data analysis with windowing
For z axis
Acceleration vs Frequency (without data window)
1.2
Acceleration (m/s^2)
1
0.8
0.6
0.4
0.2
0
0
-0.2
200
400
600
800
1000
Frequency (Hz)
Figure 2.5 shows FFT data analysis without windowing
1200
Acceleration vs Frequency (with data window)
Acceleration (m/s^2)
1.2
1
0.8
0.6
0.4
0.2
0
0
200
400
600
800
1000
1200
Frequency (Hz)
Figure 2.6 shows FFT data analysis with windowing
Our experiment is using a flattop window with a block size of 8192. It is because flattop
window gives a better amplitude accuracy in frequency domain. Flattop window is
typically employed on data where frequency peaks are distinct and well separated from
each other. So, from our data from the three axes. It is clearly seen that the peak of
acceleration is increases after we apply windowing.
Figure 2.7 shows the FFT analysis from the Dasylab
The first peak shows the acceleration vortex speed (0.42 m/s^2) of the standing fan with
5.25 Hz. The second peak shows speed of the fan which is (0.43 m/s^2) with 22.5 Hz.
The amplitude records the highest at 100 Hz. This is an abnormal situation which may
be due by other components inside the standing fan.
3. Velocity
Velocity is related to the destructive force of vibration, making it the most important
parameter. It places equal importance on both high and low frequencies. Usually, the
RMS value of velocity shows the best sign of vibration severity. For the velocity
analysis, we use digital filter to filter unwanted noise. The digital filter is setting by
filter using low pass with limit frequency 0.5 Hz and filter order of 8 for the three axes.
Velocity vs Time
0.07
Velocity (m/s)
0.06
0.05
0.04
0.03
0.02
0.01
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Time (s)
Figure 3.1 shows the velocity time trend for x axis from 0 to 4 seconds
RMS value= 0.0588
Peak value= 0.1003
The velocity of fan keeps constant for about 0 to 1.75 seconds, then the velocity was
gradually increasing for until 4 seconds.
Velocity vs Time
1.5
Velocity (m/s)
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-0.5
-1
-1.5
Time (s)
Figure 3.2 shows the velocity time trend for y axis from 0 to 4 seconds
RMS value= 0.5015
Peak value= -0.2039
The velocity of fan shows increases from negative direction to positive direction, then
it back slowly to negative direction again.
Velocity vs Time
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Velocity (m/s)
-0.05
-0.1
-0.15
-0.2
-0.25
Time (s)
Figure 3.3 shows the velocity time trend for z axis from 0 to 4 seconds
RMS value= 0.0206
Peak value= 0.0012
The velocity of fan was zero for 0 to 1.25 seconds, then the velocity of fan shows
negative direction and the value was gradually increases for until 4 seconds.
Peak Amplitude is the maximum excursion of the wave from the zero or equilibrium
point. Root Mean Square Amplitude (RMS) is the square root of the average of the
squared values of the waveform.
CONCLUSION
Vibration analysis of industrial machinery has been around for many decades, but gained
prominence with the introduction and widespread use of the personal computer. Vibration
Analysis refers to the process of measuring the vibration levels and frequencies of industrial
machinery, and using that information to determine the response of the machine, and its
components.
When an industrial machine (such as a fan) is operated, it generates vibration. This
vibration can be measured, using a device called an accelerometer. An accelerometer
generates a voltage signal, proportional to the amount of vibration, as well as the frequency
of vibration, or how many time per second or minutes the vibration takes place. This voltage
signal from the accelerometer is fed into a data collector, which records this signal as either a
time waveform (amplitude vs. time), as a Fast Fourier Transform (amplitude vs. frequency),
or as both. This signal can then be analysed by a trained vibration analyst, or by the use of a
“smart” computer program algorithm. The analysed data is then used to determine the
“health” of the machine, and identify any impending problems in the machine.
As an example, if we took a general fan, removed one of the fan blades, and started
the fan up, we could expect the fan to vibrate, due to an unbalanced fan wheel. This
unbalance force would occur one time per revolution of the fan. If we re-installed the fan
blade, this vibration would be reduced. The use of vibration analysis can determine problems
caused due to improper installation, machining errors, insufficient lubrication, improper shaft
or sheave alignment, loose bolting, bent shafts, and much more. It can, in most cases, detect
these problems long before the damage can be seen by maintenance, and long before it
damages other machine components.
REFERENCES
The electric fan is referred to as an electric fan, May 04, 2019
BASIC VIBRATION THEORY, Ralph E. Blake