MCE 311 Engineering MeasurementsSpring 2015

Experiment No: 9

Title: AccelerometerDate: 12 / 05 / 2015

Group: 5

Student Name ID

Gautam Unnikrishnan 49224Fahad Ali Syed Arif 48274Syed Hamdan Mustafa 50262Afria Sadia 46873Asim Reyazuddin 45389

Item Max Grade

Title and Format 5

Abstract 5

Introduction 5

Theory 10

Experimental Procedure 10

Data and Results 15

Discussion and Analysis 25

Error/Sensitivity Analysis 10

Overall impression 5

Figures, Tables, and References 5

Appendix: Raw Data Summaries 5

Total 100

Abstract

This lab experiment involved understanding the construction, principle and workings of

the accelerometer. The accelerometer is a device that measures the proper acceleration associated

with the weight experienced by a mass that is in the frame of reference of the accelerometer.

Accelerometers are sensing transducers that produce an electrical output signal that is

proportional to the acceleration in the aspect of motion, vibration, and shock. The report includes

the conceptual knowledge of the accelerometer, followed by the procedure of the experiment. In

addition, the results are illustrated and the graphs of the relations were plotted and analyzed, and

they verify the theory discussed earlier. The errors involved while conducting the experiment

such as the varying voltage from the power source and the magnetic interference in the room.

2

Table of Contents

Introduction.................................................................................................................................................5

Theory.........................................................................................................................................................6

Accelerometer.........................................................................................................................................6

Experimental Procedure..............................................................................................................................7

Data and Results..........................................................................................................................................9

Discussion and Analysis............................................................................................................................12

Error/Sensitivity Analysis..........................................................................................................................14

Conclusion.................................................................................................................................................15

References.................................................................................................................................................16

Appendix...................................................................................................................................................17

3

List of figures

Figure 1: Breadboard circuit for the experiment.............................................................................7

Figure 2: Acceleration changes with change in position.................................................................9

Figure 3: Acceleration vs Time as breadboard was in horizontal position....................................10

Figure 4: Acceleration vs Time as breadboard was in negative x direction..................................10

Figure 5: Acceleration vs Time in negative y direction................................................................11

Figure 6: LabView block diagram.................................................................................................17

4

Introduction

The main objective of this lab experiment is to describe the construction, characteristics

and working principle of the accelerometer.

An accelerometer is a device that measures its proper acceleration. This proper

acceleration is associated with the weight experienced by a sample mass that is in the frame of

reference with the accelerometer, which is not the same as the coordinate acceleration (velocity

change of the device in space). Measuring acceleration via the accelerometer can be

demonstrated through several examples. One such example can be a situation where the device is

on the ground. Even though they do not experience a change in velocity, it will measure a value

since the masses have weight. However, when the accelerometer is experiencing gravitational

free fall motion, it is in an inertial frame of reference in which its weight is zero, and will

therefore give a value of zero.

The unit of measuring values by the accelerometer is called the specific force, which is

weight per unit mass.

Accelerometers have many applications in engineering. It is used in measuring vehicle

acceleration, allowing a performance evaluation in both engine and braking systems. They are

also used to measure vibrations on machines, buildings and safety installations, and can also

measure seismic activity with or without the presence of gravity.

The following are the apparatus that are required to perform this lab experiment:

Accelerometer Sensor ADXL150EM-3

Digital Multimeter

DAQ assistant

5

Computer with LABVIEW software

Theory

Accelerometer

A device that measures the proper acceleration of the device is known as accelerometer.

Acceleration associated with the weight experienced by a mass that is in the frame of reference

of the accelerometer and is not the same as coordinate acceleration, which is the change of

velocity of the device in space, is proper acceleration. The device will show a value even when

its resting on the ground since masses on the ground have weights even though they do not

change velocity. However, when the accelerometer is in gravitational free fall toward the Earth it

is in an inertial frame of reference where its weight equals zero, and therefore the accelerometer

will show value of zero.

Accelerometer measures values in a unit called specific force or g-force, which is weight

per unit of (test) mass.

One application of accelerometer is that it can be used to measure vehicle acceleration,

which allows for performance evaluation of both the engine/drive train and the braking systems.

It can also be used to measure vibrations of cars, machines, buildings, process control systems

and safety installations. It also measures seismic activity with or without gravity.

Acceleration can be calculated as follows:

V out=Vs2

− sensitivity∗Vs5

∗acceleration

which can be rearranged to give:

6

Acceleration=−V out−Vs

2sensitivity∗Vs

5

where the sensitivity of the sensor is 200mV/g.

Experimental Procedure

The accelerometer was first calibrated in the z axis and then the acceleration in three dimensions

was measured for different breadboard orientations. Here is the procedure:

1. Check the accelerometer for the 5 different positions (COM, Vs, X, Y, Z etc) and place it

carefully on the breadboard. The circuit should look like:

Figure 1: Breadboard circuit for the experiment

2. Connect the accelerometer to the DAQ using wires.

3. Use the power supply to supply 3 V of voltage to the circuit.

4. Start LabView and construct the block diagram as shown in the Appendix section.

7

5. Open the connection diagrams and place the wires in the respective positions.

6. Enter the formula in the formula block and start the process.

7. Change the breadboard position to investigate the changes in acceleration.

8. After the calibration is successful, connect the other two axes (x and y) to the DAQ as

well.

9. Run the simulation again.

10. Investigate the changes in acceleration with the changing of the positions.

11. Take screenshots of the graphs.

12. Switch off the power supply.

8

Data and Results

The experiment was performed on an accelerometer. The accelerometer was first calibrated. The

acceleration in z was calibrated only. Here are the results for the calibration:

V s=3V

The formula entered in the formula block of LabView is:

Acceleration=−V out−

V s2

Sensitivity

Acceleration=−(V out−1.5)/3

The breadboard was tilted up and down and the effect was displayed on the graph:

Figure 2: Acceleration changes with change in position

The value was approximately 1.22.The acceleration in all three axes are then measured using the same calibration. Here are the

effects as the position of the breadboard was changed:

9

Note that white denotes acceleration in z, green denotes acceleration in x and red denotes

acceleration in y.

Figure 3: Acceleration vs Time as breadboard was in horizontal position

Figure 4: Acceleration vs Time as breadboard was in negative x direction

10

Figure 5: Acceleration vs Time in negative y direction

11

Discussion and Analysis

The accelerometer was calibrated for z direction. Vs was obtained to be 3V which was used in

the formula provided. Here is the formula:

Acceleration=−V out−

V s2

Sensitivity

It can be noted that the acceleration here depends on the output voltage, supply voltage, and the

sensitivity. Therefore, a change in any of the corresponding will produce the change in

acceleration accordingly. The sensitivity of the sensor plays a crucial role. The high sensitivity of

the sensor used in the experiment allows for the use of low speed counter for PWM decoding in

parallel to maintaining high resolution. The labview graph was generated that displayed the

changes in acceleration with respect to changes in position. The graph illustrated the relative

effect upon tilting the breadboard up and down. A value of 1.22 was obtained in correspondence

to 0.939 for the calibration. The same calibration was used in further analysis of the acceleration

in all three axes as the position of the breadboard was changed.

It can be noted for the graph of acceleration versus time where the breadboard was in horizontal

position that the acceleration in x is a straight line and displays 0 acceleration while the

acceleration graphs for y and z are close to each other and above the acceleration graph of x with

respect to time.

When the breadboard was in the negative x direction it can be seen from the graph that the

acceleration for z is close to 0 and the acceleration in x is below than what is obtained in z and is

obtained to be negative. Acceleration in y is not visible in this graph; it is possible that it

overlaps one of the graphs that are visible.

12

When the breadboard was in negative y direction it could be noted that the graphs of acceleration

in y and x were not only close to each other but also close to 0 acceleration while the

acceleration in y was obtained to be negative. An important point to mention again is the

calibration that was considered to be the same as considered in the first part of the experiment.

The same range for the time and acceleration axis was considered in each graph.

13

Error/Sensitivity Analysis

There were very few errors associated with the experiment produced results that were expected.

The small discrepancies in the results could have resulted from:

The sensor being faulty

The varying of voltage from the power source

Random errors

Human errors.

The results were confirmed because when the circuit was placed in the normal position, the

acceleration showed 1g which is how it should be. The opposite placement of the breadboard

resulted in an acceleration of -1g. The same conclusions can be reached with the accelerations in

x and y.

The random errors discussed earlier could have affected the results. They are almost

impossible to avoid and they affect every kind of experiments. The sources of the random errors

are:

Radio Frequency Interface which can be due to mobile phones [2]

Magnetic Interference in the room [2]

Vibrations, shocks due to the presence of the students [2]

Temperature Oscillations [2]

However, these errors mentioned did not have a huge effect on the results since the result were

satisfactory.

14

Conclusion

After completing the experiment, students were able to describe the basic working principles

define the characteristics of an accelerometer. Also, the experimental setup required and the

various measurement techniques involved were learned during the experiment. Moreover, the

errors obtained were reasonably low; a few inaccuracies could be due to random errors discussed

earlier. The results for the accelerometer were analyzed and studied in the lab. The experiment

has served the students with an understanding of an accelerometer as well as enhanced their

skills that could be helpful in many fields in the future. These measurement devices hold extreme

importance in the fields of research and experimentation.

15

References

[1] Lab Manual (MCE 311L), (15 April, 2015). The American University of Sharjah. Retrieved

from

https://ilearn.aus.edu/bbcswebdav/pid-679624-dt-content-rid-3735836_2/courses/

MCE311L_21318_S15/MCE311%20Lab%20Manual%20ABET%202011%281%29.pdf

[2] Dr. Bassam Abu-Nabah. General Characteristics of Measurement Systems (MCE 311), (15

April, 2015). The American University of Sharjah. Retrieved from

https://ilearn.aus.edu/webapps/portal/frameset.jsp?tab_tab_group_id=_2_1&url=

%2Fwebapps%2Fblackboard%2Fexecute%2Flauncher%3Ftype%3DCourse%26id

%3D_36513_1%26url%3D

16

Appendix

Figure 6: LabView block diagram

17