Vibration Meter Readout Calibration

Paul Gibson

John Winchester

Fahad Khan

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Table of Contents:

Purpose 3

Abstract 4

Background 5

Apparatus 7

Diagram(s) 8

Procedure 9

Results 10

Appendix 15

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Purpose:

Calibrate a vibration meter using an electrodynamic exciter and a

vibration pickup. The standard for displacement will be a ‘V’ scope.

The standard for frequency will be an oscilloscope (time). Compare ‘V’

scope and oscilloscope derived values of displacement, velocity and

acceleration with meter values.

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Abstract:

Vibration occurs if displacement and time are continuous with a

repetitive nature. Vibration is not an event that occurs one time;

furthermore, it is not an event that may show vibratory characteristics

that slowly decay with time. The latter case would be an example of a

shock. Velocity, acceleration and displacement are not examples of

vibration.

Vibration was measured in this lab using a vibrating wedge; it is

nothing more than a piece of paper with a scale drawn on it. This wedge

is taped to the vibrating member and used to measure the amplitude of

motion. A picture of this device is provided on the next page. Both

measured gravitational force and measured velocity in were compared

with calculated values using predetermined formulas. The results of

these comparisons are provided in tabular form in the results section of

this report.

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Background:

As everyone already knows, there are many different types of

motion. Some of the more common forms of mechanical motion are velocity

and acceleration. Vibration is a special kind of motion however.

Vibration occurs if displacement and time are continuous with a

repetitive nature. Vibration is not an event that occurs one time;

furthermore, it is not an event that may show vibratory characteristics

that slowly decay with time. The latter case would be an example of a

shock.

Although shock and vibration are not similar types of motion they

do share several characteristics, they both, possess frequency,

amplitude and some kind of waveform. Measuring of both shock and

vibration usually consists of a common method of using time-based

relationships for velocity, acceleration and displacement.

Assuming that the amplitudes of motion are greater than about

inches than a rather simple, almost archaic tool known as a vibrating

wedge may be used to measure the amplitude. Literally, all this

measuring device is a piece of paper or other thin material attached the

vibrating apparatus. This wedge has a scale drawn on it that is used to

measure the amplitude. As vibration occurs, the wedge moves to two

extreme positions, resulting in a double image that is very defined.

The center of the image, which is shown in the diagram below as ‘X’,

appears noticeably darker (as it pertains to this diagram. Our actual

wedge was not exactly this) than the surrounding area of image. You can

obtain a measurement of amplitude by noting the location of this center

position; it is at this point where the width of the wedge is equal to

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twice the amplitude. A diagram of this simple device and how it

operates is provided below.

This lab also used an electronic meter to measure the mils, ,

and gravitation force. Both measured gravitational force and measured

were compared with calculated values using predetermined formulas.

The formulas used for this process are below.

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Apparatus:

The equipment needed for this experiment is as follows (Refer to

figure):

1. Oscilloscope

2. Vibration Meter

3. Digital Counter

4. Oscillator

5. Power Amplifier

6. Shaker

The oscilloscope is manufactured by Hitachi. The model number is

VC-6224. The serial number is 1120276.

The vibration meter is manufactured by Vitec. The model number is

654. The serial number is 14870-qm.

The Oscillator is manufactured by Hewlett Packard and is model

number HP 209.

The manufacturers of the power amplifier and the digital counter

are unknown. The model number of the power amplifier is 2125MB.

The shaker is produced by MB electronics and its model number is pm 25.

The serial number is 372.

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Diagrams:

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Procedure:

1. Setup the apparatus as shown in the diagram above.

2. Construct a vibrating wedge to measure displacement. Its

dimensions should be 2 inches by 150-200 thousandths. Place

the wedge on the shaker and be sure it is horizontal.

3. Set the frequency on the HP oscillator to 20 Hz. Confirm this

setting on the oscilloscope. Turn up the power to maximum on

the power amplifier.

4. Slowly turn up the gain on the HP oscillator, and you will see

the shaker will begin moving. Turn up the gain until the

displacement on the vibrating wedge reads 0.04 inches.

5. Take the reading for mils, g’s and velocity from the vibration

meter.

6. Raise the gain to produce the following displacements: 0.08,

0.12, 0.16, and 0.2. Take the same readings as above at each

increment and record all data.

7. After going through all of the set displacements for 20 Hz,

follow the same procedure for 30 Hz, 40 Hz, 50 Hz, 60 Hz, and

80 Hz. Record all data.

8. Plot the following data on charts: Vibrating Wedge displacement

versus Vibration meter displacement, Calculated velocity versus

Vibration meter indicated velocity, and Calculated acceleration

versus Vibration meter indicated acceleration.

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Results:

The following tables show all the data we collected for this

experiment. Some of the data reads maximum. This is where either the

power amplifier would shut off, or the vibration meter would not give a

reading. The remaining data was linear, as it should be. This confirms

that the vibration meter confers with our calculated data, and is

measuring data with reasonable accuracy and precision. There is one

area where the calculated data and measured data were not relating very

well. This was for a frequency of 30 Hz. This could have occurred

because of calculation errors or because of lack of familiarization with

the vibration meter.

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Frequency Wedge Scope Meter Calculated Meter Calculated Meter  Displ. Frequency Displ. Velocity Velocity Accel. Accel.20 0.04 20 49.7 2.50 2.9 0.81 1.00  0.08 20 81.8 5.03 5.0 1.63 1.70  0.12 20 117.5 7.54 7.3 2.40 2.45  0.16 20 161.4 10.05 10.0 3.26 3.50  0.20 20 188.2 12.57 11.7 4.08 4.1030 0.04 30 49.9 3.77 6.1 1.84 3.80  0.08 30 78.8 5.03 9.6 3.67 6.10  0.12 30 114.2 11.31 13.8 5.51 8.80  0.16 30 156.5 15.08 14.2 7.34 6.80  0.20 30 198.2 18.85 18.0 9.18 8.7040 0.04 40 53.9 5.03 6.5 3.26 4.10  0.08 40 86.1 10.05 10.4 6.53 6.60  0.12 40 126.6 15.08 15.3 9.79 9.70  0.16 40 165.3 20.11 20.0 13.06 12.60  0.20 40 max 25.13 24.7 16.32 15.6050 0.04 50 42.7 6.28 7.4 5.10 6.00  0.08 50 84.8 12.57 13.0 10.20 10.40  0.12 50 123.0 18.85 18.8 15.30 15.00  0.16 50 162.8 25.13 25.2 20.40 20.10  0.20 50 max 31.42 31.2 25.50 25.0060 0.04 60 59.3 7.54 10.9 7.34 10.50  0.08 60 91.3 15.08 17.0 14.69 16.20  0.12 60 127.3 22.62 23.4 22.03 22.50  0.16 60 max 30.16 max 29.38 max  0.20 60 max 37.70 max 36.72 max80 0.04 80 47.5 10.05 11.7 13.06 15.00  0.08 80 max 20.11 max 26.11 max  0.12 80 max 30.16 max 39.17 max  0.16 80 max 40.21 max 52.22 max  0.20 80 max 50.27 max 65.28 max

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Appendix:

The appendix section follows from here on.

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