Vibration Application Data(1)

S E N S O R S

APPLICATION DATA

V I B R A T I O N

T R O L E X L I M I T E D , N e w b y R o a d , H a z e l G r o v e , S t o c k p o r t , C h e s h i r e S K 7 5 D Y, U K . Tel: +44 (0)161-483 1435 Fax: +44 (0)161-483 5556 E-mail: [email protected] Internet: www.trolex.com

Issue B. 10/02

2

CO N T E N T S

INTRODUCTION

1. WHAT IS VIBRATION?

2. HOW CAN VIBRATION BE USED TO EVALUATE MACHINE CONDITION?

3. TYPES OF VIBRATION MONITORING.

4. HOW TO SELECT AND USE THE CORRECT VIBRATION EQUIPMENT.

5. TYPICAL APPLICATIONS FOR TROLEX VIBRATION MONITORING EQUIPMENT.

APPENDIX A – UNDERSTANDING AND UTILISING THE VIBRATION

INFORMATION OBTAINED.

PAGE

3

4

9

13

17

33

41

3

IN T R O D U C T I O N

This application note is intended to give the reader a basic grounding in the

causes and effects of vibration, along with methods for utilising the

information obtained from measuring vibration to diagnose machine health.

It will further discuss the merits of the various methods of monitoring

vibration and explain how these can be optimised to provide the best results.

Finally, the application notes will give some examples of how vibration

monitoring can be implemented.

4

1. WH AT I S V I B R AT I O N?

Vibration is the response of a system to an internal or external stimulus causing it to

oscillate or pulsate.

While it is commonly thought that vibration itself damages machines and

structures, it does not. Instead, the damage is done by dynamic stress, which causes

fatigue of the materials; and the dynamic stresses are induced by vibration.

Amplitude of vibration is also dependent on the “dynamic resistance” of a system.

For example, if a machine is placed on rubber mounts, the amplitude of vibration

is likely to increase due to less dynamic resistance for the same imposed dynamic

forces. The transmission of vibration to the floor and surrounding structures will be

less, but the vibration within the machine will likely increase.

However, no additional damage will be done to the machine since the same forces

(and therefore, fatigue stresses) will remain the same within this machine (as

compared to when the machine was directly mounted to the floor).

Vibration has three important parameters which can be measured:

1. Frequency – How many times does the machine or structure vibrate per minute

or per second?

2. Amplitude – How much vibration in microns, mm/sec or g's?

3. Phase – How is the member vibrating in relation to a reference point?

5

1.1 What is vibration frequency and how does it relate to a time waveform?

The figure below shows how the frequency can be calculated from the

displacement waveform, by measuring the time period (T) of one cycle and

inverting to determine the frequency Hz. This is an example of a time waveform

which plots Vibration Amplitude versus Time. This waveform is a truly sinusoidal

waveform from which direct comparisons can be made between its Peak-to-Peak,

Peak and RMS amplitudes (see section 1.5).

Frequency is expressed in Hertz (where 1 Hertz or Hz = 1 cycle per second).

Time waveforms are an excellent analytical tool to use when analysing gearboxes.

The sensor can be attached close to the input or the output shaft bearing to check

for broken or chipped gear teeth. The following is a typical example of how a display

for one broken tooth would appear as a time waveform, shown in Figure 2.

Note, however, that imbalance, misalignment, bent shaft, eccentric rotor, and

other problems also often produce a similar display in the frequency domain.

Time waveforms are particularly useful for low-speed shafts and gears, even if some

never rotate a full revolution (basically just rocking back and forth). In this case,

time waveforms are virtually the only analytical tool which can be effectively used.

Figure 2

Figure 1

TIME

Period (T)(1 complete cycle)

UPPER LIMIT

NEUTRAL POSITION

LOWER LIMIT

Frequency = 1/Period = 1T

DIS

PLA

CE

ME

NT

TIME(sec.)

AM

PLI

TUD

E

1 Rev.1 Rev.1 Rev.

+

–

0

ONE IMPACT EVERY REVOLUTIONFROM THE BROKEN TOOTH

AM

PLI

TUD

E

FREQUENCY

1 x RPM

Here is how it would typically be displayed in the frequency domain:

6

1.2 What is vibration amplitude?

What is Vibration Displacement?1.2.1

Displacement is a measure of the total travel of the mass – back and forth.

Displacement is usually expressed in microns (where 1 micron, µ = .001 millimetre).

When a machine is being subjected to excessive dynamic stress at very low

frequencies, displacement may be a good indicator of vibration severity since the

machine (or structure) may be flexing too much, subjected to impacts, or simply

being bent too far.

What is Vibration Velocity?1.2.2

The velocity of the vibration is a measure of the speed at which the mass is moving

or vibrating during its oscillations. The faster a machine flexes, the sooner it will fail

in fatigue. Vibration velocity is directly related to fatigue.

Note from the example of the oscillating mass suspended from a spring in Figure 3,

that velocity reaches its maximum value (or peak) at the neutral position where the

mass is fully accelerated (acceleration is zero) and now begins to decelerate as

shown in Figure 3. Velocity is expressed as millimetres per second (mm/sec).

However, if an analyser were used to directly measure peak velocity, it would select

the highest peak or excursion that the velocity time waveform would make. From

an oscilloscope display, the peak velocity would be the highest peak in the display

as shown in Figure 4. In this case, it is 0.7 mm/sec because it is the highest peak,

position or negative.

Figure 3

VELOCITY FROM THEDISPLACEMENT CURVE.

Figure 4

HOW TO DETERMINEPEAK VELOCITY FROMAN OSCILLOSCOPEDISPLAY.

UPPER LIMIT

TIMENEUTRAL POSITION

LOWER LIMIT

MinimumVelocity

MinimumVelocity

MaximumVelocity

DIS

PLA

CE

ME

NT

VE

LOC

ITY

0.2

–0.2

0.3

–0.3

+

–

0

0.4

–0.7

0.4

–0.5

Vibration amplitude can be expressed in terms of displacement, velocity or

acceleration.

7

What is Vibration Acceleration?1.2.3

When a machine housing vibrates, it experiences acceleration since it continually

changes speed as it oscillates back and forth. Acceleration is greatest at the instant

at which velocity is at its minimum. That is, this is the point where the mass has

decelerated to a stop and is about to begin accelerating (moving faster) again in

the opposite direction. Acceleration is the rate of change in velocity and is normally

measured in units of g's (where 1g = 9.81ms–2). The greater the rate of change of

velocity, the greater will be the forces (and stresses) on this machine due to the

higher rate of acceleration. At high frequencies, failure of a machine may result

from excessive forces which break down the lubrication allowing the surface of

bearings to fail (due to metal-to-metal contact). These excessive forces are directly

proportional to acceleration (Force = mass x acceleration). Acceleration is probably

the most difficult measure of vibration amplitude to grasp, but this is the parameter

most often directly measured in the field with the use of an accelerometer. Thus, it

is important to gain a good understanding of it.

1.3 What is vibration phase?

Phase is a measure of how one part is moving (vibrating) in relation to another part,

or to a fixed reference point.

Phase is mostly used as an analytical tool, when initially setting up a machine, to

ensure it has been mounted and aligned correctly. It is rarely used for continuous

monitoring of machine condition.

1.4 What is a vibration spectrum (also called an "FFT" or "signature")?

This frequency domain presentation of a time waveform is called a "spectrum". This

is sometimes referred to as a "vibration signature" or an "FFT" if an FFT analyser is

used.

Trolex can provide a range of vibration sensor capable of connection to most

industry standard FFT analyser.

8

1.5 The difference between RMS, peak and peak-to-peak amplitude.

It is possible to convert from one amplitude parameter to another, using either

electronic conversion or mathematical formula. However, if a peak reading is taken

of one parameter, then the parameter which is being calculated will also be a peak

value.

The electronics or software, can also convert between rms (root mean square), peak

and peak-to-peak.

Figure 5 shows the relationship between rms, peak and peak-to-peak, for a purely

sinusoidal waveform.

However, when the time waveform is not sinusoidal in nature (see figure 6), peak

and peak-to-peak readings become less useful and rms is most often used.

rms amplitude gives a more accurate representation of the energy within the

vibration and hence the force that will be exerted by the vibration.

Figure 5

RELATIONSHIP BETWEENrms, PEAK AND PEAK-PEAK ON A PURELYSINUSOIDAL WAVEFORM.

UPPERLIMIT

NEUTRALPOSITION

LOWERLIMIT

rms

PEAKPEAK-TO-PEAK

AVG

SINUSOIDAL MOTION

PEAK-TO-PEAK

PEAK

rms

AVERAGE

1.000

.500

.354

.318

2.000

1.000

.707

.636

2.828

1.414

1.000

.900

3.142

1.571

1.5

1.000

MULTIPLYVALUE OF

TO OBTAIN

BY

PEAK-TO-PEAK

PEAK rms AVERAGE

Figure 6

AM

PLI

TUD

E

TIME

9

2. HO W C A N V I B R AT I O N B E U S E D T O E VA L U AT E

M A C H I N E C O N D I T I O N?

The causes of vibration in rotating machinery are numerous. These can originate

from machine set-up problems such as:

• Imbalance of system

• Mis-alignment of shafts

• Bent shafts

• Mechanical looseness

• Ineffective mounting structures

Alternatively, they can be caused by dynamic problems such as:

• Bearing deterioration

• Loose parts

• Build up on fan blades

• Chipped blades/rotors

• Geartooth wear/breakage

• Loss of lubrication

If these problems are left unattended, some quite catastrophic problems can

result. These can vary from downtime, lost whilst a seized bearing is replaced, to

a fan that completely disintegrates when the out-of-balance causes blades to

impact on the casing.

By utilising vibration monitoring, an early warning of impending failure can be

obtained, allowing preventative maintenance to be instigated. Analysis of the

vibration by a skilled engineer using frequency analysis can allow the problem to

be pinpointed.

10

2.1 When to use displacement, velocity or acceleration

Displacement is generally thought to be the most useful vibration parameter when

vibration frequencies are less than 10Hz. However, to be applicable in analysis of

the vibration severity, the displacement must be assessed in conjunction with the

frequency (Hz).

Figure 7 gives an indication of severity levels with regard to displacement and

frequency.

Figure 7

VIBRATIONDISPLACEMENT &VELOCITY SEVERITYCHART FOR GENERALHORIZONTAL ROTATINGMACHINERY.

VERY ROUGH

ROUGH

SLIGHTLY ROUGH

FAIRGOODVERY GOOD

SMOOTH

VERY SMOOTH

EXTREMELY SM

OOTH

100.0

80.0

60.0

40.0

30.0

20.0

10.0

8.0

6.0

4.0

3.0

2.0

1.0

0.8

0.6

0.4

0.3

0.2

0.1

0.08

0.06

0.04

0.03

0.02

0.01

100

200

300

400

500

1,00

0

2,00

0

3,00

0 4,

000

5,00

0

10,0

00

20,0

00

30,0

00

40,0

00

50,0

00

100,

000

VIBRATION FREQUENCY - HzV

IBR

ATI

ON

DIS

PLA

CE

ME

NT

MIC

RO

NS

rm

s

16.0 mm

/sec.8.0 mm

/sec.4.0 mm

/sec.2.0 mm

/sec.1.0 mm

/sec.0.5 mm

/sec.0.25 mm

/sec.0.125 mm

/sec. VIB

RA

TIO

N V

ELO

CIT

Y -

mm

/sec

- P

EA

K

µ

11

Figure 8

VIBRATIONACCELERATION &VELOCITY SEVERITYCHART FOR GENERALHORIZONTALROTATING MACHINERY.

VERY ROUGH

ROUGH

SLIGHTLY ROUGH

FAIR

GOOD

VERY GOOD

SMOOTH

VERY SMOOTH

EXTREMELY SMOOTH

30

10

5

1

.5

.1

.05

.01

.005

.001 10,000

9000

8000

7000

6000

5000

4000

3000

2000

1000

900800

700

600

500

400

300

1.57

.785

.392

.196

.098

.049

AC

CE

LER

ATI

ON

- G

's P

EA

K

VIB

RA

TIO

N V

ELO

CIT

Y -

mm

/sec

pk-

pk3.146.28

FREQUENCY - Hz

Acceleration is most widely used when the vibration frequency is in excess of 1kHz.

Again, acceleration needs to be used in conjunction with vibration frequency to

analyse the results. Figure 8 gives an indication of severity levels with regard to

acceleration and frequency.

Velocity is the most commonly used vibration signal and is fairly independent of

vibration frequency over the range 10Hz to 1kHz. This is useful for monitoring

slowly rotating machines.

Trolex manufactures a range of displacement, velocity and acceleration sensors that

are specifically designed for use with the wide range of monitoring and analysis

equipment available. These have been optimised for use with the Trolex range of

monitoring equipment.

g

mm/sec

12

2.2 How much is too much vibration?

Through the years, the general vibration severity chart (Figure 9) has been used to

assess machine condition. However, this was intended to be used as a guide and not

an absolute reference. Installation of the equipment and maintenance will have a

significant effect on the vibration levels seen.

Although the chart can be used as a general indication, trending of the vibration levels

with time will give a better indication of the change in condition of the machine. On

fixed monitoring equipment, warning and alarm levels can be set to be within the

“good” condition zone.

rms – velocity v (mm/s) CLASS I CLASS II CLASS III CLASS IV

0.280.450.711.121.802.804.507.10

11.2018.0028.0045.00

N O T U S A B L E

G O O D

B L E

E N T I

U S A

A T T

O N

CLASS I: Individual parts of engines and machines, integrallyconnected with the complete machine.

CLASS II: Medium or large machines, (typically electrical motors with 15 to 75KW output)

CLASS III: Large prime movers and other large machines with rotating masses mounted on rigid and heavy foundations.(300KW output).

CLASS IV: Large prime movers and other large machines or turbineswith rotating masses mounted on foundations which arerelatively soft.

Figure 9

13

3. TY P E S O F V I B R AT I O N M O N I T O R I N G

Vibration monitoring systems have two constituent parts:

• The sensing element

• The monitoring equipment

The sensing element provides an output proportional to the level of vibration

being monitored. The output will depend upon the type of sensor being used.

The range of monitoring equipment available varies from simple alarm devices

to real-time spectrum analysers.

Figure 10

3.1 Types of sensor

Piezo-electric accelerometers3.1.1

The piezo-electric accelerometer is widely used for vibration measurement. Its

construction consists of a crystal of piezo-electric material to which is attached a

seismic mass (See Figure 10). When the crystal is stressed in tension or compression,

it generates an electrical charge which is proportional to the acceleration level it is

experiencing. Internal circuitry converts this signal into a voltage (mv/g) output or

current output (4–20mA) for data collectors or process control loops.

This robust device has no moving parts and offers long term stability and reliability.

It has very wide frequency and dynamic ranges and signals can be integrated to

give velocity and displacement values.

These accelerometers tend to be lower cost than the alternatives and are available

for a wider range of arduous applications. eg. high temperature, submersible use

and corrosive media.

1

4

3

5

2

1. Mounting stud

2. Base

3. Piezo-electric crystal

4. Mass

5. Braided, screened cable

Piezo-electric technology is the basis of the Trolex TX5630 range of vibration

sensors. These are available with standard 100mV/g, ac output or conditioned

4–20mA output, corresponding to a specific velocity or acceleration amplitude range.

14

Piezo-resistive accelerometers3.1.2

These sensors monitor the force exerted on a beam, by a mass, utilising straingauge

technology.

The frequency range of this device is lower than piezo-electric versions, but has the

advantage of being able to monitor static or dc acceleration levels.

Because of its ability to monitor acceleration down to 0Hz, the piezo-electric

accelerometer is not as robust as the piezo-electric version. Its use, therefore is not

as widespread and the cost is usually higher.

Trolex can supply these sensors to suit specific applications.

Eddy current probes3.1.3

Eddy current probes monitor displacement using a non-contacting or proximity

method. The eddy current probe is widely used for measuring distances on static

and rotating machines. Both the ac vibration and dc gap can be measured by the

non-contact method. The simplicity of the probe lends itself to being used in harsh

conditions.

Trolex have a number of eddy current probes capable of monitoring displacement

from 0 to 12mm, at frequency from 0Hz up to 10kHz.

Figure 11

Figure 12

15

Contacting displacement sensor3.1.4

There are a number of different types of contacting displacement sensors. The most

popular version being the LVDT type.

The use of these sensors, is usually limited to very specific applications, due to its

need to have direct contact with the surface being monitored.

Figure 13

LVDT Assembly

Machine Housing

Non-metallic tip

Shaft surface

16

3.2 Vibration monitoring equipment

Overall level vibration monitors3.2.1

As the name implies, these instruments measure overall vibration amplitude.

Overall vibration refers to the overall or total amplitude summation of all the

vibration in the form of acceleration, velocity or displacement parameters. They are

used extensively due to their simplicity and cost. Although most of these

instruments are not able to display or store either spectra or time waveforms and

have limited operating frequency ranges.

Many early instruments have no method for recording the vibration and this had

to be done manually. However, instruments such as the Trolex TX9042/4 now have

both datalogging and communication facilities allowing trending of general

vibration levels to be more easily recorded.

A good preventative maintenance program is likely to use both overall monitoring

and specific analysis (e.g. FFT Analyser).

The type of vibration monitoring equipment used will depend upon the type

of sensor and the requirements of the monitoring process.

FFT Programmable Data Collectors3.2.2

There are a number of FFT analysers available in the market, which allow vibration to

be monitored in the frequency spectrum, simplifying diagnosis of machine problems.

However, due to cost, these instruments are rarely used for fixed installations. They are

usually used as portable instruments to diagnose problems found by overall vibration

level analysis instruments.

Trolex accelerometers (TX5630) can be connected directly by industry standard FFT

analysers.

‘Real-time’ Spectrum Analysers3.2.3

Because of the processing power required, most FFT analysers work on stored

vibration readings.

If “real-time” monitoring is required, a “real-time” spectrum analyser should be used.

However, with the constantly increasing capabilities of today’s data collectors, they are

no longer an absolute necessity for a “complete” condition monitoring programme

and their cost and size usually prohibits use in all but exceptional circumstances.

The Trolex range of vibration sensors (TX5630) can be used with most industry

standard spectrum analysers.

17

4. HO W T O S E L E C T A N D U S E T H E C O R R E C T V I B R AT I O N

E Q U I P M E N T

4.1 Selection criteria for sensors

The following items should be considered when selecting a suitable sensor for the

application:

• SENSITIVITY RANGE – Sensitivity is the capability of the sensor to

determine the amplitude of vibration (displacement, velocity, or acceleration)

from the amplitude of the voltage signal. For example, an accelerometer may

have a sensitivity of 100mV/g. This means that if this 100mV/g accelerometer

saw 0.1g at a particular frequency, it should convert this vibration to an output

of.

• FREQUENCY RANGE – Frequency range is the measuring capability of the

sensor from a low limit to a high limit of frequency. Each sensor has its own

frequency range which will need to be matched to the process being monitored.

Typically, the frequency response of the sensor is specified at an amplitude

tolerance such as ±5%, ±10% and/or ±3dB.

• USABLE TEMPERATURE RANGE – This is the minimum and maximum

temperature that a sensor can withstand without significantly affecting its

response capabilities. This is especially important when selecting sensors to

be mounted permanently on machinery that is subjected to very high or low

temperatures.

• MEASUREMENT DIRECTION – Piezo-electric sensors measure only in the

mounting direction axis (with only a small percentage reaction to vibration in

directions perpendicular to the mounting axis – typically 3% to 6%).

• SENSOR POWER SUPPLY – Trolex TX9042/4 Programmable Sensor Controller

and TX9130 Programmble Trip Amplifier have been specifically

designed to interface to the whole range of Trolex TX5630 Vibration Sensors as

well as other industry standard sensors. Care should be taken when connecting

sensors to other monitoring equipment as some vibration sensors have very

specific requirements.

0.1

1x 100 = 10mV

18

• MOUNTING SENSITIVITY – There are many ways to mount sensors (hand-

held probes, magnetic connectors, permanent stud mounts, adhesive mounts,

etc.). Each has a significant effect on the ability of the sensor to measure the

vibration accurately and produce repeatable results. This one fact is often critical

to obtaining accurate and repeatable data (section 4.4).

• ELECTRICAL INTERFERENCE – Accelerometers can be extremely sensitive to

electrical interference. Good electrical practice should be followed in earthing

machinery and instrumentation grounding to ensure correct operation

(see section 4.6).

19

4.2 Vibration sensors available from Trolex

ac Output Versions (TX5631, TX5632 and TX5633)4.2.1

This range of vibration sensors is available with an ac output voltage compliant with

industry standard ICP interface. This provides for precision vibration measurement

for machine condition monitoring.

These sensors feature:

Trolex can provide a range of piezo-electric vibration sensors as standard. In

addition, piezo-resistive and eddy-current sensors can be provided to specific order.

•••••••••••••••• ac output signal for discreet vibration

frequency monitoring.

•••••••••••••••• rms indication of acceleration velocity, or

displacement.

•••••••••••••••• Programmable function and setpoint

alarms when used with

TX9137 Programmable Trip Amplifier.

TX9042/4 Programmable Sensor Controller.

•••••••••••••••• High integrity vibration monitoring for;

generators, pumps, compressors, turbines

and engines.

•••••••••••••••• Intrinsically Safe versions available

for hazardous areas.

Order Reference

VIBRATION SENSOR ac.(GENERAL PURPOSE).

T X 5 6 3 1

VIBRATION SENSOR ac.(I.S. GROUP II).

T X 5 6 3 2

Technical Details

Sensing Principle: Piezo electric accelerometer.

Frequency Range: 1Hz to 20kHz.

Sensitivity Range: 100 mV/g.

Linearity: ±1%.

Temperature Limits: –25°C to 140°C.

Supply Voltage: 12 / 24V dc.

Material: Stainless steel.

Protection Classification: IP67.

Mounting: M8 x 8 stud.

Ex Certification: EEx ia I. (TX5633).

EEx ia IIC T6. (TX5632).

Options: • Cable length to specification.

• MS plug and socket connection.

VIBRATION SENSOR ac.(I.S. GROUP I).

T X 5 6 3 3

20

Conditioned 4–20mA versions (TX5634 – TX5639)4.2.2

This range of vibration sensors provides a 4–20mA output proportional to a fixed

range of either velocity or acceleration. This allows the sensor to be connected to a

PLC or other standard monitoring equipment.

These sensors feature:

•••••••••••••••• Programmable function and setpoint

alarms when used with

TX9131 Programmable Trip Amplifier or

TX9042/4 Programmable Sensor Controller.

•••••••••••••••• High integrity vibration monitoring;

generators, pumps, compressors, turbines

and engines.

•••••••••••••••• Intrinsically Safe versions available

for hazardous areas.

Order Reference

VIBRATION SENSOR/TRANSMITTER.Acceleration (I.S. GROUP II).

T X 5 6 3 4

VIBRATION SENSOR/TRANSMITTER.Acceleration (GENERAL PURPOSE).

T X 5 6 3 5

Technical Details

Sensing Principle: Piezo electric accelerometer.

Frequency Range: 2Hz to 1KHz.

Linearity: 1%.

Temp. Limits: –25°C to 80°C.

Analogue Output: 4 to 20mA.

Supply Voltage: 12 / 24V dc.

Material: Stainless steel.

Protection Classification: IP67.

Mounting: M8 stud orquickfit adaptor.

Ex Certification: EEx ia I.

EExia IIC T6

Options: • Cable length to specification.

VIBRATION SENSOR.Acceleration (I.S. GROUP I).

T X 5 6 3 6

VIBRATION SENSOR/TRANSMITTER.Velocity (I.S. GROUP II).

T X 5 6 3 7

VIBRATION SENSOR/TRANSMITTER.Velocity (GENERAL PURPOSE).

T X 5 6 3 8

VIBRATION SENSOR.Velocity (I.S. GROUP I).

T X 5 6 3 9

21

4.3 Selection of monitoring equipment

The range of vibration sensors provided by Trolex has been designed to interface to

a large range of monitoring equipment. This can be specific vibration equipment

such as dataloggers and FFT analysers or general equipment such as PLCs.

Trolex can also provide a range of equipment designed to provide a cost effective

vibration monitoring solution, from a single point alarm to a comprehensive

multi-point, datalogging and communicating system.

22

TX9030 Programmable Trip Amplifiers4.3.1

These instruments can be used to provide a readout of vibration level and provide

a relay output contact, to alarm when levels exceed a pre-determined value.

There are versions to accept the ac signal from vibration sensors as well as the

conditioned output from 4–20mA sensors.

TOTAL PROGRAMMING VERSATILITY IN A SINGLE UNIT WITH DIRECT FINGERTIP SELECTION OF ALL INPUT AND OUTPUT CONTROL AND DISPLAY FUNCTIONS.

•••••••••••••••• Easy to operate 'menu' programme.

•••••••••••••••• Large digital LCD panel with function display and input signal display.

•••••••••••••••• Analogue or frequency inputs.

••••••••••••••••• Dual set point, relay output.

•••••••••••••••• Latch or auto-reset.

•••••••••••••••• Hysteresis selection.

•••••••••••••••• Power-on delay.

•••••••••••••••• Output time delay.

•••••••••••••••• Signal update selection.

•••••••••••••••• Permanent data memory.

•••••••••••••••• Engineering units menu.

•••••••••••••••• 4 to 20mA repeater signal.

Technical Details


Display: LCD, dot matrix, 16 characters.

Supply Voltage: 24V dc at 50mA.

Input Signal Capability: Current (4 to 20mA).Frequency (0.1Hz to 5KHz).

Output Relays: 2 with programmable setpoints, time delay hysteresis, rising/falling, latching/pulsing, power on delay, configurable time delay.

Signal Update Period: 0 to 120 seconds.

Set Point Adjustment: 0 to 99%.

Hysteresis Adjustment: 0 to 99%.

Information Display: Menu of 30 standardunits, (g, mm/s, ft/s, etc.).Programmable scale/zero. Signal bar graph, set point value display. Signal tendency, alarm indicators. Signal line monitor, peak/low indicator.

Options: • 4 to 20mA Repeater Output Signal.

Order Reference

PROGRAMMABLE TRIP AMPLIFIER.(4-20mA, Panel/DIN Rail Mount).

T X 9 0 3 1

PROGRAMMABLE TRIP AMPLIFIER.(ac, Panel/DIN Rail Mount).

T X 9 0 3 7

23

TX9130 Programmable Trip Amplifier4.3.2

This range of Programmable Trip Amplifiers is certified, Intrinsically Safe, for use in

Group I (mining) hazardous areas.

These instruments can be used to provide a readout of vibration level and provide

a relay output contact, to alarm when levels exceed a pre-determined value.

There are versions to accept the ac signal from vibration sensors as well as the

conditioned output from 4–20mA sensors.

TOTAL PROGRAMMING VERSATILITY IN A SINGLE UNIT WITH DIRECT FINGERTIP SELECTION OF ALL INPUT AND OUTPUT CONTROL AND DISPLAY FUNCTIONS.

•••••••••••••••• Easy to operate 'menu' programme.

•••••••••••••••• Digital LCD panel with function display and input signal display.

•••••••••••••••• Analogue or frequency inputs.

••••••••••••••••• Dual set point, relay output.

•••••••••••••••• Latch or auto-reset.

•••••••••••••••• Hysteresis selection.

•••••••••••••••• Power-on delay.

•••••••••••••••• Output time delay.

•••••••••••••••• Signal update selection.

•••••••••••••••• Permanent data memory.

•••••••••••••••• Engineering units menu.

Technical Details


Display: LCD, dot matrix, 16 characters.

Supply Voltage: 12V dc (nominal).

Input Signal Capability: Current (4 to 20mA).ac Vibration (1 to 20KHz).

Output Relays: 2 with programmable setpoints, time delay hysteresis, rising/falling, latching/pulsing, power on delay, configurable time delay.

Signal Update Period: 0 to 120 seconds.



Information Display: Menu of standardengineering units, (g, mm/s, ft/s, etc.). Programmable scale/zero. Signal bar graph, set point value display. Signal tendency, alarm indicators. Signal line monitor, peak/low indicator.

Certification: EEx ia I.

Options: • Repeater Output Signal.(0.4 to 2V/ 4 to 20mA/ 5 to 15Hz)

Order Reference

PROGRAMMABLE TRIP AMPLIFIER. 4 to 20mA.

T X 9 1 3 1

PROGRAMMABLE TRIP AMPLIFIER. ac.

T X 9 1 3 7

Options

DIN RAIL MOUNTMaterial: ABS.Protection: IP20.

PANEL MOUNTMaterial: ABS.Protection: IP65.

19" RACK MOUNTMaterial: ABS.Protection: IP20.

24

TX9042/4 Programmable Trip Amplifier4.3.3

The TX9042/4 is capable of monitoring up to 8 channel of vibration. However, its

great flexibility is that it is capable of monitoring a large range of input signals.

The TX9042/4 is capable of monitoring not only vibration, but a wide range of

condition monitoring sensors. Datalogging and communication facilities allow for

trending of vibration. This simplifies monitoring of machine deterioration.

MONITORS ANY COMBINATION OFEIGHT ANALOGUE SENSORS OR UP TO SIXTEEN ON/OFF DIGITAL INPUTS OR FREQUENCY INPUTS.

•••••••••••••••• Menu operated function selection:Scale, units and offset.

•••••••••••••••• Four programmable output relays:Set points, time delay hysteresis, relay function selection.

•••••••••••••••• Simultaneous display of input signal levels.

•••••••••••••••• Signal tendency display.

•••••••••••••••• Signal bar graph.

•••••••••••••••• Peak/low data display.

•••••••••••••••• Datacomms for RS232/RS485. TTL DIGITAL (MODBUS).

•••••••••••••••• Sensor data exchange ability.

•••••••••••••••• 26,000 point data logging.

•••••••••••••••• Line monitoring.

•••••••••••••••• Signal fault alarm.

•••••••••••••••• Choice of mounting formats.

Technical Details

Mounting: DIN rail/ Front of panel/19" rack.

Display: LCD, dot matrix, 20 characters x 4 lines.Eight way simultaneous display with individual channel close-up facility.

Supply Voltage: 12V/24V dc at 120mA.

Input Signal Capability: Current (4 to 20mA).Voltage (0 to 10V).Thermocouple (Type J or K).Platinum Resistance (PT100).Bridge (0.1mV/V to 100mV/V).Digital (on/off).Frequency (0.1Hz to 5KHz).ac Vibration (1 to 20KHz).

Set Points: 2 per channel.Programmable set point level, time delay, hysteresis, rising/falling, latching/pulsing, power on delay.

Output Relays: 4, with configurablefunction grouping.



Information Display: Menu of 30 standardengineering units, (bar, m/s, rpm, etc.), programmable scale/zero, signal bar graph, signal tendency, signal fault alarm, peak/low data retention, channel reference text entry.

Data Log: 26,000 point data log event recording on each channel.

Ex Certification: EEx ia I.

Data Comms: RS232, RS485. TTL DIGITAL.

Order Reference

PROGRAMMABLE SENSOR CONTROLLER.(Group I – Mining).

T X 9 0 4 2

PROGRAMMABLE SENSOR CONTROLLER.(General Purpose).

T X 9 0 4 4

25

TX2100 Commander4.3.4

The TX2100 has the same functionality as the TX9042/4, but has the added

capability of increasing the number of points that can be monitored.

••••••••••••••••• Bus expandable to 256 channels of I/O.

••••••••••••••• Configurable input signals and output drivers.

•••••••••••••••• Programmable sensor response functions.

•••••••••••••••• Programmable logic control functions.

•••••••••••••••• Data logging.

•••••••••••••••• Datacomms for distributed systems.

•••••••••••••••• Intrinsically Safe for hazardous area operation.

••••••••••••••••• Sensor Input Signal ValuesIndividual or multisensor display with signal bar-graph trending and text entry for sensor duty.

••••••••••••••••• Control Output Signal StatusIndividual or simultaneous display of output function and text entry for control duty.

••••••••••••••••• Data HistoryData storage of Peak/low values and graphical trending.Data logging of sensor data and output events withtime, date and identification.

••••••••••••••••• Sensor Signal Function ProgrammingCharacterisation of sensor response including;Rising/falling signal, Hysteresis, Scaling, Units, Offset, Damping, Sample Rate and Fault monitoring.

••••••••••••••••• CommandbusExtendible I/O channel communication bus with power supply distribution to each channel.

••••••••••••••••• DatacommsProprietory datacomms for distributed monitoring and control systems with conventional or optic fibretransmission.

MODBUS • SAP • ETHERNET

26

4.4 How to mount a vibration sensor

There are 5 commonly used sensor mounting methods. These are shown below,

along with the maximum acceptable frequency that can be monitored together

with the typical resonant frequency of the mounting method.

Stud mount 16kHz 30kHz

Quickfit stud mount 6kHz 10kHz

Magnetic mount 7.5kHz 12kHz

Handheld 800Hz 1.5kHz

Adhesive mount 9kHz None

Maximum AcceptableFrequency

Resonant Frequency(Mount)

Incorrect mounting can cause the readings obtained from the sensor to be

inconsistent.

Figure 14

STUD(BEST)

MAGNET(GOOD)

PROBE (POOR)

ADHESIVE(VERY-GOOD)

Adhesive bondto flat surface

SiliconeGrease

FlatMounting

Suface

27

In order for the vibration sensor to reproduce precisely the vibration generated by

the machine under surveillance, it is imperative that its mounting face, in effect,

becomes a solid part of the structure. The sensor mounting face should see a flat

surface at the machine interface, and not an irregular or curved plane, which would

compromise the correct transmission of the vibration.

Avoid the common pitfalls below.

It is also recommended that the sensor cable is looped and then tied with a cable

tie to the main body in order to avoid excessive wear.

Stud mount4.4.1

Stud mounting is used for permanently mounted sensor applications. Sometimes,

an adhesive will be used in combination with mounting thread to prevent the

sensor from losing its torsion under vibration conditions. Stud mounting is not

always practical for all applications, but it is the preffered method.

Figure 15

Integral Conical Integral Stud

Figure 16

Curved Surface Flat Surface

Loose cable causesvibration and wear

Secure Cable

Figure 17

Tapped holetoo shallow

Tapped holehas clearance

28

Adhesive mount4.4.2

Adhesive mounts should be utilised as an alternative to stud mounting where a stud

cannot be fitted. Great care should be taken in preparing the surface when using

an adhesive, to ensure a permanent bond, because a bad joint will work loose over

a period of time.

An alternative to magnetic or portable mounts is to glue a quickfit mount onto the

machine.

The type of adhesive must be appropriate for the materials and the environment in

which it is to be used. The adhesive must also provide a rigid base. Soft set adhesive

will cause the higher frequencies to be absorbed.

Magnetic mount4.4.3

Magnetic mounts are generally used with portable diagnostic instruments when

data collecting.

The magnetic mount does give repeatable data over the frequency range for which

it is suitable.

An alternative to magnetic or portable mouts is to glue a quickfit mount onto the

machine.

Quickfit Glue

Figure 18

29

Handheld4.4.5

This is the least acceptable method of mounting and is only really useable on

vibration frequencies below 1kHz.

A handheld probe is of use when other mounting options cannot be used.

Quickfit stud mount4.4.4

Quickfit stud mounts are also extensively used for collecting data with portable

instruments. Repeatability of readings within its acceptable range is good, making

it suitable for use with most data collectors.

Figure 19

Quickfit Stud

30

Sensors should be mounted such that the axis of the sensor passes through the

centre of the shaft and as close as possible to the shaft centre line.

Readings taken on foundations are not representative of shaft and bearing vibration

and should only be used when structure vibrations are being monitored.

Care should be taken to ensure that the sensor is mounted on a substantial part of

the machine, such as the motor case. Avoid mounting on thin sheet metal

structures such as outer casings.

Figure 201

2

3

In order to ensure that vibration problems are diagnosed correctly, it is essential

that information received from sensors is not only good, but representative of the

actual vibration on the machine part being monitored. Correct selection of the

sensor for the vibration being monitored is imperative, but equally important is the

mounting of the sensor.

When monitoring bearings, the sensor should be located as close to the source of

vibration as possible. These should be within the load zone of the bearing. This is

particularly important where high frequency components of vibration are being

monitored.

Ideally, horizontal (1) and vertical (2) measurements should be taken. However,

where cost is significant, a compromise solution of a sensor fitted at 45° to the

horizontal can be used (3).

4.5 Where to mount the sensor

31

Figure 21

GOOD AND POORMEASUREMENTLOCATIONS.

TYPICAL MACHINE WITH FABRICATED BASE

Vertical

Axial Horizontal

PILLOW BLOCK BEARING MOTOR DRIVE END MOTOR FAN GUARD END

Choose foot for axial measurement if goodaccessible locations near shaft are not available.

32

In order to avoid electrical pickup through the case of the sensor from the machine

being monitored, the machine should be properly earthed in compliance with local

regulations. If a good earth is not possible, the sensor and the cable overbraid

should be electrically isolated from the machine.

The screen of the cable should be connected to earth at the monitoring equipment.

IT SHOULD NOT BE EARTHED AT THE MOTOR. The cable overbraid should be

left unconnected

4.6 Cabling to the sensor

Because of the low level of signal produced by most vibration sensors, it is

important that good electrical practice is followed in cabling the sensor, on fixed

installations.

Accelerometers are usually fitted with screened PVC cable encased in an

overbraided stainless steel sheath. This offers excellent protection for the arduous

environment in which vibration sensors are used. However, long lengths can be

difficult to control on a stud-mounted sensor. Options include connector versions,

quickfit mounts and a local junction box.

It is recommended that the cable is looped (where possible) and tied to the sensor.

This avoids excessive wear and stress at the cable/sensor junction.

Figure 22

Figure 23

Figure 24

Insulating Blocks

Use a cable tie

Sensor

TX9042ProgrammableSensorController

33

5. TY P I C A L A P P L I C AT I O N S F O R TR O L E X V I B R AT I O N

M O N I T O R I N G E Q U I P M E N T

Trolex TX5633 vibration sensors are mounted at 45° to the horizontal on each of

the bearings on the fan (positions 1 to 4). These are connected to the TX9042 as

shown below.

5.1 Underground booster fan monitoring utilising the Trolex TX9042

Programmble Sensor Controller and the TX5633 vibration sensor

Figure 25 2. Drive End

3. Drive End

MotorFan

4. Non-Drive End1. Non-Drive End

Figure 26

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

TX5633Motor NDE

AccelerationChannelFan DE

VelocityChannelFan DE

AccelerationChannelFan NDE

VelocityChannelFan NDE

AccelerationChannel

Motor NDE

VelocityChannel

Motor NDE

AccelerationChannel

Motor DE

VelocityChannel

Motor DE

Core SCNCore SCN

TX5633Motor DE

TX5633Fan DE

CoreSCNCoreSCN

TX5633Fan NDE

TX9042/4Programmable

SensorController

PowerSupply

0V

+12V

34

In figure 26 channels 1,3,5 and 7 on the TX9042 Programmable Sensor Controller

are configured to monitor velocity (in mm/s) in the frequency range 10 to 500Hz.

Channels 2, 4, 6 and 8 are configured to monitor acceleration (in g) in the

frequency range 1kHz to 20kHz.

The fan is running at 1500 rpm giving a fundamental of 25Hz.

After the fan has been given time to run in, the vibration levels on each channel

should be monitored using an FFT analyser to ensure that there are no vibration

levels of concern.

The resulting vibration levels on the TX9042 should be recorded and the alarm

levels set at a suitable margin of excess vibration.

Velocity is used to monitor out-of-balance on the fan. This can be due to a

number of causes:

• Misalignment of the shaft

• Imbalance of the blades

• Dust build-up on the blades

• Chipped or broken blades

Acceleration is used to monitor bearing breakdown. This can be a result of a

number of conditions, such as lack of lubrication or long term wear and tear.

By looking at the trend of velocity and acceleration, the deterioration of the fan,

especially with respect to its bearings, can be monitored.

As well as monitoring excess vibration levels, the TX5633 (in conjunction with the

TX9042) can be used to remotely confirm that the fan is running. A moderate

level of vibration, indicates a healthy fan, running at its normal speed. Lack of

vibration would indicate a signal fail, or stationary fan.

35

5.2 Pump monitoring (non-hazardous areas)

In this application, two TX5631 sensors are mounted on the outlet end of the pump

(one vertical, one horizontal), to monitor: out-of-alignment, mounting movement,

or loose fixings.

The TX5631 Vibration Sensors are connected to two channels of the TX9044

Programmable Sensor Controller which is set-up to monitor velocity in the range

10 to 500Hz. The pump is rotating at 3000 rpm giving a fundamental frequency of

50Hz.

Figure 27

Loose Bolt

Sensor 1

Sensor 2

Figure 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18


SensorController

Sensor 1

Core SCNCore SCN

Sensor 2

0V

+24V

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

36

Alarm levels on the TX9044 are set up according to BS7854 Part 1, (ISO10816-1)

to monitor vibration severity.

As the TX9044 has spare channels available, temperature and pressure monitoring

on the pump can easily be accommodated using simple PT100 probes and pressure

sensors.

Figure 29

As with the previous example, quiescent vibration monitoring can be used to

remotely confirm that the pump is running or stopped. The TX9044 can also be

used to remotely stop/start the pump, via a data communication link and the

built-in output control relays.

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

TX5631Pump

Vibration(vertical)

TX5631Motor

DE

TX6114Outlet

Pressure

4-20mAModule

4-20mAModule

PT100Module

PT100Module

acModule

acModule

acModule

PT100Module

TX6114Inlet

Pressure

TX2072Pump

BearingTemp

TX2072LiquidTemp

TX5631Pump

Vibration(horizontal)

TX2072Motor

GearboxTemp


SensorController

37

5.3 Hazardous area, vibration monitoring

When the equipment to be monitored is in a hazardous area, certified safe

equipment needs to be used. The Trolex TX5630 Vibration sensors are certified,

Intrinsically Safe, for use in Group II hazardous areas. However, Trolex monitoring

equipment is intended for mounting in the safe area.

In order to connect to the sensors in the hazardous area, zener safety barriers or

isolators need to be used between the sensors and the monitoring equipment. The

diagrams below give typical barrier and isolator options.

3 1

4 2

IS earth

MTL728Core Core

Scn Scn

TX5632


1

2

3

4

Scn Scn


TX5634or TX5637

3 1

4 2

IS earth

MTL787s 1

2

3

4


TX5634or TX5637

5 1

6 2

MTL3041

+24V

0V

7 3

8 4

1

2

3

4

Figure 30

Figure 31

Zener Safety Barrier

Zener Safety Barrier

Isolators

38

5.4 Screening and bunker outfeed monitoring

Vibratory screens are used for the grading of product in many mining and

quarrying applications. Product is introduced onto a vibrating “sieve” and small

product passes through whilst large product is screened to the next stage.

Vibrating pans are used on the outfeed to ensure that product does not block the

outfeed chutes.

A Trolex TX5630 Vibration Sensor mounted on the vibratory screen, can monitor

the operation and condition of the screen, when connected to a Trolex TX9042/4

Programmable Sensor Controller. By setting “window” alarms, the system can

locally or remotely monitor that the screen is running correctly and that vibration

levels are not excessive. By trending vibration levels, deterioration in the condition

of the screen and its mounts can be monitored.

Similarly, the vibrating pans on the outfeed can be monitored for both operation

and excessive wear.

Bunker1

Bunker2 Vibration

Sensors

Infeed Conveyor

Screen

Large Aggregate

Small Aggregate

Vibrating PanOutfeed

Conveyors

OutfeedConveyors

Figure 32

39

5.5 Conveyor drive monitoring

A conveyor is the backbone of any product clearance system and a breakdown of

this is likely to be costly. Utilising Trolex vibration monitoring equipment, the plant

engineer can obtain an early indication of impending motor and gearbox failure.

Temperature monitoring can also be utilised to save catastrophic failure by

interlocking an excessive temperature alarm setpoint with the motor drive control.

The diagram shows how the vibration sensors and temperature sensors connected

to a TX9044 Programmable Sensor Controller and how this could be used to

disable the conveyor under high temperature conditions or excessive vibration.

MOTOR TX5631VibrationSensors

TX2072Temperature

Sensors

NAMUR Proximity Sensors

GEARBOX

Figure 33

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Vibrationvisualalarm

To conveyordrive stop

circuit

Conveyor"running"contactor

NAMUR Sensors(speed)

TX5631

VibrationSensor(motor)

TX2072(2 wire)

TemperatureSensor(motor)

TX5631

VibrationSensor

(gearbox)

TX2072(2 wire)

TemperatureSensor


SensorController

0V

+24V

Figure 34

40

NAMUR sensors can be used to indicate conveyor speed and belt slip, by

monitoring the speed of both the motor and an idler wheel.

If the temperature inputs are programmed to latch one of the output relays when

over temperature occurs, the output relay could be interlocked with the conveyor

stop circuitry to lockout the conveyor. The latched relay would then have to be

manually reset before attempting to restart the machine.

An input from the conveyor drive contactor can give confirmation that the

conveyor is running. The two spare relays could be used for remote stop/start of

conveyor if data communication was available.

NB. Care should be taken that adequate warning is given if conveyors are being

started remotely (e.g. Pre-start alarm).

41

UN D E R S TA N D I N G A N D U T I L I S I N G T H E V I B R AT I O N

I N F O R M AT I O N O B TA I N E D

It is beyond the scope of this document to give full explanation on how vibration

can be used to analyse problems on a machine. However, as an example, an

explanation will be given on how vibration can be used to monitor bearing and

gearmesh deterioration and imbalance on a ventilation fan.

Ventilation fans are used in critical areas such as underground mining and

tunnelling, where natural ventilation is not sufficient to either dilute

noxious/explosive gases or to ensure a sufficient supply of oxygen.

There are 3 areas of interest in monitoring vibration on the above installation.

Although these areas are not always as discreetly defined as shown here, they have

been separated for the purposes of this example.

MotorFan

1kHz 10kHz100Hz

FREQUENCY

VIB

RA

TIO

NA

MP

LITU

DE

Figure 35

Figure 36

AP P E N D I X A

12

3

42

Figure 37

VIBRATION DATA –FAULT DIAGNOSIS

1 -

20 k

Hz

SP

EC

TRU

M0

- 10

00 H

z S

PE

CTR

UM

BE

AR

ING

BE

AR

ING

IMB

ALA

NC

Eis

iden

tifie

d a

t a

freq

uenc

y eq

ual t

o (1

X)

the

shaf

t ro

tatio

nal f

req

uenc

y (m

otor

sp

eed

)

GE

AR

ME

SH

DE

TER

IOR

ATI

ON

is id

entif

ied

at

a fr

eque

ncy

equa

l to

the

shaf

t ro

tatio

nal f

req

uenc

y x

No.

of t

eeth

on

gear

INIT

IAL

BE

AR

ING

DE

TER

IRA

TIO

N/

LUB

RIC

ATI

ON

DE

FIC

IEN

CY

is id

entif

ied

as

bro

adb

and

spec

tral

bas

elin

e ac

tivity

and

may

be

exp

ress

ed a

s I.F

.B a

nd/o

r H

.F.B

.

MIS

ALI

GN

ME

NT/

INS

EC

UR

ITY

is id

entif

ied

at

2x, 3

x an

d 4

xth

e sh

aft

rota

tiona

l fre

que

ncy

BE

AR

ING

DE

TER

IOR

ATI

ON

is id

entif

ied

as

bro

adb

and

sp

ectr

al b

asel

ine

activ

ityan

d a

t th

e b

earin

gs c

alcu

late

d fa

ult

freq

uenc

ies.

ie. C

age,

Rol

ler

Inne

r an

d O

uter

Rac

e.

UN

ITS

VE

LOC

ITY

mm

/sec

AC

CE

LER

ATI

ON

(g)

UN

ITS

AC

CE

LER

ATI

ON

(g)

Driv

e G

ear

Driv

en G

ear

Lub

rican

t

43

5.1 Imbalance

Imbalance occurs because the machine is not perfectly balanced about the shaft

centre line. This can be caused during manufacture, installation or during operation

(eg. debris build-up on a fan blade).

Imbalance will occur at the rotational frequency of the fan. So on a fan rotating at

1500 rpm, imbalance will occur at 25Hz. As the imbalance increases, it will be seen

as increase in the vibration signal at 25Hz. This will require a monitoring instrument

capable of displaying the signal in the frequency domain (eg. FFT analyser).

If a broadband alarm monitor, such as the Trolex TX9042 Programmable Sensor

Controller is used, with a fixed, low pass filter then the general overall level of

vibration will be seen to increase. This can be compared to an alarm set-point, as

suggested by BS7854 Part 1. This alarm indication would suggest that a spectrum

analyser should be employed to define the fault more specifically.

5.2 Gearmesh problems

Vibration due to the gear teeth will be seen at the rotational frequency multiplied

by the number of teeth. So, on a machine with rotational frequency 1500 rpm and

30 teeth on the wheel, the fundamental vibration frequency is about 750Hz. As the

teeth start to deteriorate, the amplitude of the vibration, at the 750Hz fundamental,

will increase. This would easily be picked up with an instrument such as an FFT

analyser.

An alarm instrument such as the Trolex TX9042 Programmable Sensor Controller,

could also be used to indicate that the level of vibration, around the frequency of

interest, has increased.

5.3 Bearing breakdown

Bearing noise, due to imperfections in the bearing, will start at high frequency

(>1kHz). Bearing deterioration can be caused by:

• Poor quality of the bearing

• Inadequate lubrication

• Contaminated lubrication

• Poor installation

As the bearing starts to deteriorate, larger imperfections occur, increasing the

amplitude of the vibration and at the same time reducing the frequency of the

vibration. Over time, the signal will change as shown in Figure 30.

r

44

The Trolex TX9042 Programmable Sensor Controller can be used to monitor the

increase in broadband vibration, whilst disregarding the change in frequency.

Figure 38

1kHz 10kHz

3 21

Vibration Application Data(1)

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Transcript of Vibration Application Data(1)