Balancing with VibroMatrix

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IDS Innomic

Gesellschaft für Computer- und Messtechnik mbH

Balancing

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Balancing with VibroMatrix Version 1.4.0.34, 03/30/2007 Author Dipl.-Ing. Thomas Olschewski

IDS Innomic Gesellschaft für Computer- und Messtechnik mbH Zum Buchhorst 25

D-29410 Salzwedel Germany

© 2003 – 2008 All rights reserved. Reproduction (also in extracts) only with permission of IDS Innomic GmbH. VibroMatrix® InnoBeamer® InnoMaster® InnoStreamMachine® InnoMeter® InnoLogger® InnoPlotter® InnoAnalyzer® InnoScope® InnoBalancer®

are registered trademarks of IDS Innomic GmbH Windows®

is registered trademark of Microsoft Corporation

Despite accurate work we cannot exclude errors in this manual. We hereby disclaim all warranties and conditions related to this informa-tion regarding fitness for a particular purpose and non-infringement. In no event shall IDS Innomic GmbH and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortuous action arising out of or in connection with the use of information available in this manual.

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1. Introduction

We are pleased to welcome you as a new VibroMatrix user. You have purchased a pow-erful, expandable and economical solution for balancing.

The precision hardware allows balancing different rotors from cent-sized engines to generators weighing several tons.

The balancing software InnoBalancer runs on your notebook, guides you through the measurement process and clearly presents the measurement results numerically and graphically.

This manual shows you how to efficiently apply VibroMatrix for balancing your rotors.

 First, some basics explain unbalance characteristics and measurement methods.

 Afterwards you learn how VibroMatrix with its InnoBalancer software supports you when measuring and correcting unbalances.

 Practical examples for balancing of different rotors provide you with useful hints for the everyday use. As a start, balancing propellers is described.

The newest version of this manual can be found on www.innomic.com .

We are at your disposal for increments, complaints and wishes. We are sure you will use VibroMatrix successfully.

Salzwedel, 03/30/2007 VibroMatrix Development Team

Introduction

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2.Some basics

2. Some basics

Unbalance – so what?

Why is unbalance a topic of interest? Because an unbalance leads to vibrations on a ro-tating body. These vibrations are mostly disturbing and they are to be remedied. Seldom are they wanted, for instance with vibratory plates. With unbalance determination, both goals can be achieved – its reduction or adjustment to a certain level.

Unbalance and vibrations – how are they related?

Let us have a look on a discoidal rotor. It is to be a thin, rigid, ho-mogeneously built up, ideally round and centrically mounted disc. It it is put into rotation, centrifugal forces occur – everyone knows that from a carousel. Still, there are no forces in radial direction to the spindle. The reason: With our rotor, the centrifugal forces of all mass particles cancel out each other.

Now we add mass on the outer of the disc. If the rotor is put into rotation, an addition-al centrifugaddition-al force in radiaddition-al direction (i.e.

on the spindle) occurs now. It is situated in a bearing and the rotating centrifugal force stresses the bearing periodically. Vi-brations occur.

One characteristic of vibrations caused by unbalances is a vi-bration frequency which corresponds to the rotation speed of the rotating object.

Now, what is unbalance?

So unbalance and mass are closely related to each other. How-ever, not only the amount of the mass influences the centrifugal force, but also it distance from the rotating axis (radius). The same mass mounted more closely to the rotating axis causes less centrifugal forces. The amount of an unbalance is conse-quently calculated as follow: mass · radius. The unit often is gmm (gram millimeter). So simply comparing the masses in or-der to compare unbalances is only possible if the same radius is used.

Example

The exemplary unbalances have the same amount, although the mass in right picture has the double amount of the left mass. The reason: The mass is on a radius which is only half as long as the radius in the left picture.

Some basics 5 r m U = r·m m r 2·m r/2 F

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2.Some basics

For balancing, not only the amount of the unbalance must be known, but also its position.

Since rotation is a circular movement, the balancing plane is presented as a cir-cular area as well. The un-balance position is speci-fied with an angle from 0 .. 360°. The distance from the rotating axis (radius) indicates the amount of the un-balance. This form of representation can be found in the InnoBalancer as well and is called polar chart.

Purpose of balancing

During balancing, the mass allocation of a rotor is checked and afterwards improved so that the forces and vibrations caused by unbalance are within acceptable limits. By bal-ancing, a low-vibration running is achieved which has several positive effects within the machine, for instance:

 Improvement of product quality

 Extension of machine life

 Reduction of noise emission

When is a rotor balanced?

Theoretically, it is balanced when the unbalance is zero, i.e. when the center of gravity is within the rotation axis again and all centrifugal forces cancel out each other. Practi-cally, this cannot be achieved. That is why tolerances have to be defined. If the unbal-ance value is below these limits, the rotor is considered as balunbal-anced. There are different ways of defining a tolerance. If you are not responsible for defining the tolerance, you will have to act in accordance with the specifications.

1. As tolerance, a maximum unbalance can be defined. You can check it directly with the InnoBalancer then. In its polar chart, it fades in a green tolerance circle. An unbalance outside this circle exceeds the tolerance. Within the circle, the tol-erance is adhered.

2. As tolerance, a maximum mass can be defined which is related to a given radius. This tolerance can be checked with the InnoBalancer as well, because it can dis-play unbalance or mass.

3. With rotating machines, the effects of unbalance, i.e. the caused vibration, is of-ten regarded as success criterion. For instance, many manufacturers define maxi-mum vibration severities for their machines acc. to DIN ISO 10816-2. In this standard, vibration velocity as r.m.s. value in a frequency range from 10..1000 Hz is defined. This value can be measured easily with the VibroMatrix instru-ment InnoMeter. Some basics 6 180° 90° 270° 0°

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2.Some basics

When using the last method, you should keep in mind that an unbalance at the rotor can be one reason for vibrations, but not the only one. For instance, bearing damages can cause vibrations as well. Now, how do now whether the vibrations of the examined ro-tor are caused by unbalance or not?

Every vibration signal can be decomposed into different frequency parts. Such a decom-position is displayed by the InnoAnalyzer. The following pictures show an example: An engine runs with 6600 1/min. By means of a gear, a propeller with 1:3.3 is stepped down, which means it runs with 2000 1/min.

The graphics show the situation before and after balancing. The time signal is displayed by the InnoScope, the frequency analysis is carried out by the InnoAnalyzer. The In-noMeter measures vibration velocity in the frequency range of 10..1000 Hz (600.. 60000 1/min).

In the upper picture, the unbalance of the propeller is dominant and the biggest part of the 14.133 mm/s vibration severity. The lower picture shows the vibrations after balanc-ing. The vibration caused by the propeller could be reduced to under 1 mm/s. But since the vibrations before the gear are not changed by balancing the propeller, they cause the remaining vibration severity now. So balancing the propeller cannot make a contribu-tion to a further improvement of the total vibracontribu-tion situacontribu-tion any longer now.

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2.Some basics

Types of unbalance

Two basic types of unbalance are distinguished. The first one has already been ex-plained with the disc rotor example.

1. If an unbalance is added at the radial plane located in the center of gravity of an absolutely balanced ro-tor then the unbalance is named static unbalance. Such unbalances have been known for millennia, e.g. at water wheels on mills. They could be

correct-ed by oscillation on cutting correct-edges or rollers or by empiric attachment of masses. A static unbalance can be measured in one plane by one vibration sensor.

2. In these days, couple unbalance was unknown. It was discovered when the first fast-running ma-chines appeared. Two unbalances equal in magni-tude at both bearings, but 180° opposite in direction are not obvious in neutral state or at slow rotation speeds. But they create an overturning moment at higher rotation speeds. The measurement in two

balancing planes (with two vibration sensors) is necessary to correct a couple unbal-ance.

Most common are combinations of both types, which are called dynamic unbalances. The part of couple unbalance can be neglected in most cases of discoidal rotors. Single-Plane-Balancing is sufficient here. For all other rotors, Two-Single-Plane-Balancing is recom-mended.

InnoBalancer can correct static unbalances as well as combinations of static and couple unbalances - dynamic unbalances.1

1 In the aircraft industry the term „Dynamic Balancing“ has become wide spread to name balancing of driven rotating parts. This term is used to distinguish from passive oscillation of rotors which is a historic method for balancing. The measurement of a static unbalance is called dynamic balancing as well in this sector, if measurement is per-formed on active rotating objects.

Some basics

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3.Balancing with VibroMatrix

3. Balancing with VibroMatrix

The measurement system VibroMatrix consists of matched electronic and software components for measuring, analyzing and reducing vibrations. The latter is carried out by balancing.

3.1. Measurement hardware

The kit for balancing includes all required components. For different industrial branches it is available in different variants. The following exemplary picture shows the equip-ment for balancing propellers.

3.2. The balancing software

VibroMatrix is a modular system for vibration measurement. Like a building set it in-cludes components which work stand-alone but which can also be combined for more complex measuring tasks. For balancing, the InnoBalancer was designed.

Additional measurements, for instance frequency analysis, are carried out by other in-struments from the VibroMatrix system. All inin-struments can work simultaneously and display the measured data immediately (called on-line or real-time measurement).

The balancing software 9

Photoelectric reflex switch with 2 m cable Relection foil, self-adhesive

InnoBeamer – Digital DAQ device

USB cable for

connection with the PC

Piezoelectric precision vibration transducer with 5m cable

Pocket scale with 0.1 gramme resolution

Calibration weights for pocket scale

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Some instruments from the VibroMatrix system

InnoAnalyzer for frequency analysis InnoBalancer for balancing InnoMeter

InnoPlotter for long-term mea-surements

The operation of all instruments is explained detailed in the VibroMatrix manual. You can find the InnoBalancer there as well.

3.3. Measuring arrangement for balancing

Unbalance cannot be measured di-rectly. The measured parameters are the effects of unbalance. Either the centrifugal forces or the vibrations caused by rotating centrifugal forces are measured.

In order to determine the amount of the unbalance, accelerometers are applied with VibroMatrix. Position information is acquired contactlessly by means of a photoelectric reflex switch.

Preferably bearing cases or other lo-cations close to the bearings are used for sensor mounting the vibration sensors because vibrations can be

measured best here. One accelerometer is sufficient for Single-Plane-Balancing, two for Two-Plane-Balancing.

The photoelectric reflex switch can be positioned advantageously for example by means of a suitable stand. A reflecting label is stuck on the rotor.

Before the measuring run is carried out, the correct registration of the label can be checked by means of a flashing LED on the reflex switch.

All sensors are directly connected to the InnoBeamer and supplied by this device.

Measuring arrangement for balancing

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1 Vibration sensor balancing plane A

2 Vibration sensor balancing plane B (for Two-Plane-Balancing) 3 Photoelectric reflex switch

4 Reflection foil

5 InnoBeamer connects sensors and PC 6 To the PC via InnoBeamer

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2

4

3

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3.Balancing with VibroMatrix 3.4. Measurement process

Effects of the unbalance are measured with two measuring runs:

1. Initial unbalance run: First, the vibration signals of the rotor in the present state are recorded.

2. Calibration run: Then, a known unbalance is generated at the rotor by adding a mass with known amount and mounting angle. The altered vibration signals are recorded now.2

By comparing the signals from the initial unbalance and calibration run, the InnoBal-ancer calculates the originally existing unbalance.

After compensation, a test run is recommended. With clear instructions, the In-noBalancer guides the user through the measurement process.

3.5. Compensating an unbalance

After having measured an unbalance, it is compensated. This procedure is called correction. The objective is to achieve a mass allocation in a way that no centrifugal forces occur any longer. There are two general ways for mass allocation:

 Removing mass at the unbalance position.

 Adding mass on the opposite of the unbalance position. For both ways, several technical methods exists. They are all supported by the InnoBalancer. The software calculates the respective parameters for each method and indicates the compensation information directly in the polar chart. In the InnoBalancer, methods for removing mass are la-beled with – and methods for adding mass with ++.

Methods for removing mass at the unbalance position

Removing mass in general

This correction method indicates how much mass is to be removed at the unbalance position in general. As a parame-ter, the maximum mass can be specified in case of having a technological limit.

2 During Two-Plane-Balancing, two calibration runs are carried out, one for each plane.

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Drilling in radial direction

From the given maximum number of drill holes, maximum drill hole depth, drill diameter and drill bit angle, the actual drilling depth required for the unbalance correction is cal-culated.

The rotor density is important as well. It is specified in the rotor characteristics and it also influences the unbalance correction by milling.

Milling

From the given maximum milling depth and the milling cutter diameter, the actual milling depth required for the unbalance correction is calculated.

Set screws

Set screws are moved in radial direction. Before balancing, they are put into a neutral position, i.e. they are put on the outer edge of the rotor. Parameters to be entered into the software are screw mass and maximum screw depth. The InnoBalancer calculates the actual screw depth for each screw. Since this screws can be found at fixed angle positi-ons only, fixed positipositi-ons are to be defined in the rotor cha-racteristics.

Methods for adding mass on the opposite of the unbalance position

Adding mass in general

This correction method indicates how much mass is to be added on the opposite of the unbalance position in general. As a parameter, the maximum mass can be specified in case of having a technological limit.

Mounting the mass, for instance by screws, adherence or welding, must ensure a secure hold at all rotation speeds occurring during operation.

Counterweight list

It is often more efficient to combine prefabricated counter-weights in a way that altogether, they achieve the the mass to be added. The InnoBalancer is able to determine the op-timum combination very fast, so that there is no extensive trying.

Entering a counterweight list has to be done only once. More information can be found in the VibroMatrix manual.

Compensating an unbalance

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Balancing rings

When using this correction method, two similar weights on fixed radius can change their angle position and be arrested in this position. In machine construction, a version as swi-vels has developed, slide blocks are applied with many ge-nerators.

Before balancing, the balancing rings are brought into a neutral position by placing them with their unbalance 180° opposite to each other. The ring unbalance is entered in the InnoBalancer, which calculates the angles which lead to an unbalance correction.

3.6. Useful hints for balancing

 Accelerometers should be mounted as close as possible to the bearings.  All balancing runs must be performed at the same rotary speed.

 Do not change the measuring setup (sensors, reflecting label) during the balancing

process.

 With VibroMatrix, all angles refer to the position of the calibration mass. If the

po-sition of the calibration mass is defined as 0°, all other measurements and correction measures can be referred to this point.

 The angle positions of InnoBalancer are always measured against the rotary

directi-on of the rotor.

 The calibration mass is to be removed after the calibration run.  After compensation, a test run is recommended.

 A step-by-step procedure with repeated calibration can be necessary.

 InnoAnalyzer and InnoMeter can be used to check whether the total vibration

beha-vior is influenced by an unbalance or other sources.

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4.Balancing propellers

4. Balancing propellers

The balancing of aircraft propellers ensures an operation without too heavy vibrations. The life of machine parts and instruments is extended, the noise level is reduced, the flight comfort is increased. With a little routine, the whole procedure does not take more than 30 minutes.

4.1. Preparations

Balancing is carried out on ground. Since the engine is started and the propeller put into rotation, the machine must be locked sufficiently. Balancing can be carried our by on person alone. He or she must have the ability and permission to start the engine on ground. An environment with only little wind enhances the measurement accuracy con-siderably with regard to fine balancing. If such an environment does not exist, the wind should cross the propeller sideways.

The occurring vibrations are caused by the unbal-anced propeller. In order be able to well measure the vibrations caused by the unbalance, the measurement is carried out near the propeller. It is often advanta-geous to mount the sensors on the engine respective-ly the gear. The cowling is to be removed.

4.2. Mounting the sensors

The vibration sensor (1) is mounted in radial direction to the propeller axis. A reflecting label is stuck to the base-plate of the spinner and the reflex switch (2) is oriented towards it. You do not need to use the complete (50 cm²) reflection foil. A small part suffices. However, the length of its edges should be at least 2 cm.

Both sensors are to be mounted se-curely, that means in a way they can-not loosen or detach themselves dur-ing propeller rotation. Vibration sen-sor and reflex switch can be mounted

by screwing. The vibration sensor provides an M5 thread in base. The reflex switch pro-vides drill-holes and inside threads for M4 screws. By simple adapters, both sensors can be mounted on different engines. Due to the variety of engines, adapters are not normal-ly included in delivery.

Mounting the sensors

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4.Balancing propellers 4.3. Laying sensor cables

The small USB box Inno-Beamer is preferably posi-tioned in the cockpit. Sensor cables transfer the signals for digitization. Cables should not be in contact with hot parts and they should be fixed at suitable places (for instance with cable ties) to ensure that they do not flutter during propeller rotation.

4.4. In the cockpit

The notebook can be placed on the seat of the copilot, the InnoBeamer plus connected cables can be stored on the ground of the cockpit. The vibration sensor is connected with the input ACh1, the reflex switch is connected with the DCh input.

When the notebook is switched on, the In-noBeamer and connected sensors are sup-plied as well. Now you check the reflex switch once again. If it detects the

reflect-ing label , a yellow LED in the reflex switch flashes.

The control center InnoMaster RT can be started on the notebook now. If now workspace for propeller balancing has been configured yet, some settings are to be made. For the following steps, take a look into the VibroMatrix manual.

1. The purchased sensor should be entered to the sensor database.

2. The vibration sensor is assigned to measuring channel 1 of the active InnoBeamer. 3. The balancing software InnoBalancer is started.

Two settings are to made in the InnoBalancer. Basically, this can be done at any time, also after measurement. The InnoBalancer simply recalculates all results then. But since we want to see valid results immediately after the measurement, it is a good opportunity to enter the data now.

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1. As unbalance quantity, we want to use a mass in gram referring to a fixed rotor radius. An un-balance is often defined as mass x radius. But if the radius remains the same – like in our ex-ample –, the mass alone can be regarded as well. When balancing propellers, the unit gram is suitable.

2. The radius of the rotor is to be entered. As ra-dius, the distance from the rotating axis to the circumference where the calibration/correction masses are attached. For instance, this could be the baseplate of the spinner (also compare chapter 4.6 page 17).

4.5. Initial unbalance run

The first measuring run is called initial unbalance run. The propeller is measured in its original state with a still unknown unbalance. Therefore, a constant rotation speed is set, possibly similar to the one during machine operation.

If you are sure not to endanger nearby persons or objects, the engine can be started. We recommend to warm up the engine one or two minutes before first-time measurement. This process does not require full throttle. Then the gear is to be set to the constant rota-tion speed.

With a click on the „Start“ button in the InnoBalancer, the rotation speed recognition is started. The rotation speed is indicated in the user guide. It should be plausible. When estimating roughly, a possible gear transmission ratio is to be taken into account.

Now simply keep a constant rotation speed. The InnoBa-lancer continuously monitors the rotation speed stability and only carries out the mea-surement at constant rotation

speed. During the measurement, the rotation speed is monitored as well. If the rotation speed varies too much during the measurement, the measurement automatically starts anew. A certain number of revolutions is read. The standard number is 100. If the In-noBalancer has read all revolutions, the user guide informs you to stop the engine now. The initial unbalance run is finished then.

4.6. Calibration run

The second measuring run is for calibration. At a defined position, a known mass is mounted. Now some considerations with regard to mounting the calibration respectively correction masses are necessary.

Calibration run

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Mounting calibration/correction masses on the propeller

The correction of an unbalance is preferably achieved by adding masses opposite to the unbalance. They are mounted – if existing – on the baseplate of the spinner. If not, other places must be found where masses (for instance washers) can be mounted without interfering with the propeller operation. The closer you come to the rotation axis, the heavier the correction masses. Except the InnoBalancer Light, all versions are able to handle fixed positions. If there are mounting places for masses on the propeller, which are evenly allotted on the circumference, the InnoBalancer can take them into consideration. Then it will calculate a mass allocation for these fixed positions only, which also corrects an unbalance between the fixed positions.

Therefore, the

num-ber of fixed positions is entered into the rotor proper-ties, The angle of the first fixed position should re-main zero, then the first fixed position will be at 0°. The minimum number of fixed

positions is 3. If you enter a val-ue below 3, the calculation with fixed positions will be deactivated. Correction masses have to be mounted at the angles indicated by the software. In this case, self-adhesive mass pieces like in the automotive industry can be ap-plied. For long-time adherence, the respective point is to prepared accordingly, i.e. it must be free of fat and dirt. An additional assur-ance by means of epoxy glue is recommended. For an exact correc-tion, the mass of the additional adhesive must be included in the total mass.

Preparations for the calibration run

After having decided whether to use fixed positions or not, the calibration mass is mounted. A value of approx. 1000 gmm is recommended after tests on ultralights. For example, this means: At a radius of approx. 100 mm, 10 gram apply and respectively 20 gram at a radius of 50 mm. But this value should be considered as approximate value only.

The calibration mass is entered into the calibra-tion control panel of the InnoBalancer software. The angle position is to be entered as well. The angle of 0° is not given by the reflecting label. The angle can be chosen completely freely, for example the angle of 0° can have the position of the calibration mass. But with all following tests,

you have to refer to this position as 0°. Angles are always counted from the defined zero angle against the rotary direction.

Calibration run 17

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Carrying our the calibration run

If you had to remove the spinner for mounting the calibration mass, you must mount it again now. All measuring runs have to be carried out with the same superstructural parts. When mounting the spinner, take care to mount it in the same way like before and not turned by 180°. A small label on the spinner /baseplate is useful.

The measurement is carried out in the same way like the initial unbalance run. The propeller is put into ro-tation with a constant roro-tation speed, in fact the rota-tion speed of the initial unbalance run. The InnoBal-ancer recognizes the constant rotation speed, carries out the measurement and asks you to stop the pro-peller.

With these both run, amount and angle position of the unbalance have determined. They are displayed in the InnoBalancer now.

4.7. Correction

Now the known unbalance should be corrected. Therefore the correction control panel has to be ac-tivated in the InnoBalancer. Different correction methods are available. For our example, we use the correction by adding mass (Weight ++) on the op-posite of the unbalance.

In case of having a technological limit, enter the maximum mass. When balancing with fixed posi-tions, the InnoBalancer allocates the total mass to different fixed positions, so that the maximum mass is exceeded at no position.

The polar chart displays position and amount of the mass to added, provided the unbalance exceeds the entered tolerance. If the unbalance is within the tol-erance circle, no correction method is indicated. The tolerance can be adjusted in the rotor characteristics. When balancing propellers, 5 gram on the baseplate of the spinner (radius approx. 100 mm) can be con-sidered as a realistic result. In case of having good measurement conditions, results of below 1 gram can be achieved.

When mounting the counterweight, the calibration mass is to be removed. The position for the counter-weight is to be counted from the zero angle against the rotary direction.

Correction

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10 gram calibration mass are still mounted The calibration mass was removed, the correction mass was mounted in the indicated angle against the rotary direction.

4.8. Control run

After correction, the unbalance is to be measured again. The procedure is the same again. The propeller is put into rotation with a constant rotation speed, in fact the tion speed of the initial unbalance run. The InnoBalancer recognizes the constant rota-tion speed, carries out the measurement and asks you to stop the propeller.

The indicated unbalance should be considerably reduced now. By means of further cor-rections, a further correction of the unbalance can be achieved step by step.

To make sure that the measurement conditions allow a further unbalance correction, a control run can be carried out two or three times without adding correction masses. If the indicated unbalance has a similar amount and position in all measuring runs, a fur-ther correction is possible. If the result varies, no improvements can be expected from a further correction.

Balancing with VibroMatrix

IDS Innomic

Gesellschaft für Computer- und Messtechnik mbH

Balancing

Contents

1. Introduction

2. Some basics

3. Balancing with VibroMatrix

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4. Balancing propellers

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