ofv534_0907_07e

Title

User Manual

Fiber-coupled VibrometerSensor Head

OFV-534

Warranty and Service

The warranty for this equipment complies with the regulations in our general terms and conditions in their respective valid version.

This is conditional on the equipment being used as it is intended and as described in this manual.

The warranty does not apply to damage caused by incorrect usage, external mechanical influences or by not keeping to the operating conditions. The warranty also is invalidated in the case of the equipment being tampered with or modified without authorization.

To return the equipment always use the original packaging. Otherwise we reserve the right to check the equipment for transport damage. Please mark the package as fragile and sensitive to frost. Include an explanation of the reason for returning it as well as an exact description of the fault. You can find advice on fault diagnosis in CHAPTER 6.

Trademarks

Brand and product names mentioned in this manual could be trademarks or registered trademarks of their respective companies or organizations.

Identification Labels

Sensor Head

41252-Man-Vib-OFV534-0907-07e

Contents

Contents

1 Safety Information 1-11.1 General Safety Information ................................................................................................. 1-11.2 Information on Laser Safety ................................................................................................ 1-2

1.2.1 Safety Information ..................................................................................................... 1-21.2.2 Safety Precautions .................................................................................................... 1-31.2.3 Laser Warning Labels ............................................................................................... 1-3

1.3 Information on Electrical Safety .......................................................................................... 1-41.3.1 Safety Information ..................................................................................................... 1-41.3.2 Safety Precautions .................................................................................................... 1-5

2 Introduction 2-12.1 Area of Application.............................................................................................................. 2-12.2 Operating Principle ............................................................................................................. 2-1

3 First Steps 3-13.1 Unpacking and Inspection ................................................................................................... 3-13.2 Operating and Maintenance Requirements ......................................................................... 3-23.3 Control Elements ................................................................................................................ 3-3

3.3.1 Laser Unit ................................................................................................................. 3-33.3.2 Sensor ...................................................................................................................... 3-5

3.4 Installation .......................................................................................................................... 3-7

4 Setting up the Optimal Stand-off Distance 4-14.1 Coherency between Stand-off Distance and Visibility Maximum .......................................... 4-14.2 Stand-off Distances ............................................................................................................. 4-2

5 Operating the Sensor Head 5-15.1 Switching On and Off .......................................................................................................... 5-15.2 Blocking the Laser Beam .................................................................................................... 5-15.3 Indicating Laser Activity ...................................................................................................... 5-15.4 Focusing the Laser Beam (only Standard Sensor) .............................................................. 5-25.5 Locking the Focus Position (only Standard Sensor) ............................................................ 5-25.6 Using the Signal Level Display............................................................................................ 5-35.7 Using a Microscope Lens (only Standard Sensor) ............................................................... 5-35.8 Transfer the Video Signal (optional) .................................................................................... 5-3

6 Fault Diagnosis 6-16.1 No Laser Beam ................................................................................................................... 6-16.2 No Measurement Signal...................................................................................................... 6-2

i

Contents

7 Technical Specifications 7-17.1 Standards Applied ...............................................................................................................7-17.2 General Data .......................................................................................................................7-17.3 Optics ..................................................................................................................................7-37.4 Dimensions..........................................................................................................................7-5

7.4.1 Laser Unit ..................................................................................................................7-57.4.2 Sensor .......................................................................................................................7-7

7.5 Video Camera (optional) ......................................................................................................7-9

Appendix A: Basics of the Measurement Procedure

Index

ii

1 Safety Information


1.1 General Safety Information

Notes Please read this manual before using the instrument. It will provide you with important information on using the instrument and on safety. This will protect you and prevent damage to the instrument. Pay particular attention to the basic safety information in CHAPTER 1 and the information on installation, operation and maintenance in CHAPTER 3.

Please keep this manual in a safe place and make it available to people using the instrument. Never pass the instrument on without the manual.

In this manual the following graded safety and warning labels are used:

Intended use The instrument is intended for laboratory use and for use in an industrial environment. It may only be used within the limits given in the technical specifications (refer to CHAPTER 7).

Faultless and safe operation of the instrument depends on correct and proper transport and storage, installation and assembly as well as careful operation of the instrument.

When assembling, installing and operating the instrument, the safety and accident-prevention regulations for the respective use must be adhered to.

Qualification This instrument may only be operated by persons who are familiar with electrical measurement equipment and have been instructed in the use of lasers. Please pay attention to the information on laser safety in SECTION 1.2.

Intervention for maintenance and repair work may only be carried out by the manufacturer himself or by qualified personnel authorized by the manufacturer.

Disposal An instrument which is no longer required must be disposed of according to local regulations unless otherwise provided for by the manufacturer.

NOTE!

Identifies action required to simplify using the instrument !

CAUTION!

Danger from "Reason for Danger" ! - Identifies the danger caused by an action which could result in damage to the instrument if it is not avoided !

WARNING!

Danger from "Reason for Danger"! - Identifies a possible danger resulting from an action which could lead to death or (serious) injury if it is not avoided !

1-1


1.2 Information on Laser Safety

1.2.1 Safety Information

The light source of the instrument is a helium neon laser. It is important to understand that laser light has different properties from ordinary light sources. Laser light is generally extremely intense due to the beam's low divergence. When handling lasers, great care should be taken in any case to make sure that the direct or reflected beam does not enter the eye.

The protective measures taken described in the following support compliance with the safety standards for laser class 2:

• Polytec instruments generally comply with the standards IEC and EN 60825-1, and US 21 CFR 1040.10 and 1040.11 respectively except for deviations pursuant to Laser Notice no. 50, dated 26 July 2001.

• The optical output power of the laser beam emitted from the sensor is less than 1mW provided the equipment is used in the manner for which it was intended. This means that the instrument conforms with laser class 2 and is generally very safe. It is thereby usually assumed that eyes are protected by prevention mechanisms including the blink reflex. This reaction offers appropriate protection under reasonably foreseeable operating conditions. This includes the use of optical instruments for observing the laser beam. Even when optimally focused, the laser beam is not intense enough to harm the skin.

• The sensor is equipped with a beam shutter to block the laser beam during the warm-up phase, or when the vibrometer is not in use, although switched on.

• An emission indicator on the laser unit indicates the activity of the installed laser and thus the potential hazard of laser beams emitted.

• The laser is switched on using the key switch or mains switch on the controller. The key can only be removed if the controller and therefore also the laser is switched off.

• The user should not attempt to open the housing of the instrument which contains the laser unit as he could be exposed to a higher level of laser energy that is potentially hazardous.

NOTE!

Please see CHAPTER 7 for the detailed technical specifications !

WARNING!

Danger from uncontrolled light emission! - Use of controls or adjustments or performance of procedures other than those specified herein may result in

hazardous radiation exposure.

1-2


1.2.2 Safety Precautions

Pay attention to the following safety precautions when using the instrument:

• Only qualified and fully trained persons should be entrusted with setting up the instrument, adjusting and operating it !

• Avoid looking directly into the laser beam with the naked eye or with the aid of mirrors or optical instruments ! It can be dangerous to look directly into the laser beam for any length of time.

• Never intentionally direct the laser beam at anyone!

• Only open the beam shutter when making measurements !• To position the sensor, always close the beam shutter. The beam shutter

should not be opened until the sensor has been roughly aligned and mounted securely !

• The laser beam should be terminated at the end of its intended path where this is practically possible.

• Instruments which are not in use should be stored in places which unauthorized persons do not have access to.

1.2.3 Laser Warning Labels

Warning labels The laser warning labels for the sensor are shown in FIGURE 1.1. For the countries in the European Union (EU), label 2 is affixed in the language of the customer's country (see right-hand-side).

NOTE!

Wear suitable laser protection glasses when you have to look at the target area of the laser beam long and hard to set it up !

WARNING!

Danger from laser light ! - Do not use any reflective tools, watches etc. when you are working in the beam path of the laser !

Figure 1.1: Laser warning labels for the sensor

Laserstrahlung

Nicht in den Strahl blicken

Laser Klasse 2

Nach EN 60825-1 (2001)

P 1 mW/cw; = 620-700 nm� �

Laser RadiationDo not stare into beamClass 2 Laser Product

According to IEC/EN 60825-1 (2001)Complies with 21 CFR 1040.10 and 1040.11

except for deviations pursuant toLaser Notice no. 50, dated 26 July 2001

P 1 mW/cw; = 620-700 nm� �

1

2

1-3


Position The position of the laser warning labels on the sensor is shown in FIGURE 1.2.

The position of the laser warning labels on the sensor with telephoto lens is shown in FIGURE 1.3.

1.3 Information on Electrical Safety

1.3.1 Safety Information

The instrument complies with the electrical protection class 1 in accordance with the EU directive 2006 /95 /EC (low voltage directive). With correct mains connection and intended use, exposure to electric current is prevented by the closed, grounded metal housing.

The instrument complies with the EU directive 2004 /108/EC (EMC directive) and is accordingly fail-safe (refer to SECTION 7.1).

Figure 1.2: Position of the laser warning labels on the sensor

Figure 1.3: Position of the laser warning labels on the sensor with telephoto lens

12

Beam

Beam

12

NOTE!

Please note that the information on electrical safety and EMV mentioned here, only applies to controllers permitted by Polytec. You will find the

corresponding declaration of conformity in the user manual of the controller.

1-4


1.3.2 Safety Precautions

Pay attention to the following safety precautions when using the instrument:

• The controller is only to be connected up using a three-pin mains cable to AC systems 50/60Hz with a grounded protective conductor with a nominal voltage of between 100V and 240V.

• Defective mains fuses in the controller may only be replaced by fuses of the same kind with the rating given on the back of the instrument.

• If the mains switch or key switch on the controller is not freely accessible, use the mains plug to disconnect the device in case of danger. This means that the mains plug needs to be freely accessible. Otherwise an additional disconnection device must be installed.

• The housing may not be opened when using the instrument as intended. Opening the housing will invalidate the warranty. None of the equipment may be operated with opened housing.

• Air inlets and outlets must always be kept free to ensure sufficient cooling. If you notice that the cooling fan in the controller is not working, immediately switch the instrument off.

NOTE!

Before removing parts of the housing for servicing purposes for installation and servicing purposes, as a general rule the mains plug should always be

unplugged.

WARNING!

Danger from electrical current ! - Intervention for maintenance and repair work may only be carried out by the manufacturer himself or by qualified

personnel authorized by the manufacturer.

CAUTION!

Danger from heat accumulation! - If you mount the controller into a switching cabinet, pay attention that the air inlets in the bottom plate must

always be kept free !

1-5


1-6

2 Introduction

2 Introduction

2.1 Area of Application

The fiber-coupled sensor head OFV-534 is suitable for a wide range of stand-off distances. Even almost inaccessible measurement points can be reached by using the flexible and slim optical fiber cable. An integrated video camera can optionally be used for online monitoring of the measurement volume. In addition, a microscope lens can be fitted directly onto the sensor head which makes it possible to measure vibration on microstructures.

You can use the sensor head with all following vibrometer controllers:

• OFV-5000 (as of firmware version 2.03)• OFV-2500 (as of firmware version 1.4)• OFV-2570 (as of firmware version 1.1)• VDD-E-600 (as of firmware version 1.2)

2.2 Operating Principle

The laser vibrometer uses the principle of the heterodyne interferometer to acquire the characteristics of mechanical vibrations or transient motion processes. With this type of interferometer, a high-frequency carrier signal is generated on the photo detector with the aid of a Bragg cell. To make the vibration measurement, the beam of a helium neon laser is pointed at the vibrating object and scattered back from it. Velocity and displacement amplitude of a vibrating object respectively generate a frequency or phase modulation of the laser light due to the Doppler effect. This modulation is recovered in the signal processing unit with the aid of suitable demodulators (or decoders).

NOTE!

You can use the sensor head also with other controllers (center frequency 40MHz), e.g. OFV-2510 or OFV-2502, however with the limitation, that the

signal level display on the sensor head does not work.

2-1

2 Introduction

The velocity information is recovered from the frequency modulation of the Doppler signal, while the displacement signal can be reconstructed from the phase modulation available at the same time. A schematic layout of both signal paths is shown as a diagram in FIGURE 2.1.

Figure 2.1: Signals in the vibrometer

Sensor head

�

U

��

U

v(t)

x(t)

Object

x(t)v(t)=dx/dt

f�

�, �

f

Velocitydecoder

Dopple

rsig

nal

Displacementdecoder (optional)

2-2

3 First Steps

3 First Steps

3.1 Unpacking and Inspection

Unpacking The fiber-coupled vibrometer sensor head is made up of the following components:

• Standard sensor (or sensor with telephoto lens) with laser unit

• Connecting cable from the controller to the laser unit (length 5m)

Optional:

• Video camera (built-in the sensor) with video cable• Microscope lenses

Inspection Please pay attention to the following steps when unpacking:

1. Check the packaging for signs of unsuitable handling during transport.

2. After unpacking, check the sensor head for external damage (scratches, loose screws, damaged lenses etc.).

3. In the case of a wrong delivery, damage or missing parts, please inform your local Polytec representative immediately and give them the serial number of the sensor head. The identification label can be found on the back of the laser unit and also on the inside cover of this manual.

4. Carefully retain the original packaging in case you have to return the instrument.

NOTE!

You receive a standard sensor or optional a sensor with telephoto lens. It is not necessary to open the housing of the sensor when using the equipment as intended and will invalidate the warranty. Exchanging objectives may only be

carried out by authorized service personnel of Polytec.

CAUTION!

Danger from hard jolting! - Protect the unpacked sensor head from being shaken as this can lead to the interferometer becoming misaligned !

CAUTION!

Danger from scratching! - Handle the front lens with great care! Dirt may only be removed carefully using a soft, dry cloth, an optics brush and bellows !

3-1

3 First Steps

Install the vibrometer and carry out a first functional test as described in the controller manual.

3.2 Operating and Maintenance Requirements

Ambient conditions

The vibrometer can be operated in dry rooms under normal climatic conditions (refer to the specifications in CHAPTER 7). In particular the optical components in the sensor head are sensitive towards moisture, high temperatures, shocks and dirt.

If the vibrometer is taken into operation after being stored in a cold environment, a sufficient acclimatization period should be allowed before switching it on. Avoid condensation on the optical components caused by a rapid change in temperature.

Assembly The sensor should not be set up provisionally, but mounted with the fixing screw thread on an optional adapter plate or a stable tripod. The laser unit can be mounted on an optional adapter plate.

Cooling It is very important to ensure that there is sufficient air circulation to cool the sensor.

Connecting cable

As a general rule, the vibrometer may not be switched on until all connecting cables have been connected up. Make sure that all connectors are connected properly and firmly.

Warming-up The helium neon laser in the sensor will take a little while to reach the optimal operating temperature after it has been switched on. The vibrometer therefore reaches its optimal properties after a warm-up period of approx. 20 minutes. After that you can be sure that all components are working properly in accordance with the specifications. Less accurate measurements, such as to align the vibrometer for example, can however be carried out with usefully results before this warm-up period has expired.

NOTE!

You can use the sensor head only with certain vibrometer controllers (refer to SECTION 2.1).

NOTE!

Before you mount the laser unit on an optional adapter plate, remove the rubber feet at the bottom side!

CAUTION!

Danger from mishandling! - Protect all connecting cables from mechanical damage and from high temperatures. - The bending radius of the fiber-optic

connecting cable should not fall below 54mm.

3-2

3 First Steps

Cleaning The housing surface of the sensor head can be cleaned with mild detergent or disinfectant solutions. Organic solvents must not be used.

Optical components

Handle all optical components with great care. Dirt may only be removed carefully using a soft, dry cloth, an optics brush and bellows!

Opening the instruments

Opening up of the equipment without authorization is not necessary for its operation and will invalidate the warranty.

3.3 Control Elements

3.3.1 Laser Unit

Front panel The front panel of the laser unit for the sensor head OFV-534 is shown in FIGURE 3.1.

1 EMISSION LED The LED lights up when the beam shutter key LASER is pressed thus emitting the laser beam. At the same time the LED STANDBY goes off. If the beam shutter key LASER is pressed a second time, the beam shutter is closed, the LED EMISSION goes off and the LED STANDBY lights up again.

2 STANDBY LED

The LED lights up when the controller is switched on. This shows that the laser is on. However the laser beam is not yet emitted as the beam shutter is still closed (LED EMISSION is off). The LED STANDBY goes off if the beam shutter key LASER is pressed and thus the laser beam is emitted (LED EMISSION is then on).

Figure 3.1: Front view of the laser unit for the sensor head OFV-534

EMISSION

STANDBY

LASER

OFV 534LASER UNIT

1

2

3

3-3

3 First Steps

3 LASER key for the beam shutterThe beam shutter is opened by pressing the key and is closed again by pressing it a second time (refer to SECTION 5.2).

Back panel The back panel of the laser unit for the sensor head OFV-534 is shown in FIGURE 3.2.

1 VIDEO output (BNC jack)connection for the video cable to the PC or monitor for the transmission of the video signal

2 CONTROLLER connection (Sub-D jack)Connector for the connecting cable to the controller

3 Fiber-optic connecting cable to the sensor

WARNING!

Danger from laser light ! - Only open the beam shutter when you are making measurements !

NOTE!

The beam shutter is automatically closed when the controller is switched on.

Figure 3.2: Back view of the laser unit for the sensor head OFV-534

3

1

2

Manufactured by:

GmbH

D-76337 Waldbronn, Germany

Model No.:

Serial No.:

Mfg.-Date:

OFV 534

x xx xxxx

mm.yyyy

4

CAUTION!

Danger from mishandling! - Protect all connecting cables from mechanical damage and from high temperatures. The bending radius of the fiber-optic

connecting cable should not fall below 54mm.

3-4

3 First Steps

4 Identification labelOn the identification label you will find, among other things, the serial number of the instrument.

3.3.2 Sensor

Standard The views of the sensor are shown in FIGURE 3.3.

1 Protective cap for the front lensRemove the protective cap to make measurements.

2 Focusing ring on the front lensRing to focus the laser beam (refer to SECTION 5.4)

3 Clamping screw to fix the focus positionUse this screw to fix the focus position after focusing the laser beam.

4 Signal level displayThe length of the bar is a measure of the amount of light scattered back from the surface to be measured.

NOTE!



Figure 3.3: Views of the sensor

1 2 3

4 5

3-5

3 First Steps

5 Fiber-optic connecting cable to the laser unit

With telephoto lens

The top view of the sensor with telephoto lens is shown in FIGURE 3.4.

1 Signal level displayThe length of the bar is a measure of the amount of light scattered back from the surface to be measured.

2 Fiber-optic connecting cable to the laser unit

CAUTION!

Danger from mishandling! - The bending radius of the fiber-optic connecting cable should not fall below 54mm.

NOTE!



Figure 3.4: Top view of the sensor with telephoto lens

1 2

CAUTION!

Danger from mishandling! - The bending radius of the fiber-optic connecting cable should not fall below 54mm.

3-6

3 First Steps

3.4 Installation

To install the sensor head, please proceed as follows:

Preparing 1. Ensure, that the key switch and respectively the mains switch on the controller is on position O.

2. If applicable for your controller, check the setting on the mains voltage selector as well as the fuses on the back of the controller.

Cabling 3. Plug the connecting cable of the laser unit into the Sub-D jack CONTROLLER on the back of the controller and into the corresponding Sub-D jack on the back of the sensor. Secure all the connections with the screws provided.All connections must be easy to plug in. If not, check the plugs for bent contact pins to avoid serious damage being incurred.

4. Use the mains cable to connect up the controller to an earthed socket.

Now carry out a first functional test as described in the user manual of the controller.

NOTE!

You can use the sensor head only with certain vibrometer controllers (refer to SECTION 2.1).

3-7

3 First Steps

3-8

4 Setting up the Optimal Stand-off Distance


4.1 Coherency between Stand-off Distance and Visibility Maximum

Visibility maxima

The light source of the vibrometer is a helium neon laser. This is a multimode laser in which, depending on the laser cavity length, one or a maximum of two modes can exist. The laser cavity length can vary caused by small changes in temperature. Thus the laser changes between the status of having one or two modes. If two modes exist, interference effects cause the intensity of the resulting optical signal varying periodically with the stand-off distance.

The diagram in FIGURE 4.1 shows the signal level depending on the stand-off distance. In the special case of having two modes with equal magnitude (black line), you have the strongest loss of signal level if the object is located inside a visibility minimum. But generally there are two modes of different magnitudes. In this case the signal level is hardly fluctuating (grey line). If only one mode exists, the signal level is always maximum, independent from the stand-off distance (dashed grey line).

The stand-off distances at which the signal level is maximal are called visibility maxima. The visibility maxima recur every 204mm (±1mm) corresponding to the laser cavity length.

Generally it is not necessary to search for the visibility maximum as the vibrometer is sensitive enough to make a measurement even close to the minimum. A visibility minimum is indicated during the warm-up phase by periodic fluctuation of the optical signal level. If you need an optimal resolution and sensitivity, you should select a stand-off distance close to the visibility maximum. As a rule of thumb it can be said, that the resolution and the sensitivity just degrades insignificantly in the range of ±90mm around the visibility maximum.

4-1


Stand-off distance sensor

The stand-off distance is measured from the front edge of the sensor housing (refer to FIGURE 4.1).

4.2 Stand-off Distances

Standard sensor The optimal stand-off distances for the sensor are shown in FIGURE 4.2.

Figure 4.1: Measuring the stand-off distance with standard objective

Sig

na

lle

ve

l

Stand-off distance

Visibility maximumVisibility minimum

2 modes with equal magnitude

2 modes with different magnitude

1 mode

Stand-off distance

Object

Laser beam

Figure 4.2: Optimal stand-off distance

Sig

na

lle

ve

l

Stand-off distance in mm

91 295 499 ... +204

2 modes with equal magnitude

2 modes with different magnitude

1 mode

Visibility minimum Visibility maximum

4-2


The visibility maxima for the sensor are at:

Positions of the visibility maxima = 91mm + (n · l)mm

With telephoto lens

The stand-off distance for the sensor with telephoto lens is 502mm and is measured from the front edge of the sensor housing (refer to FIGURE 4.3).

n = 0; 1; 2; ... l = 204mm±1mm

i.e. for l = 204mm the optimal stand-off distances are:91 mm; 295 mm; 499 mm etc., refer also to SECTION 7.3 and SECTION 7.4.

NOTE!

You can reach the stand-off distance of 91mm only with a microscope lens.

Figure 4.3: Measuring the stand-off distance with telephoto lens

Laser beam

Stand-off distance

Object

Working distance

4-3


4-4

5 Operating the Sensor Head


5.1 Switching On and Off

You switch the vibrometer and thus also the laser on by pressing the key switch on the front panel of the controller to position I and respectively the mains switch on the back panel of the controller to position I.

On the front of the controller a LED or display lights up and shows that the controller is ready to operate. If the connecting cable from the controller to the sensor is installed correctly, also the LED STANDBY at the front panel of the laser unit lights up and shows that the sensor is ready and the laser is active, even if the beam shutter is closed (refer to SECTION 5.2).

5.2 Blocking the Laser Beam

The sensor is equipped with a beam shutter. This can be used to block the laser beam without switching off the laser. This keeps the system in a thermal equilibrium.

The key for the beam shutter is on the front of the laser unit and is labeled LASER. After switching the controller on, the beam shutter is automatically closed. You open the beam shutter by pressing the LASER key. You close the beam shutter again by pressing the LASER key a second time.

5.3 Indicating Laser Activity

On the front panel of the laser unit you will find the LEDs STANDBY and EMISSION, which show whether the laser is active. The LED STANDBY lights up, if the laser is switched on (mains switch on the back of the laser unit in position I) and the beam shutter is closed. The LED shows that the laser is working but no laser beam is emitted. The LED EMISSION lights up as soon as the beam shutter is opened (LASER key is pressed) and shows that the laser beam is emitted.

NOTE!

Remember, that the vibrometer reaches its optimal properties after a warm-up period of the laser of approx. 20 minutes.

WARNING!

Danger from laser light ! - Only open the beam shutter when you are making measurements !

WARNING!

Danger from laser light ! - To position the sensor, always close the beam shutter. Only open the beam shutter once the sensor has been roughly

aligned and mounted securely, if applicable on an adapter plate!

5-1


5.4 Focusing the Laser Beam (only Standard Sensor)

To get the highest possible quality of the measurement signal, the laser beam has to be optimally focused. The laser beam is optimally focused when the diameter of the laser spot on the object is as small as possible. Due to overload effects on the target area, it is often difficult to ascertain when the smallest diameter has been reached. For this reason you can view the signal level display either on the sensor. The more signal level is shown, the better the focus of the laser beam.

As the actual aim of focusing is to minimize the undesired noise signals, you can also orientate yourself directly towards the output signal from the controller when focusing. Observe the output signal e.g. on an oscilloscope while focusing the laser beam on the object under investigation. The better the focus of the laser beam, the smaller the amplitude of the noise. See the user manual of the controller on this.

You can focus the laser beam, by rotating the focusing ring at the sensor.

When you are looking into the direction of the emitted laser beam, the following applies:

5.5 Locking the Focus Position (only Standard Sensor)

The laser beam can at any time be focused manually directly using the focusing ring on the sensor. The focus position can be locked at the sensor. This stops you unintentionally defocusing the laser beam.

To lock the focusing position, hand-tighten the clamping screw on the sensor clockwise (refer to FIGURE 3.3).

WARNING!

Danger from laser light ! - Avoid looking directly into the laser beam with the naked eye or with the aid of mirrors or optical instruments !

• To focus on infinity: Turn clockwise (to the right)• To focus close-up: Turn counterclockwise (to the left)

NOTE!

Hand-tight means: Tighten the screw firmly that it can not loosen itself. Do not use any excessive force and avoid serious damage the thread.

5-2


5.6 Using the Signal Level Display

The signal level display helps you to optimize the focus of the laser beam. The signal level is shown as a bar display on the sensor.

5.7 Using a Microscope Lens (only Standard Sensor)

By using different microscope lenses for the sensor the vibrometer can be optimally adapted to different areas of stand-off distances and different requirements to the depth of field for vibration measurements on microstructures.

Suitable objectives

You can use following microscope lenses:

• 10x microscope lens VIB-A-10xLENS (working distance 37.3mm)• 20x microscope lens VIB-A-20xLENS (working distance 21.7mm)

Mount the objective

To mount the microscope lens, proceed as follows:

1. When you look into the direction of the emitted laser beam, turn the focusing ring on the sensor clockwise until the laser beam is collimate. Alternative you can also focus an far off object sharply with the objective when you watch the camera image.

2. Tighten the clamping screw on the sensor hand-tight.

3. Carefully screw the microscope lens on the focusing ring.

5.8 Transfer the Video Signal (optional)

If the sensor is equipped with the optional video camera, you can add a video cable at the back panel of the laser unit to transfer the video signal to a monitor or a computer (VIDEO IN).

NOTE!

Hand-tight means: Tighten the screw firmly that it can not loosen itself. Do not use any excessive force and avoid serious damage of thread.

NOTE!

Make sure, that the focusing ring on the sensor does not move during assem-bly, because otherwise the focus position will be changed.

5-3


5-4

6 Fault Diagnosis

6 Fault Diagnosis

Simple tests are described in the following for you to carry out yourself in the case of malfunction. In the case of more difficult problems with the individual functions, please contact our service personnel. The tests described here are not meant to lead you to carry out maintenance work yourself, but to provide our service personnel with information which is as accurate as possible.

Checking the vibrometer is limited to such tests in which the housing does not have to be opened. Opening the housing without authorization will invalidate the warranty.

If required, please contact our service department. Based on your fault description, further procedure will be determined.

If the vibrometer has to be sent back for repair, always use the original packaging and enclose an exact description of the fault.

Please use the corresponding checklist in the user manual of your controller if you contact Polytec or your nearest representative.

6.1 No Laser Beam

If no laser beam is emitted, please check the following:

1. Has the connecting cable between the controller and the sensor head been installed correctly?

2. Have the plugs on the connecting cable been screwed in?

3. Does the LED STANDBY on the front of the laser unit light up after the controller has been switched on?

If the LED is not lit up, it can be assumed that there is a fault in the mains supply of the controller. Disconnect the mains plug and check the fuses on the back of the controller. Please note that there are two active fuses which can both lead to failure.

WARNING!

Danger from electrical current ! - Working on an open housing can lead to personal injury !

NOTE!

Before checking the fuses, as a general rule the mains plug must be disconnected !

6-1

6 Fault Diagnosis

4. Has the beam shutter key LASER on the front of the laser unit been pressed once after switching the controller on?The LED EMISSION lights up if the beam shutter key LASER has been pressed once, thus emitting the laser beam. At the same time the LED STANDBY goes off. If the beam shutter key LASER is pressed a second time, the beam shutter is closed, at the same time the LED EMISSION goes off and the LED STANDBY then lights up again.

5. Can you assume a break in the fiber-optic connecting cable?If so, contact the next representative of Polytec.

6.2 No Measurement Signal

If the laser beam is emitted but there is no measurement signal, please check the following:

1. Put reflective film in the beam path according to the information on optimal stand-off distances given in CHAPTER 4.

2. Focus the laser beam on the reflective film. Does the signal level display light up?If the signal level display does not light up, then the input section of the controller is faulty or the controller is unsuitable for the sensor head (refer to SECTION 2.1).

If the malfunction can not be sorted through the tests described above, then proceed with the fault diagnosis as described in the user manual of your controller.

6-2

7 Technical Specifications


7.1 Standards Applied

7.2 General Data

Laser

Ambient Conditions

Electrical Data

Laser safety: IEC/EN60825-1:2003-10(Safety of Laser Products, complies to US 21 CFR 1040.10 and 1040.11, except for deviations pursuant to Laser Notice no. 50, dated 26 July 2001)

Electrical safety: IEC/EN 61010-1:2002-08(Safety requirements for electrical equipment for measurement, control and laboratory use)

EMC: IEC/EN 61326-1:2006-10 (EMC requirements on Emission and Immunity - Electrical equipment for measurement, control and laboratory use)Emission: FCC Class B

IEC/EN 61000-3-2 and 61000-3-3Immunity: IEC/EN 61000-4-2 to 61000-4-6

and IEC/EN 61000-4-11

NOTE!

The standards about electrical safety and EMC above are only valid with from Polytec licensed controllers. You will find the corresponding declaration of

conformity in the user manual of the controller.

Laser type: helium neonWavelength: 633nmCavity length: 204mm ±1mmLaser class: 2Laser power: < 1mW

Operating temperature: +5°C...+40°C (41°F...104°F)Storage temperature: −10°C...+65°C (14°F...149°F)Relative humidity: max. 80%, non-condensing

Power consumption: approx. 15WCarrier frequency: 40MHz

7-1


Housing Laser Unit

Housing Sensor

Standard sensor

Sensor with telephoto lens

Vibration Reliability Tested According to EN 60068-2-6 (IEC 68-2-6)

Shock Reliability Tested According to EN 60068-2-29 (IEC 68-2-29)

Dimensions (without cable): refer to SECTION 7.4.1 Weight: 4.2 kgLength of the fiber cable: 3 mMinimal bending radius: 54mmProtection rating: IP50

Dimensions: refer to FIGURE 7.4 Weight: 1 kgProtection rating: IP64

Dimensions: refer to FIGURE 7.5 Weight: 1.5kgProtection rating: IP64

CAUTION!

Danger from water penetration! - Please note, that the sensor head does not comply with the protection rating mentioned above, if water is retained on

the lens.

ConditionsFrequency range: 10...150HzAcceleration amplitude (peak): 20m/s2

Frequency cycle: 1 octave/minTesting direction: 3 axesNumber of frequency cycles: 20 per axis

ConditionsNumber of shocks per direction:

1000

Maximum acceleration: 100m/s2

Shock duration: 16msTesting direction: 6 directions

7-2


7.3 Optics

Standard Characteristics

Stand-off distance1

mm

1 Measured from the front edge of the sensor housing without microscope lens (refer to SECTION 7.4.2)

Spot diameter (1/e2)µm

Depth of fieldmm

200 25 ±1300 40 ±3400 56 ±5500 70 ±10600 86 ±14700 102 ±20800 118 ±25900 132 ±33

1000 148 ±401500 224 ±952000 302 ±170

For larger distances

Minimum stand-off distance: 200mm

Aperture diameter (1/e2): 6.2mm ...5.2mm (depending of the stand-off distance)

Spot diameterwith 10x microscope lens: 3.0µm (with 37.3mm working distance)Spot diameterwith 20x microscope lens: 1.5µm (with 21.7mm working distance)Visibility maxima: 91mm+n · (204mm ± 1mm), n=0; 1; 2;...

measured from the front edge of the sensor housing (refer to FIGURE 4.2).

Stand-off distance [m] 150μm⋅1m

---------------------------------------------------------------------------------- Stand-off distance [mm]2

25000mm------------------------------------------------------------------±

NOTE!

You can reach the stand-off distance of 91 mm only with an microscope lens.

7-3


Table of the Visibility Maxima

With telephoto lens

Figure 7.1: Spot diameter plotted over the stand-off distance

Visibility maxima (in mm) for l = 204mm 91 1111 2131 3151 4171 5191

295 1315 2335 3355 4375 5395499 1519 2559 3559 4579 5599703 1723 2743 3763 4783 5803907 1927 2947 3967 4987 6007

2000 400 600 800 1000

20

40

60

80

100

120

140

160

0

Stand-off distance [mm]

Spotsiz

e(1

/e)

[m

]2

�

Working distance: 320mm

Aperture diameter (1/e2): 30mm

Spot diameter: 15µmDepth of field: ± 80µmStand-off distance: 502mm

7-4


7.4 Dimensions

7.4.1 Laser Unit

With Rubber Feet

Figure 7.2: Views of the laser unit (dimensions in mm)

VID

EO C

ON

TR

OL

LE

R

EM

ISS

ION

STA

ND

BY

LA

SE

R

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45.50

82.50

20

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154

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27

2.8

0

38

0.6

0

32

1.4

0

64

Ap

pro

x.

80

mm

exp

an

sio

nsp

ace

for

ca

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7-5


With Adapter Plate (optional)

Figure 7.3: Views of the laser unit with adapter plate (dimensions in mm)

EM

ISS

ION

STA

ND

BY

LA

SE

R

OF

V534

LA

SE

RU

NIT

125

20

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30

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1.2

6.40A

pp

rox.

80

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exp

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7-6


7.4.2 Sensor

Standard

Figure 7.4: Views of the sensor (dimensions in mm)

Beam�

30

39

70

.15

26.50133.50

Stand-off distance

201

30 30

37.05

2

4.0

2

16

.50

1/4” 20UNC (9 deep)

6

40

30 30

42.50 42.50

56.50

1/4” 20UNC (12 deep)

2 x M6 (4.5 deep)

26

.50

4.0

2

2

approx. 100 mmexpansion spacefor cable

� 4 (5 deep)F7

� 4 (3 deep)F7

1

41

7-7


With telephoto lens

Figure 7.5: Views of the sensor with telephoto lens (dimensions in mm)

� 59

33

2

26

.50

13

3.5

0

6

40

30

30

42

.50

42

.50

56

.50

1/4” 20UNC (12 deep)

2 x M6 (4.5 deep)

�4

2

ap

pro

x.

10

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me

xp

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F7

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�4

(3d

ee

p)

F7

17

6

24

� 37

1

83.65

40

38

.5

68

7-8


7.5 Video Camera (optional)

Standard

With telephoto lens

Type: CCD color cameraVideo system: NTSC/PALSensor size: 1/4"Active pixels (HxV): 510 x 492Signal-to-noise ratio: >48dBLens aperture: F/4.5; (F/8 telephoto lens)Horizontal resolution: ≥ 330 TV linesShutter speed: Automatic from 1 /60 to 1 /100 000Video output: Composite (CVBS), 1Vp-p /75Ω

Minimum illumination: 0.5 luxVideo cable: 1 x BNC plug, 1 x cinch plug; length: approx. 1m

Stand-off distance1

mm

1 Measured from the front edge of the sensor housing (refer to SECTION 7.4.2)

Field of viewmm x mm

200 10 x 8300 17 x 13500 31 x 24

1000 64 x 492000 130 x 1005000 333 x 257

with 10x microscope lens 1.36 x 1.04with 20x microscope lens 0.68 x 0.52

Working distance: 320mmField of view: 3.8 mm x 2.9mm

7-9


7-10

A Basics of the Measurement Procedure

Appendix A: Basics of the Measurement Procedure

A.1 Theory of Interferometric Velocity and Displacement Acquisition

Optical interference can be observed when two coherent light beams are made to coincide. The resulting intensity e.g. on a photo detector varies with the phase difference ϕ between the two beams according to the equation

. Equation A.1

The phase difference ϕ is a function of the optical path difference L between the two beams according to

, Equation A.2

whereby λ is the laser wavelength.

If one of the two beams is scattered back from a moving object (the object beam), the path difference becomes a function of time L = L (t). The interference fringe pattern moves on the detector and the displacement of the object can be determined using directionally sensitive counting of the passing fringe pattern.

The velocity component in the direction of the object beam is a function of the path difference L according to

. Equation A.3

For a constant movement v

Equation A.4

applies with

. Equation A.5

Thus a constant movement of the object causes a frequency shift at the object beam which is called Doppler shift fD. Superimposing object beam and internal reference beam, i.e. two electromagnetic waves with slightly different frequencies, generates a beat frequency at the detector which is equal to the Doppler shift. The ratio A.5 to determine the velocity is, however, independent of its sign. The direction of the velocity can be determined by introducing an additional fixed frequency shift fB in the interferometer to which the Doppler shift is added with the correct sign.

l ϕ( )lmax

2--------- 1 ϕcos )+(⋅=

ϕ 2π Lλ---⋅=

dL t( )dt

------------- v t( ) 2⋅=

dL t( )dt

-------------λ

2π------ dϕ

dt-------⋅ fD λ⋅ v 2⋅= = =

fD 2 vλ-----⋅=

A-1

A Basics of the Measurement Procedure

Thus the resulting frequency at the detector fmod is given by

. Equation A.6

Interferometers of this type which are directionally sensitive are described as heterodyne.

A.2 Optical Configuration in the Sensor Head

In Polytec's vibrometers, velocity and displacement acquisition are carried out using a modified Mach-Zehnder interferometer.

The optical configuration in the sensor head OFV-534 is shown schematically in FIGURE A.1.

The light source is a helium neon laser which provides a linear polarized beam. The beam splitter BS1 splits the beam into the object beam and the reference beam.

The object beam passes through the polarizing beam splitter BS2 as well as a λ/4 plate, is then focused by the lens on the object and scattered back from there. The polarizing beam splitter BS2 then functions as an optical directional coupler together with the λ/4 plate, and deflects the object beam to the beam splitter BS3. The interference signal occur out of the optical path difference between reference and laser beam. The distance to the object goes into the optical path difference with a factor of 2. The objective displays the object at the camera. If the spot diameter on the object is minimal, the video image is sharply focused.

The Bragg cell in the reference arm of the interferometer generates the additional frequency offset to determine the sign of the velocity.

The resulting interference signal of the object beam and reference beam is converted into an electrical signal in the photo detector and subsequently decoded in the controller.

fmod fB 2 vλ---⋅+=

Figure A.1: Optical configuration of the interferometer in the sensor head

BS 1 ObjectBS 2Laser

Reference-Beam

Object Beam

Fiber Objective

Camera(optional)

Prism

Bragg Cell

Detector

BS 3

�/4

A-2

Index

Index

Aacclimatization period 3-2adapter plate, dimensions 7-6air circulation 3-2ambient conditions

operating requirements 3-2specifications 7-1

aperture diameter 7-3assembly

microscope lens 5-3optional adapter plate 3-2

Bback panel, control elements laser unit 3-4basics, measurement procedure A-1beam shutter

blocking the laser beam 5-1key on the laser unit 3-4

beat frequency A-1bending radius, fiber-optic connecting cable 3-4blocking, the laser beam 5-1bragg cell A-2

Ccabling 3-7carrier frequency 7-1cavity length

optimal stand-off distance 4-1specifications 7-1

characteristicsoptimal 3-2specifications, optics 7-3

clamping screwlock the focus position 5-2on the sensor 3-5

cleaninghousing 3-3optical components 3-3

climatic conditions 3-2coherent light beams A-1components

cleaning 3-3cooling 3-2inspection 3-1unpacking 3-1

configuration, optical A-2connecting cables, operating requirements 3-2

control elementsback panel, laser unit 3-4front panel, laser unit 3-3sensor 3-5

controller specificationsshock reliability 7-2vibration reliability 7-2

CONTROLLER-connection, at the laser unit 3-4cooling 3-2

Ddamage 3-1depth of field 7-3detergent solution, cleaning 3-3dimensions

laser unit 7-5laser unit with adapter plate 7-6sensor 7-7specifications 7-5

disinfectant solutions, cleaning 3-3displacement acquisition, interferometric A-1disposal of the instrument 1-1doppler frequency A-1

Eelectrical data, specifications 7-1electrical safety

safety information 1-4standards applied 7-1

EMC, standards applied 7-1emission 7-1EMISSION-LED, at laser unit 3-3EU countries, laser warning labels on the

sensor 1-3

Ffault description 6-1fault diagnosis

advices on 6-1no laser beam 6-1no measurement signal 6-2

fiber-optic connecting cableat the laser unit 3-4on the sensor 3-6specifications 7-2

focuslock 5-2optimize 5-3

focusing ring, on the front lens 3-5focusing, the laser beam 5-2frequency offset A-2frequency shift A-1frequency, on the detector A-2fringe counting A-1

i

Index

front optics, cleaning 3-3front panel, control elements laser unit 3-3

Ggeneral data, specifications 7-1general safety, safety information 1-1

Hhelium neon laser, optimal stand-off distance 4-1heterodyne interferometer A-2housing

cleaning 3-3laser unit, specifications 7-2sensor, specifications 7-2

Iidentification label

at the laser unit 3-5inspection 3-1

immunity 7-1inspection of the components 3-1installation 3-7instruments, opening 3-3intended use 1-1intensity fluctuation A-1interference fringe pattern A-1interference, optical A-1interferometer, directionally sensitive A-2interferometric measurement A-1

Kkey LASER, on the laser unit 3-4

Llabel

identification label 3-5laser warning labels, on the sensor 1-3

Lambda/4 plate A-2laser

specifications 7-1stand-off distance 4-1warming-up 3-2

laser activity, indicating 5-1laser beam

basics of measurement procedure A-1blocking 5-1fault diagnosis 6-1focusing 5-2lock focus 5-2optimizing the focus 5-3

laser cavity lengthoptimal stand-off distance 4-1specifications 7-1

laser class 7-1

laser power 7-1laser safety

safety information 1-2standards applied 7-1

laser type 7-1laser unit

dimensions 7-5dimensions with adapter plate 7-6protection rating 7-2

laser warning labelslabels for the sensor 1-3position, on the sensor 1-4position, on the sensor with telephoto lens 1-4

laser wavelength 7-1LASER-key, on the laser unit 3-4LED

EMISSION, at laser unit 3-3indicating laser activity 5-1STANDBY, at laser unit 3-3

light beams, coherent A-1lock, focus position 5-2

MMach-Zehnder interferometer A-2mains connection 3-7maintenance requirements 3-2malfunctions, fault diagnosis 6-1measure, stand-off distance 4-2measurement procedure, basics A-1measurement signal, fault diagnosis 6-2missing parts 3-1moisture 3-2, 7-1multi-mode laser 4-1

Nno laser beam, fault diagnosis 6-1no measurement signal, fault diagnosis 6-2

Oopening, the instruments 3-3operating requirements 3-2operating temperature

specifications 7-1warming-up 3-2

operating, the sensor head 5-1optical components, cleaning 3-3optical configuration A-2optical interference A-1optics, specifications 7-3optimal stand-off distance 4-2optimizing, focus of the laser beam 5-3optional accessories, unpacking 3-1

ii

Index

Ppath difference A-1phase difference A-1photo detector A-1position, identification label 3-5power consumption 7-1precautions

electrical safety 1-5laser safety 1-3

protection ratinglaser unit 7-2sensor 7-2

protective cap, for the front lens 3-5

Qqualification of the user 1-1

Rreference beam, basics of measurement

procedure A-1relative humidity 7-1return 3-1

Ssafety

electrical, safety information 1-4general safety information 1-1laser, safety information 1-2

safety informationelectrical safety 1-4general safety 1-1laser safety 1-2

safety precautionselectrical safety 1-5laser safety 1-3

sensordimensions 7-7protection rating 7-2

sensor headdescription 2-1operating 5-1warm-up period 3-2

serial number, inspection 3-1shock reliability, controller specifications 7-2signal level display

on the sensor 3-5, 3-6optimizing the focus 5-3

specifications, technicaldimensions 7-5general data 7-1optics 7-3standards applied 7-1video camera 7-9

spot diameter 7-3

standards, specifications 7-1stand-off distance

diagram 4-2minimal 7-3optimal setting up 4-2

storage temperature 7-1switching off, vibrometer 5-1switching on, vibrometer 5-1system components, inspection 3-1

Ttable, visibility maxima 7-4technical specifications

dimensions 7-5general data 7-1optics 7-3standards applied 7-1video camera 7-9

telephoto lens 3-6tests, for fault diagnosis 6-1theory A-1transport packaging check 3-1

Uunpacking, components 3-1use, intended 1-1using a microscope lens 5-3

Vvelocity acquisition, interferometric A-1vibration reliability, controller specifications 7-2vibrometer

switching on and off 5-1unpacking 3-1

video cable 7-9video camera

specifications 7-9transfer the video signal 5-3

VIDEO-output, on the laser unit 3-4visibility maxima

optimal stand-off distance 4-1table 7-4

visibility minimum 4-1

Wwarming-up, laser 3-2warning labels, laser on the sensor 1-3warranty, invalidate 3-3wavelength 7-1weight

laser unit 7-2sensor 7-2

working distance, with telephoto lens 7-4wrong delivery 3-1

iii

Index

iv

Contact

Polytec Deutschland Polytec International

POLYTEC GmbHHauptsitzPolytec-Platz 1-776337 Waldbronn

France (F)Polytec-PI, S.A.32 rue DélizyF-93694 Pantin

Tel.:Fax:E-mail:Internet:

(07243) 604-0(07243) [email protected]://www.polytec.de


+33 (0) 1 48 10 39 34+33 (0) 1 48 10 09 [email protected]://www.polytec-pi.fr

POLYTEC GmbHVertriebs- und Beratungsbüro BerlinSchwarzschildstraße 112489 Berlin

Great Britain (GB)Lambda Photometrics Ltd.Lambda House, Batford MillGB-Harpenden, Hertfordshire AL5 5BZ


(030) 6392-5140(030) [email protected]://www.polytec.de


+44 (0) 1582 764334+44 (0) 1582 [email protected]://www.lambdaphoto.co.uk

International from outside Germany (D)POLYTEC GmbHHeadquartersPolytec-Platz 1-7D-76337 Waldbronn

Japan (J)Polytec JapanHakusan High Tech Park1-18-2 Hakusan, Midori-kuJ-Yokohama-shi, 226-0006 Kanagawa-ken


+49 7243 604-0+49 7243 [email protected]://www.polytec.com


+81 (0) 45 938-4960+81 (0) 45 [email protected]://www.polytec.co.jp

USA WestPolytec, Inc., North American Headquarters1342 Bell Avenue, Suite 3 -ATustin, CA 92780Tel.:Fax:E-mail:Internet:

+1 714 850 1835+1 714 850 [email protected]://www.polytec.com

USA MidwestPolytec, Inc., Midwest Office3915 Research Park Dr., Suite A-12Ann Arbor, MI 48108Tel.:Fax:E-mail:Internet:


USA EastPolytec, Inc., East Coast Office25 South Street, Suite AHopkinton, MA 01748Tel.:Fax:E-mail:Internet:


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