Polytec OFV-3001 User manual

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Laser Doppler Vibrometer
Controller OFV-3001
Sensor Heads OFV-303/-353
OFV-511/-512
Advanced Test Equipment Rentals
www.atecorp.com 800-404-ATEC (2832)
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The warranty for this equipment complies with the regulations in our general terms and condi-
tions 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 influ-
ences 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 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.
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Brand and product names mentioned in this manual could be trademarks or registered trade-
marks of their respective companies or organizations.
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Controller Sensor Head

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1.1 Laser Safety ....................................................................................................................... 1-1
1.2 Laser Warning Labels ......................................................................................................... 1-2
1.2.1 EC Countries.............................................................................................................1-2
1.2.2 Non-EC Countries..................................................................................................... 1-4
1.3 Electrical Safety.................................................................................................................. 1-5
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2.1 System Overview................................................................................................................ 2-1
2.2 Component Summary ......................................................................................................... 2-2
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3.1 Operating and Maintenance Requirements ......................................................................... 3-1
3.2 Unpacking and Inspection...................................................................................................3-2
3.3 Control Elements of the Vibrometer ....................................................................................3-3
3.3.1 Controller .................................................................................................................. 3-3
3.3.2 Sensor Head OFV-303 .............................................................................................. 3-7
3.3.3 Sensor Head OFV-353.............................................................................................. 3-8
3.3.4 Sensor Head OFV-511 .............................................................................................. 3-9
3.3.5 Sensor Head OFV-512 .............................................................................................3-11
3.4 Installation and Functional Test......................................................................................... 3-13
3.4.1 Vibrometer with Sensor Head OFV-303/-353........................................................... 3-13
3.4.2 Vibrometer with Sensor Head OFV-511/-512 ........................................................... 3-14
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4.1 Start-up............................................................................................................................... 4-1
4.1.1 Vibrometer with Sensor Head OFV-303/-353.............................................................4-1
4.1.2 Vibrometer with Sensor Head OFV-511/-512 ............................................................. 4-2
4.1.3 Displaying the Output Signals ................................................................................... 4-3
4.2 Selecting Suitable Settings ................................................................................................. 4-4
4.2.1 Velocity or Displacement Measurement?................................................................... 4-4
4.2.2 Settings for Velocity Measurement ............................................................................ 4-5
4.2.3 Settings for Displacement Measurement (optional)...................................................4-11
4.2.4 Optimal Stand-Off Distances for the Sensor Heads ................................................. 4-15
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5.1 Switching On and Off.......................................................................................................... 5-1
5.2 Beam Shutter and Emission Indicator .................................................................................5-1
5.3 Signal Level Display ........................................................................................................... 5-2
5.4 Focusing the Laser Beam ................................................................................................... 5-2
5.5 Exchanging the Front Lens ................................................................................................. 5-4
5.6 Making Single Point Measurements with the Sensor Head OFV-512................................... 5-5

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5.7 Fixing the Focus (only OFV-353) .........................................................................................5-6
5.8 Transport Safety Mechanism (only OFV-511/-512)...............................................................5-6
5.9 Operating the Vibrometer via the Display of the Controller...................................................5-7
5.9.1 Operating Philosophy.................................................................................................5-7
5.9.2 Organization of the Menus.........................................................................................5-8
5.9.3 The Individual Menus.................................................................................................5-9
5.10 Setting Measurement Ranges and Filters ........................................................................5-11
5.11 Displaying the Configuration of the Controller ..................................................................5-11
5.12 Configuring the Interfaces................................................................................................5-11
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6.1 General Tests ......................................................................................................................6-1
6.2 No Laser Beam....................................................................................................................6-2
6.3 No Measurement Signal ......................................................................................................6-3
6.4 Checklist for Fault Diagnosis ...............................................................................................6-5
6.4.1 Controller OFV-3001 with the Sensor Head OFV-303/-353.........................................6-5
6.4.2 Controller OFV-3001 with the Sensor Head OFV-511/-512.........................................6-6
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7.1 Controller OFV-3001............................................................................................................7-1
7.1.1 General Data .............................................................................................................7-1
7.1.2 Interfaces...................................................................................................................7-1
7.1.3 Low Pass Filter ..........................................................................................................7-1
7.1.4 Signal Voltage Output VELOCITY OUTPUT...............................................................7-2
7.1.5 Signal Voltage Output DISPLACEMENT OUTPUT (optional)......................................7-5
7.2 Sensor Head OFV-303/-353.................................................................................................7-6
7.2.1 General Data .............................................................................................................7-6
7.2.2 Optics ........................................................................................................................7-6
7.3 Sensor Head OFV-511/-512.................................................................................................7-8
7.3.1 General Data .............................................................................................................7-8
7.3.2 Optics ........................................................................................................................7-8
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The light source of the vibrometer is a helium neon laser. It is important to
understand that laser light has different properties than ordinary light sources.
Laser radiation is generally extremely intense due to the beam’s low diver-
gence and great care should be taken when handling laser instruments that
the direct or reflected beam does not enter the eye. To ensure this, the follow-
ing precautions have been taken:
 In general, Polytec equipment complies with the standards (1
(DIN VDE 0837) and &)5 (US).
 The optical output of the laser is less than 1mW providing the equipment
is used in the manner for which it was intended. This means that the vibro-
meter conforms with ODVHUFODVV,, and is generally very safe. Even when
optimally focused, the laser radiation is not intense enough to harm the
skin.
 The sensor head has been equipped with a EHDPVKXWWHU which can be
used to block the laser beam during the warm-up phase or when the vibro-
meter is not in use, although switched on.
 The HPLVVLRQLQGLFDWRU on the sensor head indicates the activity of the
laser and thus potential harm caused by emitted laser beams.
 The beam shutter is always OHVVWKHQPDZD\ from the aperture of the
laser beam. Special editions of the fiber optical sensor heads with fiber
lengths of 3m are fitted with an additional emission indicator which is inte-
grated in the fibers.
 The laser is switched on via a NH\VZLWFK on the controller. The key can
only be removed when the controller is switched off.
 It is QRWQHFHVVDU\WRRSHQ the housing of the sensor head when using
the vibrometer as intended. Opening the housing will invalidate the war-
ranty.
3OHDVHSD\DWWHQWLRQ to the following VDIHW\SUHFDXWLRQV when using the
vibrometer:
 Never look directly into the laser beam with the naked eye or with the aid
of mirrors or optical instruments!
 Only switch the beam shutter to the ON position when you are making
measurements!
 To position the sensor head, switch the beam shutter to the OFF position.
Only when the sensor head is roughly in place and has been fixed in a
stable position, switch the beam shutter to ON.
 Do not use any reflective tools, watches etc. when you are working in the
path of the laser beam!

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The laser warning labels for the vibrometer in EC countries are shown in
figure 1.1. Label 2 is affixed either in English, French or Spanish. Their posi-
tion on the sensor head OFV-303/-353 is shown in figure 1.2 and on the sen-
sor head OFV-511/-512 in figure 1.3.
Figure 1.1: Laser warning labels for the vibrometer in EC countries
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French
Spanish

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Figure 1.2: Position of the laser warning labels on the sensor head OFV-303/-353 in EC
countries
Figure 1.3: Position of the laser warning labels on the sensor head OFV-511/-512 in EC
countries
1 2
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2
SIGNAL
PRO CESSOR
ACHTUNG!
Bitte vordem Transport
die Transportsicherung betätigen
CAUTION!
Please secure transportm echanism
b e fo r e s h ip m e n t
M EASUREM ENT TRANSPORT

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The laser warning labels for the vibrometer in non-EC countries are shown in
figure 1.4. Their position on the sensor head OFV-303/-353 is shown in
figure 1.5 and on the sensor head OFV-511/-512 in figure 1.6.
Figure 1.4: Laser warning labels for the vibrometer in non-EC countries (*only within the USA)
Figure 1.5: Position of the laser warning labels on the sensor head OFV-303/-353 in non-EC
countries
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The vibrometer complies with the electrical safety class I. Electrical shock
protection is achieved by a fully metallic housing connected to protective
ground. Please pay attention to the following safety precautions when using
the vibrometer:
 The vibrometer should only be connected via a three pin mains cable to
an AC mains supply 50/60Hz with a grounded protective conductor with a
nominal voltage which corresponds to the voltage set on the voltage
selector.
 Defective mains fuses may only be replaced by fuses of the same kind
with their rating given on the back of the controller.
 None of the equipment may be used with open housing. As a general rule,
before removing parts of the housing, the mains cable has to be
unplugged.
 Air inlets and outlets must always be kept uncovered to ensure effective
cooling. If the cooling fan stops working, the vibrometer is to be switched
off immediately.
Figure 1.6: Position of the laser warning labels on the sensor head OFV-511/-512 in non-EC
countries
3
1
SIGNAL
PRO CESSO R
ACHTUNG!
Bitte vordem Transport
die Transportsicherung betätigen
CAUTION!
Please secure transportm echanism
b e fo r e s h ip m e n t
MEASUREM ENT TRANSPO RT

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Polytec vibrometers are instruments for non-contact measurement of surface
vibrations based on laser interferometry. The vibrometer consists of the con-
troller OFV-3001 and the sensor head OFV-303/-353 or OFV-511/-512. The
signal paths in the vibrometer are shown schematically in figure 2.1.
The beam of a helium neon laser is focused on the object under investigation,
scattered back from there and coupled back into the interferometer in the sen-
sor head. The interferometer compares the phase ϕ
mod
and frequency f
mod
of
the object beam with those of the internal reference beam ϕ
0
and f
0
. The fre-
quency difference is proportional to the instantaneous velocity and the phase
difference is proportional to the instantaneous position of the object.
In the controller, the resulting signal is decoded using the velocity decoder
and optionally the displacement decoder. Two voltage signals are generated
which are respectively proportional to the instantaneous VELOCITY and to
the instantaneous position (DISPLACEMENT) of the object. Both signals are
available at the front of the controller as an analog voltage and can be pro-
cessed further externally. Additional functions such as filters and signal level
display raise the level of comfort for the vibrometer user. The settings of the
vibrometer are selected via the display of the controller or via PC interfaces.
To display and analyze measurement results on a workstation, the Polytec
Vibrometer Software (VibSoft) is available optionally. The software is
described in a separate manual.
Figure 2.1: Signals in the vibrometer
Sensorhead
f0
ϕ0
fmod
ϕ
mod
Frequency
Phase
∆f
Velocity
decoder
V
D isplacem ent
d e c o d e r (o p tio n a l)
∆ϕ
V
v(t)
x(t)
Object
x(t)
v(t)=dx/dt

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Polytec assembles the vibrometer on the modular principle thus permitting a
user-specific configuration. The combination of the controller OFV-3001 with
the most useful decoders as well as a suitable sensor head provide the solu-
tion to a multitude of measurement tasks. Thus a manageable number of
components cover a wide range of applications. A summary of the compo-
nents is shown in figure 2.2.
The modularity is achieved initially through strict separation of optics and
electronics. Every decoder can be combined with every sensor head.
The controller is equipped with one of the two available velocity decoders as
standard. A maximum of two velocity decoders can be installed. The velocity
decoders are described in section D.4.1.
As an option, the controller can be fitted with one of the four available dis-
placement decoders as well as be supplemented by a PC-based displace-
ment decoder (refer to section D.5.2).
The various standard and fiber optical sensor heads comply with the different
requirements of the vibrometer’s optics. For every sensor head a selection of
lenses covers a wide range of stand-off distances.
Figure 2.2: Compatibility of the controller OFV-3001 with sensor heads and decoders
O FV-3001
OVD-10
OVD-20
OVD-30
OVD-40
OVD-01
OVD-02
OFV-303
OFV-353
OFV-511
OFV-512
Fiberoptical
sensorheads
Standard
sensorheads
Velocity decoders D isplacem entdecoders

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The vibrometer can be operated in dry rooms under normal climate conditions
(refer to chapter 7). In particular the optical components in the sensor head
are sensitive to moisture, high temperatures, jolting and dirt. When the vibro-
meter is taken into operation after being stored somewhere cool, a sufficient
acclimatization period should be allowed for before switching it on. Avoid con-
densation on the optical components caused by a rapid change in tempera-
ture.
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Before taking the vibrometer into operation, please ensure that the supply
voltage set with the voltage selector corresponds with the local mains voltage.
Only replace defective fuses by fuses of the same kind and equal rating.
:DUPLQJXS The helium neon laser in the sensor head requires a certain period of time to
reach optimum stability. The vibrometer should thus be switched on 20 min-
utes before the first measurements are made to ensure that it is in thermal
equilibrium with the surroundings.
$VVHPEO\ The sensor head OFV-303 should not be positioned provisionally but mounted
properly on a stable tripod using the threads provided.
7UDQVSRUW The sensor head OFV-511/-512 is equipped with a transport safety mecha-
nism which always has to be activated before moving the sensor head (refer
to section 5.8).
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As a general rule the vibrometer must not be switched on until all cables are
connected. Make sure that all jacks are connected properly and firmly. Protect
the cables from mechanical damage and from high temperatures.
&OHDQLQJ The housing surfaces of the instrument can be cleaned with mild detergent
solutions. Organic solvents must not be used.
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Handle all optical components with great care. Dirt may only be removed very
carefully with a soft, dry cloth, an optics brush and bellow.
&RROLQJ It is very important to ensure that there is sufficient air circulation to keep the
controller and the sensor head cool. The air vents of the sensor head must
never be covered up and the back panel of the controller must be at least
50mm away from the wall.
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Opening up of the equipment without authorization is not necessary for its
operation and will invalidate the warranty.

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The vibrometer consists of the following components:
 controller OFV-3001
 sensor head OFV-303/-353 or OFV-511/-512
 connecting cable from the controller to the sensor head (length 5m)
 earthed mains cable
Please pay attention to the following steps when unpacking:
1. After unpacking, check all components for external damage (scratches,
loose screws, damaged lens etc.).
2. Check the packaging for signs of unsuitable handling during transport.
3. In the case of a wrong delivery, damage or missing parts, inform your local
Polytec representative immediately and give them the serial number of the
sensor head and the controller. The identification labels can be found on
the back of the instruments and also on the inside cover of this manual.
4. Carefully retain the original packaging in case you have to return the
instrument.
5. Install the vibrometer and carry out a first functional test as described in
section 3.4.1 (sensor head OFV-303/-353) or section 3.4.2 (sensor head
OFV-511/-512).
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Protect the unpacked sensor head from hard jolts as these can lead to misalignment of the
interferometer!
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Handle the front lens of the sensor head with great care! Dirt may only be removed very
carefully with a soft, dry cloth, an optics brush and bellow!

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The front panel of the controller is shown in figure 3.1.
 32:(5 - L ED
The L ED lights up when the key switch on the controller is turned to posi-
tion I and indicates that the controller is ready to operate.
 0DLQV6ZLWFK
This key switch disconnects the vibrometer from the mains (position O)
and is used to switch it off in the case of danger.
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This display shows the configuration and the settings of the vibrometer.
The organization of the display and how to use it to operate the vibrome-
ter are described in detail in section 5.9.
 )81&7,21 - keys
Using these keys the cursor is moved vertically up ( ↑) or down ( ↓ ) on the
display. This is used to select parameters or to change between menus
(refer to section 5.9.1).
 6(77,1* - keys
Using these keys the settings are changed to higher (+) or lower (-) values
(refer to section 5.9.1).
Figure 3.1: Front view of the controller
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VIBRO M ETER CO NTRO LLER
3
213 12 11 10
LLO REM OTE RESET
FUNCTION SETTING
4 5 6 7
+
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OVER OUTPUT
VELO CITY
DISPLACEM ENT
CLEAR
OUTPUT
9 8
I
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$OZD\V connect the connecting cable to the sensor head EHIRUH switching the controller
on!

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 29(5 - indicator for the velocity
The L ED lights up when the output voltage exceeds either of the positive
or negative full scale of the velocity measurement range. If it lights up per-
manently, the next highest velocity measurement range must be selected
(refer also to section 4.2.2).
 Analog  voltage 287387 for the 9(/2&,7< signal (BNC jack)
The voltage at this output is proportional to the instantaneous vibration
velocity of the object under investigation. The voltage is positive when the
object is moving towards the sensor head.
 &/($5 - input for the displacement decoder (BNC jack)
This input is only active, if a displacement decoder is installed. It allows
synchronized resetting of the displacement decoder. This can be used to
remove a DC component which is superimposed on a periodic vibration
(refer to section 4.2.3).
 Analog voltage 287387 for the ',63/$&(0(17 signal (BNC jack)
This output is only active, if a displacement decoder is installed. The volt-
age at this jack is proportional to the instantaneous displacement of the
object to be measured. The voltage increases when the object is moving
towards the sensor head.
 &/($5 - key for the displacement decoder
This key is only active, if a displacement decoder is installed. Using this
key the displacement decoder can be reset manually (refer to
section 4.2.3).
 5(6(7 - key
Using this key the controller processor can be reset. The setting of the
controller is subsequently the same as it was straight after switching on
the mains.
 5(027( - L ED
The L ED is lit when the controller is being operated remotely via one of the
PC interfaces (refer to appendix E). Manual operation with the keys ↑ , ↓ ,
+, - is also still possible (as oppose to the status Local Lock Out).
 //2 - L ED
This L ED is lit when the status / ocal / ock 2 ut has been activated via one
of the PC interfaces (refer to appendix E). The keys ↑ , ↓ , +, - are then
deactivated and the controller can only be operated via the PC interfaces.

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The back panel of the controller is shown in figure 3.2.
 ,17(5)(520(7(5 - connector (Sub-D jack)
Jack for the connecting cable to the sensor head
 0DLQVFRQQHFWLRQFRPELQDWLRQ
Socket for standard power cord with built-in fuses and mains voltage
selector (refer to section 3.1)
 (;7 ernal '(& oder - interface
Interface for the optional PC-based displacement decoder OFV-600 (refer
to section D.5.2)
 5(027()2&86 - interface
Interface for the optional hand terminal OFV-310 to focus the laser beam
(refer to section A.1)
 6,*1$/ - output (BNC jack)
The DC voltage at this output is proportional to the logarithm of the optical
signal level.
 *3,%  ,((( - interface
Jack for the IEEE-488/GPIB cable (refer to appendix E)
Figure 3.2: Rear view of the controller
INTERFERO M ETER
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EXT.DEC. SIG NAL REM O TE FO C U S
G P IB / IE E E -4 8 8
6 7 8 1 2
5 4 3
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$OZD\V disconnect from the mains EHIRUH checking the fuses!
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$OZD\V check the setting of the voltage selector as well as the fuses EHIRUH installing the
controller!

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 56 - interface (Sub-D jack)
Jack of the serial interface (refer to appendix E)
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This opening must DOZD\V be kept free to ensure sufficient cooling. The distance from the
wall should be at least 50mm!

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The back panel and the front panel of the sensor head OFV-303 are shown in
figure 3.3.
 %HDPVKXWWHU
In position OFF the laser beam is blocked.
 &21752//(5 - connector (Sub-D jack)
Jack for the connecting cable to the controller
 6LJQDOOHYHOGLVSOD\
The length of the bar is a measure of the amount of light scattered back
from the surface of the object.
 /$6(5 - L ED
The L ED lights up when the laser is switched on (key switch on the control-
ler in position I) i.e. even if the beam shutter is closed (refer to
section 5.2).
 Switch $8720$1
This knob is used to switch between remote-controlled and manual focus-
ing (refer to section 5.4).
 )URQWOHQV
Exchange of the front lens is described in section 5.5.
 )RFXVLQJULQJ
Focusing ring for manual focusing of the laser beam (refer to section 5.4)
Figure 3.3: Rear view and front view of the sensor head OFV-303
CONTROLLER
OFF
ON
EM ISSION
LASER
S
I
G
N
A
L
123567
4
AUTO MAN
8
:DUQLQJ 
2QO\ switch the beam shutter to position ON when you are making measurements!


)LUVW6WHSV
6HQVRU+HDG2)9
The back panel and the front panel of the sensor head OFV-353 are shown in
figure 3.4.
 %HDPVKXWWHU
In position OFF the laser beam is blocked.
 &21752//(5 - connector (Sub-D jack)
Jack for the connecting cable to the controller
 6LJQDOOHYHOGLVSOD\
The length of the bar is a measure of the amount of light scattered back
from the surface of the object.
 /$6(5 - L ED
The L ED lights up when the laser is switched on (key switch on the control-
ler in position I) i.e. even if the beam shutter is closed (refer to
section 5.2).
 Switch %5$.(21  2))
This knob is used to fix the focus (refer to section 5.7).
 )URQWOHQV
Exchange of the front lens is described in section 5.5.
 )RFXVLQJULQJ
Focusing ring for focusing of the laser beam (refer to section 5.4)
Figure 3.4: Rear view and front view of the sensor head OFV-353
ON OFF
BRAKE
8
567
3
2
1
4
EM ISSION
OFF
ON
CONTROLLER
LASER
S
I
G
N
A
L
:DUQLQJ 
2QO\ switch the beam shutter to position ON when you are making measurements!