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4-6

4 Making Measurements

in these ranges the permissible frequency decreases with increasing
amplitude. If the condition

is infringed upon, the signal is seriously

distorted. In this case, a higher velocity measurement range has to be
selected.

In all velocity measurement ranges the L

ED

OVER on the front of the

controller lights up if either the positive or negative end of range is exceeded.
As a general rule, the next highest measurement range should then be
selected. Please note however, that the L

ED

is activated by very short

overrange already which could be caused by noise spikes. In such cases the
velocity measurement range can be retained as long as it is suitable for the
amplitude of the required signal. Observing the signal on the oscilloscope will
provide clarification on this (refer to

Tracking filter

The tracking filter is used to improve the signal-to-noise ratio of the input
signal from the sensor head. This is advantageous to bridge short dropouts in
particular, which always occur due to the speckled nature of the light
scattered back from the object. The bridging capability is generally better with
a high time constant SLOW, however it may not be possible to follow highly
dynamic signals any more. In this case FAST or OFF has to be selected. The
best setting therefore has to be determined from case to case or be estimated
based on the range diagram in

. The range diagram shows the dynamic

limits for both settings of the tracking filter, plotted versus the frequency.

A constant velocity limit of approximately 3 m / s is characteristic for the lower
frequency range. If the velocity exceeds this value, the tracking filter can
generally not be used and has to be switched off. For special applications a
tracking filter can be installed for which this velocity limit does not apply. This
is however coupled at worse noise suppression.

In the medium frequency range, the velocity limit changes over to become an
acceleration limit i.e. the velocity limit decreases inversely proportional to the
frequency (refer to equation

Figure 4.1: Range diagram of the tracking filter

V e l o c i t y / m / s

1 0

3

1

0 . 3

0 . 1

0 . 0 3

F r e q u e n c y / k H z

0 . 0 1

0 . 0 3

0 . 1 0 . 3 1

3

1 0

3 0 1 0 0 3 0 0

v e l o c i t y l i m i t 3 m / s

S L O

W

a c c

e l e r

a t io

n lim

i t

fre

qu

en

cy

lim

it 1

00

kH

z

«
...
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33
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»

Содержание OFV-3001

Страница 1: ...Title User Manual 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 Established 1981...

Страница 2: ...d 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...

Страница 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...

Страница 4: ...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...

Страница 5: ...on is not intense enough to harm the skin The sensor head has been equipped with a beam shutter which can be used to block the laser beam during the warm up phase or when the vibrometer is not in use...

Страница 6: ...gure 1 1 Label 2 3 and 4 are affixed or enclosed in the language of the customer s country Their position on the sensor head OFV 303 353 is shown in figure 1 2 and on the sensor head OFV 511 resp OFV...

Страница 7: ...ble to affix it on the mini sensor due to its size Please affix this label clearly visible near the mounted mini sensor or fiber head Figure 1 2 Position of the laser warning labels on the sensor head...

Страница 8: ...sor heads 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 resp OFV 512 in figure 1 6 Laser class II for...

Страница 9: ...its size Please affix this label clearly visible near the mounted mini sensor or fiber head Figure 1 5 Position of the laser warning labels on the sensor head OFV 303 353 in non EC countries 1 4 2 3 B...

Страница 10: ...ns 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 sa...

Страница 11: ...er 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 VELOCIT...

Страница 12: ...ndard 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 displacement dec...

Страница 13: ...h the surroundings Assembly The sensor head OFV 303 should not be positioned provisionally but mounted properly on a stable tripod using the threads provided Transport The sensor head OFV 511 512 is e...

Страница 14: ...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 th...

Страница 15: ...f the display and how to use it to operate the vibrometer are described in detail in section 5 9 4 FUNCTION keys Using these keys the cursor is moved vertically up or down on the display This is used...

Страница 16: ...DISPLACEMENT signal BNC jack This output is only active if a displacement decoder is installed The voltage at this jack is proportional to the instantaneous displacement of the object to be measured...

Страница 17: ...terface for the optional hand terminal OFV 310 to focus the laser beam refer to section A 1 5 SIGNAL output BNC jack The DC voltage at this output is proportional to the logarithm of the optical signa...

Страница 18: ...7 Cooling Fan 8 RS 232 interface Sub D jack Jack of the serial interface refer to appendix E Caution This opening must always be kept free to ensure sufficient cooling The distance from the wall shoul...

Страница 19: ...aser is switched on key switch on the controller in position I i e even if the beam shutter is closed refer to section 5 2 5 Switch AUTO MAN This knob is used to switch between remote controlled and m...

Страница 20: ...ghts up when the laser is switched on key switch on the controller in position I i e even if the beam shutter is closed refer to section 5 2 5 Switch BRAKE ON OFF This knob is used to fix the focus re...

Страница 21: ...mitted yet as the beam shutter is still closed LED ON is out The LED goes out when the beam shutter key is pressed and thus the laser beam is emitted LED ON is then on 3 LASER ON LED The LED goes on w...

Страница 22: ...ety mechanism The transport safety mechanism is de activated by turning the screw with the Allen key provided refer to section 5 8 Note Each mini sensor is exactly adjusted to its fiber Never exchange...

Страница 23: ...out The LED goes out when the beam shutter key is pressed and thus the laser beam is emitted LED ON is then on 3 LASER ON LED The LED goes on when the beam shutter key LASER is pressed and thus the l...

Страница 24: ...rt safety mechanism The transport safety mechanism is de activated by turning the screw with the Allen key provided refer to section 5 8 Note Each mini sensor is exactly adjusted to its fiber Never ex...

Страница 25: ...correctly the LED LASER on the sensor head also lights up Laser light is not yet emitted as the beam shutter is still closed 6 Before now opening the beam shutter remember the information on laser saf...

Страница 26: ...ck of the controller as well as the fuses Cabling 5 Plug the connecting cable into the Sub D jack SIGNAL PROCESSOR on the back of the sensor head and into the Sub D jack INTERFEROMETER on the back of...

Страница 27: ...level display will fully light up 12 If you have not been able to observe the effect described under 11 check the signal level again after 20 minutes After this warm up phase the laser has reached it...

Страница 28: ...3 16 3 First Steps...

Страница 29: ...lease allow 20 minutes for the laser to warm up before making measurements On the front of the controller the LED POWER lights up Providing the connecting cable has been installed correctly the LED LA...

Страница 30: ...oller on by turning the key switch to position I Please allow 20 minutes for the laser to warm up before making measurements On the front of the controller the LED POWER lights up Providing the connec...

Страница 31: ...vel of the velocity output decreases The minimum noise level shows the optimal alignment and focusing for the surface quality present Displacement signal optional 4 Connect an oscilloscope to the BNC...

Страница 32: ...surement In contrast the resolution in velocity measurement is only limited by the background noise With good optical signals e g on reflective film and a spectral resolution bandwidth of several Hert...

Страница 33: ...he velocity is often not enough as the various velocity decoders and measurement ranges have different bandwidths and maximum accelerations The respective values are given in the specifications refer...

Страница 34: ...back from the object The bridging capability is generally better with a high time constant SLOW however it may not be possible to follow highly dynamic signals any more In this case FAST or OFF has t...

Страница 35: ...is will cause serious signal distortions an example of which can be seen on the oscilloscope trace in figure 4 2 The signal A shows a sinusoidal velocity signal with the tracking filter in position OF...

Страница 36: ...frequency the amplitude error is less than 5 This range can be considered to be exact for amplitude measurement Up to 70 of the cutoff frequency the amplitude error increases to about 15 The upper 30...

Страница 37: ...ure 4 5 Figure 4 4 Amplitude error of a 3rd order Bessel low pass filter in the passband Figure 4 5 Phase frequency response of a 3rd order Bessel low pass filter in the passband 3 0 2 5 2 0 1 5 1 0 5...

Страница 38: ...asurement ranges however several counts per fringe are generated by interpolation whereby bandwidth and count frequency multiply correspondingly refer to section D 5 3 As a result the maximum permissi...

Страница 39: ...OVD 40 0 1 1 0 2 5 5 0 1 0 0 2 5 0 5 0 0 1 k 2 5 k 5 k 1 0 k 2 5 k 5 0 k 1 0 0 k 2 5 0 k 0 2 5 0 5 1 2 5 5 1 0 2 5 5 0 1 0 0 2 5 0 5 0 0 1 0 0 0 2 5 0 0 5 0 0 0 1 0 0 0 0 2 5 0 0 0 5 0 0 0 0 1 0 0 0...

Страница 40: ...the displacement signal breaks down the next highest velocity measurement range has to be selected If however the optical signal is constantly good the range 1 000 should be selected as it does not li...

Страница 41: ...tself Each zero crossing of a rising velocity signal then resets the displacement decoder This requires however a certain quality of the velocity signal If it is too noisy the displacement signal beco...

Страница 42: ...d The optimal stand off distances are n 0 1 2 i e at 63mm 266mm 469mm etc Maxima of visibility The light source of the vibrometer is a helium neon laser This is a multimode laser in which a maximum of...

Страница 43: ...the beam shutter is on the back of the sensor head and is labeled EMISSION ON OFF To block the laser beam turn the knob clockwise until the red mark points at OFF The emission indicator is the LED LAS...

Страница 44: ...f the controller remotely with a PC via the interfaces RS 232 or IEEE 488 GPIB remotely with the hand terminal OFV 310 optional You can switch between manual focusing and remote focusing with the knob...

Страница 45: ...nto the front panel of the sensor head 5 To fix the focus press the knob BRAKE ON OFF into the front panel until it stops refer also to section 5 7 OFV 511 512 To focus the laser beam you proceed as f...

Страница 46: ...as follows 1 Turn the threaded cover 5 anti clockwise until it can be removed 2 Remove the mount 4 for the 4 plate and put it to one side 3 Pull the front lens 3 out of the lens mount 1 4 Carefully pu...

Страница 47: ...because each mini sensor is exactly adjusted to its fiber 2 Screw the reference head onto the end of the fiber until it is securely fixed The reference head can now be used 5 7 Fixing the Focus only O...

Страница 48: ...t safety mechanism To activate the transport safety mechanism you proceed as follows 1 Turn the screw on the back of the sensor head to position TRANSPORT A 5mm Allan key is supplied for this purpose...

Страница 49: ...on the right The cursor on the left marks a selected parameter The setting of the parameter is changed to higher and lower values with the keys and Adjusted settings are activated straight away As the...

Страница 50: ...hing on the controller or after RESET SETTINGS This is the most important menu in which all settings for a measurement are made i e the measurement ranges and the filters are selected It also displays...

Страница 51: ...D 02 is installed with 4 velocity measurement ranges Displacement Decoder This line is only present if a displacement decoder is installed This line shows the number of available displacement measurem...

Страница 52: ...ge The possible settings depend on the velocity decoder selected You will find information on setting the velocity measurement range in section 4 2 2 Velocity Filter In this line you can set the cutof...

Страница 53: ...d filters via the RS 232 interface or the IEEE 488 GPIB interface on the back of the controller Adjusting the settings via the PC interfaces is described in appendix E 5 11 Displaying the Configuratio...

Страница 54: ...5 12 5 Operating the Vibrometer...

Страница 55: ...n 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 us...

Страница 56: ...e laser is operating OFV 511 512 6 Is the LED LASER STANDBY on the front of the sensor head lit up after switching the controller on If the LED is not lit up it can be assumed that there is a a fault...

Страница 57: ...rmally a DC voltage of less than 20mV can be measured 4 Set the oscilloscope to 1V DIV and block the laser beam Is the output signal noisy or is a straight line shown Noise must occur when the laser b...

Страница 58: ...6 4 6 Fault Diagnosis Figure 6 1 Pin configuration of the Sub D jack INTERFEROMETER A 2 A 1 7 1 1 5 8...

Страница 59: ...5 Does the signal level display on the back of the sensor head react Yes 6 Does the signal level display on the display of the controller react Yes 7 Does the output signal VELOCITY OUTPUT on the fro...

Страница 60: ...isible No 6 Does the signal level display on the front of the sensor head react Yes 7 Does the signal level display on the display of the controller react Yes 8 Does the output signal VELOCITY OUTPUT...

Страница 61: ...on condensing Dimensions 450mm 355mm 135mm Weight 10 8kg Calibration recommended every 2 years Electrical safety EN60950 IEC950 EN61010 IEC1010 EMC Emission EN50081 1 FCC Class B Immunity EN50082 1 EN...

Страница 62: ...range indicator threshold typ 95 of full scale Maximum DC offset 20mV Velocity decoder Measurement range Full scale output Resolution1 1 Resolution is defined as the signal amplitude rms at which the...

Страница 63: ...nt relative deviation of the scale factor referred to the scale factor under calibration conditions One particular range Overall of rms reading of rms reading OVD 01 0 5 1 0 OVD 02 1 0 2 5 Velocity de...

Страница 64: ...on the measurement range set Harmonic Distortions Velocity decoder Measurement range Time delay td typ Specific phase roll off pd typ s kHz OVD 01 1 23 9 8 6 5 7 1 2 56 25 and 125 6 0 2 15 1 000 5 2 1...

Страница 65: ...0 0 250 100 320 5 120 1 3 10 0 250 100 1 280 20 480 5 0 10 0 250 100 5 120 81 920 20 10 0 250 100 OVD 20 0 5 8 0 002 0 06 0 25 10 and 2 32 0 008 0 25 0 75 15 OVD 40 8 128 0 032 1 0 75 25 20 320 0 08 2...

Страница 66: ...65 C 5 F 149 F Relative humidity max 80 non condensing Dimensions refer to figure 7 1 Weight 3 5kg Front lens1 1 A label on the side of the sensor head shows the front lens model which is fitted Long...

Страница 67: ...and bottom view of the sensor head OFV 303 353 dimensions not specified are given in mm C O N T R O L L E R L A S E R E M I S S I O N O F F O N S I G N A L 1 2 0 8 0 3 4 3 5 2 8 0 2 6 0 2 4 5 1 4 0 3...

Страница 68: ...er safety class 3R in non EC countries IIIa Laser output power 5mW 1mW per fiber Length of fiber cable from housing to Y junction 1 500mm 2 400mm for option OFV C 21 Y junction to fiber head 500mm 600...

Страница 69: ...2 OFV 5122 two point measurement 2 Difference between the stand off distances of both arms 0mm n 203mm n 0 1 2 OFV 5121 single point measurement with the reference head OFV 151 63mm n 203mm n 0 1 2 f...

Страница 70: ...ensions not specified are given in mm OFV C 110 Figure 7 3 View of the side exit head OFV C 110 dimensions not specified are given in mm OFV 151 Length ca 70mm Diameter 20mm Diameter of the focusing r...

Страница 71: ...s If the keys are pressed for more than approximately one second the motor switches over to fast mode For fine positioning the keys can be repeatedly pressed briefly At the end of the adjustment range...

Страница 72: ...tained because a high reflectivity mirror is used and the protective window is tilted Assembly To mount the side exit adapter proceed as follows 1 Turn the threaded cover on the sensor head anti clock...

Страница 73: ...ted with an interference filter for the laser wavelength 632 8nm to enhance the spot in daylit conditions The ready assembled tip tilt stage is shown in figure A 3 The underside of the assembly has st...

Страница 74: ...d side view of the OFV P5 with fitted targeting telescope and sensor head All dimensions are given in mm 1 5 0 1 8 5 1 2 0 1 1 8 2 5 0 6 5 3 1 O F V 3 0 3 2 8 0 1 6 0 4 2 6 2 x M 6 T e l e s c o p e w...

Страница 75: ...measurements which have to be carried out near a maximum of visibility but in which the stand off distance of the fiber head can not be changed e g using the fiber head OFV 130 3 or OFV 130 5 Using t...

Страница 76: ...the reference fiber and keep in a safe place because each mini sensor is exactly adjusted to its fiber 2 Slide the swivel nut over the end of this fiber 3 Screw the adapter onto the end of the fiber a...

Страница 77: ...e exit head proceed as follows 1 Place the mini sensor 4 into the side exit head as far as the shoulder of the connector for the mini sensor is positioned at the edge of the opening 5 The distance fro...

Страница 78: ...an now be used Assembly OFV 200 The fiber head OFV 200 is equipped with a Nikon bayonet mount which can take a Nikon camera lens To mount this head onto the fiber it has to be partially opened and the...

Страница 79: ...ed mounting holes refer to figure B 5 Alternatively the flexible arm can be attached to any magnetic surface which is large enough using the magnetic base The flexible arm is shown in figure B 4 1 Bas...

Страница 80: ...ries for the Sensor Head OFV 511 512 Figure B 5 Base plate for the flexible arm OFV 039 dimensions not specified are given in mm 0 5 0 1 8 A A 8 5 2 x 4 5 A A M 8 1 0 0 1 2 0 C o u n t e r s i n k i n...

Страница 81: ...ined using directionally sensitive counting of the passing fringe pattern On scattering from the object the object beam is subjected to a small frequency shift which is called Doppler shift fD and is...

Страница 82: ...ectional coupler together with the 4 plate and deflects the object beam to the beam splitter BS3 As both arms of the internal interferometer are symmetrical the optical path difference between the obj...

Страница 83: ...from there The polarizing beam splitter BS2 then functions as an optical directional coupler together with the 4 plate and deflects the object beam to the beam splitter BS3 As both arms of the interna...

Страница 84: ...ism in the reference arm is replaced by another beam splitter BS4 which has the same characteristics as the beam splitter BS2 The signal measured here is thus the relative velocity or displacement bet...

Страница 85: ...s generated which is proportional to the instantaneous velocity of the object with the aid of so called FM demodulators In the displacement decoder optionally the phase of the RF signal is demodulated...

Страница 86: ...f the input signal level The measurement of the input signal level is required to provide the user with information of the back scattering properties of the object and as a help to optimally focus the...

Страница 87: ...e wheel is At the same time the flywheel however loses the ability to follow rapid changes in the revolutions per minute i e the dynamic response of the drive system gets worse The same correlation al...

Страница 88: ...s produced by the so called local oscillator in a fixed relationship to the drive frequency of the Bragg cell D 3 Oscillator Section The oscillator section generates all drive frequencies for operatin...

Страница 89: ...r with high resolution The upper four measurement ranges can be used up to frequencies of 50kHz and higher while retaining their good characteristics however amplitude accuracy and linearity decrease...

Страница 90: ...lter The signal generated by the FM demodulator always contains spurious RF components and its noise bandwidth corresponds with the maximum frequency of the respective measurement range A subsequent l...

Страница 91: ...ders OVD 10 and OVD 20 For certain applications in particular for low frequency vibrations the limitation of the measurement range to 1 3mm in the direct counting mode due to the 12bit counting range...

Страница 92: ...ction 4 2 3 CLEAR function To be able to present the displacement signal in real time with an oscilloscope e g the counter content is converted by a 12bit digital to analog converter into an analog vo...

Страница 93: ...unter thus very accurately corresponds with the instantaneous position of the object independent of the influence from electronic components The same applies for the extended measurement ranges where...

Страница 94: ...D 10 D Functional Description of the Controller...

Страница 95: ...9 3 RS 232 The two following configurations are possible 9 600Baud 8 data bits 1 stop bit no parity bit factory setting 4 800Baud 8 data bits 1 stop bit no parity bit IEEE 488 GPIB For the interface...

Страница 96: ...el and via the interface The status REMOTE is set when an IEEE 488 GPIB bus controller asserts the signal REN and addresses the controller LLO LOCAL LOCK OUT The status LLO can only be set from the st...

Страница 97: ...1 VELO9 VELO1 VELO9 Sets the corresponding measurement range refer to table below VELO1 VELO9 VELO Loads the initialization setting for the measurement range refer to command RENDCL VELO OVR Queries w...

Страница 98: ...ation settings for the measurement range refer to command RENDCL AMPL RES Triggers the reset function of the displacement decoder RES Measurement range Range number m V OVD 10 OVD 20 0 5 0 2 1 8 2 20...

Страница 99: ...TRACK3 TRACK4 Sets the tracking filter to this value TRACK1 TRACK3 TRACK4 TRACK Loads the initialization setting for the tracking filter refer to command RENDCL TRACK Command Description Answer Answer...

Страница 100: ...LEV0 LEV40 Command Description Answer Answer with ECHOON l Slowly drive the motor to the left until the command N is received l L Quickly drive the motor to the left until the command N is received L...

Страница 101: ...berlin polytec de http www polytec de Tel Fax E mail Internet 33 1 48103930 33 1 48100803 info polytec pi fr http www polytec pi fr Great Britain GB Lambda Photometrics Ltd Lambda House Batford Mill G...

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