The oscillator section generates all drive frequencies for operating the oThe oscillator section generates all drive frequencies for operating the otherther
subassemblisubassemblies in the es in the vibrometervibrometer. The drive . The drive frequency for the Bragg cell is frequency for the Bragg cell is ofof
central importance as it directly determines the optical frequency offset in thecentral importance as it directly determines the optical frequency offset in the
interferometinterferometer and thus er and thus the center frequency of the the center frequency of the carrier signal.carrier signal.
The variable mixing frequency fThe variable mixing frequency f
LOLO
is automatically set by the system controlis automatically set by the system control
dependent on the dependent on the selected velocity measurement range.selected velocity measurement range.
Technically it is just about impossible to attain all desirable and realizableTechnically it is just about impossible to attain all desirable and realizable
characteristcharacteristics of the ics of the velocity decoder in a velocity decoder in a single universal subassemblysingle universal subassembly. The. The
modular concept of the controller thus permits the use modular concept of the controller thus permits the use of three differentof three different
velocity decoders whereby a maximum of two can be installed at the samevelocity decoders whereby a maximum of two can be installed at the same
time. The selection of the decoders depends on time. The selection of the decoders depends on the application. The modelsthe application. The models
available are the OVD-04, OVD-04HF and PLL-DC which feature the followingavailable are the OVD-04, OVD-04HF and PLL-DC which feature the following
characteristics.characteristics.
The OVD-04 as a broad The OVD-04 as a broad band decoder is band decoder is suitable universally for almost allsuitable universally for almost all
vibrometer applicatvibrometer applications in the frequency range up to 250ions in the frequency range up to 250 kHz. FourkHz. Four
mmeeaassuurreemmeennt t rraannggees s ffrroom m 110 0 tto o 1 01 0000 0 ccoovveer r mmoosst t tteecchhnniiccaall
applications with sufficient amplitude resolution. Characteristic is applications with sufficient amplitude resolution. Characteristic is the excellentthe excellent
amplitude and phase frequency response with extremely good amplitudeamplitude and phase frequency response with extremely good amplitude
flatness up to the highest frequencies. A special feature of flatness up to the highest frequencies. A special feature of the OVD-04 is thethe OVD-04 is the
DDC C ccaappaabbiilliitty y oof f tthhe e mmeeaassuurreemmeennt t rraannggees s 11225 5 aannd d 1 01 00000 . . FFoorr
detailed information, please request the respective application note.detailed information, please request the respective application note.
The OVD-04HF is a special version of the OVD-04 which provides anThe OVD-04HF is a special version of the OVD-04 which provides an
extended frequency range up to 1.5extended frequency range up to 1.5MHz when operating in the measurementMHz when operating in the measurement
rraannggees s 2255 ; ; 11225 5 aannd d 11 000000 ..
The PLL-DC is a The PLL-DC is a decoder which has been decoder which has been specially developed for applicationsspecially developed for applications
at the lower end of the velocity and frequency range of vibrations. It is anat the lower end of the velocity and frequency range of vibrations. It is an
excellent supplement to the broad band decoder OVD-04, as with its threeexcellent supplement to the broad band decoder OVD-04, as with its three
mmeeaassuurreemmeennt t rraannggees s 11 , , 5 5 aannd d 225 5 iit t eexxtteenndds s tthhe e aapppplliiccaattiioonn
range for low frequencies to cover also very low velocities. The lowerrange for low frequencies to cover also very low velocities. The lower
frequency limit of the PLL-DC is 0frequency limit of the PLL-DC is 0Hz, i.e. there is no amplitude roll-off at veryHz, i.e. there is no amplitude roll-off at very
low frequencies. Thus it is optimally suited for low frequencies. Thus it is optimally suited for vibration measurementvibration measurements overs over
long distances on buildings or other structures with low long distances on buildings or other structures with low resonanceresonance
frequencies.frequencies.
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