Hi Mario, I don't have that much experience with that specific model, but the gain (appropriate range for the vibrations you are measuring ) is usually set on the instrument itself. Setting gain on the data acquisition board won't help you much if you're not in the right measurement range. (It is also possible that you're vibrations are too small or large...)

If you look in the metrology section here that might help: https://www.polytec.com/fileadmin/d/Vibrometrie/OM_DS_PDV-100_E_42474.pdf

Natasha Mhatre, thank you for your answer. I will check this information in the source you pointed out. Anyway, if I can make an additional clarification, the measurements are being made no more than 1 m away from the intended targets. Vibrations vary, but also could be large, since the physical environment through which they are traveling is the leaf litter. Best regards.

Hi Mario,

I'm using a PDV100 together with the VIB-E-220 from Polytec to record vibrations from insects and spiders. I always use the most sensitive measuring range ("Velo" on 20 mm/s, set directly on the PDV100); as far as I know, the USB-Box just converts the analogous output from the laser to the digital output for your Computer (so no change of any gain parameters here). This has always worked for me, but depends also a lot on the signal-to-noise ratio... (check the overrange inidcator on the laser). The only problem I ever had was that the USB plug of the Box easily gets full of dirt (especially when used in the field a lot), so you loose the connection every know and then (usually when you're in the middle of a really promising recording ;) ). I hope that helps! Cheers, Monika

Hi Monika J.B. Eberhard, thank you for your advice. I am using the same settings (Velo set to 20 mm/s, cutoff frequency of the low pass filter set to 22kHz). I am afraid none of the interface options I mentioned are rugged/stable enough for prolonged fieldwork as I would like to. That is why I tried the very small SB Play!, but the resulting signals were kind of awkward. Thanks once again and my best regards.

Just a technical note, to avoid confusion: the "20" setting on the PDV-100 doesn't mean 20 mm/s, but 5 mm/s/V. Perhaps this will help you set gain. Though, in my experience, that laser produces comparable voltage to microphones when recording vibrational signals of insects, so I never had to play with gain to obtain good recordings. Could you explain what you mean by "awkward" signals? Perhaps it's a different issue.

Jernej Polajnar Hi Jernej. Thank you for your comment. You are correct. 20 mm/s is the full scale value range as shown in the LCD and 5 mm/s/V is the respective scaling factor, corresponding to the output voltage swing of ±4V. What I meant by "awkward" is that the signal was amplified (over 40 dB FS) in an undesirable way when I used SB Play! It is curious, because this did not happen with the SB X-fi, whose only practical difference is having a volume control dial. I had to craft a BNC to RCA/P2 cable to use this interface, so there may be a problem with this connection and I have not yet been able to detect. Regards, Mario.

Hi Mario, I have never used the interfaces you mentioned, but in my experience, when using a generic audio interface, you should set the gain using an oscilloscope. May be this is why the signal was amplified. Does it sound reasonable or you were already using the oscilloscope?