Phase-measurement, PXI-4461

[sveinErik]

Hi

I would like  to do a hydroacoustic measurement with a common signalsource and two hydrophones. The hydrophones are mounted in parallell (same direction) at a fixed distance, - and is directed towards the signalsource with a given angle. This means that if I give an impulse from  the signal source, the soundwave will reach the two hydrophones in the same moment IF the angle is zero. If the angle is larger than zero, the soundwave will reach the nearest hydrophone first. I would then like to find the delay between "signal-aproach" on the two hydrophones, because this will give me the actual angel to the signalsource in the actual plane. Frequency is 20-100kHz, ane I need a lot of "dynamic space". Is 4461 the right alternative, and how acurate can I do this angle-measurement ? Can I do it this way at all ??

Svein Erik

[dousley]

Hi Svein,

Since you are wanting to find out time delay between two signals you will definitely want synchronization. So any of the DSA devices should work well for that since they use one ADC per channel and all the channels are synchronized. Additionally there are some S-series boards which can sample a little faster up into the MHz range. These S-series boards are lower resolution: 14-18 bits instead of 24 bits, however they are simultaneously sampled so you can maintain tight synchronization between channels. 

I'm not sure how to quantify "a lot of dynamic space,"  but I will say that a 446x family is going to be one of the best options when it comes to dynamic range both because it has a high dynamic range and it has many input ranges. I don't know how much you really need however, so that's difficult to say. There are other higher channel count offerings in the DSA family that may have the functionality you want. https://www.ni.com/en-us/shop/category/sound-and-vibration.html

If you are considering eventually doing three-dimensional algorithms, then I suppose you will need more than two input channels. The 4462 shares the same architecture as a 4461 but has four input channels instead of two inputs and two outputs.

How accurately can you make the measurement?  The DSA family generally publishes an "AI Interchannel Phase Mismatch" spec. It is on page 10 of the 446x specifications https://www.ni.com/docs/en-US/bundle/ni-4461-4462-specs/resource/373770k.pdf . So depending on which input range you want to use, you could have as good 0.08degrees or better. But it would depend on your application.

Hope that helps.

Daniel

Conditioned Measurements Hardware