Distance transmitter to sampling volume

Hello everyone!

I want to know the exactly distance between the transmitter of my Vectrino and the middle of the sampling volume.

I read in the manual that the exact position is stored in Vectrino´s head configuration file. How can I reach this file?

Thank You!

Markus

Dear Markus,

You can retreive the exact position with the following procedure:

1. Open terminal emulator
2. Press the 'Log file...' button
3. Send the command 'GH' (Get Head Configuration)
4. Press the 'Stop logging' button
5. Open the log file in a binary editor. C6 (hex.) is the sampling volume. Convert the hex. value into a decimal value. 
6. Use formula [mm = 0.5*((1.5*n)^2 - (622.98))/(1.5*n-5.7)] to calculate the position.

It is a little bit difficult so we will extract and show the position in the next Vectrino software release!

Best regards

Marius Mathisen

Hello Marius Mathisen

Thank you for your information!

Best regards

Markus Schmitt

Hi Marius,

we just bought a Vectrino for use in a Lab Flume. Now, I tried to figure out the distance to sampling volume, too (as described above). Actually I did not quite understand which hex-value I have to convert. I mean C6 is 198 or so?? That's certainly not what you mean, right?

And furthermore - in the formular for calculating the actual distance - does "n" stand for the decimal value converted from the hex value? Thanks in advance! - you have to excuse my nescience

regards

Thomas

Hi Thomas,

Sorry for the late answer, but if you take a look at the attached image you can see the position of the hex-value marked with the blue rectangle. The output is from the GH command directly in the terminal emulator with binary output enabled. The distance is then found from

>> n=hex2dec('0043')  (Note the byte swapping here which is due to little endian represantation)
n = 67
>> 0.5*((1.5*n)^2 - (622.98))/(1.5*n-5.7)
ans =   49.9856

So in this example the distance from the transmit (centre) transducer to the mid point of the sampling volume is 50.0 mm

Best regards,

Sven Nylund

Great! Now I got it! Thanks a lot for the quick answer.

Thomas

Hi,

I have done some experiments on bottom roughness with Vectrino Plus. Since the results are quite sensitive to the actual distance of measurement from the bottom, I would like to know what is the usual range of distance between the mid-point of the sampling volume and the probe tip? Is it common for it to be off by 10% from the distance of 5cm which is stated in the manual?

As I don't have the instrument with me now, is it possible to retrieve the data mentioned in this thread (for calculating the actual sampling volume distance) from the .vno file?

Thanks!

Ken

The distance to the sampling volume normally varies less than 5%. 

The output from the *vno file contains the estimate of the distance that is collected at the beginning of the sampling period (and found in the *.hdr file).

Best regards, Atle Lohrmann

Hi Atle,

Thanks for your information.

As for the distance in *.hdr file, I found that it is the distance between the probe tip and the bottom of my flume. What I would like to have is the distance between the probe tip and mid-point of the sampling volume. With that I would be able to know the exact variation of this distance from the standard 5cm mentioned in the manual, so that I could adjust accordingly my z-axis (ie. elevation from bottom) in my roughness plot. Can this distance be found in *.hdr file or other output files?

Thanks and best regards,

Ken

Hi Ken,

Are you having trouble with the method Marius and Sven detailed in earlier posts in this thread? The method they describe will give you the distance you want, i.e. the distance from the central transducer (probe tip) to the midpoint of the sample volume. If you are please let me know and we can help you out with obtaining the needed information. This information isn't in the header file but the distance should not vary significantly from 5 cm.

P.J.

Hi P.J,

I had done some experiments and found that the measured flow roughness is lower than that obtained for a smooth turbulent flow, which is practically impossible. I suspect it could be due to error in my z-axis, ie. the measurement elevation might be off by a certain small margin. Since my experiment involves very small flow roughness, an error in the elevation of measurement by a few mm will affect my results considerably.

And another problem is that I'm currently away and don't have the ADV with me. So I'm wondering whether I can retrieve this info from any of the output files? And is this distance going to vary each time i start my ADV measurement? The method that Marius and Sven discussed can be used only if my ADV is connected to the software. AM I right? 

Thanks!

Best regards,

Ken 

The distance from probe tip to center of the Sample Volume will change with the speed of sound because fixed timing is used when listening to the echos from the Sample Volume. The method Marius and Sven describe can only be used when connected to the instrument, but there is a way to obtain this information from the binary data files. Please contact me at pj@nortekusa.com and I can help you with this. I also just realized after reading your first post this is what you wanted to know all along. Apologies for not catching that earlier.

P.J.

i still don't quite understand

what do you mean by

 n=hex2dec('0043')

as the number showed on the attachment is 43 00

and how did you convert this to n?

what is hex 2 dec?

sorry it might be a silly question

ray

Hi, hex2dec is Matlab function:

D = HEX2DEC(H) interprets the hexadecimal string H and returns in D the equivalent decimal number.  
EXAMPLES:  hex2dec('12B') and hex2dec('12b') both return 299

Best regards, Atle Lohrmann

Many thanks Atle!

Ray