LMS Test.LAB: Acoustic order tracking measurement ...


Dear all,


I had measured an acoustic order tracking. Then I can create a picture with the acoustic order. In this picture I can calculate on the y-axis under processing a weighting e.g. like A. When I want the same with the overall level of the acoustic channel then I get the message from the program: Weighting can only be applied on frequency spectra.


My question: Why can I calculate only the orders not the the overall level with a weighting?


The weighting with an overall level I can only create with the a measurement under Online Processing. It is not possible, when I forgot a weighting e.g. A at the measurement with an overall level, to make a subsequent calculation in a picture.


Why not?


The only way to calculate it later, is the detour via the Time Data Processing.


Is there an easier way ?


Thank you for your reply.


Re: LMS Test.LAB: Acoustic order tracking measurement ...

Siemens Phenom Siemens Phenom
Siemens Phenom

The situation is exactly as you outlined, applying A-weighting to an overall level in an active picture or display by using the "Processing" option on the Y-axis is not possible. It is necessary to reprocess the data to get the A-weighting.


Here is a bit of an explanation why this is the case:


With an order, each rpm data point corresponds to one frequency value (rpm/60*order number).




And in the A-weighting curve, there is a specific gain/attentuation value for each frequency:





So the calcuation can be done using just the order data in the display.


The overall level is very different.  Each value in the curve is the rms summation of all frequencies at a given rpm. This is shown in the picture below. 





There is not a one to one correspondence between the rpm value and a single frequency in the A-weighting curve.  As a result, when displaying an overall level (and not having the corresponding waterfall somewhere to reference), the A-weighting calculation cannot be done.  The display only knows about the overall level versus rpm and nothing else.


I know if the overall level is not calculated during the acquisition, this requires reprocessing.  Just one thing to point out that may help.  Both a linear and A-weighted overall level can be calculated simultaneously during acquisition:





Obviously this needs to be done upfront, but hopefully it helps a little anyway.