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Kai Klaas
11/15/05 08:32
Read: 942 times

#103750 - Periodic interference can make them fail
Responding to: Frieder Ferlemann's previous message
Frieder said:
You might find a median filter (read f.e. 5 values, sort them, then take the middle one) to give good and robust results.

Median filters and similar methodes can be very annyoing, if periodic interference is superimposed to signal!

When I was at CERN we had big troubles in reading out our MX7-chip mounted at the LEP (large electron positron storage ring), because we used ready made data aquisition software, which sorted a portion of about 30 samples and removed the five most deviating ones afterwards. The result then was some strange noise, we couldn't find an explaination for.

What has happened?
Due to a hum loop, hum was introduced to signal, which could have been nearly totally averaged out, when, yes, when all the samples would have been taken into consideration with the averaging process. But, removing even only one of the samples will result in an imbalance, and the averaging can fail!

The same with median filters: If periodic interference is superimposed to signal, then removing a number of samples and focusing on certain other ones which seem to be representative can result in big errors.


List of 16 messages in thread
Weight Scale Avarging method      Thakkar Bhaskar      11/12/05 02:20      
   Filter providing two time constants      Kai Klaas      11/12/05 07:31      
      median filter, simulate algo on PC      Frieder Ferlemann      11/12/05 07:47      
         Periodic interference can make them fail      Kai Klaas      11/15/05 08:32      
            Acknowlegded.      Frieder Ferlemann      11/16/05 08:24      
               Agreed      Kai Klaas      11/16/05 09:24      
                  50Hz sampling      David Smith      11/17/05 03:54      
                     Anti-aliasing filter will help      Kai Klaas      11/21/05 06:27      
                        what this is all about      Erik Malund      11/21/05 06:37      
   Moving average window.      Graham Cole      11/14/05 01:50      
      Average on condition      Kai Klaas      11/15/05 07:29      
         is that not SOP (standard operating proc      Erik Malund      11/15/05 07:41      
            Hallelujah!      Kai Klaas      11/15/05 07:55      
   meaningless      Erik Malund      11/14/05 06:34      
   What are you using that one for in a wei      Erik Malund      11/14/05 09:14      
   hello from chhatraliamd for weight scale      Chhatralia Mansukhbhai Dh      12/27/05 01:01      

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