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David Smith
11/17/05 03:54
Read: 982 times
Nottingham
Uk


 
#103848 - 50Hz sampling
Responding to: Kai Klaas's previous message
Something that caught me out once with FIRs: If you sample at precise 50Hz in order to cancel mains hum, the mains varies +/-1Hz (sometimes worse). You end up with a 'beat' signal of 0-1Hz on the output! This is virtually impossible to get rid of.

I actually changed to sampling rate of 60Hz - beat was now 9-11Hz - further filtering could now tackle this. Ultimately forgot FIRs and moved to IIRs, sampling at 50Hz, which removed the effect. And saved me copious RAM... Not so effective though.

(For the US and Far East, swap 50 and 60 in the above text...)

Dave

List of 16 messages in thread
TopicAuthorDate
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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