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???
08/26/05 12:48
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 		 #100144 - Filtering MUST help. So, there's a mista
Responding to: ???'s previous message
Chris said:
+/- 0.5C is acceptable, but due to interference from local 3 phase inverter speed controllers (without any EMC compliance)
the actual noise induced on the probe cables causes a shift of about +/- 2.0C depending upon inverter speed settings, local earthing (seems to depend on weather) etc.etc. I have tried filtering/averaging etc without success.

There must be something wrong with your setup! As PT100 signals are nearly DC you can filter out nearly every noise by a simple RC low pass filter. No interference should have any influence on this!!

So, if you result with +-2°C error even with filtering, then there must be something wrong with your setup! I assume a ground routing mistake of the cable shields and/or ground lines of PT100 elements.

Could you publish your scheme?

Kai

List of 37 messages in thread
TopicAuthorDate
Analog mux for Pt100            01/01/70 00:00      
   Precision            01/01/70 00:00      
      Precision is the same?            01/01/70 00:00      
         Err            01/01/70 00:00      
            Inertia!            01/01/70 00:00      
               Precision.            01/01/70 00:00      
                  Precision            01/01/70 00:00      
                     PT100 sensors            01/01/70 00:00      
   try another way, have a look at Linear T            01/01/70 00:00      
      No choice            01/01/70 00:00      
         it is still valid            01/01/70 00:00      
         The usual solution is...            01/01/70 00:00      
            As I said before            01/01/70 00:00      
               Whats the problem ?            01/01/70 00:00      
                  Acceptable limits            01/01/70 00:00      
                     hooking the PT100s up to differential in            01/01/70 00:00      
                        Thanks            01/01/70 00:00      
                           4 wire ?            01/01/70 00:00      
                     Filtering MUST help. So, there's a mista            01/01/70 00:00      
                        Ditto, filtering must work            01/01/70 00:00      
                           Exactly!            01/01/70 00:00      
                     Errm.            01/01/70 00:00      
   Look at existing products for ideas            01/01/70 00:00      
      that will give you more problems than it            01/01/70 00:00      
         It's not what I suggested            01/01/70 00:00      
            No chance            01/01/70 00:00      
               Again, not what I meant            01/01/70 00:00      
                  Sorry            01/01/70 00:00      
   Switched Higher Current does help            01/01/70 00:00      
      I am interested, it took some search, fo            01/01/70 00:00      
      I heavily doubt this            01/01/70 00:00      
         not as to noise, but it does have the ef            01/01/70 00:00      
         higher current does help            01/01/70 00:00      
            You can use pulsing and filtering            01/01/70 00:00      
               It's the same as DC measurement            01/01/70 00:00      
                  How pulsing improves performance            01/01/70 00:00      
   Averaging(filtering) has the same effect            01/01/70 00:00      

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