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08/22/05 15:55
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 		 #99833 - Analog mux for Pt100
I have a problem as follows:

8 X Pt100 3-wire sensors are multiplexed using an analog multiplexer circuit and 8052 which selects and measures the appropriate sensor - approx 1ma is used as the exitation current. Although this works reasonably well, I would like to increase the immunity to noise
(probe lengths are very long and customer is fond of speed controllers!) by using a pulse method e.g. say 100ma for 10ms/Second. Has anyone seen any mfr apps. or any ideas where I could find out any possible problems with this approach?
It seems logical to me, but why cant I find any info?
Thanks
Chris.

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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