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???
09/02/05 03:43
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 		 #100428 - Switched Higher Current does help
Responding to: ???'s previous message
Hi all,

Just dropped in, so I share my 2cents:

I use higher switched current in most of my projects. But definitely not 100mA but around 8..10mA activ for about 1 msec per 100msecs (heating of PT100 goes with square of current). Then I have RC filtering for High Frequency pulses, plus I do averaging. Thus I get resolutions of better than 0.1°C even with 10bit internal AD converters of Atmel or Infineon or Philips chips. To improve accuracy, I use a spare PT100 input with a precision 100Ohm resistor to take drift of the current source into account.
One thing about using 4052 muxes: they are sensitive to ESD. Maxim offers a pin compatible 15kV ESD rated Mux for aobut 3$, I usually place zener diodes of 4V7 parallel to inputs to help this.

Werner

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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