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Last update:
Oct 31/16 (65)

    

Defective 1-Wire Temperature Sensors
    

I recently received (Sep/09) some DS1820 temperature sensors from a supplier.  In doing test hookups I discovered that 4 of the 5 sensors were giving erroneous readings.  

This is what I saw: 
  a. Connected to a K145, 3 sensors had constantly changing readings, 
        fluctuating between roughly -127 and +127 degree C.  A 4th sensor 
        was stuck at a continuous +85 degree C.  
  b. Connected to a K190, these same 4 sensors all were stuck at a 
        continuous +85 degree C.
  c. The 5th sensor appeared to be giving okay readings 
        (when compared to a known good sensor) 
All sensors were connected either directly to kit terminals, or through short (6") lengths of cable, 
so cable length would not have had an influence.     

The 4 "bad" sensors all had the same numbering on the package, like so: 
  Dallas 
  DS1820 
  0345B7  
  118AA 
From this I guessed it might be a bad manufacturing batch.  It turns out that's so, but with a broader scope.  See the 1Wire.org website...  under "Reference Materials", have a look at the "1-Wire Chip Problems" page.  Apparently the B7 chip die is known to be bad.  This affects both DS18S20 and DS18B20 sensors.     

Sadly, my 5th new sensor also has the B7 designation, so is suspect, too.  My supplier has agreed to provide replacements, once he's sourced a supply of non-B7 sensors.  

For those of you reading this: forewarned is forearmed.     

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