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Thread Closed: Off-topic

Michael Karas
07/07/05 00:29
Read: 837 times

#96750 - Current Source
Responding to: Oleg Sergeev's previous message
The LM4120 is configured to produce current 0f 1 mA through the silicon diode. The reference part is essentially a voltage regulator producing a precise 3.3 volts across the 3.3K ohm resistor. The current through this resistor is thus 1 mA. The total current through the silicon diode is the sum of the 1mA plus the GND lead bias current of the LM4120.

At a constant current the forward voltage across the diode will be nicely linear over a working temperature range from -55C to +125C. It should be possible to achieve linearity to around a degree or so (if my memory from a project I did years ago serves me correctly). The circuit output voltage is about 0.6 volts at room temp and will go down for higher temps and go higher for colder temps. The voltage change is about 2.2 mV / deg C. A 12 bit A/D works reasonably well but it may be advisable to condition the signal via some gain at the input of the A/D converter. If the conditioner has a negative gain the response slope measured by the A/D converter will match the temperature change slope.

Michael Karas

List of 16 messages in thread
measuring water temp inside tube      Juan Arredondo      07/06/05 12:19      
   re: measuring temp      Jacob Boyce      07/06/05 12:31      
   ir thermometers      Jez Smith      07/06/05 12:33      
      failling that .....      Jez Smith      07/06/05 12:35      
   Non-contact temperature measurement        Joseph Hebert      07/06/05 12:39      
      re:measuring temp.      Jacob Boyce      07/06/05 12:51      
      Auto Clave!      Mehdi      07/06/05 21:39      
         Auto Clave!      Mehdi      07/07/05 01:25      
   Why rubber ?      Steve M. Taylor      07/06/05 14:26      
   insulate?      Jan Waclawek      07/06/05 14:33      
   My Idea....      Michael Karas      07/06/05 23:11      
      explain      Oleg Sergeev      07/07/05 00:11      
         Current Source      Michael Karas      07/07/05 00:29      
   Is isolation necessary?      Michael Karas      07/06/05 23:54      
   Where is Juan?      Jacob Boyce      07/07/05 14:35      
      Dunno      Steve M. Taylor      07/07/05 15:07      

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