Help with PT 100

Discussion in 'General Electronics Chat' started by aquib, Jan 20, 2008.

  1. aquib

    Thread Starter New Member

    Feb 26, 2007
    I need to design a sensing system using the PT 100. My sensing range is 30 to 50 degree centigrade.
    Using a 1ma source which is recommended, the voltage drop across the PT 100 is 0.11167vfor 30 degrees (resistance is 111.67ohms) and 0.1194 for 50 degrees (resistance is 119.4 ohms). My ADC has a analogue range of 0 to 3.3 v.

    Using the y-=mx+c formula, I get a gain requirement of approximately 427 and a offset adjustment of - 47v approximately.
    The values for gain and offset are too high. Can you please help me in designing the signal conditioning circuit.

    Aquib Fateh
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Here is a link to a good article on the resistive characteristics of an PT-100. It also provides a different expression for the relationship between temperature and resistance for the sensor.