XTR105 with RTD application(PT100)

Hello,

Looking in the XTR105 datasheet, you will find some calculations on pages 7-8 that should help you for either 2-wire or 3-wire configuration.  Page 8 of the datasheet shows calculation of PT100 resistance values for given temperatures, which in this case (0C and 100C) would be 100ohms and 138.51 ohms, respectively.  From there, you would calculate the component values per instructions on page 7 (for 2-wire) or instructions on page 8 (for 3-wire).   

For example, in 2-wire configuration, you would look to page 7 and set Rz = 100 ohms, or the RTD resistance at 0C.  R1 = 119.40 ohms, or the RTD resistance at 50C.  And R2 = 138.51 ohms, the RTD resistance at 100C.  From there, you would plug those values into equation (2) and (3) on page 7 to calculate Rg and Rlin1. 

Please note for 3-wire configuration page 8 has a table of given values already provided as well.

The XTR105 datasheet is linked here:  http://www.ti.com/lit/gpn/xtr105

Please post here with any additional questions/concerns. 

hey, Patrick Galvin, thanks for your help. i know how to calculate the value of the resistor. the datasheet has given me a lot of equation. but still i have some questions:

1: the word from the XTR105 datasheet "the XTR105 is available in DIP-14 and SO-14 surface-mount packages and is specified for the -40 degrees celsuis to +85 industrial

temperature range", and i donnt understand the word clearly.  and my understanding is that: the measure temperature range of PT100 is just -40 to + 85, but what i want to 

measure is 0-100, the desired temperature range(0-100)  is beyond of the datasheeet temperature range(-45 to +85). i donnt know whether i am right.

2: From the datasheet, the IC output is 4-20 mA. that's to say, in the minimum temperature ,the output is 4mA, in the maximum temperature ,the output is 20 mA. but it doesn't

give the resolution. my mean is that: if the temperature is 50.1 degrees celsuis, what the XTR105 will output ?

i donnt konw whether you understand what i mean. looking forward to your reply.

thanks.

1)  When discussing temperature range, the datasheet means the part itself can tolerate -40 to 85 C.  The PT100 however will tolerate a much wider range, and the part will be able to calibrate accordingly.  The part is usually remotely loctaed from the actual temperature sensor itself.  For example, if your temperature sensor was located in a liquid tub, the temperature in that tub could go up to 800C, however the XTR105 itself would be located elsewhere, and could calibrate for that temperature without a problem, even though it could not tolerate a temperature at 800C. 

2)  Page 11 of the datasheet gives example calculations regarding possible error percentage based on things like offset voltage, current reference accuracy, gain error, etc.  With calibration the max error should be less than 1%. 

Please let me know if this helps or if there are further questions.

Thanks and best regards,

hey, Patrick Galvin, i am really thank you. you helped me a lot. now, i have no questions about the application of the XTR105. let's just stop here. i know what to do now. thanks again.