Weller WSD81 conversion for WEP70 handle

[mb.raghavendra@gmail.com]

Hi All,
 Looking for help with conversion of WSD81 station to work with WEP70 handle(Iron). . . I have added schematic for WSD81, Temp to ohm measurement of WEP70 . 
Can someone calculate how to change values near op amp to get work WSD81 with WEP70 handle? Please look in to Opamp circuit and guide me how to calculate gain. i am unable to understand amplifier circuit.

Also observed that WEP70 sensor output is 42uv per deg C. Connected MAX31856 Thermocouple to Digital Converter  as K type and there is difference up to 30 deg C. If used as J type, 10 deg C difference .  i want use existing circuit ofWSD81 with amplifier modification.

 I disconnected op amp output from uC(PIC 16F833) and added 0-5V power supply. Then I measured changes voltage on uC input to temperature on display.



3.76V -> 450C
3.6V -> 430C
3.5V -> 420C
3.08V -> 350C
2.76V -> 300C
2.41V -> 250C
2.06V -> 200C
1.72V -> 150C
1.55 -> 125C
1.31 -> 100C

Temp vs Ohm for WEP70
https://drive.google.com/file/d/1rnwCHuXmn1hN-6EV6Uaop-YM5JTENz22/view?usp=sharing

WSD81 Thermocouple amplifier
https://drive.google.com/file/d/1UEseWgFicUVtNYRAA5qM3oc3ciavH3Uy/view?usp=sharing

WSD81 Schematic
https://drive.google.com/file/d/13FuGd4SxCQ4SbISW1Xo0eS6DBc5uD1Re/view?usp=sharing

Some information from other post, may be useful.
https://www.eevblog.com/forum/repair/weller-we1010-conversion-for-wsp80-handle/