Hello
regarding precision / accuracy level if I refer to There are two resistance tolerances specified in DIN/IEC751:
Class A = ±(0.15 + 0.002*t)°C or 100.00 ±0.06 O at 0ºC
Class B = ±(0.3 + 0.005*t)°C or 100.00 ±0.12 O at 0ºC
Two resistance tolerances used in industry are:
1/3 DIN = ±1/3* (0.3 + 0.005*t)°C or 100.00 ±0.10 O at 0ºC
1/10 DIN = ±1 /10* (0.3 + 0.005*t)°C or 100.00 ±0.03 O at 0ºC
I think I can sort 1/3 ( cheaper ) to select some low tolerances value and match 2 sensor as the purpose is a differential measurement as I succeed to match /sort SMD resistor I can succeed to match/sort Pt100 sensor
I suppose than metrology Pt100 probe are selected or perhaps built as wire wound resistor https://instrumentation.com/5615-secondary-reference-probes-instrumentation.aspx , for information this probe is in range of 1700 USD !!!!!! new
one connector = 40 USD
one meter / 3 feet of quality cable / wire = 40 USD
one cable spring holder = 20 USD
one SS 319 probe sleeve tubing = 150 USD
one handle in SS304 = 150 USD
Not included the calibration and the assembly . that let a bit of budget for the sensor itself
For the setup the two main type of measure are contact or non contact which are the same than thermocouple temp measurement , in my case I can use both but for initial setup I prefer contact sensor to metal
I usually use 3M sealant glue over the sensor and not between the sencor and the metal part I also glue the wire to avoid any ''pull force affect '' on the small sensor
Calibration probe are not Pt100 contact probe as the probe is protected by a stainless steel shield / tube , the problem is the reaction time when measuring air temperature ( grill shield ) or thermal conductivity plain shield , same the same again with thermocouple probe
Fast temperature measurement are done by using very thin thermocouple with direct contact on the surface , problem is the accuracy / precison as difficult with thermocouple to reach accuracy of a Pt100 sensor .
I use 2 pair wire cable with braided shield , wire are copper silver plated ( military surplus wire )
Regards
OS