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Message ID: 2799     Entry time: Thu Aug 4 10:16:04 2022
Author: Radhika 
Type: DailyProgress 
Category: Emissivity estimation 
Subject: Megastat RTD calibration 

[Clare, Radhika]

We performed a calibration procedure on the newly ordered RTDs for Megastat, in LN2 and ice water. We noted that these are 1kohm RTDs at 0C, as opposed to the 100ohm RTDs previously calibrated that are inside the chamber. We chose to calibrate 6 RTDs and labeled them alphabetically starting with G.

The first calibration point was taken at the boiling point of LN2. We dispensed the LN2 into a dewar and dipped each RTD just below the surface of the liquid. Since the temperature right below the surface is 77K with relatively high accuracy, we only took 1 measurement of each RTD resistance. The results are tabulated below:

RTD LN2 measurement 1 (ohms)
G 196.8
H 197.0
I 196.9
J 196.4
K 197.2
L 197.1

The second calibration point was the melting point of ice. We created an ice bath by filling a beaker with crushed ice and adding deionized water until 1/2" below the surface of the ice. We let this equilibriate for a few minutes and then proceeded to dip each RTD and record its resistance. When we started this process, we realized we had not let the system equilibriate for long enough, since the temperature of the water was dropping with every measurement. The water surrounding the ice had not yet been cooled sufficiently. We scrapped the first set of resistances, but the 2 rounds of valid measurements are tabulated below. The multimeter was overloaded when set to display the resistance in ohms, so we had to display kohms and thus lost a significant figure. 

RTD H2O measurement 1 (kohms) H2O measurement 2 (kohms)
G 0.990 0.990
H 0.992 0.989
I 0.991 0.992
J 0.992 0.993
K 0.992 0.993
L 0.992 0.991

RTD G was dropped and lost after calibration, but we calibrated more than we needed in anticipation of an accident like this. 

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