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Message ID: 2118     Entry time: Thu Aug 2 08:25:37 2018
Author: Mandy  
Type: DailyProgress 
Category: Temperature Sensing 
Subject: RTD Calibration Update  
 
Note: Before we found a calibrated diode to work with, we went ahead with fixed-point calibration baths: liquid nitrogen, ice water, and boiling water. However, the accuracy is questionable considering things like impurities in the water, and the just-realized strange behavior of the RTDs. 
 
 
Prep
I started with the RTDs in room temperature, wrapped them individually in foil (the RTD mounted between two silicon disks was first placed in a case that I punctured to run the wires through), and placed all three RTDs in a plastic baggy that I checked was water-proof. The opening of the bag was sealed with Kapton tape. I checked that there weren’t any strange or major changes in the readout, having placed the RTDs in the foil and baggy. There was a spare RTD with leads that weren’t soldered to a Lemo connector, I prepped that one the same way as a tester for the baths. 
(Attachment 1)
 
Liquid Nitrogen 
I filled the Nalgene dewar with liquid nitrogen, placed the tester RTD in for about 5 minutes, then placed the RTDs in around 1216932900. I replaced the dewar cover once the RTDs were in.
(Attachment 2)
 
Ice Water
I filled the dewar completely with ice (there is an ice machine in the Blacker basement!!!) and filled in the space with water, keeping a high ice-to-water ratio. While I let the mixture settle for about 10 minutes, I replaced the bag that was used in the nitrogen bath. After testing the dummy RTD for about 5 min, I placed the RTDs in around 1216071824. I replaced the cover once the RTDs were in. 
(Attachment 3)
 
Boiling Water
I found a 2000ml Pyrex beaker, filled it with water, and placed it on a hot plate. I covered the beaker with foil. After the water came to a boil, I placed the tester RTD in for about 5 min. After checking that the tester RTD survived, I placed the RTDs in around 1216937100 and replaced the foil cover. 
(Attachment 4) 
 
Conclusion
Because we had found a calibrated diode to use, I never finished getting the calibration curve from this set of data. I went back this morning and did it very quickly, just picking out averaged points from the curve where the voltage stayed consistent after submersion, and found the values to be about: (RTD1) m = 0.0082, b = 0.1256; (RTD2) m = 0.0092, b = -0.0883; (RTD 3) m = 0.0093, b = -0.1472. These approximate values are just in case we want to do some further troubleshooting with the current RTD setup, but it is likely that we will be building a new circuit next week anyways.
 
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