You can see here that some of the units that were 1pt low between 350-380 change over to 1pt high down around 300. Once they are all roughly classified I bring up the sensors from each designated band to check if the high/low behavior of all the units in the group is stable over a larger section of the curve: Once a sensor is labeled I hide it from view (by un-checking the box), so that I can click & label the remaining sensors. I right-click on the lines and label the nodes with their behavior in Excel. although they tend to toggle up or down over the length of the curve. These sensors usually tend to have stable offsets to within 1 LSB, so they group together naturally into ‘bands’ of 2pt high, 1pt high, 1pt low, etc. The Thermapen reference line is the one with round markers, and has been converted to equivalent integer values)
On a batch of about forty sensors, you see a spread something like this: I ignore the first few high temp readings as the bath convection stabilizes, and focus in on the curve at my temperature band of interest, which for the next deployment will be about 24☌. ( The Thermapen has a resolution of 0.01☌ & accuracy of☐.04☌ – so not quite the ☐.01☌ accuracy I should be using for my ☐.1☌ target, but more affordable at ~$200 and it has a NIST traceable calibration certificate.) I cover the whole thing with towels for insulation, turn off the bath heater and, manually take reference readings every 1/2 hour as the water cools from about 40☌ to around 10☌. The copper tube lets me keep the tip of a Reference Thermapen right in the center of the bunch.
STM32 1 WIRE LIBRARY SERIAL
After attaching crimp pins & assigning each sensor a serial number, I put several groups of them together in the water bath by binding them around a short length 1/2″ copper tube that has a felt plug at the bottom. The somewhat annoying folding off/on feature of the Thermopen design forces you to take it out of the bath every 10 minutes as the unit times out.Īs I dive into another batch of cheap DS18B20’s for a new set of temperature strings, I thought I should post a note about the pre-filtering I do with these guys before investing effort to properly calibrate and epoxy them.
I use the same thermometer for individual sensor calibration later on, but in that case it’s the DS18B20 probe that moves in and out of the copper sleeve, while the Thermapen stays in the Calibration Bath most of the time. Without the dryer lint stuck in the end, the last digit on the Thermapen sometimes does not settle.
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