Ok many know of my original goal to solder wires directly to CPU and then submerge in water bath to calibrate with Digitec 5810 dual linear thermistors. Well the last two days I have been getting with the program.
First step: Soldering. I took care of this like the professional that I am; I used way too much solder on the wire and once I got a good connection with the pin I then used solder wick to clean the adjacent pins
The key is to strip the wire nice and long and then wrap it like a noose around the pin. You can get a really good mechanical connection then and just solder the wire to the pin. Much easier to geta good joint.
Once the CPU was prepared, I had to set up a bath with stirrer. For this I used a Fisher Scientific digital hot plate magnetic stirrer with a stir bar:
Supposedly accurate to 1C but I had problems with the hot plate part. It is just not designed for low temp precision work. I had very little luck getting the damn thing to warm the water at all. Instead, I ended up putting a pot of water on to boil and exchanged water in the beaker for hot water to get to a higher temperature. Oh I put the CPU in a layer of Saran Wrap and held it with the core completely submerged and not touching the side of the beaker. The other temp probe is that of a Digitec 5810 dual linear thermistor. For diode readings I am using a Maxim 6655 diode reader system that connects to parallel port and has 0.125C resolution. I was hoping to get close to that in accuracy after calibration against the digitec
Here's the result:
Looks great! BUT
Those are the average of about 50 readings (4/sec) of the maxim reader per point. The average has a very good correlation obviously. But the std deviation is quite large (0.45-0.55). I suspect that the magnetic stirrer was the exact wrong thing to use and that it was generating noise that was making its way into my diode readings. I got the CPU a little wet, so I will try the calibration again tomorrow (or maybe later tonight) sans stirring.
Your thoughts?