A little status report;
Well I am starting to get a good feel for the accuracy and repeatability of the equipment. In terms of accuracy of the sensors and the calibrations for them I am pretty happy, I am satisfied that they are accurate where they need to be and that they are being consistant.
One exception is the flowrate calculation at higher flows, it uses the water in-out delta T and places impossible demands on this number above about 5-6lpm. I would need a resolution in excess of 0.001° in order to generate an accurate number at these rates, that at a heat input of 60W. At lower power levels the problem gets even worse.
Still, this gives me info about the water temperature accuracy, by varying input power I can detect these small errors and make a correction to at least keep the flowrate the same over varying power levels. This is a really small correction 1 or 2 lsb's (0.005-0.01°C) and has absolutely no visible impact on for example waterblock C/W. This particular calculation (flowrate) is also affected by the calculated heat flux but the sensitivity is far less, requiring a die sensor offset in excess of 0.4°C to produce the same error. I choose to believe that I am far better than this, accuracy for these low resolution sensors being better than I am able to resolve (~0.025°C for "in copper" thermistors, ~0.005°C for water sensors) That might sound a little weird, but with averaging you can exceed the resolution of the system in accuracy, if the measured quantity varies in absolute terms. (Perturbation theory anyone?) Also the Steinhart-Hart system for calibrating thermistors is industry standard and has measured errors in the region of less than 0.001°.
What I am not happy with is the mechanics of my setup. I am finding it extremely difficult to mount properly with the smaller die, I am getting tilted mounts rather frequently, this will require lots of practice, remounts and new thermal paste before I get confident of repeatablity. The previous die at 12x12mm was an order of magnitude easier despite not having the fluxblock alignment supports I have now. I could get the same results every time with little effort. This I would put foward as the single biggest reason for NOT using a 10x10mm die for testing. However, for now I guess I just need practice.
Warning about the above series of posts, these have all been for the purpose of verifying the equipment and are the results of ONE mount. I am not confident that this was a "good" mount so expect future readings to vary a bit. I will built up a mount history before posting any results as absolute.
I am confident that it is possible to generate absolute numbers using this technique.
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