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Creating a TCR profile ( not using steam engine curves)


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How does one go about finding the proper value for wire not profiled on steam engine (or listing incorrectly) or rather determining the coefficient?

I have a lot of stainless wire that isn't working properly with any of the steam engine values downloaded and sent to the dna mod. I would like to find a way to profile that specific wire to ensure accuracy but dfo not know how to measure the appropriate values - or how people are measuring at steam engine, specific vendors, etc.

Thanks for any information - I'm hopeful the downside is that it's time consuming, not that it needs specific equipment etc.

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It is time consuming and requires accurate measuring equipment.  You need a way to measure ohms to the thousandth and a very accurate temperature measuring system.  This post and the thread it is in will be a start:

https://forum.evolvapor.com/topic/68195-topic/?do=findComment&comment=913245

Alternatively you can write to the steamengine creator and talk about what you see as wrong with the profiles created.

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By the material:

From a consistency standpoint, the problem with Stainless is that it is an alloy - a mixture, not a pure element - and graded by mechanical properties, not electrical properties.


By the coil design:

Because SS's electrical resistivity changes less with temperature than other metals, there is a greater need for mod resistance to be correct (something, ideally, the manufacturer would have measured and set, and many do), and mostly importantly, a higher resistance would help. Here's an example:

Say our coil is 0.06, and the mod resistance is 0.02. A worst case scenario. Honestly, most mods have half or less this mod resistance. At temperature, say, 400F, the coil resistance will rise 20%.

If the mod resistance is set correctly, it will read the coil at 0.060 cold, and be 0.072 hot. This does mean the full temperature range is 0.012 Ohms. That's 0.012 Ohm/330F, you're literally talking 25 degrees per milliohm. This will be very hard to control accurately. It will average 400F though.

If the mod resistance is not set (that is, set to 0), it will read the coil at 0.080 cold, and a 20% rise is 0.096. The actual coil will be 0.060 cold, and 0.076 hot. This is a 26% rise instead of 20%. It will average 510F -- an error of 110F. This error in mod resistance corresponds to 70F on Nickel.

Now, say we double the coil resistance to 0.12. Because this doubles the number of Ohms in the full temperature range, it doubles the precision with which temperatures can be measured. Additionally, if the mod resistance is set wrong, let's do the calculation again: 0.120 cold reads 0.140. 20% rise is 0.168, so 0.148 on the real coil instead of 0.144 if mod resistance were right. 23% rise. About a 60F error. Better. If we double it again, twice as good again...


So:

(1) correct mod resistance helps to avoid offset errors, which are magnified by SS's less changing electrical resistivity
(2) for Stainless, a higher cold resistance would mean a greater range when it's hot, so better ability to accurately measure the material
(3) even if you do both of these, SS is still an alloy so, unless you control a steel mill, you are going to have trouble getting consistent electrical properties between orders... and because of SS's electrical resistivity, even small errors in what goes into the CSV will translate into large errors in temperature. Good luck. :)

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I don't have the necessary measuring equipment myself, so I rely on information that is publically available, or sent to me, in order to update Steam Engine. For the reasons listed by James, I don't believe we will ever have accurate standard SS files anyway. It is better to use NiFe or Ti if you want accuracy, IMHO. I suspect that the people using SS adjust to taste and call it good enough - which is fine if that's what you want.

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