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What is TCR or Temperature Coefficient of Resistance?
Every wire material has a specific resistivity. As a wire heats up, its resistance will increase in a predictable way based on its TCR.
TCR for a material is usually measured by the wire manufacturer using MIL-STD-202 Method 304, which uses a series of test temperatures. The first series is 25°, 0°, -15°, and -55°C; the second series are 25°, 50°,75°, 100°, 125°, 200°, 275°, and 350°C. The lowest test temperature in the first series, and the highest test temperature in the second series, are used as two points to create a linear TCR value.
What is TFR or Temperature Factor of Resistance?
Some materials may not follow a linear TCR completely accurately, so a TFR is based on observed resistance changes at a series of set temperatures that often follow a slight curve instead.
Here’s an exaggerated image showing the difference.
You can see the difference between a linear TCR and a TFR curve.
So why are you telling us this?
Well, being boffins, we created individual precise TFR’s for our Stealthvape wires that are suitable for use in temperature control. We built a very accurate PID controlled hotplate and monitored resistance changes in various coils suspended in a bath of silicone oil.
We used a platinum PT100 temperature sensor and also 2 k-type themocouples and recorded temperatures from -17c to 0c and from 25c to 300c in 25c increments.
Lars from the mighty Steam Engine helped us use that information to create unique CSV’s for Evolv DNA boards which can be uploaded to devices using Escribe . These CSV's for temperature control are available below.
Please right click and save as to download the following files:
If using a mod that doesn't accept TFR’s, you can often enter the TCR manually. Different mods sometimes expect a slightly different format.
Sometimes Ni200, for example, is usually 6000 but needs to be entered as 600, or 0006.
Based on the TFR test results, we’d suggest using the following values depending on the format the mod is expecting:
NifFe30 : 4920 or 492
316L : 883 or 88
Ni200 : 6230 or 623
Wires like Kanthal A1 and Nichrome 80 / Ni80 have a very low TCR, so don't work in temperature control mode. Evolv DNA250C boards are able to use the Replay feature with Nichrome coils (with varying degree of sucess) by activating the "Allow on Dubious Coils" setting in Escribe. We won't however be including Nichrome or Kanthal wires in our TFR measurements.