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Temperature Control Explained

Published by Coastal Cowboy in the blog Coastal Cowboy's blog. Views: 593

A mod that is in temperature control mode seeks to provide a pleasurable vape by measuring the cold resistance of your coil, monitoring the resistance change caused by heat when you use the device, and adjusting the amount of power delivered to maintain a specified temperature based on the resistance of the coil.

There is no thermometer or thermo-coupling device on your coil or in your atomizer. Coil temperature is estimated by your device using a mathematical relationship between a metal’s temperature and its resistance.

You start this by allowing the device to read the resistance of the coil at about room temperature. This is the “cold resistance.” You then select the temperature you wish to use and a starting wattage. When you press the fire button, the device applies the starting wattage and monitors the resistance of the coil. The chip in the device is programmed to calculate the temperature based on the change between cold resistance and “live resistance.” Each wire type has a different relationship between its temperature and its “resistivity.”

Without getting into all of the math, understand that the relationship for each metal is defined by its “temperature coefficient of resistance,” or TCR. TCR is always a positive number because resistance always moves in the same direction as temperature—either up or down. TCR defines the rate of change in resistance. A higher TCR means that resistance increases faster for a certain temperature increase and a lower TCR means the opposite.

Currently, only Stainless Steel, Nickel and Titanium wires are supportable using temperature control. There are device manufacturers working on a TC algorithm that supports Nickel Chromium (NiChrome) but results are inconclusive as of February 2018. Your device is either pre-programmed with the data needed to perform the calculation, or the user provides the data through the device’s menu system or a program on your computer.

Here are the basic steps to getting a temperature controlled vape:
  • User installs temperature compatible coil (see above).
  • User selects temperature to vape and sets the starting wattage.
  • Device measures the resistance of your coil and stores it.
  • User presses fire button to begin vaping.
  • Device continuously measures coil resistance, calculates temperature and throttles or increases power based on the difference between starting resistance and live resistance.
It's a good idea to set the starting wattage somewhere higher than you would normally use with that coil. If you're a 50-Watt vaper, pick 55-ish. This gives you a quicker ramp up and lets you vape at temp sooner.

There is no way to vape at a wattage that will produce a temperature higher than your set temp. If you want to vape at 50 Watts and the mod is throttling back to 40, it means that 40 Watts is what is necessary for that temperature. If 50 Watts is too hot, it's too hot.

If your device has the ability to lock the starting resistance then you should take advantage of it. Locking cold resistance allows the device to more accurately estimate temperature. Say you’ve been vaping a while and your tank and device are warm. If your resistance has significantly increased since the coil was first read, the mod may not be able to correctly estimate temperature.

This confuses some people. Their vape may seem too hot for the set temperature, or temperature control is throttling back power because the change in resistance indicates that the set temp has been reached. If you don’t lock resistance or the mod isn’t programmed to do it for you, then you will be constantly fiddling with the temperature setting.

If you don't get starting resistance right, or if you cannot or do not lock starting resistance, your chances of success are very low.

Most people have a happy zone that’s somewhere between 380° F and 480° F. Below 380° F produces a very cool and weak vapor. Above 480° F the vapor is too warm and probably harsh. Cellulose, which is the fiber used in 99% of our devices, begins scorching at about 450° F. If your temperature setting is outside of this range, something is wrong. If your setup never reaches a set temp inside this range, something is wrong.

Electronic nicotine delivery has only been around about ten years. Temperature controlled vaping has only been around about two. Both technologies are developing and changes are coming rapidly. This entry was posted in March 2018. If more than a year has elapsed, things are probably very different.

More on the science:

Be it TC or DNA Replay, the thing is that we're dealing with a model of a real world phenomenon. The model is a mathematical relationship between at least one dependent variable and at least one independent variable.

Here's a simple univariate model where there is one dependent variable whose change in value depends on the change in the independent variable. Dependent variables are always measured by the vertical axis; independent always on the horizontal.

Say this is the TC model. Temp is x (horizontal) and Resistance is y (vertical).

upload_2018-4-9_12-9-24.png
In order for TC to work as designed, two parameters have to be reasonably accurate. The value of y at the beginning of the red line and the value that represents the change in the slope of the red line.

We call the first parameter the intercept because it's the point where the red line intercepts the y axis. We call the second parameter the coefficient because it's the measure of change in y given a change in x.

In TC, starting resistance is the intercept and the coefficient is TCR.

All models have to be calibrated, which means their model runs have to be compared to their real world phenomenon and adjusted until the model models reality.

There are two ways to calibrate the model. One is changing the intercept. Two is changing the coefficient. In some realities changing the intercept (starting resistance) for the model is enough to produce acceptable results if you are sure the coefficient is accurate. In others (complex, multi-wire builds) that's not enough and the TCR has to be changed. In really fun situations both need modification.

Changing the intercept by adjusting the starting resistance shifts the entire red line up or down in the same direction and by the same amount at all points. You start lower (or higher) and end lower (or higher).

Changing TCR changes the slope of the red line so that it gets steeper or flatter. Increasing TCR makes it steeper and decreasing it makes it flatter. Nickel has a very high TCR, so the slope for a Nickel wire is much steeper than that for Stainless Steel. Kanthal has an almost nonexistent TCR, so it's slope is very flat (which is why it is unsuited for TC.).
  • Old Greybeard
  • Coastal Cowboy
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