Resistance locking: Why you shouldn't

[KurtVD]

When I did a search on how to set up TC, the first thing I found was that it was important to read the resistance of the coil at room temperature and then lock it. Then I realized that in both programs (eScribe and Arctic Fox), you can just as well NOT lock the resistance, and it didn't seem to make a difference, so I wondered: what is the advantage of locking it?

From what I can tell, both my mods (VT Inbox with the DNA75 and istick Pico 75W) 'know' what the cold resistance of the coil is. You can open the device monitor and it will show your cold resistance, no matter how warm your mod or your coil are at that moment. And if you do not lock the resistance, the mod will simply use this value as base value. If you enter this value manually and lock it, it will not change anymore, even if your coil's resistance changes slightly over time (which can happen). However, if you do not lock it, you can get your mod to read your coil's resistance and set it as a new base line any time you want, for example if you feel that the temperature of your vapour is off, without connecting it to the computer. With dna mods, simple disconnect the atomiser and reconnect it, and when you press the fire button, instead of firing, it will ask you on the screen to confirm or not (+/-) the new value of the coil. With Arctic Fox, you can set a shortcut to do that.

Is there really any reason (anymore) to lock the resistance?

 

[KurtVD]

However, if you do not lock it, you can get your mod to read your coil's resistance and set it as a new base line any time you want, for example if you feel that the temperature of your vapour is off, without connecting it to the computer.

I might add, you have to let your coil cool down to room temperature before you set the new base resistance. Also, on DNA mods, you have to press the fire button once while the atomizer is disconnected, before you reconnect it, otherwise it won’t read the resistance and let you set it.

 

[tailland]

How would the TC mode know that a value is the desired baseline value, if you don't tell it by locking it into place?

 

[Eskie]

Just a side note. Typically DNA mods should not have the resistance locked. The board continues to refine the base resistance over time. Other boards may behave differently, and locking the resistance may well be the only way those boards will function without tossing you out into power mode when the base resistance drifts.

 

[KurtVD]

How would the TC mode know that a value is the desired baseline value, if you don't tell it by locking it into place?

I don’t know, but I would guess that it uses the mod’s built in thermometer to calculate the baseline resistance of the coil.

 

[KurtVD]

The board continues to refine the base resistance over time.

Are you sure about that? Because in this case, it wouldn’t be good to have it manually re-read the resistance, since that would reset the refinement process.

 

[Eskie]

Are you sure about that? Because in this case, it wouldn’t be good to have it manually re-read the resistance, since that would reset the refinement process.

That is a standard feature of DNA boards.

 

[tailland]

I don’t know, but I would guess that it uses the mod’s built in thermometer to calculate the baseline resistance of the coil.

The mod's inbuilt thermo sensor senses the the temperature around its sensor, meaning to protect the chipset/board, but has nothing to do with the coils. The coil temp is calculated by the change in resistance in the coil, not sensed.

Having the correct baseline temp is crucial for TC to work. Of course the mod can still fire up a coil without having a correct baseline reading, but it will then apply the wrong power to it, rendering TC's purpose inactive. The result is everything from no vapor to burning the coil/cotton - the exact opposite of what you wanted it to do.

 

[DaveP]

I thought that the base cold coil resistance was read when you installed the cold atty. Hence the need to make sure it's room temp when first installed.

 

[KurtVD]

The mod's inbuilt thermo sensor senses the the temperature around its sensor, meaning to protect the chipset/board, but has nothing to do with the coils. The coil temp is calculated by material/resistance, not sensed.

Yes, of course. But the mod’s thermometer could very well be used to determine the approximate ambient temperature, and with this value, and given the measured resistance, calculate the theoretical resistance at 70F/20C.
Do you own a DNA mod or one with Arctic Fox? Have you ever connected it to the computer and opened the device monitor? There, you will find the value ‘Cold resistance’. The fact is, you can lock it or not, the mod will calculate this value anyway (how, I’m not sure, but it’s there). But if it changes, and you had it locked, the old value will still be the baseline, whereas if you don’t lock it, it will adapt the baseline. I think that’s the difference between locking the resistance or not, on boards that support this feature, of course.
Please read Eskie’s posts as well, he seems to know the DNA boards well.

 

[KurtVD]

I thought that the base cold coil resistance was read when you installed the cold atty. Hence the need to make sure it's room temp when first installed.

Yes, I mentioned that. But this base resistance can change over time. If you read Eskie’s post, not locking it allows the mod to automatically adapt to the changing baseline resistance (on DNA boards).

 

[tailland]

I used AF for my devices. Sure, I tested the device monitor (and unrelated, found a bug) - the monitor software reads the momentary resistance, and takes the lowest resistance it has read during the session and assumes it's your baseline. That's all it can do, since it has no magical powers. If you just vaped and your mod is cooling down, that value goes down and down the more your device cools.

The mod itself of course reads sensor data as well, but it has to know some things in order to offer TC functionality. Only by your interaction, it knows a certain resistance to be the "true" baseline, without having to do a minutelong measurement process. And yes, resistance changes over time, but in a miniscule way - no comparison to the changes during the heating/cooling process. And that's good enough for the mod's approximate calucations. It's never 100% precise.

Just a side note. Typically DNA mods should not have the resistance locked. The board continues to refine the base resistance over time..

That's some advanced use of information over time. Nice. Probably expensive ^^

Generally speaking, I do have a bit of admiration for the principle behind TC. Whoever came up with the method to make it work gets a thumbs up. Firing up a coil, measuring the change in resistance, determining if the material is stable enough in its change to be controllable, identifying the material by the amount of its resistance change.. and all of that within a period of .. how much is it? 5 milliseconds? That's cool.

 

[KurtVD]

I used AF for my devices. Sure, I tested the device monitor (and unrelated, found a bug) - the monitor software reads the momentary resistance, and takes the lowest resistance it has read during the session and assumes it's your baseline. That's all it can do, since it has no magical powers. If you just vaped and your mod is cooling down, that value goes down and down the more your device cools.

The mod itself of course reads sensor data as well, but it has to know some things in order to offer TC functionality. Only by your interaction, it knows a certain resistance to be the "true" baseline, without having to do a minutelong measurement process. And yes, resistance changes over time, but in a miniscule way - no comparison to the changes during the heating/cooling process. And that's good enough for the mod's approximate calucations. It's never 100% precise.

That's some advanced use of information over time. Nice. Probably expensive ^^

Generally speaking, I do have a bit of admiration for the principle behind TC. Whoever came up with the method to make it work gets a thumbs up. Firing up a coil, measuring the change in resistance, determining if the material is stable enough in its change to be controllable, identifying the material by the amount of its resistance change.. and all of that within a period of .. how much is it? 5 milliseconds? That's cool.

Well, however it works, it certainly does work without locking the resistance, I just made a test: I've changed my coil, connected my mod to eScribe where I had to change to coil material (from NI to SS), but that's all I did, everything else I left the same (temperature, wattage, resistance not locked). Of course, before connecting it, I made sure that the atomiser was at room temperature. Now I'm vaping at the same temperature setting as before with the NI coil, same juice, and I get the same vapour.
P.S: In eScribe, unlike in Arctic Fox, if you deselect 'Lock Resistance', the field where you would normally enter the resistance value disappears. So the mod is 'on its own' to determine the base resistance. Probably, in AF, if you set the resistance to 0.000 and deselect 'Lock Resistance', it will be the same.

 

[ShamrockPat]

Typically DNA mods should not have the resistance locked. The board continues to refine the base resistance over time. Other boards may behave differently, and locking the resistance may well be the only way those boards will function without tossing you out into power mode when the base resistance drifts.

Yup. Page 6 of the datasheet, and only ever mentioned once. Refine no longer mentioned in either of the Color datasheets, but cold ohm value still determined.

Here's what my cold ohm value looks like right now on a Color Board. -> 0.433349609Ω @ 73.859375°F

 

[Zipslack]

Unless you have a thermocouple installed in your coil, there is no "temp measurement". It's all done using voltage and current and calculating how much current should be seen at a particular temp (based on expected resistance at that temp).

My best guess is that newer chips and firmware don't need to be locked...it's a hold-over from previous generations. As noted by others, the initial resistance of a new coil is used....why bother to lock? Because you're used to seeing that feature. If it wasn't there, you would consider it a defect or missing feature (Apple headphone debacle). My Anita doesn't even have the option to lock the resistance...no problem.

 

[Eskie]

Unless you have a thermocouple installed in your coil, there is no "temp measurement". It's all done using voltage and current and calculating how much current should be seen at a particular temp (based on expected resistance at that temp).

.

In truth, the coil itself is the thermocouple. A thermocouple works by measuring the change in resistance of a wire with a known TCR placed in an environment. The only difference is a thermocouple wire is usually covered in some type of material so there is no direct contact between the wire and environment you're measuring the temperature of.

@mikepetro inserted a thermocouple into a wicked coil and compared the temperature reported by the probe and the reported temperature of the wire on a DNA board. The result was within 10F across the range of temperature selections (don't remember the full range, but it was typical vaper stuff).

He's also extremely knowledgeable about temp control and specifically about temp control and DNA boards. I defer to his expertise as to how the whole refinement feature is actually implemented.

As a side note, there is a case analyzer utility in eScribe that will test the thermal characteristics of the mod case to provide even finer calculations when looking at the ambient temp. I personally have not found the results that come back having any real effect on real life performance, but it seems kinda cool.

 

[zoiDman]

In truth, the coil itself is the thermocouple. ...

 

[Zipslack]

In truth, the coil itself is the thermocouple.

True, but thermocouples don't actually "measure" temp. And our coils aren't as good as purpose-built NTC/PTC thermocouple probes. They're okay for this application that doesn't require high precision.

 

[Eskie]

No, they measure the resistance and the temperature is calculated, and clearly what goes on in a tank is not precisely the same as it it is wire itself changing the temperature. That's why Mike measured actual temperature with a thermocouple at the wire/cotton interface and found agreement +/- 10F. Not quite the range you'd want your room thermostat to perform at, but quite good at the temperatures we typically use in temp control mode.

 

[zoiDman]

True, but thermocouples don't actually "measure" temp. And our coils aren't as good as purpose-built NTC/PTC thermocouple probes. They're okay for this application that doesn't require high precision.

Just Curious...

But what Device/Equipment actually Measures Temperature?