Cold ohms is not correcting itself/updating on my DNA 250c

[bluegray]

I just got my new DNA250C mod and I'm still getting used to it, as there are some differences from the DNA60 I'm used to and have been using for quite a while.

For one, I have never seen cold ohms to be corrected after letting it sit for a while. Cold ohms is not locked as far as I can tell.

I've tried deliberately remeasure cold ohms with a warmish coil, so I know it will need to be adjusted, which it normally does on my DNA60. But it seems that this behaviour has changed on the DNA250C. The only way to correct it, is to wait for the coil to stabilise and manually remeasure.

Is this the expected behaviour? I'm on the latest SP38 firmware.

 

Another slight niggle is the fact that you cannot change temp/watts directly with the up/down buttons. You have to select the field first and then edit. This is probably to allow for more theme customisability, but I do miss that I cannot easily change as I would on the DNA60. 

[Wayneo]

2 hours ago, bluegray said:

For one, I have never seen cold ohms to be corrected after letting it sit for a while. ....................
Is this the expected behaviour? I'm on the latest SP38 firmware.

Quick easy answer: Yes!

Longer answer: Architecture/thought process change with the C boards. On the C boards, both the resistance and the temp it was measured at is written into the profile number you are/were in. From there the cold ohms at 70F can be calculated (like the 60) and used inTC. OR in theme designer you can change the value displayed to you, to what it would be at 70F.   

[bluegray]

So no automatic correction for cold ohms over time like the older boards used to do?

If so, then what is the ohms lock for?

[Ak89]

@bluegray

No "auto-correction". It would be counter-productive because of the multi-profile design of the board. (ie You can set a profile for each  atomizer. Helpful if one rotates tanks regularly.)

As for ohms lock, I find that it is helpful if I remove my rta/rda while the coils are warm. The DNA board will detect the absence, and when I screw it back on it assumes that I have provided "new" coils of a different resistance. A "new coil?" prompt can be annoying when it happens a lot. (I clean dust and stuff from my mod often. Hazards of work.)

FYI, Ohms lock is per profile. Setting it does not change non-active profiles...

[bluegray]

I don't think I quite understand what you mean by auto correction being counter productive as ohms lock can be set for each profile separately as well.

Auto correcting cold ohms has been a standard feature in all non color DNA boards afaik, and they all have ohms lock as a per profile setting. It seems to me that the  ohms lock function on the color boards is not doing anything at all. Cold ohms is effectively always locked as far as I can tell. 

I contacted evolv support as well to get a definitive answer. So far I only got a handful of unrelated copy/paste replies that does nothing to explain cold ohms locking behaviour for the new color boards. So it seems not even evolv knows what the lock setting actually does...

[Ak89]

@bluegray

The 250c does a lot of math when calculating resistance and TCR. I assume in order to get replay to function. 

When resistance is set on a profile, the board also saves ambient temp readings from a built on sensor. The board then calculates "expected" resistance changes based on changing ambient Temps and Coil material saved in the profile. 

As far as I know, the older boards lacked the ambient (room) temp sensor. Meaning that they were making calculations based on live ohm changes instead of any form of baseline, which the resistance lock may have made up for. 

So, on the 250c, say I am running a profile with ss316l and tc,  coils measuring 0.2ohms at 75F degrees. If I am outside in the cold for a while the temp lowers, and so does the Coil resistance. If I vape, the Coil resistance rises but ambient temp does not.  But based on the TCR of ss316l, the 250c recognizes the change as being normal. 

However, if I remove and reinstall my rta while the coils are warm, the detected changes in resistance (from nothing to, say, 0.24ohms) would be outside of the TCR possibilities and the board asks if they are new coils. Had I locked the resistance (ohms) the board would seemingly ignore the above mentioned wild swing and simply assume the coils are the same regardless of their current state or measured resistance. 

Another possible use of the "ohms lock" would be setting profiles for multiple Atomizers, each with differing builds. Assume that Mod and Atomizers were the same temp when profiles were set up, but the mod stays in a pocket all day while the additional Atomizers may be sitting near an air conditioning vent. Temps between the two can be very different. Having the resistance already locked in the profile can allow the 250c to utilize the coils on a newly swapped atomizer accurately without any effect from differing temps/resistance or waiting for the temperatures to stabilize between the two. 

A third use could be for atomizers/coils that aren't very stable, having shifting resistance for unknown reasons. It would effectively prevent random "new coil" prompts. 

 

[bluegray]

4 hours ago, Ak89 said:

As far as I know, the older boards lacked the ambient (room) temp sensor. Meaning that they were making calculations based on live ohm changes instead of any form of baseline, which the resistance lock may have made up for. 

Thanks @Ak89 , I can't speak for older boards, but on my DNA60 both the board and room temp sensors are present.

This is going to be a little long-winded - but hopefully it clarifies better what I'm trying to convey  

On my DNA60, cold resistance is defined as the resistance of the coil at 70°F. While firing, the coil is heated and the live resistance change is measured by the device and then used to extrapolate the temperature of the coil based on the TFR curve (or TCR value) and the cold ohms value set. This is all well understood and functions the same on most TC mods. Assuming the TFR curve accurately describes the resistance change of the coil with change in temperature, the cold ohms is therefore setting a baseline value to figure out the temperature of the coil from it's resistance. 

So for most TC board, unless you connect a new coil at ambient temperature 70°F, there is no way for the board to know the true ohms at 70°F, unless you specifically set it to a previously measured value.

But by using the ambient temperature reported by the room temp sensor, and assuming the coil will also be at that temperature, the resistance at  70°F can be guessed by the board. Because there are a few factors that can influence the reported temperature readings, this is not always accurate, and there can still be a difference between the true temperature of the coil, and the temperature reported by the temp sensors. 

What makes the DNA boards more accurate, for the DNA60 at least, was that while idle, the temperature values and coil resistance values were periodically measured. When the board finds that both are reasonable stable, ie. not changing much over time, the cold ohms value was updated from the measured resistance and temperature.

Obviously, there are a few factors that can still mess with these recalculations. Room temperature is not always stable, and temperature measurements are notoriously inaccurate, since they are located inside the mod, next to batteries and coils with little airflow. Coil material and atomiser connections can also influence resistance measurements.

And this is where locking the cold ohms value comes in. I can tell the board, that I'm satisfied with the current cold ohms value, and that it does not need to refine it further if it detects changes in temperature or resistance when idle. Normally this is not needed, as refinement is usually pretty accurate, but there are circumstances where it is useful to override the automatic refinement of the board. And indeed, as far as I can tell evolv only recommended locking ohms when experiencing instability issues.

 

Now, on the DNA250C the notion of "cold ohms" is somewhat different. The temperature can be specified/saved with the resistance at that temperature. Although we don't have to specify cold ohms at 70°F anymore, it is effectively still the same thing, a specific resistance value for the coil at a specific temperature, from where the temperature of the coil can be extrapolated with the TFR curve. All the previous issues with finding accurate cold ohms values from inaccurate temperature sensors inside the mod still applies in the same way as before. The only difference is cold ohms is not necessarily defined at 70°F anymore.

This is all fine and good, but the one feature that set the DNA boards apart in my opinion, was the ability to refine the cold ohms value when idle. So far I haven't seen this happening on my DNA250C at all. The cold ohms resistance and temperature is effectively locked and no refinement takes place at all. 

Since there is very little documentation available, I'm basing this on my experience with the boards I have used for a while now. What I would like a definitive answer on, is whether the above is indeed the case and the intended behaviour. Based on @Wayneo 's answer above this seems to be the case. What is confusing to me, is that there is still a setting to "lock cold ohms" in EScribe. Either the idle refinement of cold ohms feature was removed, therefore making the lock setting obsolete (since it is now effectively always locked), or there is something wrong with my mod/board/coil, or indeed my understanding of TC on the DNA board for the last year

To further the confusion, if automatic refinement was removed, I don't understand why evolve would remove the one feature that made their boards more accurate to calculate cold ohms. Sure you can set the temp for cold ohms now, but the recommendation was always to not lock cold ohms unless you have a problematic atomiser setup that made automatic refinement inaccurate. That recommendation is contradicted by them effectively always locking cold ohms now.

I don't really care either way, as I can manually measure cold ohms quite easily, remembering that it should be done only when the mod has cooled down for a while and temp sensors are stable. But I would like to know if there is something wrong with my setup that prevents me from benefiting from automatic refinement if it is indeed still present on the DNA250C boards. As it really was the most useful feature that set DNA boards apart form other chipsets.

Edited November 25, 2018 by bluegray

[Nexolek]

I get what you're saying. As far as I've seen and tested (cause I was also curious), the C based boards don't auto-adjust cold ohms. It'd be pretty slick, but it seems that manually measuring is the way to go. I do it fairly often, especially since outside is almost always vastly different than inside round here.

I use a specific profile for a given atty cause I switch up all the time. I always keep the ohm lock on with TC coils and do a manual measurement when everything is at at a stable "cold" temperature. From there I don't need to touch it and all is well. It works for me at least 🙃

[Ak89]

@bluegray

Hmmm. You have me curious now... 

If this Behavior existed intentionally, I'd be interested to know the reasoning behind removing it. 

I know my 250c doesn't do it so I would assume there isn't an issue with yours. 

Please post what you manage to learn from evolv. I'm sure there would be others equally curious as well.