There are at least four thermistor tables out there to choose from. Zach 1, Zach 2, Jet, and Tim. The first time I updated my extruder board’s firmware with a new temperature table I used Jet’s and the second time I used Zach 1. (The second time was because the extruder spark incident and almost certainly unrelated to Jet’s table).
My understanding is that Tim’s table has a higher “resolution,” meaning there’s a lot more resistance / temperature pairs. However, I’ve been using Zach 1 without a problem so there’s no reason for me to switch.
Hi MakerBlock.
I just wandered onto your website/blog… nice work… I’ll be back ;)
I just want to clarify a little regarding my nonlinear “reloution” tables…
The reason I did what I did is because the python script in uses constant interpolation intervals… which is not very good in the areas of the thermistor curve where the rate of change of the rate of change is high… like… between 200 and 250C.
I tend to trust the results of TeamTeamUSA and Jet… they measured the thermistor curve directly… and they have very similar results (when plotted).
Zach’s come from the data sheet… and as someone pointed out… the datasheet uses the same numbers for this thermistor as it does for a completely different type… which suggests a possible printing error… and introduces doubt.
However… even if TTUSA/Jet are spot on with their calibration… the table returns an error of around 50C at 200C because of the way the lookup intervals are determined.
Really. Have a look at the graphs I posted… it’s very clear.
So my aim in increasing resolution at the top end was to increase accuracy.
All the effort in changing tables/calibrating etc is wasted if the lookup table is not suitable for the curve.
To me it really doesnt matter what the reported temperature is, so long as everyone has the same “errors” when comparing notes… So I’d rather see eveyone discuss settings with the same calibration curves, rather than the spectrum we have now… thus, I have stopped discussing it on the forum to avoid adding to the confusion.
Thanks! Turns out blogging about 3d printing is almost as much fun as printing itself. :)
I rather liked the method/tables you posted! To make matters more interesting, it looks like there’s a new thermistor in the mix from MakerBot’s latest batch.
Speaking from experience with the Zach 1 table, I find that it gives some funny fluxuations/readings sometimes. However, it has been good to me. Now that we’ve got RepG v12 with the ability to input temperature tables, it makes much of this calibration very easy. Except, as you pointed out the other tables appear to use linear (constant) interpolation rather than a curvilinear. When I used RepG to update the temperature tables, I discovered that it basically asked for two points. This suggests it is using linear interpolation and losing “resolution” at the higher temperatures, ironically the spots we care the most about.
MakerBlock
I havent tried RepG 12 yet… will later this week, though, I think.
Yeah… bit of a bummer (for a pedantic guy like me) that the resolution will be (likely) lost by the newer method… however… everyone singing from the same hymn book is probably better for collaboration and joint troubleshooting anyway.
Cheers, Tim.
RepG 12 seems fine so far. I suspect the current way of updating the thermistor tables makes it fairly easy to change the temp tables. In the long run having an easier way to do it may be better than having a higher resolution.
That said, I should think it wouldn’t be terribly difficult to allow you to upload a temp table rather than two end points for extrapolation.
Thanks,
MakerBlock