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Thermistor Table Generator for Marlin - Three Methods

by ssaggers, published

Thermistor Table Generator for Marlin - Three Methods by ssaggers Jun 14, 2013

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Summary

This spreadsheet uses 3 different methods to calculate thermistor tables for input into Marlin (sorry, I'm not sure what the thermistor data input is like in other firmware).

Useful if you've had to buy a new thermistor and you aren't sure if the default tables are right for you, or even if you just want to fine tune your thermistor to get better control of temperatures.

Instructions

You can use the following inputs:
Method 1 - R/T data tables from the thermistor manufacturer
Method 2 - Beta value for the thermistor
Method 3 - Manually measured Resistance / Temperature data

Read the instructions within the spreadsheet, to see how it works.

For a lot of us, calculating our own thermistor tables isn't really necessary, but I had an experience recently where I wasn't sure about my replacement thermistor, so I had to figure out how to use the OEM's R/T tables to configure marlin. I thought I'd share my work.

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Really Nice Instructions.

Thanks you very much!!!

Have they renamed/changed the table locations in Marlin? I can't find "Thermistortables.h"

Not as far as I'm aware, but I haven't updated my firmware recently.

Thanks, I found it in the folder but still can't locate it when I am actually in the full Marlin config. Guess I'll edit the file as a text. Should work.

Hi, I'm trying yo use Method #3....

I've got the Following readouts from my multimeter.

19 °C 79,3 kOhms
152 °C 77,5 kOhms
230 °C 72,3 kOmhs

When I enter these values un the Spreadsheet (actually as soon as I enter the second Ohms value) turns to #¡NUM! all the way in the columns from D through H...

I'm going to try with other thermistor, but any help would be appreciated.

Thanks

Hmmm. Off the top of my head, those readings don't look right, there's only a really small variation as the temperature increases. normally I'd expect to see the resistance drop off significantly as it increases to 150°C (to around 2 Ohm), and then a smaller reduction as it gets to 230°C.

What type of thermistor have you got?

Possibly my methodology may be wrong, the readings from the multimeter could be affected by the thermistor still being attached to the control board.
Try disconnecting the thermistor from your board (with the nozzle at room temp) and measure the resistance, see if it's different to what you measured when it was still attached. What reading do you get?
If the error is caused by the thermistor still being connected to the electronics, I will have a look at including a calculator to back-calculate the resistance based on the current thermistor tables in your firmware (i.e. plug in your actual temperature, your temperature setpoint, and the thermistor table value for that set point, and it will give you the resistance at the actual temp).

That would be pretty sweet. Im having a problem with a thermistor that came with a hotend reading 20-30c above what it actually is. Going to contact seller and try to get a data sheet. Thanks for the spread sheet!

Hi, Great spreadsheet! I'm feeding in the numbers right now.

However, you might want to double check the values for the table conversion. I'm using a B57560G104F, but the values are off from the datasheet I have. Then I looked at the instructions, and it appears you might be using the table for the B57560G1104F (G1104 vs G104 since the difference is easy to miss). The R/T characteristic should be 8404, I think. Here's the datasheet I'm using:

http://octopart.com/datasheet/b57560g104f-epcos-747546-16188http://octopart.com/datasheet/...

It might also be helpful to add a few entries above 300.

You may be right, I'll have to check the data I got from the supplier.

thanks very much. going to have a go now. let u know how it goes

Hi, any chance you could show me where to enter info into marlin after i have manually measured please. i have the correct thermistor selected but my room temp always comes back +20deg for some reason. any help you could offer would be fantastic!

You've got two options: either paste the generated table of values (that you get when you click the button in your calculation sheet) in to "Thermistortables.h" to replace a thermistor table that you aren't using, and specify that number for your thermistor. alternatively, insert the following into "Thermistortables.h". note: you can replace "8" with any number that you want. I'll add a photo showing where to put the table.

if (THERMISTORHEATER_0 == 8) || (THERMISTORHEATER_1 == 8) || (THERMISTORHEATER_2 == 8) || (THERMISTORBED == 8)

const short temptable_8[][2] = {

//INSERT TABLE HERE!!!!!! each row is in the format {V,T},

};

endif

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