How to input a new thermistor table ??

Hello,

So i have got a new hotend fro E3D but i am un shore how to update my melzi electronics with the new thermistor table?

I have looked at this but cannot understand where to edit it?

//===========================================================================
//=============================Thermal Settings ============================
//===========================================================================

//// Temperature sensor settings:
// -2 is thermocouple with MAX6675 (only for sensor 0)
// -1 is thermocouple with AD595
// 0 is not used
// 1 is 100k thermistor
// 2 is 200k thermistor
// 3 is mendel-parts thermistor
// 4 is 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
// 5 is ParCan supplied 104GT-2 100K
// 6 is EPCOS 100k
// 7 is 100k Honeywell thermistor 135-104LAG-J01
// 8 is Epcos B57560G104F 100K
// 9 is Epcos B57861S104F40 100K 155C for bed only


where can i input my new table whitch is this:

// /usr/local/bin/createTemperatureLookup.py --r0=100000 --t0=25 --r1=0 --r2=4700 --beta=4267 --max-adc=1023
// r0: 100000
// t0: 25
// r1: 0
// r2: 4700
// beta: 4267
// max adc: 1023
#define NUMTEMPS 20
short temptable[NUMTEMPS][2] = {
{1, 713},
{54, 236},
{107, 195},
{160, 172},
{213, 157},
{266, 144},
{319, 134},
{372, 125},
{425, 117},
{478, 110},
{531, 103},
{584, 96},
{637, 89},
{690, 83},
{743, 75},
{796, 68},
{849, 59},
{902, 48},
{955, 34},
{1008, 3}
};

i found this on the reprap wiki.

any help would be very mutch apretiated.

Many thanks

B8TFK

You need to add it as a new table at the end of thermistortables.h and reference it by table number in configuration.h.

Note that it will not be as accurate as the tables I provide because I use a more sophisticated formula based on three points rather than R0 and beta, see [hydraraptor.blogspot.co.uk]. You might want to generate a better table yourself from the thermistor datasheet, or measurements with a thermocouple if it not a 1% thermistor.

Edited 1 time(s). Last edit at 01/09/2014 05:37PM by nophead.

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[www.hydraraptor.blogspot.com]

Hi nopehead

Many thanks for that I will give it a go and try to get as accurate as poss. Do you think a multimeter with a thermocouple would be accurate enough? Would you think sticking it next to the nozzle with heat past tempory when calibrating it?

Many thanks for the reply!

A multimeter and thermocouple should be accurate but I always insert it down the filament path and measure the temperature inside the melt chamber. I always get a much higher reading than on the outside surfaces. However, I think the E3D has a spare thermistor hole that goes all the way through the block, so you might get a good reading from a thermocouple inserted there.

Beware thermocouples often have black tape at the end that melts at extrusion temperatures. I replace that with kapton tape and sleeve it with with a 3mm PTFE tube to make it easy to insert down the filament path.

Whenever I commission a new hot end for myself I measure the temperature set at 240C and always find the thermocouple agrees to within 1 degree, which is better than one would expect with 1% thermistors.

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[www.hydraraptor.blogspot.com]

That sounds excellent! I will go about it in that direction. I had read over the your blog about thermistor tables, in a nut shel am i just getting temperature to resistance?

Tanks

The thermistor converts temperature to resistance. The Melzi converts resistance to voltage with a potential divider and the ATMega's ADC converts voltage to a number.

The table generator I wrote takes three resistance - temperature pairs to make the table of ADC values.

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[www.hydraraptor.blogspot.com]

If i was to use table 55 in the thermistortable.h and change R5 on the melzi to 1k will this work as table 55 semitec is alrady there?

As im struggling on how to use your MakeTempTable.py and what vales i need from the data sheet.

Thanks

False alarm!!! i found table 5 is the best one only problem its out by 4 DegC in the negative direction. I am using a thermocouple that i checked in boiling water and it was dead on 100 DegC. The thermocouple was put in the heat chamber. Is there a way i can create a table with some help?

Thanks

Does you thermistor have a datasheet with a resistance versus temperature table?

If it does you pick three temperatures that span the range you are interested in, say 20, 125 and 250. Look up the resistance and feed the values into the script.

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[www.hydraraptor.blogspot.com]

Quote
nophead
Does you thermistor have a datasheet with a resistance versus temperature table?

If it does you pick three temperatures that span the range you are interested in, say 20, 125 and 250. Look up the resistance and feed the values into the script.

nophead, using your python script with this values:
r0=100000 t0=25
r1=1380 t1=150
r2=229 t2=250

the script had an error:
D:> python maketemptable.py --t0=25 r0=100000 --r1=1380 --t1 150 --r2=229 --t2=250 --rp=4700
Traceback (most recent call last):
File "maketemptable.py", line 101, in
main(sys.argv[1:])
File "maketemptable.py", line 96, in main
x = ((B / (3 * C)) ** 3 + (y ** 2) / 4) ** 0.5
ValueError: negative number cannot be raised to a fractional power

I'd appreciate if you can tell me what I'm doing wrong.
Thanks a lot
Javier

It means it can't fit the curve through those three values. AFAIK all real thermistors should work, are you sure your values are correct?

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[www.hydraraptor.blogspot.com]

Thanks nophead.
I will take new values using a thermocouple because before use a know honywell thermistor to collect temp values.