# Trying to figure out these thermistor tables...?

Posted by Phizinza
 Trying to figure out these thermistor tables...? October 02, 2012 11:56PM Registered: 12 years ago Posts: 160
I've finally got to the point where I'm ready to print but I can't figure out these thermistor tables. I've used the calculator supplied at [calculator.josefprusa.cz] and come up with these tables below.
My extruder thermistor is === EPCOS 100K Thermistor (B57540G0104F000) one [that's what the person who sold it to me told me]
My bed thermistor is a 100k 4400b one I got from a local electronics store which as far as I can track down is identical to this one here [www.rapidonline.com]

I don't yet have a reliable thermometer so I just slowly increased the extruder using Pronterface until I could extrude, this was when Pronterface said I had hit 60 degrees. Also when I started Pronterface it said the bed was at 166 degrees and the extruder 216 degrees but as soon as I Set the temps on both they changed to 3.75 and 2.5 degrees...?

Is it something to do with my wiring, electronics or the tables I've created?

// Thermistor lookup table for two different thermistors.

/*
This table doesn't depend on the type of electronics, but on the type of
thermistor(s) you use. You want one table for each thermistor type you use.
*/

// How many thermistor tables we have.
#define NUMTABLES 2

// Names for our tables, so you can use them in config.h.
// Table numbering starts at 0.
#define THERMISTOR_EXTRUDER   0
#define THERMISTOR_BED        1

/*
You may be able to improve the accuracy of this table in various ways.

1. Measure the actual resistance of the resistor. It's "nominally" 4.7K,
but that's ± 5%.
2. Measure the actual beta of your thermistor:
[reprap.org]
3. Generate more table entries than you need, then trim down the ones
in uninteresting ranges.

In either case you'll have to regenerate this table with
createTemperatureLookup.py, which requires python, which is difficult to
install on windows. Since you'll have to do some testing to determine the
correct temperature for your application anyway, you may decide that the
effort isn't worth it. Who cares if it's reporting the "right" temperature
as long as it's keeping the temperature steady enough to print, right?
*/

// The number of value pairs in our table.
// Must be the same for all tables.
#define NUMTEMPS 49

uint16_t const temptable[NUMTABLES][NUMTEMPS][2] PROGMEM = {

// Table for the Extruder.
// EPCOS 100K Thermistor B57540G0104F000

// Thermistor lookup table for RepRap Temperature Sensor Boards (http://reprap.org/wiki/Thermistor)
// Made with the online thermistor table generator by nathan7 at [calculator.josefprusa.cz]
// r0: 100000
// t0: 25
// r1: 0
// r2: 4700
// beta: 4066
{
{1, 841},
{22, 328},
{43, 272},
{64, 243},
{85, 224},
{106, 209},
{127, 198},
{148, 188},
{169, 180},
{190, 173},
{211, 167},
{232, 161},
{253, 156},
{274, 151},
{295, 147},
{316, 142},
{337, 138},
{358, 135},
{379, 131},
{400, 128},
{421, 124},
{442, 121},
{463, 118},
{484, 115},
{505, 112},
{526, 109},
{547, 106},
{568, 103},
{589, 100},
{610, 97},
{631, 94},
{652, 91},
{673, 88},
{694, 85},
{715, 82},
{736, 79},
{757, 76},
{778, 73},
{799, 70},
{820, 66},
{841, 62},
{862, 58},
{883, 54},
{904, 49},
{925, 44},
{946, 37},
{967, 30},
{988, 19},
{1009, 1},
},

// Thermistor table for the Heatbed.
// The thermistor used for this table was an NTC b4400 100k

// Thermistor lookup table for RepRap Temperature Sensor Boards (http://reprap.org/wiki/Thermistor)
// Made with the online thermistor table generator by nathan7 at [calculator.josefprusa.cz]
// r0: 100000
// t0: 25
// r1: 0
// r2: 4700
// beta: 4400
{
{1, 649},
{22, 285},
{43, 240},
{64, 216},
{85, 200},
{106, 188},
{127, 178},
{148, 170},
{169, 163},
{190, 157},
{211, 151},
{232, 147},
{253, 142},
{274, 138},
{295, 134},
{316, 130},
{337, 127},
{358, 123},
{379, 120},
{400, 117},
{421, 114},
{442, 111},
{463, 109},
{484, 106},
{505, 103},
{526, 101},
{547, 98},
{568, 95},
{589, 93},
{610, 90},
{631, 88},
{652, 85},
{673, 83},
{694, 80},
{715, 77},
{736, 74},
{757, 72},
{778, 69},
{799, 66},
{820, 62},
{841, 59},
{862, 55},
{883, 51},
{904, 47},
{925, 42},
{946, 36},
{967, 29},
{988, 19},
{1009, 3}
}
};

 Re: Trying to figure out these thermistor tables...? October 06, 2012 03:40PM Registered: 13 years ago Posts: 1,780
What is the firmware? Some firmware scale the values of the readings.
 Re: Trying to figure out these thermistor tables...? October 07, 2012 03:57AM Registered: 12 years ago Posts: 160
Firmware is Teacup
 Re: Trying to figure out these thermistor tables...? October 07, 2012 09:30AM Registered: 13 years ago Posts: 1,780
Yes. Teacup does everything in integer (no floating pt) to speed up the firmware. To increase accuracy, they scale the thermistor table. Your table doesn't match that they have for the same extruder thermistor: [github.com].

You have to use the calculator that comes with teacup.
 Re: Trying to figure out these thermistor tables...? October 07, 2012 06:54PM Registered: 12 years ago Posts: 160
Oh I see.. Thanks for this, I should have of read that more thouroghly!
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