Thermistor N03R00104 calculation problem B4400

Using an NTC Thermistor N03R00104.

Data sheet specifies

Rn @ 25C = 100K

Beta = 4400



Using Nopheads table generator with these settings provides a table loking very similar to the ones here http://reprap.org/bin/view/Main/Temperature_Sensor_2_0.

Generated table...

#define NUMTEMPS 20
short temptable[NUMTEMPS][2] = {
{1, 649},
{54, 226},
{107, 187},
{160, 166},
{213, 151},
{266, 139},
{319, 130},
{372, 121},
{425, 114},
{478, 107},
{531, 100},
{584, 94},
{637, 87},
{690, 80},
{743, 74},
{796, 66},
{849, 58},
{902, 48},
{955, 33},
{1008, 4}
};

All good so far.. code for Extruder contrller 2.1 is thus.

Alter Extruder test SW to be correct A to D channel.

#define THERMISTOR_PIN 3


Unfortunatly a Typical result from this shows an ambient temprature of 22C as 109C.

What have I done wrong?

Thermocouple measurements are perfect unforunatly I only have one AD595A amp so this is used for extruder have to use Thermistor for heated Bed control.

Edited 1 time(s). Last edit at 02/14/2010 12:04PM by BodgeIt.

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Bodge It [reprap.org]
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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

I didn't write that program, Zach did. I do the conversion on the host side so no table is needed in my firmware.

Looks like your series resistor is wrong. 109C is near the middle of the table which would correspond to half the ADC full scale, so about 2.5V. If you have a 4K7 series resistor that means your thermistor is as similar value at room temp, so can't be 100K thermistor.

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[www.hydraraptor.blogspot.com]

Sorry bout the wrong attribution..



Reading your reply and thinking Farnell must conform to BS9002 I have set about testing all the other components on all three Extruder controllers.

The 4k7 was not 47k phew but it did read low on one of the boards.

Intersting removing the 10uf cap.. corected the resistance reading..



Hmm thinking are these 10uf smt capacitors that I have robbed off an old mother board..



I'm not sure why these capacitors are causing this effect though they are definitely marked a capacitors, I had them the correct way round they appear to be 10uf at 16v or I'm being stupid. Completely removed on all 3 boards all three boards read the Thermistor are now working exactly as expected.. strange could the caps be tantalum caps is it an impedance thing?

Without capps its likely to be more susceptible to noise on PSU and leads.

Thank you for your reply.. if you have any ideas on this please let me know.

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Bodge It [reprap.org]
=======================================

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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

I am not using capacitors on my thermistor setup. It works fine. The firmware does an average of three readings anyways. See the attached image for my thermistor "board".

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]