Temperature Check on Hot End

There is a note in the Firmware that table 1 is more accurate than table 6.  I don't really know more about it than that, but that's something else to check on.

Have a look at this thread - http://forums.reprap.org/read.php?1,134 … msg-135016

It starts out on Z-lift, but moves into Thermistor Table 6

Did you get a thermistor with your J-Head?

One cool thing about the j head is there are two thermistor holes, big and small.  The included thermistor fits in the small one.  The big one looks big enough for my thermocouple so it would be easy to get apples to apples comparison on readings.   It's not as good as getting it inside the barrel, but that is only feasible for 3mm hot ends.

Yeah, I have been doing it while testing my old hot end.  My main problem is that none of the script settings have so far resulted in accurate readings as compared with my thermocouple.  Always off by a 30-50C.

Lawsy,

Do you know if the resistors on the sanguino by the temperature ports are the pullups or not?  If so, they read at 4.5K on my multimeter rather than 4.7k. So the tables generated need to take that into account, I would think.

Ahh, didn't realize the pullups were 5% tolerance.

OK. I finally got the thermistor to read within the tolerance of my thermocouple.
This is the process I followed:
1) Attach thermocouple next to thermistor.
2) measure the resistors directly next to the extruder connector (mine were 4.5K). this will be --rp.
3) Disconnect thermistor and measure room temperature resistance with your MM (Check temperature on the thermocouple) and make a note of both then reconnect thermistor (mine were 110.8K and 20C). This will be --r0 and --t0.
4) run the script with no arguments and get a default table which is added to the firmware in thermistortables.h.  Make sure you change which table you use in configuration.h to point to it.
    This is necessary so that you have fixed settings and adc values that match for the following steps.
5) compile and upload firmware.
6) Using your interface, tell the extruder to heat to 150C and take a note of the actual temperature. Then look up the adc value in the previous table for the setting and take note of that... this will be adc1 and t1.
7) Perform step 4 again at a temperature of 200.. this will be --adc2 and --t2.
8) Generate a new table using the discovered settings and use it to replace the table previously created (compile and upload).
9) start with step 6 and validate, if necessary update again to get a more accurate table.

I ended up running 3 passes from 6 to 9 to get the table below.

Here is my table:

#if (THERMISTORHEATER_0 == 56) || (THERMISTORHEATER_1 == 56) || (THERMISTORHEATER_2 == 56) || (THERMISTORBED == 56)
// SD2 - possible epcos, 100k NTC thermistor. Part Number unknown.
// ./MakeTempTable.py --r0=110800 --t0=20 --rp=4500 --adc1=170 --t1=164 --adc2=60 --t2=220
const short temptable_56[][2] PROGMEM = {
    {     115,       300     }, // r=    32 adc=7.16
    {     127,       295     }, // r=    35 adc=7.95
    {     142,       290     }, // r=    39 adc=8.85
    {     158,       285     }, // r=    44 adc=9.85
    {     176,       280     }, // r=    49 adc=10.98
    {     196,       275     }, // r=    55 adc=12.26
    {     219,       270     }, // r=    61 adc=13.69
    {     245,       265     }, // r=    68 adc=15.31
    {     274,       260     }, // r=    77 adc=17.15
    {     307,       255     }, // r=    86 adc=19.22
    {     345,       250     }, // r=    97 adc=21.56
    {     387,       245     }, // r=   109 adc=24.21
    {     435,       240     }, // r=   123 adc=27.21
    {     490,       235     }, // r=   139 adc=30.61
    {     551,       230     }, // r=   157 adc=34.46
    {     621,       225     }, // r=   178 adc=38.83
    {     701,       220     }, // r=   201 adc=43.79
    {     790,       215     }, // r=   228 adc=49.40
    {     892,       210     }, // r=   259 adc=55.77
    {    1008,       205     }, // r=   295 adc=62.98
    {    1138,       200     }, // r=   336 adc=71.15
    {    1286,       195     }, // r=   384 adc=80.39
    {    1453,       190     }, // r=   438 adc=90.82
    {    1642,       185     }, // r=   502 adc=102.60
    {    1854,       180     }, // r=   575 adc=115.86
    {    2092,       175     }, // r=   659 adc=130.75
    {    2359,       170     }, // r=   758 adc=147.42
    {    2657,       165     }, // r=   872 adc=166.03
    {    2987,       160     }, // r=  1005 adc=186.72
    {    3354,       155     }, // r=  1160 adc=209.60
    {    3756,       150     }, // r=  1340 adc=234.77
    {    4197,       145     }, // r=  1552 adc=262.30
    {    4675,       140     }, // r=  1799 adc=292.18
    {    5190,       135     }, // r=  2089 adc=324.37
    {    5740,       130     }, // r=  2430 adc=358.75
    {    6322,       125     }, // r=  2832 adc=395.11
    {    6931,       120     }, // r=  3305 adc=433.18
    {    7561,       115     }, // r=  3864 adc=472.59
    {    8207,       110     }, // r=  4525 adc=512.91
    {    8859,       105     }, // r=  5309 adc=553.68
    {    9510,       100     }, // r=  6240 adc=594.36
    {   10151,        95     }, // r=  7348 adc=634.44
    {   10775,        90     }, // r=  8669 adc=673.43
    {   11374,        85     }, // r= 10248 adc=710.85
    {   11941,        80     }, // r= 12139 adc=746.32
    {   12472,        75     }, // r= 14408 adc=779.53
    {   12964,        70     }, // r= 17137 adc=810.24
    {   13413,        65     }, // r= 20429 adc=838.33
    {   13820,        60     }, // r= 24407 adc=863.75
    {   14184,        55     }, // r= 29226 adc=886.50
    {   14507,        50     }, // r= 35081 adc=906.69
    {   14791,        45     }, // r= 42212 adc=924.45
    {   15039,        40     }, // r= 50922 adc=939.94
    {   15254,        35     }, // r= 61590 adc=953.34
    {   15438,        30     }, // r= 74694 adc=964.87
    {   15595,        25     }, // r= 90841 adc=974.72
    {   15729,        20     }, // r=110800 adc=983.07
    {   15842,        15     }, // r=135552 adc=990.13
    {   15937,        10     }, // r=166353 adc=996.06
    {   16016,         5     }, // r=204818 adc=1001.01
    {   16082,         0     } // r=253030 adc=1005.12
};
#endif

I found this script on nophead's blog due to the link Ian posted earlier.
The script is located at: https://github.com/nophead/Marlin/blob/ … mpTable.py

I don't think we can make any conclusions from one data point. What we need is more information. I don't know my thermistor part number and neither does anyone else. Some people might not have updated to lawsy's firmware, and so could have a different temp table (at least, back when SD was using something different). 

To add to the data, we need people to measure their thermistor, check the pullup resistor and check their temps with a thermocouple (using the default table).  Then update to my new table and see the difference. It would also help if SD would tell us the thermistor part number and all previous part numbers. Then we would know for sure. So far, they have never answered that question.

Also, I know we were told that 200C on an SD is like 230C for other printers, but I don't know how that was determined.  What I do know is that when I started measuring my actual temperature, it was off in the other direction.

As an additional point of reference, my printer is serial #1350. All measurements were made with the original hot end, though I don't think that will matter much as long as the original thermistor is used for doing the measurements.

Ian
I sent you a private message of a data logger I will be getting after I receive my SD3
I am going to permently mount the TC wires to the extruder & bed.

Let me know what you think