M308 B parameter, what's it mean?

[airscapes]

Hi, I am configuring a Duet 3 mini for a Makergear M2. I have an existing and functioning M2 with a Duet 2 and I am manually doing the config.g. for the new system . I probably did the initial config on the Duet 2 with the config tool so maybe that is where this came from. I have M308 S0 P"temp0" Y"thermistor" T100000 B4072 for bed and same B 4072 for the Hot end Thermistor, what does the 4072 signify? I am assuming it has something to do with the type of Thermistor but I see no reference on where that is found. I assume it is correct but would like to understand where that came from.
Thanks!

[droftarts]

@airscapes See https://docs.duet3d.com/User_manual/Reference/Gcodes#m308-set-or-report-sensor-parameters and https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermistors_PT1000#thermistor-parameters

Bnnn Beta value, or the reciprocal of the Steinhart-Hart thermistor model B coefficient

The B parameter (B4725) means that the thermistor B value over the temperature range of interest is 4725. The B values quoted in thermistor datasheets are typically quoted over a range 25 to 75C, which may be OK for bed thermistor but is too low a range for a hot end thermistor. That's why the B values recommended by RRF differ from the values in the datasheet. Also, if the C parameter is used then the B value has to be adjusted.

Most thermistors will specify their Beta value; it's kind of necessary.

Ian

[gloomyandy]

@airscapes It is sort of explained in the gcode dictionary for M308:

Bnnn Beta value, or the reciprocal of the Steinhart-Hart thermistor model B coefficient

See: https://en.wikipedia.org/wiki/Steinhart–Hart_equation and here: https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermistors_PT1000#thermistor-parameters

So it is basically one of the numbers that characterises a thermistor and how the resistance maps to actual temperature. Some common values are given here: https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermistors_PT1000#typical-parameter-values
and some more (mainly older ones) are here:
https://reprap.org/wiki/Thermistor

[airscapes]

@gloomyandy Maybe I just guessed.. 5.3 EPCOS 100K Thermistor (B57560G1104F) has a value of 4072 and the only info I can find is that the M2 uses and 100K EPCOS compatible thermistor. No marking on the can and only marking are that of the shrink tubing.
I sent a mail to Makergear to see if they have a copy of the datasheet.. Guess it is time to move on to then next sections of the config.
Thanks!
Doug

[dc42]

@airscapes said in M308 B parameter, what's it mean?:

B57560G1104F

The datasheet of that thermistor at https://www.tdk-electronics.tdk.com/inf/50/db/ntc/NTC_Glass_enc_sensors_G1560.pdf gives a resistance vs temperature table (it's the 8304 column on page 6 onwards, multiplied by 100kohms). So for best accuracy you can plug three temperature and resistance values into the calculator in the configuration tool, and let it calculate the parameters. For example: 100000 ohms @ 25C, 16419 ohms @ 150C and 2261.5 ohms @ 250C.

[airscapes]

@dc42 & @gloomyandy
Info back from Makergear
"The thermistor we use for both the hot end and the HBP is an EPCOS thermistor. The part number is B57560G1104F000"

Looks like this is the data sheet from a search of that generic number.
https://www.farnell.com/datasheets/2130808.pdf
If I read it right the 100K is the RT part 8304 and the B value (page 6-7) for 25/100C is 4092
I see no C value.
Using the calculator with 3 values as suggested above does not seem to work and that does not seem to give me the C Coefficient:
Any more help would be appreciated, most of that sheet is Greek to me..
Thanks,

[droftarts]

@airscapes You don't need a C parameter, just use the B parameter. eg:

M308 S1 P"temp1" Y"thermistor" A"Nozzle" T100000 B4092     ; configure sensor #1

The B57560G1104F thermistor is one of the few that's pre-defined in the configtool.

Also, I'm afraid @dc42 's numbers were incorrect, it should have been 100000 ohms @ 25C, 1641.9 ohms @ 150C and 226.15 ohms @ 250C (the last two resistances were out by a factor of 10)! This gives:

M308 S1 P"temp1" Y"thermistor" A"Nozzle" T100000 B4617 C8.987154e-8     ; configure sensor #1

I doubt there's really much difference in the temperature reading you'll get between the two.

Ian

[airscapes]

@droftarts Thank you soo much!
Bed heater is 60w and slow auto tune say
M307 H0 R0.150 K0.155:0.000 D15.28 E1.35 S1.00 B0
If I change to B1 will it heat faster?