Using custom thermistor
May 29, 2014 05:37AM
Hi everyone.

I have a problem. When I calibrated bed on my RepRap, I tore my Semitec 103gt-2 thermistor. And it's unreal to solder it cause it's very small.

When I went to local radio market, I didn't find no one thermistor, which included in official list (with already calculated table of ADC counts vs. temperature). I bought no name thermistor so seems like I need to calculate ADC counts manually.

Could somebody who already do it give me advices?

In particular, I'm interesting in:

1) What are the requirements for thermistor?
Logically, its Operating Temperature Range must handle the 110 °C and it will be cool if it has a datasheet... what else? What are best, 100K or 10K thermistors? Must it be only Negative Temperature Coefficient (NTC) temperature sensitive resistors? And, are these requirements are critical?

2) How to measure thermistor ADC counts in home conditions?
What is general algorithm of measurement? What is the optimal heater? What scripts can be used for calculations? How to reach maximum automatation and acсuracy of measurement process? What equipment is necessary for it?

Any help will be highly appreciated.
Re: Using custom thermistor
May 29, 2014 05:56AM
I would not use a 10k thermistor. You can see in the Marlin firmware why.

Also, to be safe, what I did, was just order a couple off of ebay, that way I at least was sure that I had a few that were known and had a table in Marlin already.

Sorry that I don't give an exact answer, but I've had some trouble with thermistors in the past and didn't want to bother with them again. Sometimes the 'easy' way isn't a bad choice winking smiley
Re: Using custom thermistor
May 29, 2014 09:45AM
See http://hydraraptor.blogspot.com/2012/11/more-accurate-thermistor-tables.html if you haven't already.

I think nophead uses a Fluke meter with a small thermocouple pushed down through the filament path into the melt chamber to do his calibrations. I use a thermocouple attached to a cheap PID controller, but I'm not tremendously confident in the controller's calibration. Still, measuring the temperatures is far better than extrapolating a Beta25C/75C curve out past 200C.
Re: Using custom thermistor
May 30, 2014 03:50PM
Quote
DaveX
See http://hydraraptor.blogspot.com/2012/11/more-accurate-thermistor-tables.html if you haven't already.

I think nophead uses a Fluke meter with a small thermocouple pushed down through the filament path into the melt chamber to do his calibrations. I use a thermocouple attached to a cheap PID controller, but I'm not tremendously confident in the controller's calibration. Still, measuring the temperatures is far better than extrapolating a Beta25C/75C curve out past 200C.

If I understand it well, the thermistor is meant to go onto the heated bed. so I think it won't go over 110 degrees celsius smiling smiley
Re: Using custom thermistor
May 30, 2014 10:11PM
Quote
Ohmarinus
Quote
DaveX
See http://hydraraptor.blogspot.com/2012/11/more-accurate-thermistor-tables.html if you haven't already.

I think nophead uses a Fluke meter with a small thermocouple pushed down through the filament path into the melt chamber to do his calibrations. I use a thermocouple attached to a cheap PID controller, but I'm not tremendously confident in the controller's calibration. Still, measuring the temperatures is far better than extrapolating a Beta25C/75C curve out past 200C.

If I understand it well, the thermistor is meant to go onto the heated bed. so I think it won't go over 110 degrees celsius smiling smiley

Doh! You are right, Serikov was talking about the bed. I wonder if many folks calibrate their bed thermistor readings?
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