I am tired of thermistors and I think we all need to look for a better solution

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vreihen

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jzatopa
I would like to point out that the solution doesn't really need to be a thermocouple. If we could find an M3 threaded thermistor that operated up to 300C we would have an ideal solution. I just can't seem to find one.

Did you check eBay?

http://www.ebay.com/itm/Modular-Screw-on-M3-Stud-Thermistor-for-Reprap-Prusa-3D-Printer-Hot-End-Hotend-/221312429218?pt=LH_DefaultDomain_0&var=&hash=item33873faca2

Not currently in stock, but it appears to be nothing more than an M3 brass standoff with a thermistor attached with JB Weld or something similar.

If you can find a thermistor small enough, they even make M2 brass standoffs if you want to DIY your own:

http://www.ebay.com/itm/100-Pcs-Male-to-Female-Screw-Brass-Pillars-Standoff-Spacer-M2x3mmx6mm-/131106624103?pt=AU_B_I_Electrical_Test_Equipment&hash=item1e86905267

What size thread is the set screw on an E3D hotend?

How the extra mass and metal will impact the temperature measurement accuracy is the big question.....

So I went ahead and ordered one of those thermistors and one of their hotends to test out. I think I need to do a hotend shootout one of these days with all the different ones I am trying out.

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I'm just thinking...
Are there any possibilities to use the logic and instead read out ex. resistance from heatbed/hotend instead?
/darneg

Here's a cartridge heating element with a built in thermocouple. Cartridge might be a bit long, though.
[www.aliexpress.com]

They have one that is 6mm x 20mm:

http://www.aliexpress.com/item/Heater-Cartridge-12-V-40-W-OD6-x-20-mm-for-3D-printer/1656199662.html

It appears that you can custom-order many different sizes and configurations. At $4.26 each shipped (minimum quantity 10), it really isn't a bad price if it works and has a K-type thermocouple. If it is only a few bucks more, getting one with aright angle cable exit and/or strain relief would be another huge plus over current 3D printer heaters in the supply chain.....

At first glance this appears to be a nice solution, but I don't think it really is.

I don't think locating the temperature sensor within the heater cartridge is going to match the temperature of a thermistor mounted near the nozzle.
An integrated temperature sensor is not going to sense the diffused heat at the nozzle.
You'll probably be operating at a lower temperature.
I think you'll end up having to calibrate it by offsetting the temperature within the heater cartridge to the actual (i.e. desired) temperature at the nozzle.

I would like to see this work, testing/validating should be performed.

I think this needs some testing. I could see temperature fluctuations being an issue with depending on the size and material. In reality though it may only require the temps being off set a few degrees to compensate. If so this would be a great step towards hotend simplicity.

Edited 1 time(s). Last edit at 04/09/2014 11:52AM by jzatopa.

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The beauty is that current hotends are still drilled for thermistors, so you can run the thermistor and the heater's K-type thermocouple side-by-side to chart the fluctuations and see what the actual difference is. Unfortunately, I am still swamped with trying to get a solid printer running, so I personally don't have time or a test environment to pursue this further at the moment.....

For a test, plug the integrated heater cartridge K-type thermocouple into a handheld multimeter, and compare it to the thermistor temperature.

After I get some things off my plate I will try one of these with multimeter, it may take a while though.

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WWW.ZATOPA.COM - Your Place for high quality 3D Printing Filament and accessories

I found thermistors quite unattractive as well and designed a small thermocouple amplifier board. It's based on an AD8495 thermocouple amplifier chip, which is not the cheapest option, but offers reasonabl accurate temperatures. However, it is still less expensive than the other popular thermocouple amplifier choices for Repraps. The board is mounted near the hotend, so the fragile thermocouple wires do not need to move around. To the firmware, it just looks like another analogue temperature sensor, so the only things that need to be adapted are the thermistor tables. Thermocouples are nice for high temperatures, they're also inexpensive and quite robust. Of course, they do not offer the extreme amount of accuracy that thermistors can offer. However, I don't think this is important for these applications. Is there an interest in the board files/BOM/etc.?

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fr
I found thermistors quite unattractive as well and designed a small thermocouple amplifier board. It's based on an AD8495 thermocouple amplifier chip, which is not the cheapest option, but offers reasonabl accurate temperatures. However, it is still less expensive than the other popular thermocouple amplifier choices for Repraps. The board is mounted near the hotend, so the fragile thermocouple wires do not need to move around. To the firmware, it just looks like another analogue temperature sensor, so the only things that need to be adapted are the thermistor tables. Thermocouples are nice for high temperatures, they're also inexpensive and quite robust. Of course, they do not offer the extreme amount of accuracy that thermistors can offer. However, I don't think this is important for these applications. Is there an interest in the board files/BOM/etc.?

Yep, there is interest from me at least!