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

Posted by jzatopa 
I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 12:32AM
I am sure that I am not alone when I say, "I hate messing with thermistors on my hotend". Honestly they are a fiddly pain in the ass and are a very weak part of our designs. The amount of time you are done soldiering, taping, mounting, re-taping for a hotend is way to much. So how do we fix this? We move to threaded thermocouplers and start asking the board manufactures to support them out of the box. I have made a quick search and I have found this guy. He only costs about $5 and has a 6mm thread. He's not bad but there has to be better out there. Does anyone know of a thermocoupler in the same price range that has a 3mm or smaller thread? I want something I can screw into my hotend and call it a day.

Edited 1 time(s). Last edit at 03/31/2014 12:33AM by jzatopa.


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 02:08AM
buy these [www.ebay.com]

don't look back
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 02:29AM
thermistors are only a fiddley pain beause everyone has been using ones which require kapton tape to mount, it's one of the reasons i went to the axial through hole arrangement i have with my hotends:



the issue you'll have with thermocouples is that the wire they are built from is solid and won't handle the movement as long




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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 02:54AM
..or this type

[www.ebay.com]


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 05:31AM
Such threaded couplers have substantially more mass. As a result, your regulator will respond slower to heat consumption. These miniature thermistors have the advantage of responding very quickly, so you get better, more constant temperature regulation.

And all this has nothing to do with thermistor vs. thermocouple. I'm pretty sure there are thermistors with a threaded mount, too.


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 06:15AM
Quote
thejollygrimreaper
the issue you'll have with thermocouples is that the wire they are built from is solid and won't handle the movement as long

Mitsumi has a few specifically for moving applications, with relief springs on the wire. Unfortunately, they cap out at 300C, so you don't get the most desirable benefit from changing to a thermocouple which is breaking the 300C barrier.....
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 06:17AM
Quote
Traumflug
Such threaded couplers have substantially more mass. As a result, your regulator will respond slower to heat consumption. These miniature thermistors have the advantage of responding very quickly, so you get better, more constant temperature regulation.

And all this has nothing to do with thermistor vs. thermocouple. I'm pretty sure there are thermistors with a threaded mount, too.

I've mounted a few inside brass bolts before today , simply put a hole through it and make the hole the wires come out of smaller than the thermistor




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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 07:01AM
What about these little guys?
H3457 Fast Response Micro Probe
Sensor: NTC thermistor; M3 thread


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 08:23AM
You might want to have a look at the Prometheus hot end thread.
We were discussing thermistor vs thermocouple issues in that thread, too and RP Iron Man seems to have come up with a neat solution.
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 10:15AM
I've been experimenting with thermocouples andd did have good experiences with the board from E3D using a SparkFun thermocouple. I then had some Ultimaker TC1 boards made up and I soldered them all up and had one working for a while and then all of the sudden I started to get 10-15C oscillations that occured nearly every second. I have tried everything with it including using a different analog input, different 5v/GND supply from Ramps, isolating the supply using buck converter off of 24v supply, changing thermocouple, covering it in kapton for electrical isolation, changing AD597 chip and even going back to the E3D board but I can not fix the issue so for now I have gone back to thermistors

I have a schemtic from Kreature in IRC that has much more filtering than the TC1 board does so I may try to get that drawn in Eagle and sent to OSHPark soon and if I can find time I may hook the TC1 up to my oscilloscope to try to find the issue but at this point it doesn't matter to me because I had to stop using the E3D because I could not keep it from jamming with PLA.
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 10:31AM
Quote
Mogal
What about these little guys?
H3457 Fast Response Micro Probe
Sensor: NTC thermistor; M3 thread

The first listing does not mention temperature range (odd thing to omit from the specs listing), and the second one tops out at 125C.....
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 12:44PM
Mogan that second one would be perfect if it hit 300C.

Gluing one into a small bolt isn't a bad idea but then you still need to insulate the leads and then lengthen them. There has to be a plug-n-play thermistor or thermocouple out there. The best hotend thermistor setup I have seen is on the B3 Pico.


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VDX
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 04:22PM
... for some special heating applications, where I was in need for a sensor capable of measuring between 0 degC and up to 600 degC I've started with PT100, PT1000 and NI200.

The PT's are pretty linear, so could be the most reliable/accurate sensor system ... especially when measuring with 12Bit or better ...


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The reasons we are still using thermistors is because:

- They are cheap
- They are easily accessible
- They are compatible with all electronics boards
- They are reliable up to 300C which is good enough for the majority of applications

I really think that we should be moving toward thermocouples as the standard for temperature sensing. The standard cheap M6 threaded fibreglass insulated thermocouples look neat (no annoying assembly), can be used up to 400C operating temp, and will provide more accuracy at higher temps than NTC thermistors. Do a quick search on Aliexpress and you will see them.

I think the biggest barrier is the lack of thermocouple integration with standard electronics boards. The actual thermocouples are not too much more expensive than thermistors but it becomes a PITA when you have to buy an external expansion board $15-20USD eye popping smiley just to use a thermocouple. On top of that, there is the chance that it won't end up working simply because there are problems that have not been debugged (as someone described earlier in this thread).

It would be great if someone could come up with a RAMPS 2.0 that is affordable and has thermocouple support built in.

I have been thinking about this problem and I just decided to redesign my heater block to accommodate a Kapton-Tape-free method of securing the thermistor while allowing for a future upgrade to standard M6 threaded thermocouples. You can check out the Prometheus Hot End thread to see the detailed drawings. The modern hot end designs are ready for thermocouples it's just that the electronics boards are lagging behind. Also, not many people would be willing to buy a new electronics board just to use a thermocouple with their hot end...

Unfortunately, it is going to be a very slow transition between thermistors and thermocouples yawning smiley


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 06:46PM
its a shame that PTC sensors are such a pain to use too, they would be a good option, i have 20 of them i need to figure out what to do with.


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Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 06:59PM
Quote
RP Iron Man
It would be great if someone could come up with a RAMPS 2.0 that is affordable and has thermocouple support built in.

If you want it today, the Megatronics 2.0/3.0 boards both include built-in support for two K-type thermocouples via screw terminals, and the 3.0 board also has headers to connect an additional two external thermocouple cards if you find yourself needing four thermocouples (and four thermistor inputs as well).....
A2
Re: I am tired of thermistors and I think we all need to look for a better solution
March 31, 2014 09:09PM
Q: what filaments requires >300C, got a list?
VDX
Re: I am tired of thermistors and I think we all need to look for a better solution
April 01, 2014 03:03AM
Quote
A2
Q: what filaments requires >300C, got a list?

... my hightemp-experience was with presintered sticks of glass/polymer-ceramic mixtures.

One of the 'low-temp'-glasses melted the first time at 360 degC, after cooling down/settling it needs above 700 degC for remelting.

Another mixture containing a polymer was extruded at around 280 degC and after fabbing it was sintered/burned in a kiln at around 900 degC to full solidity ...


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--------
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Re: I am tired of thermistors and I think we all need to look for a better solution
April 01, 2014 05:49AM
Some Polycarbonate or PC-ABS filaments seem to have terrible layer adhesion when printed with anything below 300°C. My interim solution was to print as low and slow as possible to transfer enough energy into the previous layer so that everything fuses together nicely.
Obviously, this solution sucks, so a higher printing temperature might be quite handy for these kinds of plastics.

Edit: This issue might also be related to the nozzle shape. I am using an E3D V4.1 hotend with a nozzle that is narrow near the tip. Thus, the heat doesn't transfer as easily to the tip as with a blunt nozzle like stratasys uses. Maybe the plastic is already too cool to really fuse with the previous layer when it comes out of the nozzle. Air turbulences and draft might exacerbate the situation even further. The narrow tip is excellent for PLA for example, though.
Maybe a compromise like the Makerbot nozzle style might offer the best of two worlds?

E3D nozzle:


Stratasys nozzle:


Compromise?:


Edited 1 time(s). Last edit at 04/01/2014 10:02AM by uGen.
Re: I am tired of thermistors and I think we all need to look for a better solution
April 01, 2014 03:30PM
Quote
RP Iron Man
I think the biggest barrier is the lack of thermocouple integration with standard electronics boards. The actual thermocouples are not too much more expensive than thermistors but it becomes a PITA when you have to buy an external expansion board $15-20USD eye popping smiley just to use a thermocouple. On top of that, there is the chance that it won't end up working simply because there are problems that have not been debugged (as someone described earlier in this thread).

The alternative to a $20 expansion board is a main board that is (maybe) $15 more expensive (per supported thermocouple). The advantage of an expansion board is that it can be mounted to the extruder, which means no flexing for the thermocouple wires. I would pay an extra $5 to have a separate board for the thermocouple, and only pay for the number of them that I need. Most setups would only need one, but many people would want support for two or more.


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Re: I am tired of thermistors and I think we all need to look for a better solution
April 03, 2014 09:00PM
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.


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Re: I am tired of thermistors and I think we all need to look for a better solution
April 03, 2014 09:30PM
Quote
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? winking smiley

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? grinning smiley

How the extra mass and metal will impact the temperature measurement accuracy is the big question.....
Re: I am tired of thermistors and I think we all need to look for a better solution
April 03, 2014 11:13PM
Obviously I didn't spinning smiley sticking its tongue out

That is actually perfect. My whole goal is a plug and play solution and that looks a great solution, now I just need to wait until they get stock.


*hops on soapbox*
HEY HOTEND MANUFACTURES, MAKE M3 THREADED HOLES THE STANDARD. WE WILL ALL BENEFIT

THANK YOU
*hops off soapbox*

Edited 1 time(s). Last edit at 04/03/2014 11:14PM by jzatopa.


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Re: I am tired of thermistors and I think we all need to look for a better solution
April 03, 2014 11:37PM
Quote
jzatopa
Obviously I didn't spinning smiley sticking its tongue out

That is actually perfect. My whole goal is a plug and play solution and that looks a great solution, now I just need to wait until they get stock.


*hops on soapbox*
HEY HOTEND MANUFACTURES, MAKE M3 THREADED HOLES THE STANDARD. WE WILL ALL BENEFIT

THANK YOU
*hops off soapbox*

i can do this already on my hotends ( just have to tap the hole),




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Re: I am tired of thermistors and I think we all need to look for a better solution
April 04, 2014 06:04AM
Quote
jzatopa
My whole goal is a plug and play solution and that looks a great solution, now I just need to wait until they get stock.

If you read the description, the seller simply glued a thermistor into the brass fitting. It took me all of five seconds to realize that the brass fitting was a simple M3 chassis standoff, sold by the pound/kilogram:



Given the near-negligible cost, I want to know what are everyone's thoughts about replacing the set screw in an E3D or other hotend design with a side-drilled M3 (or even M2) hole that uses one of these standoffs as both the set screw for the heater cartridge *and* the thermistor housing? By having direct contact with the heater cartridge the sensor delay from additional heated mass of the standoff should be somewhat mitigated.....
Re: I am tired of thermistors and I think we all need to look for a better solution
April 04, 2014 06:45AM
Quote
vreihen
Quote
jzatopa
My whole goal is a plug and play solution and that looks a great solution, now I just need to wait until they get stock.

If you read the description, the seller simply glued a thermistor into the brass fitting. It took me all of five seconds to realize that the brass fitting was a simple M3 chassis standoff, sold by the pound/kilogram:



Given the near-negligible cost, I want to know what are everyone's thoughts about replacing the set screw in an E3D or other hotend design with a side-drilled M3 (or even M2) hole that uses one of these standoffs as both the set screw for the heater cartridge *and* the thermistor housing? By having direct contact with the heater cartridge the sensor delay from additional heated mass of the standoff should be somewhat mitigated.....

M3 would be easier for manufacturing with the aluminium or brass heater blocks, M2 is getting into the too small territory




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Re: I am tired of thermistors and I think we all need to look for a better solution
April 04, 2014 09:30AM
Quote
vreihen
Given the near-negligible cost, I want to know what are everyone's thoughts about replacing the set screw in an E3D or other hotend design with a side-drilled M3 (or even M2) hole that uses one of these standoffs as both the set screw for the heater cartridge *and* the thermistor housing? By having direct contact with the heater cartridge the sensor delay from additional heated mass of the standoff should be somewhat mitigated.....
But in the process, you're also moving your thermistor away from where you're actually trying to measure the temperature, as well as adding a heat sink since the thermistor would be in the section that protrudes from the heater block. Yeah it might look better, but you're not going to get a more accurate reading.

Also if you're going for high temp readings of 300+ degrees C, even high temp JB Weld epoxy isn't rated for that temperature. JB Weld high temp is only rated for intermittent use up to 550 degrees F (288 degrees C). For higher temperatures use a metal-based muffler putty if you want to use something that's readily available.
Re: I am tired of thermistors and I think we all need to look for a better solution
April 04, 2014 12:27PM
Quote
vreihen
Quote
jzatopa
My whole goal is a plug and play solution and that looks a great solution, now I just need to wait until they get stock.

If you read the description, the seller simply glued a thermistor into the brass fitting. It took me all of five seconds to realize that the brass fitting was a simple M3 chassis standoff, sold by the pound/kilogram:



Given the near-negligible cost, I want to know what are everyone's thoughts about replacing the set screw in an E3D or other hotend design with a side-drilled M3 (or even M2) hole that uses one of these standoffs as both the set screw for the heater cartridge *and* the thermistor housing? By having direct contact with the heater cartridge the sensor delay from additional heated mass of the standoff should be somewhat mitigated.....

I think m3 is the way to go.

Your idea is a good one the only problem I see is that if you try to replace the grub screw with the thermistor, you have no way to tighten the heating element.


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Quote
vreihen
Given the near-negligible cost, I want to know what are everyone's thoughts about replacing the set screw in an E3D or other hotend design with a side-drilled M3 (or even M2) hole that uses one of these standoffs as both the set screw for the heater cartridge *and* the thermistor housing? By having direct contact with the heater cartridge the sensor delay from additional heated mass of the standoff should be somewhat mitigated.....

Think about where you want to close the control loop. If your goal is to keep the heater cartridge at a steady temperature, than this is probably the way to go. But I think we're more interested in the temperature at the melt zone.
Re: I am tired of thermistors and I think we all need to look for a better solution
April 04, 2014 06:33PM
Quote
jzatopa
Your idea is a good one the only problem I see is that if you try to replace the grub screw with the thermistor, you have no way to tighten the heating element.

My thought was that the block could be drilled so that the length of the threaded part of the standoff would act as the grub screw to hold the heater. Also, at least on the E3D, the grub screw hole would have to be moved from the bottom of the block to the side, as the standoff would be hanging lower than the nozzle even without wires.....
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