Extruder Temperature Sensors

I designed and manufactured my pure silver heater block with the idea of mounting the temperature sensor, in the form of a ring lug device, under an Inconel Belleville washer between the nozzle and the sensor. Methods of establishing the correct crush of the Belleville washer are not germane to this discussion ;-)

My design requirements are 500-600C maximum temperature, and interface with existing electronics. Standard 3mm diameter x 15mm length "probes" are not acceptable. Any other suggestions are fair game.

I have a choice between thermocouple (low accuracy, requires interface board to controller); NTC thermistor (cheap, accurate, bad form factor at high temps); PT1000 platinum RTD (cheap, accurate, standard interface to electronics). I'm leaning toward the PT1000, if only because a platinum sensor on a silver block with a diamond nozzle just kidding) and have samples on the way, but:

I would love to get any feedback on what would be preferable. Pros, cons, experiences, thoughts.

All-up weight as shown is 148 grams. The silver heat block alone is 24 grams! It better be worth it (and probably won't be, but it has been a fascinating exercize, at least to me).

Edited 1 time(s). Last edit at 08/19/2021 06:28PM by rq3.

... for high-temp measuring and temp-controlling I were using PT100 and NI200 sensors with high resolution 24Bit AD-controllers (AduC847) -- for testing and adjusting I've combined two PT100 "back to back" and heated (and measured) of up to 800°C with them (they were max-rated for 650°C)

Beside the common "flat" type there are cylindrical 2mm-types in a ceramic housing (could be aluminium-oxide), what's easy to insert and clamp into a 2mm-bore ...

Here is a similar type, only rated to 400°C:
[www.temperaturmesstechnik.de]

Edited 1 time(s). Last edit at 08/19/2021 06:44PM by VDX.

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Viktor
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Quote
VDX
... for high-temp measuring and temp-controlling I were using PT100 and NI200 sensors with high resolution 24Bit AD-controllers (AduC847) -- for testing and adjusting I've combined two PT100 "back to back" and heated (and measured) of up to 800°C with them (they were max-rated for 650°C)

Beside the common "flat" type there are cylindrical 2mm-types in a ceramic housing (could be aluminium-oxide), what's easy to insert and clamp into a 2mm-bore ...

Here is a similar type, only rated to 400°C:
[www.temperaturmesstechnik.de]

Most excellent! Thank you, that's exactly the kind of feed-back I need. Keep it up, folks!

... glad, I could help!

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

I tend to use thermocouples for hotends – this is not to disagree with your points, but I find the absolute accuracy is not too important as keeping the delivered temperature constant. From this point of view, does the temperature change with plastic flow and other causes such as unwanted nozzle cooling, limitations on the PDI control etc.. Resolution for thermocouples can be similar to thermistors and PT100/PT1000 sensors.

The clincher for me though is that fine wire thermocouples are fairly readily available ( [pkAAOSwa0VaH-16" target="_blank" rel="nofollow">www.ebay.co.uk] ) that will fit into a 0.6mm diameter pocket and this pocket can be in the nozzle or anywhere else convenient on the hotend.

Mike

I've decided to go with this:

[www.te.com]

Costs about $1, should last forever, good to 600C, and directly interfaces to the existing ADC pin.

I did not realize that platinum RTD sensors were available at low cost and in small sizes. The last time I used a PT100 sensor it was fiercely expensive, quite bulky and needed a dedicated amplifier.

For the time being I will stay with my thermocouples for the reasons stated earlier but hope to find a project where I can use a PT1000 sensor.

In passing though, to go with your platinum sensor, silver block and diamond nozzle, you could consider Edit: 24 K gold “O” rings to seal the nozzle and heat break against leakage. Gold “O” rings were used on a Kratos mass spectrometer head that I worked on and they would take being heated up to 500°C

Mike

Edited 1 time(s). Last edit at 08/21/2021 07:17AM by leadinglights.

Quote
leadinglights
I did not realize that platinum RTD sensors were available at low cost and in small sizes. The last time I used a PT100 sensor it was fiercely expensive, quite bulky and needed a dedicated amplifier.

For the time being I will stay with my thermocouples for the reasons stated earlier but hope to find a project where I can use a PT1000 sensor.

In passing though, to go with your platinum sensor, silver block and diamond nozzle, you could consider Edit: 24 K gold “O” rings to seal the nozzle and heat break against leakage. Gold “O” rings were used on a Kratos mass spectrometer head that I worked on and they would take being heated up to 500°C

Mike

I have fond memories of installing, with clean room gloves, various Con-Flat gaskets of copper, aluminum, and silver for ultrahigh vacuum work. Never ran across a gold one, but back in the day IBM used ALOT of 24K solid gold fixturing in their UHV research systems. That was when gold was priced at about where silver is today.

... when I was at university at end-80, we sometimes used gold-O-rings for UHV assemblies for GSI and Cern ... but as they were pretty expensive, whe had to "track" them constantly and return with "same weight", when dismantling the assemblies eventually

From this time I have only a bunch of Aluminium O-rings for random use ... but, years later, got some 99.999 gold-cylinders (each 2g in weight, meant as electrodes) for a microassembly development project, that weren't recalled after end

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Quote
VDX
... when I was at university at end-80, we sometimes used gold-O-rings for UHV assemblies for GSI and Cern ... but as they were pretty expensive, whe had to "track" them constantly and return with "same weight", when dismantling the assemblies eventually

From this time I have only a bunch of Aluminium O-rings for random use ... but, years later, got some 99.999 gold-cylinders (each 2g in weight, meant as electrodes) for a microassembly development project, that weren't recalled after end

Should I gold flash the silver heat block? It's immersion gold, takes 30 seconds. Pros, Cons? Looks cool, costs money, wastes resources, adds corrosion protection (not).

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rq3
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Should I gold flash the silver heat block? It's immersion gold, takes 30 seconds. Pros, Cons? Looks cool, costs money, wastes resources, adds corrosion protection (not).

While I don't know for sure if silver will tarnish in a hotend/plastic fume environment, I can offer the following supporting evidence:-

• My pure copper hotend bodies were insulated with cuttlefish bone but after several years got a thich, even and very black oxide coating. This was blacker than I would expect from copper in similar environments.
• The standard wire used in British aircraft was called Uninyvin. The specification for the conductor was changed from silver plated copper wire to nickle plated copper wire in the late 50s (from memory) because the silver would get a black tarnish in the engine bay due to heat and jet fuel fumes.

In addition, looking cool is something we need more of.

Mike