Thermocouple Upgrade

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Dionysus480
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Thermocouple Upgrade

Postby Dionysus480 » Sun Apr 30, 2017 11:47 pm

I've been getting a ton of hot end temperature faults lately, and after about 10 faults today, I've decided to invest in a Thermocouple board and Thermocouple from Filastruder. I was trying to ensure I had all of the items I needed.

I'm ordering a copper heater block and heatbreak for my E3Dv6, and the cartridge Type K thermocouple as well as the Duet interface board.

Do I need any insulation to protect the leads from the heat? The way the thermistor leads needed the fiberglass shield. Also, can I put a connector in the circuit, or does the lead have to go directly to the board?

Does anyone have a strong feeling that the PT100 is a better choice?

One other issue. I've primarily using PETG at (yes thermistor) 247C. I added a BERD Air recently. I've noticed the heater having trouble keeping the temp up that high once the BERD Air is on to 50%. I figure its getting a lot of the air reflected off the surface, which might be causing the cooling?

Also, PETG is pretty goopy. This silicone socks do help keep things clean, but does anyone have a great way to clean the "loop" tube from the BERD Air? The PETG seems to adhere and clog the holes.

As always, thank you guys for your expertise.
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Xenocrates
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Re: Thermocouple Upgrade

Postby Xenocrates » Mon May 01, 2017 12:06 am

I feel a PT100 is better than a thermocouple due to the higher resolution. At one point, the mechanical stability was a lot better as well. Since you're using a rambo still (from a quick scan of your history), it's rather irrelevant. With a thermocouple, they really want a proper thermocouple connector. Another thing is that if the board is in an area that gets warm over time, the reference point will shift (this is part of why I use a PT100, since at one point the amplifier was up top, and that gets rather warm with a heated chamber. I assume the same would occur on a V3 with a heated chamber.). The cartridge thermocouple should ship with proper insulated leads, and should be used with same leads. If you need more length, you need K type thermocouple wire (Again, accuracy thing. You could use normal wire, but I dis-recommend it).

I recently had GF PETG get stuck on my berd-air. My advice is to as a first step, take it off and use a barbecue lighter to warm the loop enough to remove it, then a hot air gun and a compressed air supply to help clear the holes (Or use acetone if you're not in hurry or lack a good pressure supply).
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Dionysus480
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Re: Thermocouple Upgrade

Postby Dionysus480 » Mon May 01, 2017 12:22 am

Thanks so much for the quick reply.

For the record, I'm on the older Duet, so I was ordering the Duet interface board.

I'm also getting jamming on PLA. I've ben thinking it was heat creep, since it tends to occur about 10-20 layers into each print. Hopefully the better temp measurements clear up the situation and I can correct it. I'm also replacing the heatbreak, since some supposedly have some sort of burr. (Note: I print PETG and ABS with no jamming.)

I have an enclosure, but lately I've been printing with the sides removed. I was trying to determine if the heat buildup inside the enclosure was contributing to the jamming issues with PLA. Hasn't seemed to help much.

Current setup: Rostock MAX v2 with Raymond style enclosure, Duet 0.8.5, TPlink router to Ethernet for wireless, 7" PanelDue, E3Dv6, 713 maker mount and effector, Astrosyn Dampers, E3D Titan Extruder, BERD Air.

Thanks again.
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Re: Thermocouple Upgrade

Postby Dionysus480 » Mon May 01, 2017 11:26 pm

OK - I did a bit more reading, and I switched to a PT100. Question - is it better to have longer leads between the boards, or from the interface to the sensor. I was thinking I'd install the interface in the top, and run leads down to my duet that lives in the base (v2). That makes the wires to the sensor shorter.

Not sure if it matters. But wondering.
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Re: Thermocouple Upgrade

Postby mhackney » Tue May 02, 2017 12:20 pm

If you are getting jamming printing PLA then 1) don't expect a PT100 or themocouple to be miracle cure and 2) you have some other issue and my bet would be on too long of retracts or too high extrusion temperatures but there are many other reasons too. An E3D V6 can print PLA reliably all day every day until the cows come home. I have several that print 5+ hrs a day 5 days a week for 2 years with not a single jam or other issue. That's an accumulated 6000 hrs of print time - plus the many others I have that get less heroic use.

Read David Crocker's guide on PT100s with Duet on his blog @ https://miscsolutions.wordpress.com/201 ... d-silence/. He advocates using 4 wires to the board even if the board is 2 wire. In the end he doesn't think it makes a practical difference but it is a better way to do it.

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Dionysus480
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Re: Thermocouple Upgrade

Postby Dionysus480 » Tue May 02, 2017 1:43 pm

Thanks for the information and link. I understand that the PT100 won't be a miracle for the jamming, but I'm trying to figure out if the hotend is +15-20C or something. I've been pretty happy with PETG until recently, when I can't seem to slow the machine down enough to keep small parts from deforming, even with a BERD Air at full blast. I have followed your guide to profiling my favorite filaments, so thank you for that as well. I've got a silver PETG dialed in so tight I feel like I can print about anything will it. The black melts like a candle if its printed at the same settings (temp issue or chemisty issue?) PLA jams. Clearly something isn't right.

The faults I'm seeing may actually indicate the cartridge thermistor is toast. Its pretty darn new, so that is disappointing. My filament profiles seem like they're lower over time, so I'm wondering if the hotend is heating to higher temps over time. I think my PETG was extruding fine at like 225, when I'm used to printing it in the 240 range.

So - new temp sensing and back to re-profile the filaments! I actually enjoy this stuff.
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Re: Thermocouple Upgrade

Postby mhackney » Tue May 02, 2017 1:55 pm

I'm putting a PT100 on one of my deltas today in fact, just as a reference point. Should be interesting.

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Re: Thermocouple Upgrade

Postby dc42 » Tue May 02, 2017 5:29 pm

Thermistors are cheap, easy to use, not very susceptible to interference (depending on your electronics), but not very accurate.

PT100 sensors can be much more accurate if you use an interface that doesn't introduce errors. On the Duet we use a digital interface so that only 2 components have to be accurate: one precision resistor, and the converter chip. Resistance in the wiring between the PT100 sensor and the interface board will affect the reading if you use a 2 wire connection, but is eliminated if you use a 4 wire connection. Interference from stepper motor cables can be a problem. I use a dedicated unshielded 4 core cable for the PT100 on my delta and I don't have any problems. Some users report having to use shielded cable.

Thermocouples can also be more accurate than thermistors, but they have some disadvantages. To get an accurate reading, you need to run the thermocouple wire right back to the interface board so that the interface chip can do cold junction compensation. This means you can't use a hot end connector for quick hot end swapping. The thermocouple produces a very small output voltage, so the wires pick up interference by induction very easily. Using twisted pair wires is essential. Shielding the wires in unlikely to help.

So my recommendation is:

- if absolute accuracy doesn't matter and the budget is tight, use a thermistor
- if absolute accuracy matters, use a PT100
- only use a thermocouple if the other options are not suitable, e.g. at high temperatures

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Re: Thermocouple Upgrade

Postby mhackney » Wed May 03, 2017 12:42 pm

David, is there a symptom if the PT100 wires are picking up interference? Fluctuating temp reading or similar?

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Re: Thermocouple Upgrade

Postby dc42 » Wed May 03, 2017 5:53 pm

On the Duet, the symptom is temperature spikes of 2000C, indicating that the converter chip failed to get a good reading several times in succession.

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Re: Thermocouple Upgrade

Postby mhackney » Wed May 03, 2017 7:34 pm

Ouch, that's hot! j/k

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Re: Thermocouple Upgrade

Postby Dionysus480 » Fri May 19, 2017 2:17 pm

I purchased the Think3dPrint3d pt100 daughterboard, but I need to create a wire harness for my Duet 0.8.5. The Duet's expansion header is well documented. I'm having trouble locating information on pinout of the daughterboard so I know which pins carry which signals.

Anybody have a reference, diagram or pictures of how to wire these two together? Perhaps I am ignorant of a particular standard nomenclature when I'm looking at the available information. Any help appreciated.

DK
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Re: Thermocouple Upgrade

Postby dc42 » Fri May 19, 2017 5:26 pm

The table at https://duet3d.com/wiki/Connecting_PT10 ... 6_or_0.8.5 relates the signal names to the Duet 085 expansion connector. To relate the signal names to the connector underneath the daughter board, see connector J37 (SPI0) in the schematic at https://github.com/T3P3/Duet/blob/maste ... _v1.02.pdf remembering that this is as viewed from the top.

HTH David

PS the signal names are also shown on the daughter board schematic at https://github.com/T3P3/TempDaughterboa ... empRTD.pdf.

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Re: Thermocouple Upgrade

Postby Dionysus480 » Fri May 19, 2017 8:14 pm

Thank you so much. I think I've got it mapped. I really appreciate it.
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Re: Thermocouple Upgrade

Postby Dionysus480 » Thu May 25, 2017 9:15 pm

Just wanted to close this one out. Thanks to all that helped. I converted to a PT100 with the Duet interface board from Filastruder. I ran 4 wires to the sensor, and I routed the wires through heatshrink (unheated) tubing external to the expandable nylon loom/sleeve. I figure it creates a little distance that may help reduce interference. (Note I'm also converting to direct extrusion with an Aero, so I have the extruder wires as well as the hotend heater and the fan. I didn't want the PT100 wires running through all those wires carrying current.)

I also added a copper heater block, copper nozzle and ensured I could put a sock on it (ordered a dozen extra so I don't run out.)

The temperature variation I was seeing is down to about 0.1C now. It looks pretty rock solid.

For anyone looking to do this upgrade, its pretty straightforward. The diagrams provided above do help with wiring to older Duets.

Thanks again to all.
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