Adapting 2 wire PT100 to 4 wire
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David (dc42) could you comment please, very grateful if you could.
Keith
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Which version of the Duet PT100 boar do you have? The Wiki should have you covered in any case.
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I have the Duet 2 Ethernet. Unfortunately the Duet wiki doesn't cover it, it's a simple codge up devised by David to make the 2 wire PT100 more reliable in the case of not being able to get hold of a 4 wire version which appear to be a bit rare and of course the 2 wire is cheaper
Keith
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Okay, you want to turn the cheap 2 wire into a 4 wire like he did?
Then do it like the picture, and wire the outer most wires to the outermost terminals, and the innermost wires to the innermost terminals.
The 2x5 connector is just a 10pin connector for easy disassembly and doesn't affect 2 or 4 wire connection.
Edit: maybe a copy/paste collage form the blog/wiki helps?
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(Duet 2 Ethernet doesn't have PT100 inputs, you need the PT100 daughter board, which is what version I was asking about)
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@bearer
That's it, thank you ! It's exactly what I've been looking for and haven't found. Can you link me to it please.
Keith
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@bearer Yep, I have the appropriate daughterboard
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It is described in the wiki; but ref picture in post above.
However depending on the version of the PT100 board you may have to remove jumpers, cut bridges or even desolder bridge/0R resistors for it to work as a 4-wire input. (All of that is also described in the Wiki)
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@bearer Yep, I'm up to date with the daughterboard, I actually have 3, a pre-production where you cut the track, the first production with the solder bridge jobby and the current version with the jumpers, which I'm using in my latest printer.
What I'd like to see is the page where you found the pic, I never came across that after searching for sever hours across the net. Could you give me the link to the page you got the pic. Thanks
Keith
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At the end of the day there is absolutely no difference between a 4 wire and 2 wire sensor itself. The probe is the same. All they do is add the extra wires like in the photo above when they make them. I work in the irrigation industry and we use them for our submersible pumps. Generally we use 3 wire pt100’s which we assemble ourselves. We have pumps that can be over 200m from the controller and 3 wire sensors are accurate enough. We are working on a 5-10 degree temp increase from standard running temp to trip temp (most motors will run at 35 degrees) so we do need some accuracy. All it is doing is measuring the resistance down the pair of legs to help compensate to make the reading more accurate. When you actually look at the lengths of the runs we use for the printers, it is not necessary to run a 4 wire sensor. At the temps we run 0.4 ohms equates to about 1 degree (I think it is slightly bigger as it gets into the negatives) and I don’t think you would even have that much resistance down the cables so it won’t effect your reading enough to warrant to do it. Plus I have sausage fingers and trying to get the wires into those tiny terminal blocks is hard enough just with 2
Kind Regards,
SamCustom Core-XY
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@kayjay said in Adapting 2 wire PT100 to 4 wire:
What I'd like to see is the page where you found the pic, I never came across that after searching for sever hours across the net. Could you give me the link to the page you got the pic. Thanks
I copied the hotend picture from Davids blog, and the PT100 picture from the wiki, and placed them next to each other. It is only described with words how to do the wiring in the wiki. Hopefully the collage makes it clearer.
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@bearer that's what's odd about the pic with the hot end. If you follow that link I put in the first post it leads to David's blog but that pic isn't there, that's why I wanted the link, so I could see the page it came from. I've searched high and low to find that info, I'm amazed you found it for me, you certainly have my thanks but can you give me the link please, I'd like to get to the bottom of why I can't see it and you can.
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@samlogan87 Thanks Sam, I read somewhere on here about the 0.4 ohms equating to 1 degree, I suppose an extra foot of wire needed to reach the controller wouldn't make that much difference as you say. I think I'll forget all about adding the extra wires, I don't have sausage fingers but I have 67 year old eyes that don't work all that well even with my reading glasses on
Keith
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@samlogan87 said in Adapting 2 wire PT100 to 4 wire:
When you actually look at the lengths of the runs we use for the printers, it is not necessary to run a 4 wire sensor.
It's not just about the length, it also helps reject the electrical noise interference from being run alongside other wires like the heaters and endstops and steppers.
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@phaedrux I would be very interested to know how much of an effect it has. We have 3 wire ones running parallel to sometimes 500A continuous loads and we don’t tend to have to many issues with temperature.
Kind Regards,
Sam -
Well going from reports here on the forum switching to 4 wire has helped some people.
I'm not an electrical engineer though. My understanding stops at 2 wires good, 4 wires better.
For what it's worth I run about 2 meters of 4 wire PT100 in a bundle to the hotend along with the heater, BLTouch, 2 fans, and stepper wires, and haven't had any issues.
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@kayjay said in Adapting 2 wire PT100 to 4 wire:
@bearer that's what's odd about the pic with the hot end. If you follow that link I put in the first post it leads to David's blog but that pic isn't there, that's why I wanted the link, so I could see the page it came from. I've searched high and low to find that info, I'm amazed you found it for me, you certainly have my thanks but can you give me the link please, I'd like to get to the bottom of why I can't see it and you can.
I combined to two for you to help illustrate the instructions in the wiki.
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@bearer Yes, it had just come to me that that was what you had done. So in actual fact, that may not be the solution. It could still be that it is wired the same as a two wire.
Never mind, I'll stick with it as a two wire, if I get discrepancies I'll search out a genuine four wire PT100
Thanks again
Keith
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@kayjay said in Adapting 2 wire PT100 to 4 wire:
So in actual fact, that may not be the solution. It could still be that it is wired the same as a two wire.
No, that photo is correct.
From the PT100 wiki page: https://duet3d.dozuki.com/Wiki/Connecting_PT100_temperature_sensors
To connect a 4-wire PT100 sensor:
Connect the two wires that go to one end of the PT100 resistance element to pins 1 and 2 (it doesn't normally matter which wire in each pair goes to which terminal)
Connect the two wires that go to the other end of the PT100 resistance element to pins 3 and 4 -
@bearer Do you mind if I add your image to the PT100 wiki?
