Thermocouple and Nichrome wire

I am a bit confused on the use of the Thermocouple and Nichrome wire. I understand electricity passes through the Nichrome wire and it heats up. so I need this circuit of electricity. but what is the Thermocouple wire for. do I need to connect the ends at the tip or strip them? then how do you connect the 4 or 2 wires to the controller board?

Down at the bottom of this page: [www.reprap.org]

He shows both connections (just before the firmware section)

If your facing the cat5 port away from you, the nichrome connects to the left two ports, the thermocouple connects to the right two.

If I have it correct the thermocouple detects the temperature of the tip by the hot-tip manager. Anyone check me on that.

so how does the thermocouple connect. do the two wires have to touch or are they connected to something at the tip?

There are two wires that come out of the one wire piece they sent you (its wrapped in a weave of something). Each of those goes in a separate connection to the board. So one will go in the right most hole, the other will go next to that. It doesn't matter which goes in which because techzone took care of that difference in the software.

Hope that helps?

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[omemon.wordpress.com]

how do they connect to the tip of the extruder. should they touch there?

The thermocouple wires are connected to each other at one end. That's the measuring end which you would attach to the tip. The other ends that are loose connect to the thermocouple A-D board. If you look at the board, there are 4 terminals. The two next to the chip on the board are the terminals for the thermocouple.

I would recommend that you make sure that you have the thermocouple hooked up correctly and it's reading the correct temperature before connecting the heater wires.

The thermocouple which is the sheathed wire with 2 other wires in it (1 red material & one in a yellow material this makes it a K type I think) has the bare ends twisted together at one end and when you assemble the hot end you need to get that twisted end as close to the end of the hot end as possible, but for reliability it is best if it does not touch the brass(of the tip) or the nichrome when you seal it up with the goop (my experience in other feilds tells me that points of contact are places of failure and the heater element shorted to the thermocouple would not be a good thing). Further reliability is achieved by soldering the twisted end (you need soft silver solder and liquid flux to do this reliabily, & you can use this to solder the nichrome to copper connections as well).
So to finally answer the question the hot tip manager cct board has 4 screw connections & a RJ 45 connection & the heater wires go into one pair and the thermocouple wires into another pairs as per the diagram on the build a Huxley Wiki. Before you connect them you can test the thermocouple by measuring the millivolts across the red and yellow wires and if you hold the tip in your hand the millivolts will change in 1 direction and if you let go they will go the other direction if you do this to the ungooped thermocouple you will see that it is highly responsive and will change if you breath on it. (it goes without saying if the wires are open cct on a resistance check you have a different issue) also there should be no connection between the element and the thermocouple.
Sorry its so long winded but I hope it helps

sweet! that is what I was looking for! how do you keep the thermocouple from touching the brass tip? would a thin dab of heat goop work and then coder it all. or would that insulate the wires to much?

Stephen Lane wrote:
That about how I've done it

Regards

Yep it works great. see my initial oozing: [vimeo.com]

That post helped me a lot. I've been having trouble finding documentation for many of the finishing touches on the huxley kit I got from techzone. When you said thermocouple did you mean nichrome? I have one thick (thicker than the thermocouple) wire, that has two other wires in it (red and white). I tried running the tip from repsnapper before and the tip heated up, but the monotronic lights came on and off, and it made a chirping sound. I turned it off, I'm assuming it's because I didn't have the two wires correct in the tip manager, does anyone have any better pictures of the wiring?

cyborg527 Wrote:
-------------------------------------------------------
> That post helped me a lot. I've been having
> trouble finding documentation for many of the
> finishing touches on the huxley kit I got from
> techzone. When you said thermocouple did you mean
> nichrome? I have one thick (thicker than the
> thermocouple) wire, that has two other wires in it
> (red and white). I tried running the tip from
> repsnapper before and the tip heated up, but the
> monotronic lights came on and off, and it made a
> chirping sound. I turned it off, I'm assuming it's
> because I didn't have the two wires correct in the
> tip manager, does anyone have any better pictures
> of the wiring?

from http://reprap.org/wiki/TechZone_Tip_Assembly



Techzone's tip comes with 2 wires.

First is a single strand of nichrome wire that's wrapped in insulation, about 1 foot long - this is the heater.

Second is a pair of wires that are separated at one end, and twisted around each other at the other end. The wires have different colors of insulation on them, and are each made of a different metal. This is the thermocouple.

This image shows only the thermocouple connected.



While this image shows only the heater connected.



Also, the thermocouple wiki is worthwhile reading, if you're interested in knowing how it works.