Well I couldn’t find a thermocouple of the right design (I want to monitor the temperature of the cooling fluid as it leaves the laser tube with perhaps a second sensor to monitor the coolant entering the tube) so I decided to make my own. On the offchance anyone is interested in thermocouples I have attached a few pictures…..

1.   Piece of 6mm bore stainless tube and length of ‘Type K’ thermocouple wire.
2.   This is the tricky bit, the wires are spot welded onto the tube one on top of the other.
3.   With a simple mold I have used some car body filler to support the wires and give some protection to the weld.
4.   Completed tubular thermocouple which, with a bit of insulation, should indicate the flowing water temperature.
5.   Tested and it works.

Tweakie.

You keep amazing me, Tweakie!

So is it the special wires that do the trick? Thought a thermocouple body was the one that was bi-metal, it didn't occur to me it was the wires...

Daniel

Hi Dan,

There are many different combination's of metals / alloys which exhibit potential differences which change with temperature variation, the most common being the Type K which is Nickel-Chrome / Nickel-Aluminum alloys. Fortunately, for me the different types are color coded so at least I know what type it is that I found in my stores. One thing is curious though the Ni-Cr is non-magnetic but the Ni-Al is magnetic .
This explains thermocouples better than I can. http://en.wikipedia.org/wiki/Thermocouple

Best regards,

Tweakie.

Cool Tweak..........
Does your process meter have dual inputs ?
Are you just going to monitor the temps. or configure the meter to a Mach input ?

Looks like a nice meter with HI/LO , ALARM and configurable IO ?
Not familiar with that brand.

Very nice....will look real good mounted on your rig.
Be careful and watch the CG, it may topple over one day.

Thanks,
Russ

Hi Russ,

My plan for the temp controller was to keep it simple and hard wire the NC low output in series with my laser coolant flow sensor - if the temp rises above the preset then the switch goes open circuit and the eht unit shuts down power to the laser tube. It does only have one sensor input and I haven't yet figured out how to switch between two thermocouples, think I need inspiration here, any ideas ?.
The controller is made by IMO Precision Controls Ltd here in the UK and perhaps is not sold internationally.
You are certainly right about the C of G for my machine, bit worrying really, but I think it looks worse than it really is (fingers crossed).  

Tweakie.

I don't normally post pictures of my mistakes but this made me smile because it was just such a daft thing to do.

The spot welder applies a lot of pressure to the weld and the tube needs internal support to prevent distortion, the nearest thing to hand that fitted the tube nicely was this stainless bolt. After making the first weld it became obvious and yes you have guessed it, I have welded the bolt into the tube. 

I turned a piece of brass to fit the tube for the next one, that didn't weld in.

Tweakie.

By Golly...he is human.

Just curious Tweakie, could the attachment be made with a torch and a dab of silver solder ?

Thanks,
Russ

By Golly...he is human.

 

Hi Russ,

Just curious Tweakie, could the attachment be made with a torch and a dab of silver solder ?

No reason why not, as long as the two wires are welded together first and the join is not contaminated with other metals, I think that would have been a better (if not easier) way to do it - why didn't I think of that. 

Tweakie.

(I was just about to throw my mistake in the bin and I thought you guys would like a laugh as well).

As we all like pictures........
This bitmap image has been raster engraved, just lightly, into the surface of a piece of obechi using the Mach Impact/Laser Engraving plug-in.

Tweakie.