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-   -   Thermocouple extension wire (http://talk.craftweb.com/showthread.php?t=12449)

Ted Trower 10-16-2019 12:21 PM

Thermocouple extension wire
 
I need some help / information about using thermocouple extension wire. I'm converting an old Arrow Springs AF99 annealing - fusing kiln from analog control to digital. I'll be using it for a pickup kiln in the production of paperweights. I've wired up a box with a PID controller and SSR. Given the space available in my studio I'd like to position the controller about 6-9 feet away from the kiln. I confirmed with Craig at Arrow Springs that the kiln used a type K thermocouple. I purchased type K thermocouple extension wire and wired up a plug to mate it to the thermocouple itself. Strange thing is that now the kiln won't go above 750F (measured by my non-contact thermometer) even when the controller is set to 950F and reads 950F. It stopped at the same 750F when the controller was set to 850F. I've had this kiln up to 1200F on the analog control so that's not the issue.

Any ideas, observations, thoughts or questions are welcome. Insults accepted as warranted by the facts.

Thanks in advance!

Rick Kellner 10-16-2019 12:30 PM

Have you delved into the parameters and settings in the controller?

I had one I hadn't used in about five years, and went to put it into service for a different application. Couldn't figure out what why it wouldn't go above about 965f. Then I poked around in the settings, and realized that I had previously programmed in some overtemp safety settings, to not exceed that temperature level.

A few quick parameter changes later, and I was able to ramp it up to higher temps.

Ted Trower 10-16-2019 12:32 PM

Quote:

Originally Posted by Rick Kellner (Post 145567)
Have you delved into the parameters and settings in the controller?

I had one I hadn't used in about five years, and went to put it into service for a different application. Couldn't figure out what why it wouldn't go above about 965f. Then I poked around in the settings, and realized that I had previously programmed in some overtemp safety settings, to not exceed that temperature level.

A few quick parameter changes later, and I was able to ramp it up to higher temps.

Did that. It arrived with a max temp setting of 400F. Set it to 1050.

Rick Kellner 10-16-2019 12:40 PM

How did you terminate your extension wire? Raw wire, or with spade terminals, etc? They make special versions of the appropriate alumel and other alloys for various thermocouple types, but I still can't imagine this level of variance in temperature detection from a wonky terminal of the wrong metal.

Is your extension wire solid, or stranded? Have you verified a secure connection to controller terminals, and to the TC itself?

Somehow this still strikes me as a possible controller related issue...

Rick Kellner 10-16-2019 12:44 PM

The color coding on the thermocouple wire + and - is sort of counter intuitive. Any possibility of the polarity of the device not being wired correctly?

Ted Trower 10-16-2019 12:48 PM

Quote:

Originally Posted by Rick Kellner (Post 145570)
The color coding on the thermocouple wire + and - is sort of counter intuitive. Any possibility of the polarity of the device not being wired correctly?

Had it reversed on first assembly. But that just makes it read negative numbers, not stop the heating process.

Pete VanderLaan 10-16-2019 01:03 PM

Ted, what happens if you remove the extension wire and go back to the other configuration?

Ted Trower 10-16-2019 01:07 PM

Quote:

Originally Posted by Pete VanderLaan (Post 145572)
Ted, what happens if you remove the extension wire and go back to the other configuration?

Good question. will go try that now.

Rick Kellner 10-16-2019 01:12 PM

Aha, did not know about the negative numbers. Could be a good prank sometime!

Is your extension wire a shielded insulation version, or standard? Do you have it routed through a conduit with any line voltage conductors nearby? Could there be another source of electromagnetic 'noise' playing an interference role here?

Ted Trower 10-16-2019 01:43 PM

Quote:

Originally Posted by Rick Kellner (Post 145574)
Aha, did not know about the negative numbers. Could be a good prank sometime!

Is your extension wire a shielded insulation version, or standard? Do you have it routed through a conduit with any line voltage conductors nearby? Could there be another source of electromagnetic 'noise' playing an interference role here?

Standard wire, insulated but not shielded. It was routed close to the line routing power to the elements in

Shawn Everette 10-16-2019 02:29 PM

At that length I wouldn't expect it to be a wire problem. It's a fairly minor signal, but you're not asking it to go across a football field. I've only seen a need for shielded on R type on top of a furnace. I've also encountered nothing in the way of noise at 120v.

Does the kiln seem to be getting hotter than 750 and not reading it, or just stopping and cycling at 750? That could indicate mechanical vs pid issue.

Other possibilities; Any chance an element is shot and can't make temp? Right voltage making it to the SSR? Full bypass of the analog control or partial?

Ted Trower 10-16-2019 03:06 PM

Quote:

Originally Posted by Shawn Everette (Post 145577)
At that length I wouldn't expect it to be a wire problem. It's a fairly minor signal, but you're not asking it to go across a football field. I've only seen a need for shielded on R type on top of a furnace. I've also encountered nothing in the way of noise at 120v.

Does the kiln seem to be getting hotter than 750 and not reading it, or just stopping and cycling at 750? That could indicate mechanical vs pid issue.

Other possibilities; Any chance an element is shot and can't make temp? Right voltage making it to the SSR? Full bypass of the analog control or partial?

Kiln would not heat above 750ish.. Analog controls were completely removed. Just finished the test Pete suggested. Kiln did come to the desired 850 with the extension wire removed from the circuit. This kiln is certainly under powered and there is considerable lag in coming to temp but my previous efforts where temp was never reached went for many hours.

There is only one element and it appears to be glowing uniformly

Voltage to the SSR is in the midrange of it's specifications

Ted Trower 10-16-2019 03:16 PM

Quote:

Originally Posted by Rick Kellner (Post 145569)
How did you terminate your extension wire? Raw wire, or with spade terminals, etc? They make special versions of the appropriate alumel and other alloys for various thermocouple types, but I still can't imagine this level of variance in temperature detection from a wonky terminal of the wrong metal.

Is your extension wire solid, or stranded? Have you verified a secure connection to controller terminals, and to the TC itself?

Somehow this still strikes me as a possible controller related issue...

Extension wire is solid wire. Thermocouple is connected to the extension wire with a male/female thermocouple connector for type K wire (it's yellow). Connection to the PID is bare wire.

Connections are tight.

Ted Trower 10-16-2019 03:20 PM

Quote:

Originally Posted by Shawn Everette (Post 145577)

Does the kiln seem to be getting hotter than 750 and not reading it, or just stopping and cycling at 750? That could indicate mechanical vs pid issue.

Controller would read the setpoint temp of 950F but kiln sat at around 750.

Rick Kellner 10-16-2019 03:31 PM

What kind of controller is it? Do you have an alternate PID unit to test in comparison?

I doubt it is coming into play here, but the other day I was reading about the solid extension wire becoming problematic if you have a bunch of tight bends in the run, or basically if you bend it back and forth for any reason. Something about the crystalline structure of the alloy changing and causing inconsistencies in accuracy.

Shawn Everette 10-16-2019 03:35 PM

I think you're looking at an under voltage scr input. If you can get your hands on a transformer or rectifier that has an output closer to the max, override the the pid, but watch the temp, that would let you know. If the scr is only getting half the voltage it's only giving half the output.

Is it cycling or just staying on?

Ted Trower 10-16-2019 03:39 PM

Quote:

Originally Posted by Rick Kellner (Post 145581)
What kind of controller is it? Do you have an alternate PID unit to test in comparison?

I doubt it is coming into play here, but the other day I was reading about the solid extension wire becoming problematic if you have a bunch of tight bends in the run, or basically if you bend it back and forth for any reason. Something about the crystalline structure of the alloy changing and causing inconsistencies in accuracy.

Cheap Chinese PID from Twidec. Bought it on Amazon. Reviews were good.

Do not have a second unit on hand.

Rick Kellner 10-16-2019 03:42 PM

Did you follow an existing wiring diagram, or is this a seat of the pants wiring job? Any schematic of what you did available?

Ted Trower 10-16-2019 03:46 PM

Quote:

Originally Posted by Shawn Everette (Post 145582)
ut.

Is it cycling or just staying on?

It does cycle.

Rick Kellner 10-16-2019 03:51 PM

Only took a quick peek at the Twidec controllers on Amazon. Very inexpensive.

The ones I found seemed to have an input rating for a PT100 temperature sensor. Did you get one compatible with a type K thermocouple, or are you able to select among a variety of thermocouple options in the parameters?

Maybe this has something to do with it?

Rick Kellner 10-16-2019 03:54 PM

More money, obviously, but I've had good luck with this one. The documentation is pretty good too:

https://www.auberins.com/index.php?m...&products_id=4

Shawn Everette 10-16-2019 04:03 PM

Then it's a controller issue. It should only cycle if it thinks it has reached peak temp or maxed out.

Scr might still be under powered, which would explain how slow it is. That and not enough elements for the space.

Rick Kellner 10-16-2019 04:06 PM

I looked up that style of kiln, and it seemed like a little hotbox. Maybe 1680 watts or thereabouts. Seemed like plenty of element power for the (small) heat chamber size.

Rick Kellner 10-16-2019 04:10 PM

Quote:

Originally Posted by Ted Trower (Post 145583)
Cheap Chinese PID

My suspicion is that this might have something to do with the issue.

Shawn Everette 10-16-2019 04:10 PM

Should max at that wattage, but age you know... An under powered scr would certainly slow things down.


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