Thermocouple positioning
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Thermocouple positioning
I am having trouble with my thermocouple set up.
I have the 2 thermocouples reading within 1 ohm of each other. I corrected the values in the sestos pid so they are both reading the same in a cup of water at 80 degrees c and 1 degree difference in a cup of water at 20 degrees.
Perfect in theory, but when I put the thermocouple probes on the same cassette I get completely different readings (50/30 for example)
Now this has to be cause by the way the wires are contacting the cassette right?
I am just pushing them in a small amount between the aluminium cassette and the heat mat making sure they are not near the wires in the heat mat.
(I have them wrapped in heat shrink because I noticed I was getting heat soak on the top cassette)
How is everyone else attaching the thermocouples and how accurate are your results?
I have the 2 thermocouples reading within 1 ohm of each other. I corrected the values in the sestos pid so they are both reading the same in a cup of water at 80 degrees c and 1 degree difference in a cup of water at 20 degrees.
Perfect in theory, but when I put the thermocouple probes on the same cassette I get completely different readings (50/30 for example)
Now this has to be cause by the way the wires are contacting the cassette right?
I am just pushing them in a small amount between the aluminium cassette and the heat mat making sure they are not near the wires in the heat mat.
(I have them wrapped in heat shrink because I noticed I was getting heat soak on the top cassette)
How is everyone else attaching the thermocouples and how accurate are your results?
First is with using such short TCs you might not be reading temps within your lsminate. First thing I'd try is getting some longer fine wire TCs.then place the end on the casette where your laminate will be and try again.
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Ok I exposed more of the wire, wedged them in on the laminate side of the cassette and still one ran away from the other 60/30c.
I removed the wires and butted the tips into the side of the cassette (just holding by hand) and I got a more realistic 32/30c read out.
I definately have an issue with the way the wires are contacting the cassette.
I removed the wires and butted the tips into the side of the cassette (just holding by hand) and I got a more realistic 32/30c read out.
I definately have an issue with the way the wires are contacting the cassette.
I make skis so have the thermocouple right in the centre of the cassette. The wires run lengthwise along the cassette stuck in place by heat resistant tape. They then turn 90 degrees and exit the side of the cassette beyond where the tips end.
I stick the thermocouple and wiring to the aluminium skin with the heat resistant tape then lay the heat blanket on top of that.
I stick the thermocouple and wiring to the aluminium skin with the heat resistant tape then lay the heat blanket on top of that.
Don't wait up, I'm off to kill Summer....
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Could you please do a test for me madrussian?
Boil a cup of water and put both probes in. Note the temperature.
Do the same with a cup of cold water. This tells you if your tcs are calibrated correctly or not.
Then tape them as you normally would, except both to the same cassette and see what you get.
Im wondering if more people are operating with inaccurate thermocouple readings without knowing which could lead to a whole host of problems
Boil a cup of water and put both probes in. Note the temperature.
Do the same with a cup of cold water. This tells you if your tcs are calibrated correctly or not.
Then tape them as you normally would, except both to the same cassette and see what you get.
Im wondering if more people are operating with inaccurate thermocouple readings without knowing which could lead to a whole host of problems
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1 test in cup of water and on the cassette is not the samegozaimaas wrote:Could you please do a test for me madrussian?
Boil a cup of water and put both probes in. Note the temperature.
Do the same with a cup of cold water. This tells you if your tcs are calibrated correctly or not.
Then tape them as you normally would, except both to the same cassette and see what you get.
Im wondering if more people are operating with inaccurate thermocouple readings without knowing which could lead to a whole host of problems
2 quality of TC is important
3 meet thermometer do not help to measure temperature correctly it fluctuate a lot make matters even more complicated and frustrating. (Look my Journal)
4 I don't need to do the testing I didn't build controller I bought the unit where TC already building
5 when I did testing on the cassette when TC play side-by-side using both showing same temperature
forgot to mention TC placed in the middle of the cassette on top of it right next to layup.about 2 inches in from the edge of the blanket . I use some insulation on the wire so it doesn't get pinched or fried
Last edited by MadRussian on Sun Nov 10, 2013 3:08 pm, edited 3 times in total.
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Sorry you confused me there. What do you mean?Richuk wrote:You appear to be adding pressure into the mix when running your tests.
The pressure from the press pushing on the wire?
I also did it with the wire between the cassette/heat mat which would be softer. Same result.
I will try just taping the probe to the cassette and see what happens.
Goz. There is also some deal with grounded and non grounded thermocouples.
I don't know the exact specifics but if you are using 2 devices to measure separate TC's one could be assuming grounded and the other not.
Thinking about it I think I might have a little heat tape between the aluminium and the bare TC head. The aluminium sheet is grounded to the house ground also.
I don't know the exact specifics but if you are using 2 devices to measure separate TC's one could be assuming grounded and the other not.
Thinking about it I think I might have a little heat tape between the aluminium and the bare TC head. The aluminium sheet is grounded to the house ground also.
Don't wait up, I'm off to kill Summer....