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Are all K type thermocouples created equal?

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Are all K type thermocouples created equal?

 
Old 01-01-2019, 07:48 PM
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Default Are all K type thermocouples created equal?

Hi folks, I'm in the middle of organising per EGT monitoring into the MS3, via Quad MAX31856 amplifier. I'd love to hear from those who already are doing 4xEGT logging.
Questions:
1. K type thermocouples range from $14 (fleabay/Amazon), to $76 (Diyautotune), to over $100. But they are all visually quite similar, and the specs (when you can find any) are line ball. Do I give the Chinese thermocouples a try? Is there anyone out there who has had success/failure with using them?
2. Also closed vs open tip - do you really need an open tip for dyno tuning, are the closed tips that slow?
3. I'm assuming closed tips are safer for long-term installations because there is less chance of bits snapping off and going into the turbine blades?

If anyone who is doing EGTs could comment on their thermocouple choice, that would be peachy
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Old 01-01-2019, 08:51 PM
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I prefer The Sensor Connection EGT probes. They use the right materials, unlike most of the chinese stuff I have experience with.
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Old 01-01-2019, 09:05 PM
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I've bought a couple cheap ones -- the insulation on the wires melted and they shorted out and stopped reading properly. The one I bought from DIY has far outlasted them and is still going.

--Ian
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Old 01-02-2019, 06:19 AM
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Last edited by sixshooter; 01-02-2019 at 01:41 PM.
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Old 01-02-2019, 10:23 AM
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IMO all K types will read the same within an acceptable error limit. The difference is how long they will last.

Like others said, the cheap ones just don't last long.
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Old 01-02-2019, 01:00 PM
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All that "K-type" refers to is the bi-metal junction at the tip of the TC (and thus this metallurgy alters the Seebeck coefficient which changes the scaling/calibration curve you need to apply to turn thermoelectric voltage into temperature). This is constant regardless of mfg, but quality, durability, and packaging is what will be different.

I imagine you want something close tip, this is pretty standard for immersion in any fluid with corrosive properties (e.g. exhaust gas). Most the lab-y people I know buy all of theirs from Omega but it's pricey and you'd have to dig through the catalog to find the right application. I think the DIYAutotune probes are definitely the correct solution, but if you're on a budget I'd bet you can find a supplier selling something identical or 99% the same in around the $30/probe range. Just have to decide if your time is worth hunting them down -- it's not like DIYAutotune is bad company to support.

E: or your could read sixshooters post, thank him for the spoon feeding, and buy one of those.
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Old 01-02-2019, 08:28 PM
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Thanks heaps folks, I'm spoilt for options now. Sixshooter's choice looks particularly appealing..
Ta.
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Old 01-03-2019, 01:38 PM
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I bought mine from Motorsport Innovations about 8 years ago, and they are still working great. I remember they were in the $60-80 each. You do get what you pay for with these.
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Originally Posted by ninerwfo View Post
The “into to megasquirt thread” mentions that the MS3 basic has 5 inputs with built in pull up resistors - and I was just wondering why it would have so many, while the MS3Pro PnP has just 2 (with no pull ups?)
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