Beginning of understanding about thermocouples
Type K thermocouple (Chromel-Alumel, i.e. nickel-chrome / nickel-aluminum), is recommended for temperatures from 0 ° to 1100 ° (over a short period from –180 ° to + 1300 °).
It is the widest range of temperature, it is the most common, the cheapest; so this is the one that interests us.
According to one doc, there are 19 ways to mount thermocouples.
The one that interests us (at the lowest price) is the
"basic thermocouple": Simple thermocouple with "hot weld" (at the end), carried out under neutral gas (argon).
Several diameters are available, from 0,2 to 1,63mm.
They can be offered naked.
They can be offered in a sheath. At that time, the maximum temperature proposed with these K thermocouples, is the maximum temperature that the ducts can withstand…
PVC (-30 to +75). Silicone rubber (service: -40 to +200). PR = Crosslinked polyethylene (-30 to +75). Mica + PR (-30 to +75, but fire resistant to 750 °). Teflon (-75 to +250).
Glass silk (480, point at 540 °). High temp glass silk (800 °). Ceramic fiber (-185 to + 1400 °).
Among sellers, we offer under the name
"thermocouples" , finished sensors, ready for use (the 2 thermocouple cables were welded under argon. These "probes" can be adhesive, glued, on magnet, on collars, jacketed (Teflon, ceramic, stainless steel, platinum refractory steel, inconel ….),… Etc. The price is substantial depending on the use.
Under the name
"single thermocouples", is proposed cable in reel of 2 or 5 m, one end of which has its hot weld, made under argon.
Under the name
"extension cables" , is proposed the same type of cable, seamless, and the composition of the alloys is identical to that of the previous sensors. But, it must end with a solder on the end, which will connect the 2 cables of different composition; this solder, in contact with a temperature will create a potential difference with the "cold solder", which comes on a special assembly or on the terminals of a meter; A voltmeter can measure these –6,4 mv (-270 °) to + 54,8mv (1370 °) for a type K, cold junction at 0 °.
the "extension cable" is the most economical.
It is offered at Radiospares (price excluding tax):
-Thermocouple K, sheathed glass (-50 to 400 °), 2 m with a weld already made at the end
ref: 219-4309 at € 9,38. (we can cut ends, weld them, and redo sensors)
-K extension cables, 0,3mm, glass (+ 480 °), 10m.
ref: 219-4589 at € 15,71
-K extension cables, glass (+ 480 °), 10m ref: 151-209 at 14,74 €
Under the name "compensation cable" , it is a cable (of special composition, but of different alloys from the thermocouple cable), which makes it possible to extend the data of the sensor, over a greater distance without great attenuation, unlike simple electrical conductors in copper.
If you also want to buy a "k-type thermometer", which will read the temperature directly, you will also have to think about buying the appropriate connection connectors (quite expensive) ...
Important reminder :
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.The price was very resonable, but 500 ° c okay ?? it's just 
