K-Type Thermocouple Extension Wire, Availability

[greg-g]

As charlespax mentioned in his post the 10 m extension wire in the store is really only suitable for making cables up to three meters in length. This cable from its resistance measurements is about 30 AWG gauge.

What’s really required to make longer extension cables is 20 AWG gauge wire that has 1/10 the electrical resistance of the 30 AWG and hence could probably be used in up to 30 meter lengths.

I can’t find any at a reasonable price, does anyone know a supplier.

If the price was right I’d take 20 meters.

From my limited experience the wire can either be used as an extension cable using male and female plugs, or joined or terminated. I’ve had good results brazing with high silver (50%) brazing rods.

[greg-g]

I’ve ordered 2 x 10 Thermocouple Extension cables from this site on the basis of price, I’d prefer 20 AWG wires but I’m not after ultimate accuracy and believe I can work out adequately accurate temperature offsets. I’ll publish what I find.

These comments are in relation to discussions in
K-Type Thermocouple Extension Wire, 10 m
And
T400 battery life

[EttaTodd]

Can you please share the specifications of your thermocouple?
And what is the difference between the 10,20 and 30 guage wire?
Which one will be preferable for the thermocouple?

pcb materials

[greg-g]

AWG - American Wire Gauge
AWG refers to the diameter of the wire

AWG		Dia mm		Area mm	Resistance ohm / m
						K Type wire
10		2.59		5.26		0.19
20		0.81		0.52		1.92
30		0.255		0.0509		19.63

charlespax indicates the T400 is accurate with thermocouple resistances up to

about 100 ohms.

The 1 meter 30 AWG K Type probe has a resistance of about 22 ohms while the 10 meter

length has a resistance of about 200 ohms which is above the limit of accuracy of the device.

When using 30 AWG wire he recommends keeping the length to less than 3 meters.

Within reason the only negative with using thicker wire is cost and availability.

I don’t know of any sources for thicker K type Thermocouple wire at a reasonable price.

Using a 10 meter length of 30 AWG wire will probably cause a reading error of about

+8 deg C.

(I’m not an expert in this field, all the above information came from this forum and

the internet)

[charlespax]

I wonder if it would be sufficient to out two thermocouples in parallel.

[MLXXXp]

Something I noticed:
The 4 general purpose thermocouples included with my T400 are different than the 4 that were bundled with the extended thermocouple kit. I've forgotten which came with which but one set has plain white insulation and the other is white with a blue spiral stripe. The plain white ones have heavier gauge thermocouple wire than the striped ones.

Unfortunately, the 10m extension cable is of the striped variety and thus the thinner gauge.

[charlespax]

Shit. My supplier switched wires part way through production because they ran out of one type. I understood that they were the same wire, but maybe there was a miscommunication. I'll look into this. Thank you bringing it to my attention.

[greg-g]

I have both the blue stripe and the plain white thermocouples.

The blue stripe appear to have 30 AWG wire while and the plain white are about 28 AWG.

From my measurements the blue stripe thermocouples appear to read about 0.5 deg C higher than the plain white thermocouples.

[charlespax]

The wire style thermocouple (http://paxinstruments.com/products/sku2527/) has an accuracy of (0.75% +/- 2.5 C) at <400 C. The measurement range is -50 to 400 C.

For shorter lengths the wire gauge doesn't matter. At about three meters it could begin to matter. I have not done much testing in this area, so I can't give more accurate numbers.