Temp Tx Cable

One advantage of a 4-20mA current signal is that the transmitter adjusts its current output to compensate for resistances in the loop, up to the ability of the power supply to drive the current through the load. So even though thermocouple extension wire has considerably higher resistance than copper wire (as the table shows) the loop will function until the total loop resistance exceeds the ability of the power supply driving the loop current, usually when the loop resistance exceeds 500 ohms (depends on design).

Given that the wire is thermocouple wire, there will be an EMF (voltage) generated across the temperature gradient of the wire, polarity depending on which end is the 'hot' end and that is an error at the analog input (AI). The lower the temperature difference, the lower the error. If both ends are at the same temperature, there is zero generated EMF, zero error. If this were 'indoors' one might assume that the temperature difference those two ends is not significant, but if it is outdoors the temperature difference between the two ends could be significant.

Take an extreme example: a Canadian winter at -40°C on the field end and a hot, poorly ventilated panel at 50°C on the indoor end, a difference is a 90°C with a 250 ohm dropping resistor on the analog input. The polarity will be negative across the AI, since the field end is colder than the indoor end. A type K T/C will generate -3.2mVdc across the analog input's dropping resistor; a -0.3% error at 4.00mA (1.00V), a -0.06% error at 20.00mA (5.00V). The lower the input dropping resistor value, the larger the error. The 90°C error for a 10 ohm dropping resistor (0.04V to 0.20V) is -8.0% error at 4.0mA, -1.6% at 20mA.

If the power supply can drive the total loop resistance and the error from T/C's temperature difference can be tolerated, then you can get a signal at the analog input. It might not be best practice, but the electrons will be there.