Thermocouple compensating cables on the accuracy of distance limitation and influential measure?

Due to far away from the thermocouple to the distance of the measuring instrument, we use compensation cable, but what is the effect of limiting distance and accuracy?

in some places, such as power plants and large chemical plant, from the temperature measuring position to instrument room may have a few kilometers distance. What's the problem with that?

the thermocouple circuit, the thermoelectric emfs, in principle, only be determined by the thermocouple used materials, and at the ends of the temperature and characteristics by thermocouple wire line diameter and length. So even if the measurement part of thin and middle thick, no impact, even if use a sheet of thermocouple, measurement accuracy is no problem.

however, the thermoelectric emf measurement instrument is always has the limitation on the measuring instrument input resistance. Therefore, for power plants and other large factories, we will extend the wire diameter thicker, designed to for long distance transmission. For a manufacturer of temperature controller, thermocouple allows the signal source resistance for 100 & Omega; Or lower, resistance thermometer sensors allows the wiring resistance wire for every 10 & Omega; Or lower.

recently, sheathed thermocouples with thin outer diameter increased demand, and in some cases only thermocouple components with high resistance. We met a problem, because the error of measurement in chemical reactor is expected to increase, because the factory used in a few meters long & phi; 0. 5 sheathed thermocouples, and assumes that the resistance more than 1 k & Omega; 。 The solution is to shut down the burn out detection circuit inside the measuring instrument, the thermocouple conductor allowable resistance increase on the side.