Thermocouple wiring in trap confusion and color

This paper involves in the temperature control system on the misuse of thermocouple extension cable caused by accuracy and stability. The jungle of different cable color code is the main source of these problems.

a new wiring furnace burned all six of the element, costs about $9000. Controller in good condition and shows the normal operating temperature, although significantly more hot stove. R type thermocouple is very good and the location but somehow right controller being deceived.

the reason: extension cable for J type, should be R type. Link for + and white for the red （ The two end cross wire) 。

red as positive sounds logical, is a common practice in the world, but do not apply to the thermocouple wire in North America. This is an understandable but costly mistakes.

because after a period of time in the furnace temperature is no problem. But when the thermocouple head when heated, relative to the control terminals J type extension cable will be a big negative signals into the controller. This makes their readings as low as thermocouple head - As 5 times as the controller temperature difference, lead to the serious overheating. Extension cable and its knowledge can prevent damage of the color code. Typical symptoms:

even if the temperature controller is shown on the right, you still doubt that deal with a high temperature. After the start of the first few hours, the process seemed increasingly overheating. This usually occurs in the process of import or newly installed, or the thermocouple has to reconnect or work process.

you have confirmed with the appropriate thermocouple to measure temperature and atmosphere; It is located in the position of the working temperature, and the calibration is correct. Your controller is accurate, in view of the use of the thermocouple calibration, and adjusted in order to obtain good control stability.

how controller from the process received signal circuit shows from the hot tip of thermocouple signal path to the temperature controller. In this case use C.

graph: thermocouple wiring

there are three kinds of millivolt signal controller receives and role of contribution, in this case, a total of 200 degrees.

in the hot junction and those between the thermocouple head ( In this case is 180 degrees, and is proportional to the temperature difference) 。

produced by thermocouple extension cable between head and controller of the ( At this time to 0 degrees, because there is no difference in temperature) 。

those produced by the controller, on its own behalf, Environment) Temperature, in the example of 20 degrees. It must make a contribution to not shorter than temperature equal to the amount of their environment. This is known as the cold junction compensation.

starts, external start preheating process, make the temperature of the thermocouple head up to 40 degrees. Thermocouple signal now offers 160 degrees, the right will produce 20 degrees extension cable, said 20 degrees of end-to-end differences. Controller will still see 200 degrees. 1:

trap you use copper wire instead of extension cord.

in the example above, the copper can't produce the signal of 20 degrees, 180 degrees and controller face see rather than the real prospect of 200 degrees. However, as long as any shortage, it will start to work, and it has been switch to 220 degrees in order to meet the process. This does not cause doubt, because the controller will slowly rising in temperature in the whole process of indicating the required temperature of 200 degrees. Nonlinear,

ignore thermocouple temperature will settlement about equal to the head - too much The quantity of controller temperature difference.

trap 2: you use the correct extension cord, but through a pair of wires on both ends.

this is even worse than the use of copper. The temperature will be higher than the head to twice the temperature difference shows the temperature controller.

this error may change during the day, never clear about 100 to spend hot, depending on the proximity of thermocouple head and thermal process and process running for long time.

the double reverse connection error is very common and easy to understand, because the cathode line on all the north American extension cord is red, and may be mistaken for the anode. Japan and Germany do use red positive.

trap 3: you use the wrong extension.

please keep in mind that contribute to the millivolt signal extension cable, millivolt signal is explained by the temperature controller. The appropriate cable will match each microvolt thermocouple. Wrong cable can make the controller show that too high or too low, depending on the number of each microvolt microvolt several different with thermocouple.

burn out in the above mentioned cases, J type extension cable output is correct type R the 5 times of the cable, and also injected a few baidu's error. The combination of even worse than this.

extension cord color code six kinds of the most common type of thermocouple. It shows the various countries use five kinds of cable color code, and the IEC code. IEC code represents a single standard of the world, and began to appear in Europe on the equipment. They will eventually replace the current use of the code.

cable identification tips

from the thermocouple head to the controller, has been to see the color of the cable. Check whether both ends.

if you don't trust or can't see the color, please hot test, the polarity is not connected, the extension cables and thermocouple head and extending cable bare wire end distorted or clamped together. According to room temperature controller should now be in the position, and when you heat the joint instructions should be increased.

for J and K line, magnet test is very useful. On the J type, is conductor is iron, so is magnetic. In the line of K type negative conductor is Ni/Al and have slightly magnetic.

also note that the color of the thermocouple connector coding in accordance with the corresponding cable sheath.