Common fault analysis and processing method of armoured thermocouple

Armoured thermocouple has quick response speed, strong resistance to vibration and impact resistance characteristics, and compared with ordinary thermocouple life longer, more suitable for the harsh conditions, are now widely used. Our company is widely used in catalytic cracking unit part two wire armoured thermocouple.

armoured thermocouple is the thermocouple wire, insulation material and metal casing processing in solid cable assembly. The author based on years of experience, the armored thermocouple common fault analysis and processing method is summarized as follows, to share with you.

a, high or low

the fault phenomena belong to one of the more common in the process of daily use. Daily operation of the device, the craft operators often reflect the thermocouple indicates high or low, and armoured thermocouple is generally installed in catalytic reaction, important parts of the two, and riser, etc have also participated in the interlock device, check the operation need to be extra careful. Specific check troubleshooting method is as follows:

( 1) First need to inform operators for field operation process. If the thermocouple in fault device interlock, the need to deal with relevant equipment interlocking resection, the ticket to process operators confirmed rear can conduct site inspection job.

（ 2) Field use digital multimeter dc voltage in measuring thermocouple two terminal voltage value, fish temperature controlled indexing table, plus the room temperature is concluded that the actual measuring temperature thermocouple. This value with the distributed control system ( DCS） Display terminal of compare and calculate on business value, value for whether this difference is belong to the normal error of thermocouple. If within the error range, can be judged as operation causes the instructions of the deviation, if beyond the error range is too big, junction box should be checked for wiring terminals are strong, positive and negative polarity is, if it is loose, but wait for a phenomenon, clamp can be adjusted.

（ 3) If the above all normal, need a multimeter test thermocouple compensation wire insulation is normal, if the insulation problem, confirm compensation conductor insulation fault zone is segmented, for replacement. It is important to note that the compensating conductor insulation problems can lead to a thermocouple temperature irregular fluctuations in value.

（ 4) If the above all normal, need to check the safety barrier, such as pieces of input card measurement circuits of computer parts.

（ 5) If above all have no problem, the most likely cause of this failure of thermocouple compensation wire the polarity and the polarity of the thermocouple wire. The polarity of the compensating conductor can be judged by the color of the compensating conductor, general red line is positive. The thermocouple wire polarity judgment method is relatively complicated, the specific method is as follows:

the maintenance can be judged according to the degree of hardness and softness of thermocouple wire, in general, a hard one pole is platinum rhodium wire, for the positive, of the thermocouple is a very soft platinum wire, for the cathode of thermocouple. Digital multimeter millivolt block measurement can be used to judge the positive and negative polarity, but this method there is a risk of lapse in judgment.

2, indicating fluctuations in production process, both K type and S type armoured thermocouple are seen fluctuations of the failure, appear this kind of failure often has the following two reasons:

( 1) The thermocouple terminal connection is loose. A loose connection of thermocouple temperature measurement points are usually located in the location of the process equipment vibration is larger, or no maintenance over a long period of thermocouple. For the above two cases of thermocouple to regular inspection and maintenance, timely find anomalies.

（ 2) Thermocouple short circuit or grounded. Thermocouple is the common compensation cable, its insulation in high temperature environment for a long time, easy to aging, so that the two cables short meet each other, or contact with the metal pipe threading lead to ground, processing to find fault point, repair the insulation.

3, DCS without instructions is according to

central thermocouple temperature, indicating value is often caused by the following two reasons:

( 1) Thermocouple is damaged. Break the two thermocouple wiring, use digital multimeter electric block measure the resistance between the two terminals, if according to infinity, the thermocouple has open circuit, the thermocouple is damaged, replace thermocouple.

（ 2) Bad thermocouple of DCS channels. Inspect the site of the thermocouple, junction box connection is no problem, the response to the scene and the master control room after wiring rack, a channel for inter-school, check the DCS thermocouple channels are in good condition, if already bad should be replaced, and check the change after the thermocouple indicates whether normal.

4, thermocouple casing leakage or wear out

catalytic reaction thermocouples are installed in the presence of high temperature and high speed flow medium pipeline, due to the use cycle is long, use high environmental temperature, measuring dielectric flushing, later will often appear in a lifetime casing leakage of sand holes, and so on and so forth, maintenance personnel should strengthen the on-site monitoring of thermocouple, once found leakage, on the premise of completes the protective measures in a timely manner. In addition, the change in inspection when installing new thermocouple, shall confirm the good measuring medium flow direction, the reasonable installation outside casing protection layer, prolong the service life of the thermocouple. Five, conclusion

thermocouple is a common and wide use of the instrument, as a instrumentation bunkers, the analysis of the thermocouple common faults and eliminate ability is the assurance of safety in production, I hope that my experience to be of service, also want you to correct deficiencies. Relevant product recommendations: magnetic level gauge