【Daily Question 20090416】What types of failures have occurred with thermocouples in field use, and how were they resolved?

1 Installation site: EG refining tower ~1 }- U. Y8 R; F. o# M9. Fault symptom: DCS shows temperature fluctuations. Cause of fault: Water ingress into the protective sleeve. Y/ K: T# i8 l/ r& i. k/ M. Solution: Remove and dry it out. 2 Installation site: EO reactor 2 ~1 }- U. Y8 R; F. o# M9. Fault symptom: DCS shows temperature fluctuations. Cause of fault: The transmitter unit is damp. Y/ K: T# i8 l/ r& i. k/ M. Solution: Remove and dry it out. 3 Installation site: Ethylene feed reactor 2 ~1 }- U. Y8 R; F. o# M9. Fault symptom: Temperature appears intermittently. Cause of fault: Loose connection in the wires of the multi-core thermocouple. Y/ K: T# i8 l/ r& i. k/ M. Solution: Replace it. OP, I’m just offering my thoughts; this doesn’t count toward the first five slots. Last edited by wopale3 on 2009-4-16 08:53.]

Installation site: Preheating zone of the suspension roasting furnace. Fault phenomenon: The temperature indicated by the thermocouple experiences sudden changes of 1–2 seconds, ranging from around 350 degrees to 900 or even 1200 degrees. Cause of failure: The temperature change occurred at the site, at a certain distance from the thermocouple. I wonder if the cable passed through a high-temperature area? Solution attempted: Replaced the thermocouple, temperature sensors, and isolator, but no significant improvement was achieved. There’s no other way; it’s processed within the system, and operations are basically maintained. Thermocouples are generally used in high-temperature environments. In the case of integrated temperature sensors, it is best to use wires and compensation cables to connect them to a region at normal temperature for installation, thereby preventing instability of the sensor in high-temperature conditions.

Installation site: Laboratory. Fault phenomenon: Temperature cannot be measured. Cause of the fault: The positive and negative connections were reversed. Solution: Reverse the positions of the positive and negative connections

1. Installation site: Steam main pipe in a thermal power plant. Fault symptom: The temperature reading remained constant at 327.67. Cause of the fault: The model of the PT100 was inconsistent with the hardware configuration. Solution: Changing the configuration from climate-type to standard-type resolved the issue, and the temperature reading became normal. 2. Installation site: Bottom of the bisphosphonate synthesis reactor. Fault symptom: There was a difference of about 2 degrees between the temperature reading and that shown by the on-site instruments. Cause of the fault: The PT100 was connected using a three-wire system, resulting in resistance errors. Solution: After measuring the three-wire resistance, the temperature was corrected using the readings from the on-site instruments as a reference. I have a question: There are several different models of PT100 thermistors, yet the markings on their nameplates appear identical; I’m not sure how to distinguish between them

Installation site: Temperature in the incinerator furnace (K-type thermocouple). Fault symptom: The temperature reading rises suddenly and reaches its maximum value instantly. Cause of the fault: The exhaust outlet of the fan associated with the incinerator was blocked by foreign objects, resulting in a change from a slight positive pressure in the furnace to a positive pressure; this led to an excessive temperature rise, which in turn caused the measuring thermocouple to open circuit. Solutions: 1. Replace it with a platinum-rhodium-platinum thermocouple (S-type thermocouple). 2. Install a solenoid valve at the inlet of the fuel for the incinerator, linking it in interlock with the furnace temperature

Installation site: Styrene combustion furnace. Fault symptom: Maximum temperature reading. Cause of the fault: The high gas flow rate inside the furnace caused the temperature probe sleeve to break, resulting in a disconnected thermocouple. Solution: In cases of high flow rates, it is necessary to conduct vibration calculations on the sleeve to ensure that resonance does not occur due to the flow rate, which could lead to damage to the sleeve.

Installation site: Heating furnace. Fault phenomenon: Large temperature variations at various points. Cause of the fault: Differences in insertion depth. Solution: Adjust the insertion depth