How to deal with the issues of thermocouple temperature measurement and anti-interference

Many people don't know how to handle some problems when using thermocouples. Let me explain it to you below. Regarding the treatment of thermocouple temperature measurement and anti-interference issues, some industries currently commonly use DCS distributed computer control systems, which have strong applicability and high reliability. Monitoring and control of process parameters can be achieved through software programming. Although the hardware configuration of the DCS system is powerful, there is an issue that cannot be ignored. If the process parameter measurement signals from the site are mixed with interference signals during transmission, the DCS system itself will be difficult to suppress, and effective measures need to be taken externally to solve it. This article introduces the handling methods for faults caused by abnormal temperature measurement signals of Pt100 thermocouples.
Troubleshooting caused by abnormal thermocouple temperature measurement signals in coal mill system
Our coal mill system's bag filter ash hopper temperature and coal mill bearing temperature have successively experienced abnormal temperature display faults. The phenomenon is that the temperature display on the central control room CRT shows irregular jumping. On site inspection shows that the temperature measuring element is normal. The resistance value measured using a DT-890C digital multimeter at the relay terminal of the PC station corresponds to the actual temperature. We have taken measures such as replacing thermocouples, checking the shielding grounding of temperature measurement signal transmission cables, and replacing PC signal processing channels, but none of them have been effective. In order to find the cause of the malfunction, we laid another cable, but still couldn't solve the problem. After comparative testing, inspection and analysis, the conclusion was that interference signals were mixed in the temperature measurement signal. Therefore, we adopted the following processing methods.
1.1 Changing the signal grounding method
Thermocouple temperature measurement signals are usually wired in a three wire system, using KYVRP4 × 1.5 shielded cables to be led to the CCF relay cabinet in the DCS field station PC room. The cables are shielded and grounded inside the relay cabinet. The solution is to connect the B and B of thermocouple Pt100 to the cable shield at the relay cabinet terminal, introduce interference signals into the ground, and eliminate interference signals in this way, so as to restore the computer temperature display to normal.
1.2 Changing the Signal Transmission Method
The Pt100 thermocouple temperature converter can be installed in the on-site or on-site station PC room to convert the Pt100 resistance signal into a standard DC4-20mA signal, and the computer input signal channel can be changed accordingly. This method can also eliminate interference generated during signal transmission and restore the temperature displayed by the computer to normal. Because the anti-interference ability of DC4-20mA signals is very strong, the installation position of the temperature converter can be determined according to the actual situation on site, But it is better to choose indoor installation. The disadvantage of this method is that it increases equipment investment and requires the provision of converter power supply.
Handling of abnormal temperature in the thin oil station of the main motor of cement mill 2
Our cement mill main motor has been replaced with one new motor due to major repairs, and the bearings are lubricated with thin oil. A corresponding thin oil lubrication station has been added. The oil station is equipped with four temperature measurement points, including lubrication oil tank temperature, heating oil temperature, supply oil temperature, and return oil temperature.