Common faults and troubleshooting methods of instruments such as thermocouples and thermistors?

There is a problem with the instrument, and the reasons are quite complex. It is difficult to find the root cause at once. At this time, it is necessary to remain calm and analyze in stages. Firstly, analyze which unit the cause lies in, which can be roughly divided into three stages: on-site detection, intermediate transmission, and terminal display; At the same time, seasonal factors should also be considered, such as preventing high temperatures in summer and freezing in winter; When the parameters involved in the regulation are abnormal, first switch the regulator to manual mode, observe and analyze whether the system is being regulated, and then check other factors again.

Regardless of which type of instrument malfunctions, we first need to understand the production process and conditions of the installation location where the instrument is located, as well as the structural characteristics and performance of the instrument itself; Before maintenance, it is necessary to collaborate with the process personnel to analyze and determine the true cause of the instrument malfunction; At the same time, it is also necessary to understand whether the instrument comes with adjustment and interlock functions. After comprehensive consideration and careful analysis, it is necessary to maintain process stability as much as possible during the maintenance process.

1, On site measuring instruments. Generally divided into four categories: temperature, pressure, flow rate, and liquid level

1) Common Fault Analysis of Temperature Instrument System

(1) Sudden increase in temperature: This fault is often caused by thermal resistance (thermocouple) disconnection, loose wiring terminals, (compensation) wire breakage, temperature failure, and other reasons. At this time, it is necessary to understand the location and wiring layout of the temperature, and use the resistance (millivolt) range of a multimeter to measure several sets of data at different positions to quickly identify the cause.

(2) Sudden decrease in temperature: This fault is often caused by thermocouple or thermistor short circuits, wire short circuits, and temperature failure. Starting from weak points such as wiring ports and wire bends that are prone to faults, we should investigate them one by one. The temperature on site rises while the overall control indicator remains unchanged, mostly due to the presence of liquid (water) with a lower boiling point at the measuring element.

(3) If there is a significant fluctuation or rapid oscillation in temperature, the main focus should be on checking the process operation (including the inspection and adjustment system involved in the regulation).

2) Common faults and analysis of pressure instrument system

(1) Sudden decrease or increase in pressure or no change in indicator curve: At this time, the transmitter pressure system should be checked to check whether the root valve is blocked, whether the pressure pipe is unobstructed, whether there is any abnormal medium inside the pressure pipe, whether the discharge screw is blocked, and whether the discharge valve is leaking. Freezing of winter media is also a common phenomenon. The possibility of transmitter malfunction itself is very small.

(2) Large pressure fluctuations: This situation should first be coordinated with the process personnel, usually caused by improper operation. The parameters involved in regulation should mainly be checked for the regulation system.