Introduction
Stuck when facing instrumentation faults? This article thoroughly explains the troubleshooting methods for temperature, flow, and pressure instruments!
As the "nervous system" of industrial production, automated instrumentation systems determine the stability and efficiency of production processes. They play a decisive role especially in the petrochemical industry, making the stability of automated instrumentation systems crucial for this sector. This also places requirements on the professional capabilities, fault diagnosis skills, and operational proficiency of instrumentation maintenance personnel—factors that are key to gaining the trust of process engineers and achieving close collaboration.
1. Fault Diagnosis Principles for Instrumentation
Due to the characteristics of petrochemical production, such as pipelined operations, process-oriented workflows, and full enclosure—coupled with the high level of automation in modern chemical enterprises—process operations are closely linked to measuring instruments. Process engineers rely on various process parameters displayed by measuring instruments (e.g., temperature, material flow rate, vessel pressure and liquid level, and raw material composition) to determine whether production is normal, whether product quality meets standards, and to adjust output (increase/decrease) or even shut down operations based on instrument readings.
Abnormal instrument indications (e.g., high/low readings, no change, or instability) stem from two possible factors:
Process-related factors: The instrument correctly reflects abnormal process conditions.
Instrument-related factors: A fault in a component of the instrument (or its measuring environment) causes the indicated process parameter to deviate from the actual value.
These two factors are often intertwined, making it difficult to immediately identify the root cause. To improve fault diagnosis capabilities, maintenance personnel must not only be familiar with instrument principles, structures, and performance characteristics but also understand every link in the measurement system. Additionally, knowledge of process flows, properties of process media, and characteristics of chemical equipment helps expand their troubleshooting perspective and facilitates fault analysis.
2.Temperature Instrumentation
2.1 Fault Phenomena
Abnormal temperature indications (high/low readings, slow change, or no change).
Taking a resistance temperature detector (RTD) as the measuring element:
First, understand the process conditions by consulting process engineers about the measured medium and the instrument’s installation location (e.g., gas phase, liquid phase, or other process environments).
Since the fault occurs during normal production (not with a newly installed RTD), reverse polarity of the RTD wires can be ruled out initially.
After eliminating the above factors, follow the troubleshooting flowchart below for diagnosis and inspection.
2.2 Common Faults and Analysis of Temperature Instrument Systems
(1) Sudden increase in temperature reading: This fault is mostly caused by RTD/thermocouple disconnection, loose terminal connections, broken (compensation) wires, or temperature sensor malfunction. To identify the cause:
Understand the sensor’s installation location and wiring layout.
Use the resistance (millivolt) range of a multimeter to measure data at multiple points; the cause can be quickly pinpointed.
(2) Sudden decrease in temperature reading:This fault is mainly triggered by short circuits in thermocouples/RTDs or wires, or temperature sensor malfunction. Troubleshooting steps:
Focus on weak points prone to faults, such as wire terminals and wire bends, and inspect them one by one.
If on-site temperature rises but the central control reading remains unchanged, it is often due to low-boiling-point liquids (e.g., water) accumulating near the measuring element.
(3) Large temperature fluctuations or rapid oscillations:Prioritize checking process operations. For sensors involved in control loops, inspect the regulatory control system.
