High-pressure Service Level Transmitters Misunderstood Zero Drifts

Instrumentation engineering root cause analysis of high-pressure service displacer level transmitter zero drifts problems.

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

Level Transmitters Zero Drifts Problem

Operating crew constantly complained about 250 bars pressure vessels Displacer Level Transmitters showing below zero readings in plant shutdown and de-pressured conditions.

Author solution

The author thought over the problem and realized that the running conditions vessel synthesis gas pressure is 250 bars; its density at that pressure is 162 Kg/m³. It is comparable to the below the gas-liquid ammonia density of 640 Kg/m³.

The crew adjusts the zero for this condition. On the other hand, the vessel pressure is zero under shutdown conditions and gas/air fill density is negligible.

Hence, the displacer loses no weight. Since, the more weight the displacer loses the higher the displacer level transmitter (DLT) output, the weight not losing displacer level transmitter (DLT) reads below zero during de-pressured conditions. This is right and best left as is.

Benefits Realized

Realized benefits are:

1. Vanished frivolous work orders and efforts spent on it in making a correct reading wrong!
2. Consequent erroneous readings during normal run generated wrong data which could mislead troubleshooters

Author: S. Raghava Chari

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