New Field Guide Covers Eight Common Level Gauge Faults with a Five-Step Diagnostic Method

October 2026 — Most level instrument failures in process plants are not instrument failures at all. That is the core message of a new field guide published this week by our instrumentation engineering team, which catalogues eight recurring level gauge faults and sets out a five-step diagnostic route that maintenance crews can follow without dismantling the transmitter.

The guide draws on field service records from chemical, power, metallurgical and pharmaceutical sites, where level is one of the most heavily instrumented and least forgiving measurements: an overflow, a dry-running pump or an empty reactor can mean lost production, safety incidents or environmental releases.

Eight Faults That Cover 95% of Field Cases

According to the team, the majority of call-outs fall into a small, repeatable set of symptoms. The guide groups them as follows:

A Five-Step Route: Easy Before Difficult

Rather than starting with the instrument, the guide recommends working through five checks in a fixed order. Most faults are located within the first three.

1. Verify the symptom. Compare the local display, the DCS value and a manual dip or sight glass to establish whether the problem is in the instrument or in the process.
2. Check supply and signal. Confirm 24 V, test the 4–20 mA loop for opens and shorts, and inspect terminals for corrosion or looseness.
3. Inspect installation and sensor. Antenna build-up, coated probes and blocked impulse lines account for a large share of all level faults.
4. Review the process. Foam, steam, agitation, density changes and inlet surges can make a healthy instrument report nonsense.
5. Check parameters last. Range, zero, dead zone, medium data and false-echo suppression should only be touched once the first four steps are cleared — and recalibration must follow any change.

Technology-Specific Failure Patterns

The guide also separates failure behaviour by measuring principle, because the same symptom points to different causes depending on the technology:

• Radar and guided-wave radar: false echoes, antenna build-up and low dielectric constants.
• Ultrasonic: foam, steam, surface agitation and mounting angle.
• Magnetic level gauges: stuck floats, failed flap rotation and demagnetisation.
• Differential pressure and remote-seal types: blocked or liquid-filled impulse lines, coated diaphragms and incorrect zero elevation.
• Displacer types: build-up jamming and changes in medium density.

Aligned with JJG 971-2019

All verification recommendations in the guide follow JJG 971-2019, the Chinese national verification regulation for level gauges issued by the State Administration for Market Regulation, effective 31 March 2020 and replacing the 2002 edition. The regulation requires initial verification, periodic verification and in-service checks. The guide advises plants to retain verification records, noting that the data supports both measurement reliability and incident traceability.

“Roughly 80% of the level faults we attend are caused by medium properties, installation position or parameter settings. Genuine hardware failure is under 20%," the engineering team said. “Following the five-step route typically locates the problem within half an hour."

Availability

The full field guide, including fault-by-fault diagnostic flows, an echo curve interpretation section and a quick-reference table, is available now. Plant maintenance teams can request a copy or discuss a site audit through our instrumentation service desk.