To determine whether an ultrasonic level gauge needs replacement, a comprehensive assessment must be conducted based on the equipment’s failure frequency, performance degradation degree, maintenance costs, and safety compliance. Below are specific judgment criteria and scenarios:
After multiple calibrations (e.g., empty-tank/full-tank calibration, temperature compensation calibration), the measurement error still exceeds the equipment’s nominal range (e.g., ±0.5% FS), and the deviation persists stably (e.g., consistently higher/lower by a fixed value).
Example: For a level gauge with a 10-meter range, the actual error exceeds ±5 cm for a long time, affecting production measurement (e.g., batching, warehouse inventory statistics). If external factors such as installation, medium, and environment are ruled out (e.g., no improvement after reinstallation), it indicates that the core components of the sensor (piezoelectric crystal, signal processing circuit) have aged and failed.
Irregular occurrences of "signal loss" or "fault alarm" persist even after replacing the probe, cable, and terminal blocks. Additionally, the main unit’s self-test shows hardware abnormalities (e.g., fault codes for circuits detected by the manufacturer’s dedicated software).
Example: Under normal operating conditions (no severe interference, no medium adhesion), disconnection occurs more than 3 times per day, and the device needs to be restarted each time to recover. This severely affects automated control (e.g., loss of pump-valve linkage control).
Core components (e.g., probe, main board, power module) need to be replaced multiple times in a short period (e.g., within six months), and the cumulative maintenance cost reaches more than 50% of the price of a new unit.
Example: The probe is replaced twice within six months due to corrosion/aging, costing 1,000 yuan each time. With a new unit priced at 3,000 yuan, further maintenance is no longer economical.
After a device failure, production is interrupted due to discontinued spare parts (e.g., no replacement parts for old models) or a maintenance cycle exceeding 3 days (e.g., tank level cannot be monitored, forcing manual inspection or production shutdown during waiting). The indirect losses are far greater than the cost of a new unit.
Aging of the housing/seals (e.g., rust on the flameproof surface of explosion-proof equipment, hardening of sealing rings) leads to a decline in protection level (e.g., from IP67 to IP54). This may cause safety accidents (e.g., short-circuit leakage, flameproof failure) in humid, dusty, corrosive, or explosion-proof environments.
Example: An explosion-proof level gauge used in a chemical explosion-proof area fails to meet the Ex dⅡCT4 standard after damage to its flameproof surface. This violates safety regulations and requires mandatory replacement.
The equipment’s functions cannot meet new process requirements (e.g., the original 5-meter range is insufficient after tank expansion to 8 meters, leading to measurement failure due to over-range use); or due to updated industry standards (e.g., higher measurement accuracy requirements), the old equipment fails to meet the new standards.
Example: After upgrading to GMP certification in the food industry, level gauges are required to have sanitary-grade probes (e.g., 316L+PTFE material). However, the old equipment uses ordinary ABS material, which cannot meet sanitary requirements.
The design life of an ultrasonic level gauge is usually 5–8 years (depending on the operating environment: it may be shortened to 3 years in harsh environments, or extended to 10 years in clean, normal-temperature environments). If the equipment has exceeded its design life, even if it works temporarily, its performance may suddenly collapse due to component aging (e.g., capacitor degradation, circuit oxidation). It is recommended to replace it in advance to avoid risks.
- Measurement accuracy is out of control and cannot be calibrated;
- Failure frequency exceeds once per month with high maintenance costs;
- Safety risks exist (e.g., flameproof failure, insufficient protection level);
- The equipment has exceeded its design life with no spare parts available;
- It cannot meet current production/compliance requirements.
If the failure is occasional (e.g., loose wiring, probe contamination) and the equipment can operate stably after maintenance, replacement is unnecessary. Its service life can be extended through enhanced maintenance (e.g., regular cleaning and calibration).
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