The core goal of maintenance and upkeep of the input type liquid level transmitter is to maintain measurement accuracy, extend equipment life, and avoid sudden failures. It is necessary to combine its "contact medium+working environment" characteristics. The following is a practical guide for the system:

1、 Daily inspection (daily/weekly, quickly identify obvious problems)

Daily inspections focus on "operational status+environmental impact", without the need to disassemble equipment, and can be completed in 5 minutes:

1. Check the running parameters

Observe the output signal/display value: Confirm whether the signal is stable through PLC and digital display (no significant fluctuations in 4-20mA, no packet loss in RS485 data), and whether the liquid level display matches the actual working conditions (such as no abnormal rise or fall in the water tank liquid level);

Troubleshooting abnormal phenomena: If the signal drifts or displays jump, first eliminate the interference of working conditions (such as medium stirring, inlet and outlet turbulence, bubbles), and then record abnormal data (such as drift amplitude, triggering conditions) to provide a basis for subsequent maintenance.

2. Environment and installation inspection

Protection status: Outdoor equipment needs to check whether the cable joints are sealed (without water ingress or looseness), and whether there is corrosion or leakage at the shell/flange connections; The explosion-proof environment requires confirmation that the explosion-proof markings are intact and the cable sealing joints are not damaged;

Installation position: Avoid placing the sensor probe near the inlet and outlet of the medium or the agitator (turbulence can cause measurement fluctuations). If the probe is found to be covered by sediment or floating objects, it should be marked and cleaned;

Cable condition: Check for wear, aging, and pulling marks on the cable (especially in outdoor/vibration environments). PU material cables should be protected from direct sunlight exposure (accelerated aging).

3. Auxiliary equipment inspection

Whether the power supply of supporting instruments (such as isolators, safety barriers) is stable, and the wiring terminals are not loose or overheating;

Are the safety barriers and grounding devices in explosion-proof environments functioning properly (grounding resistance ≤ 4 Ω) to avoid static electricity accumulation.

2、 Regular maintenance (monthly/quarterly/annual, deep maintenance according to the cycle)

Regular maintenance requires adjusting the frequency according to the intensity of working conditions (harsh working conditions such as chemical and sewage can shorten the cycle), with the core of "cleaning+calibration+consumables replacement":

1. Cleaning and maintenance (monthly/quarterly)

Probe cleaning (key steps):

Turn off the power first, close the inlet and outlet valves of the container (or empty some of the medium), ensure that the probe is exposed to the liquid level before disassembling (the cable should be slowly lifted to avoid cable pulling);

Ordinary media (water, oil): Rinse the probe membrane with clean water and wipe it with a soft cloth (do not use a hard brush or sandpaper to avoid scratching the ceramic/metal membrane);

Viscous/Impurities containing Media (Mud, Slurry): Soak in warm water and neutral detergent for 10-15 minutes, soften the attachments, and rinse. If there is stubborn sediment, gently scrape it off with a soft plastic scraper;

Corrosive media (acid-base): Clean with corresponding neutralizing solutions (such as weak alkaline water for acidic media and weak acidic water for alkaline media), then rinse with clean water to avoid residual media corroding the membrane;

Check the membrane after cleaning: there are no scratches, bulges, or corrosion spots, otherwise the probe needs to be replaced.

Cable and joint cleaning: Wipe the surface of the cable with a dry cloth, check if the joint sealing rubber ring is aging (hardened, cracked), if it is aging, replace it with a new rubber ring, and tighten the joint again (ensuring IP67/IP68 protection level).

2. Calibration and maintenance (every 6 months/year)

The purpose of calibration is to correct zero drift and range deviation, which requires the use of standard equipment (such as standard pressure sources and multimeters):

Preparation work: Disassemble the sensor from the site, connect it to a standard pressure source (simulating the pressure corresponding to the liquid level), and connect it to a multimeter (measuring 4-20mA signal) or calibrator (supporting RS485/HART protocol);

Calibration steps:

Zero calibration: Connect to atmospheric pressure (gauge type) or connect to standard zero pressure, adjust the zero potentiometer of the equipment (analog type) or set it through software (intelligent type) to ensure an output of 4mA;

Range calibration: Connect the standard pressure corresponding to the full range, adjust the range potentiometer or software parameters, and ensure that the output is 20mA;

Linear calibration: Test 50% range pressure and confirm that the output is 12mA (error ≤± 0.1% FS~± 0.2% FS). If the deviation exceeds the standard, it needs to be repeatedly fine tuned;

Record calibration data: Fill in the calibration record form (including calibration date, standard equipment number, zero/range deviation, and calibrator) and archive it for future reference.

Special scenarios: For equipment such as deep water tanks and high-pressure vessels that are not easy to disassemble, remote calibration using HART/RS485 can be used (with equipment support) without the need for on-site disassembly.

3. Consumables and component replacement (annually/every 2 years)

Replacement of vulnerable parts:

Sealing rubber ring (flange/threaded interface): Aging can easily cause medium leakage, replace with the same specification of fluororubber/silicone sealing ring (corrosive media prefer fluororubber);

Cable: If aging or damage occurs, replace with waterproof and explosion-proof cables of the same specifications (ensuring consistent cross-sectional area of the wires to avoid signal attenuation);

Diaphragm protective cover (including impurity medium scenario): If the protective cover is blocked or corroded, replace it with a 316L/PTFE material protective cover.

Component inspection:

Electronic components: Open the transmitter housing (non explosion proof), check that the circuit board is not damp or oxidized, and that the wiring terminals are not loose or burned;

Explosion proof casing: In explosion-proof situations, it is necessary to check that the casing screws are complete and the sealing gasket is intact to avoid the failure of the explosion-proof rating.