I. Working Principles (Two Mainstream Types)
1. Coriolis Mass Flow Meter (Most Commonly Used, Compatible with Liquid/Gas/Slurry)
Core Principle: Coriolis effect
Operating Process: The measuring tube is driven to vibrate at its natural frequency. When fluid flows through, a Coriolis force proportional to the mass flow rate is generated, creating a phase difference or time difference on the measuring tube
Output Signals: Phase difference → mass flow rate; vibration frequency → density; temperature can be measured simultaneously
Accuracy: ±0.1%~±0.5%, no temperature and pressure compensation is required
2. Thermal Mass Flow Meter (Dedicated for Gas Measurement)
Core Principle: Thermal conduction/heat dissipation (King's Law)
Two Operating Modes:
Constant power mode: Measure the temperature difference between the heating element and the fluid, the larger the flow rate, the greater the temperature difference
Constant temperature difference mode: Maintain a fixed temperature difference and measure the required heating power, the larger the flow rate, the higher the power
Features: No moving parts, small pressure loss; highly affected by gas component changes
II. Routine Maintenance (Focus on Coriolis Mass Flow Meters)
Daily/Every Shift (5-Minute Check)
Check the display: No active alarms, stable readings consistent with working conditions
Inspect installation status: No leaks, no strong external vibration, no loose bolts, no pipeline deformation
Check surrounding environment: No corrosive substances, no direct long-term sun exposure, the junction box is fully sealed
Weekly/Monthly Check
Cleaning: Wipe the outer shell with a dry cloth; remove dust and oil stains on thermal probes; never rinse electronic components with water
Filtration system inspection: Check the Y-type filter (≥80 mesh), drain pollutants and exhaust air to ensure the measuring tube is fully filled with fluid
Wiring inspection: Tighten terminals, remove oxidation layers, confirm good shield grounding performance
Every 2~3 Months (Critical Periodic Check)
Zero calibration: Perform zero calibration under full-tube, static, single-phase flow conditions; re-calibrate immediately after dramatic changes in working conditions
Sealing inspection: Check for leakage prevention on flanges, junction boxes and sensor interfaces
System diagnosis: Check the drive gain (rising value indicates scaling), check temperature and density drift
Annual Maintenance
Full-scale calibration (recommended once a year for instruments with accuracy class ≥0.5)
Clean the measuring tube (for scaling/crystallizing media), inspect lining and material corrosion status
Check shock absorption/support structures, eliminate electromagnetic interference sources
Maintenance Prohibitions
Never knock or strike the measuring tube during operation
Forbid zero calibration with empty measuring tubes (for Coriolis meters)
When performing pipeline welding, remove the instrument completely or take cooling protection measures
Thermal mass flow meters are forbidden to operate in gas containing liquid or high dust content for a long time
III. Common Fault Analysis and Handling (Focus on Coriolis Meters)
Zero drift / Readings exist even with zero flow
Causes: Installation stress, two-phase flow (gas contained/not full tube), scaling, valve internal leakage, poor grounding
Solutions:
Re-perform zero calibration under full-tube static condition
Exhaust air and drain pollutants to ensure single-phase flow
Eliminate installation stress and reinforce supporting structures
Clean the measuring tube and check valves for internal leakage
Inaccurate flow readings / Severe value fluctuation
Causes: Entrapped bubbles/impurities, scaling, abnormal drive, incorrect parameter setting, vibration interference
Solutions:
Install exhaust devices and filters at the upstream section
Clean the measuring tube and inspect the drive gain
Verify density, measuring range and unit parameters
Add shock absorption measures and keep the instrument away from vibration sources
No display / No signal output
Causes: Power supply failure, blown fuse, wrong/loose wiring, damaged circuit board, burnt sensor coil
Solutions:
Check power supply voltage and replace the blown fuse
Tighten wiring and confirm consistency with the wiring diagram
Dry the junction box and repair damaged sealing components
Test coil resistance and return the circuit board to the factory for professional repair
Abnormal density display
Causes: Two-phase flow, scaling, temperature drift, wrong calibration coefficient
Solutions:
Eliminate two-phase flow state and clean the measuring tube
Inspect the temperature sensor and re-perform density calibration
Alarms (Overload / Vibration / Temperature)
Overload alarm: Flow exceeds full scale → Limit the flow rate or replace with a higher-range instrument
Abnormal vibration alarm: Loose support / resonance → Reinforce the bracket and add shock-absorbing gaskets
Temperature/pressure over-limit alarm: Medium exceeds rated range → Replace with an adapted model and control medium temperature and pressure within the allowed range
IV. General Troubleshooting Procedure
Prioritize checking alarm codes and built-in diagnostic information first
Verify process conditions: Is the measuring tube fully filled? Is the flow single-phase? Are temperature and pressure normal? Are there any leaks?
Inspect installation conditions: Excess installation stress? Unwanted vibration? Poor grounding? Electromagnetic interference?
Check electrical parts: Power supply status, wiring connections, fuse, communication link
Verify parameter settings: Zero point, density, measuring range, engineering unit
Inspect physical hardware: Measuring tube, drive coil, sensor, circuit board
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