Thermal Mass Flow Meter Calibration Guide

Thermal Mass Flow Meter Calibration Guide

I. Calibration Process

1. Zero Calibration Steps

Power-on operation‌: Connect the power supply and allow the meter to operate for 1 hour to several hours with the medium until the device reaches a stable state

Valve operation‌: First close the downstream valve, then close the upstream valve, ensuring the sensor is in a full-pipe state with complete fluid flow stoppage

Zero adjustment‌: Use a hand controller to zero the flow meter, observe zero fluctuations and record

Stability verification‌: Repeat zero adjustment several times until the actual zero fluctuates near zero within a range smaller than the zero stability specification

2. Range Calibration Methods

Standard comparison method‌: Use a standard flow meter (such as sonic nozzle or bell prover) installed in series with the meter to be calibrated, compare measurements and adjust parameters

Parameter adjustment‌: Adjust parameters such as meter coefficient and segmented velocity correction based on error records

Accuracy verification‌: Verify measurement accuracy using mass or volumetric methods after calibration

II. Calibration Equipment and Tools

Equipment Type Working Principle Application Scenario

Standard flow meter‌ High-precision measurement (e.g., Coriolis mass flow meter, turbine flow meter) Lab or field calibration, one accuracy grade higher than device under test

Flow calibrator‌ Generates known flow (e.g., Defender 500 series) Field calibration, provides stable gas flow output

Wind tunnel‌ Produces controlled airflow Lab calibration for large flow/high velocity

Sonic nozzle‌ Calculates flow using sonic characteristics High-velocity/large flow calibration (e.g., chemical, petroleum fields)

Hand controller‌ Parameter setting and adjustment Field zeroing and parameter setting

III. Calibration Precautions

Installation specifications‌

Ensure sufficient straight pipe length: minimum 10 pipe diameters (10D) upstream, 5D downstream

Flow direction must match meter arrow marking, avoid reverse measurement

Prohibit low-position installation to prevent water accumulation and debris collection

Environmental conditions‌

Maintain ambient temperature between 5°C-45°C

Humidity ≤85%, avoid extreme environments

Keep away from strong vibration sources and electromagnetic interference

Medium requirements‌

Prohibit acetylene gas and water/steam-containing media

Calibration medium must match actual working conditions (gas density, temperature)

Flow velocity range should be controlled between 0.5-60 m/s

Safety operations‌

No welding in explosive environments

Outdoor installations require sun/rain protection covers

Strictly follow Lockout-Tagout (LOTO) safety procedures

IV. Common Errors and Solutions

Error Type Cause Analysis Solution

Improper installation‌ Insufficient straight pipe or obstructions Reserve 20D upstream, 10D downstream

Medium contamination‌ Water condensation or coating on sensor surface Install upstream filter, regularly clean sensor

Power issues‌ Unstable power causes measurement drift Check power indicators, ensure voltage stability