How to Calibrate a Thermal Mass Flow Meter??

How to Calibrate a Thermal Mass Flow Meter??

Thermal mass flow meters require precise calibration to ensure accurate gas flow measurement. Below are the standard calibration methods and steps based on industry practices:

I. Standard Flow Meter Comparison Method?

Principle:?

The thermal mass flow meter to be calibrated is connected in series with a higher-precision standard flow meter in the same gas pipeline. The same gas flow passes through both meters under stable conditions, and the readings are compared to correct errors in the calibrated meter.

Steps:?

Select a standard flow meter? with at least one higher accuracy class (e.g., ±0.5% if the calibrated meter is ±1%).

Install both meters? in series, ensuring leak-free connections.

Adjust gas flow? across the full range (from minimum to maximum) and record readings at multiple points.

Calculate errors? at each point:

Error

=

Calibrated Meter Reading

?

Standard Meter Reading

Standard Meter Reading

×

100

%

Error=

Standard Meter Reading

Calibrated Meter Reading?Standard Meter Reading

×100%

Adjust parameters? (zero point, span, etc.) to bring errors within acceptable limits.

Advantages:? Suitable for on-site calibration in real operating conditions.

II. Flow Standard Device Calibration Method?

Principle:?

A flow standard device (e.g., bell jar or piston type) generates a precisely known gas flow. The meter measures this flow, and its readings are compared to the device’s set values for calibration.

Steps:?

Prepare the device? (e.g., fill a bell jar with gas and connect the meter to its outlet).

Release gas at controlled flow rates?, recording both the standard device’s output and the meter’s readings.

Repeat at multiple flow points? (e.g., 10%, 25%, 50%, 75%, 100% of full scale).

Calculate errors? and adjust the meter’s settings (e.g., K-factor, PID parameters) if deviations exceed limits.

Advantages:? High precision, ideal for lab environments.

III. Zero Calibration (Critical for Accuracy)?

Ensure no flow? in the pipeline and power on the meter.

Enter calibration mode? (password: typically "000000").

Stabilize the zero voltage? (e.g., wait 30 minutes for temperature equilibrium).

Confirm zero stability? (voltage fluctuations within ±0.5% FS are acceptable).

Save settings? and exit to the main interface.

Note:? Repeat if fluctuations persist.

IV. Key Considerations?

Environmental factors? (temperature, pressure, humidity) must remain stable during calibration.

Gas properties? (density, viscosity) affect readings; calibrate with the actual gas type.

Regular calibration? is recommended every 3–12 months, depending on usage and industry standards.

Summary:? Calibration ensures accuracy and compliance. Choose between ?standard meter comparison? (for field use) or ?flow standard devices? (for lab precision), and always perform zero calibration before use.