Micro Thermal Gas Mass Flow Meter for Low-Flow CO₂ Measurement

A process equipment customer recently approached Jujie Automation with a demanding requirement: measure carbon dioxide flow in the range of 0.1–1.8 L/h (approximately 1.7–30 mL/min) in a line operating at 150 kPag / 20 °C, with full integration into their control system. This article explains how we solved it with the MF52 Series micro thermal gas mass flow meter — why the measurement is difficult, how the MF52-S0 configuration meets every requirement line-by-line, and how the meter connects to a PLC/DCS.

The customer requirement

The application needed a compact, clean-gas flow meter with the following specification:

Medium:CO₂ Gas

Required operating range: 0.1–1.8 L/h, approximately 1.7–30 mL/min

Selected meter range: 1–100 NmL/min

Operating condition: 150 kPag at 20°C

Power supply: 24 VDC

Local digital flow indication

4–20 mA output

RS485 Modbus communication

Configurable PNP low-flow alarm for connection to the control system

¼-inch NPT female connections

316 stainless-steel body

Why low-flow CO₂ measurement is a challenge

At just 1.7–30 mL/min, this stream is far below what most industrial flow meters are designed for, and the process condition adds a second layer of difficulty:

Volumetric meters

• (rotameters, differential-pressure orifices) read volume, not mass. At 150 kPag the gas is compressed, so the volumetric reading changes with every pressure and temperature fluctuation even when the true mass flow is constant — and their low-end accuracy is poor at these rates.

• Coriolis meters

• measure mass accurately but are physically and economically oversized for mL/min gas service.

• The customer also needed a live alarm output and bus communication

— which rules out simple "local-reading-only" instruments.

The right technology for this window is a thermal mass flow meter: it senses the gas mass flow directly and therefore needs no temperature or pressure compensation, while its rangeability covers a 100:1 span.

Our solution: MF52-S0 micro thermal gas mass flow meter

We supplied the MF52 Series micro thermal gas mass flow meter, configured as MF52-S0:

Requirement-to-solution check

Integration highlights

Alarm to control system.

• The PNP low-flow output gives the DCS/PLC a real no-flow/dry-run signal — the trip point is set in the meter menu, no external relay logic required. An optional second PNP output (DB9 pin 9) can serve as a high-flow alarm.

Modbus data.

• Instantaneous flow (4x0001) and cumulative flow registers are readable as IEEE-754 floats, letting the customer's system log consumption and trend the flow without extra converters.

Local readout & tuning.

• The two-line display shows live and total flow on site; damping (0–20), small-signal cutoff and instrument coefficient are adjustable in the menu so response (50 ms sensor response) can be matched to process dynamics.

Wiring simplicity.

• DB9 pinout covers supply, 4–20 mA and RS485 with clearly defined terminals; the meter is ready for 24 VDC plant power.

Factory quality and support

• Manufactured under an ISO 9001 /SGS /CE /ROHS certificate as a National High-Tech Enterprise, with each unit individually calibrated before dispatch.

• JUJEA engineering support for commissioning, Modbus register configuration and alarm settings — 1-hour response to inquiries, 7×16 hotline.

Specify your own low-flow gas meter

If you measure CO₂, N₂, air or other clean gases at mL/min to low-L/min rates, confirm these six points when requesting a quote:

1. Gas (and whether it is dry/clean)

2. Flow range in normal units (e.g. 1–100 NmL/min)

3. Process pressure and temperature

4. Connection type and thread standard — NPT thread or customized connection

5. Outputs required: 4–20 mA, RS485 Modbus, PNP alarms

6. Supply voltage and body material

FAQ

Q: Can a thermal mass flow meter measure CO₂ at only a few mL/min?

A: Yes. The MF52 thermal mass flow meter measures from 1 NmL/min (air) and offers a 1:100 range ratio, so a 1.7–30 mL/min operating window sits comfortably above the minimum measurable flow with stable, repeatable readings.

Q: Why is no temperature/pressure compensation needed at 150 kPag?

A: The MEMS micro flow sensor measures mass flow directly by heat transfer, so readings are already in mass (normal-condition) units — unlike volumetric meters, which would need live pressure/temperature correction on a compressed gas line.

Q: Can the mini flow meter raise an alarm if CO₂ flow stops?

A: Yes — the configurable PNP low-flow alarm output connects directly to the control system, with the trip point set in the meter menu.

Q: How does the customer read flow data over RS485?

A: Via standard Modbus RTU, function code 03. Instantaneous and cumulative flow are exposed as IEEE-754 float registers; device address, baud rate, parity and stop bits are menu-configurable (default 9600, 8, N1).

Interested in a similar low-flow gas measurement solution? Tell us your gas, range and process conditions — our engineers will confirm the solution and configuration for you.

Explore Micro thermal gas mass flow meters

• Micro flow meter range

• Contact JUJEA engineering

Ethan Liu

Ethan Liu is JUJEA's technical content specialist, translating complex sensor integration and industrial automation concepts into practical insights for engineers, system integrators, procurement professionals, and decision-makers worldwide.