Nexisense MEMS Thermal Gas Mass Flow Sensor: High-Precision Integration Solution for Atmospheric Sampling Systems

Atmospheric sampling equipment serves as the core front-end device for environmental monitoring and pollutant analysis, relying on stable and precise gas sampling flow to ensure sample representativeness and data traceability. According to JJG956-2000 "Verification Regulation for Atmospheric Samplers", the flow indication error ≤±5%, repeatability ≤2%, and stability (ordinary type within 1h, constant temperature constant flow type within 8h) variation ≤5% have become mandatory requirements for system design and acceptance.

The Nexisense series MEMS thermal gas mass flow sensor adopts silicon-based microfabrication process and realizes direct mass flow measurement based on thermal diffusion principle. It can output standard condition or actual condition flow without additional temperature-pressure compensation, particularly suitable for portable/fixed atmospheric samplers, air quality monitoring micro-stations, and VOC/particulate matter composite sampling systems.

Thermal Mass Flow Measurement Principle and Technical Advantages

The core chip of the MEMS thermal sensor contains a heating resistor and symmetrically arranged thermopiles upstream and downstream. When gas flows through the sensitive area, the heating resistor generates a temperature difference field, with the upstream thermopile temperature decreasing and the downstream increasing. The temperature difference ΔT has a single-valued functional relationship with the gas mass flow, directly outputting mass flow (unit: g/h or sccm), unaffected by changes in gas component density.

Compared with traditional volumetric flowmeters (such as rotameters, laminar differential pressure type), Nexisense modules offer the following engineering advantages:

• Extremely low pressure drop (<100Pa@1L/min typical), suitable for low-power sampling pumps.

• Wide turndown ratio (above 1:100), covering common sampling requirements of 0.1~20L/min.

• Response time<10ms, supporting fast closed-loop regulation.

• No moving parts, resistant to vibration and dust, MTBF >10 years.

• Low power consumption (<50mW), suitable for solar-powered environmental monitoring nodes.

Main Application Scenarios and Project Integration Cases

Ambient Air Quality Automatic Monitoring Station (Micro Station)

In urban grid-based air monitoring, Nexisense flow sensors are integrated into PM2.5/PM10 cutters and gaseous pollutant sampling channels to achieve constant flow sampling (typical 1.0L/min or 16.67L/min). Through RS485 Modbus RTU protocol communication with data acquisition instruments, it supports real-time flow feedback and pump speed PID regulation, ensuring 8h stability better than ±3%.

Typical project: In a provincial ecological environment monitoring network in North China, hundreds of micro-stations were deployed. After replacing imported flowmeters with Nexisense modules, the overall system power consumption was reduced by about 25%, flow deviation improved from ±4.8% to ±1.2%, and passed provincial metrology certification.

Portable Atmospheric Sampler and Emergency Monitoring

Handheld/vehicle-mounted samplers need to maintain flow stability in complex outdoor environments. The Nexisense compact module (size<20×15×10mm) is embedded downstream of the sampling pump, supporting I²C digital output and analog voltage feedback, facilitating MCU implementation of flow closed-loop and data logging.

Case: In the Yangtze River Basin water environment emergency monitoring project, the portable sampler integrated with Nexisense sensors achieved flow repeatability<1.5% under conditions of -10~45℃ and altitude 0~3000m, supporting VOC canister sampling and filter membrane particulate matter collection, with data directly used for GC-MS analysis.

Industrial Park and Pollution Source Perimeter Monitoring

Fixed sampling systems need to adapt to high-humidity and dusty environments. Nexisense modules can be optionally equipped with hydrophobic filter screens and heating self-cleaning functions to maintain long-term zero drift <±0.5% FS/year.

Practical application: In a petrochemical park VOCs online monitoring system, Nexisense sensors are integrated with sampling pumps and cold traps to achieve constant flow adsorption tube sampling, with flow data synchronously uploaded to the environmental protection platform, supporting compliance verification of HJ 644-2013 and other standards.

Selection Guide and System Integration Considerations

Key selection parameters:

• Range: 0.05~5L/min (low flow VOC), 0.5~20L/min (particulate matter/comprehensive sampling).

• Output: I²C (default), RS485 Modbus RTU, 0-5V analog, PWM.

• Accuracy: ±(1.5% reading + 0.5% FS), resolution 0.01L/min.

• Operating conditions: -20~70℃, 0~95%RH non-condensing, withstand pressure difference <±10kPa.

• Power supply: 3.3~5.5V DC, power consumption<50mW.

Integration considerations:

• Installation direction: Gas flow direction consistent with arrow, avoid reverse flow.

• Pipe design: Upstream straight pipe section ≥10D, downstream ≥5D, to reduce turbulence effects.

• Compensation algorithm: Built-in T/P compensation optional, recommended to share environmental sensor data with sampling MCU.

• Anti-clogging: Install 10μm filter upstream, regular reverse blow cleaning.

• EMC and explosion-proof: Compliant with GB/T 18268.1, Ex ia optional for hazardous areas.

• Calibration: Supports dry air/nitrogen calibration, field verification or sending for inspection every 12 months.

• Software support: Provides SDK, Modbus register table, and flow PID reference code.

Nexisense OEM/Customization and Bulk Supply Advantages

Nexisense focuses on MEMS flow sensing technology and provides flexible B2B cooperation modes:

• Custom range, interface protocol, mechanical interface (quick connector, hose clamp).

• Firmware optimization: Integrate customer-specific flow curves, alarm thresholds, and compensation models.

• Stable bulk supply: Monthly capacity 100,000+ pcs, core chip self-encapsulated, controllable supply chain.

• Fast iteration: Sample cycle 4-6 weeks, mass production delivery 8-10 weeks.

• Technical collaboration: Provide 3D STEP models, thermal simulation reports, and joint testing support.

These services help sampling equipment manufacturers shorten time-to-market, optimize system BOM, and achieve differentiated competition.

Frequently Asked Questions (FAQ)

1. MEMS thermal mass flow sensor vs. volumetric flowmeter in sampling applications - main differences?
      Thermal type directly measures mass flow without additional compensation for temperature and pressure changes, output unaffected by gas density; volumetric type requires real-time compensation and is susceptible to environmental fluctuations leading to increased errors.

2. How to ensure the sensor meets the flow stability ≤5% requirement in JJG956-2000?
      Nexisense module adopts closed-loop heating control and digital filtering algorithm, typical 8h drift <±2%; integration recommends linkage with constant flow pump for active regulation.

3. Is the sensor susceptible to contamination in high-humidity or dusty atmospheric sampling environments?
      The module sensitive area uses hydrophobic coating and microchannel design, combined with upstream filter, can operate stably long-term under RH 95%, dust<50mg/m³ conditions.

4. Which communication interfaces are supported for integration with sampling controllers?
      Standard configuration I²C and RS485 Modbus RTU, supporting baud rates 9600~115200bps; optional 4-20mA or 0-5V analog output, compatible with most embedded acquisition systems.

5. How is flow closed-loop control implemented to maintain constant sampling volume?
      Sensor outputs real-time flow to MCU, MCU adjusts sampling pump speed via PWM to form PID closed loop; reference code supports Kp/Ki/Kd parameter tuning, steady-state error <±1%.

6. Does OEM customization support specific gas medium calibration curves?
      Supported, such as multi-point calibration for air, nitrogen, argon or VOC mixed gases, providing dedicated firmware and calibration certificates.

7. How to manage sensor zero and span drift?
      Built-in automatic zero tracking function (automatic zeroing when stationary); recommended to use standard flow source for field span verification every 6-12 months, supports remote firmware upgrade compensation.

8. What are the power consumption optimization solutions in portable solar-powered samplers?
      Module standby power consumption

   <5mw, supports="" intermittent="" sampling="" mode="" adjustable="" measurement="" combined="" with="" low-power="" mcu="" and="" efficient="" achieves="" continuous="" operation="">72h.

Conclusion

The Nexisense team has been deeply engaged in the MEMS flow sensing field, committed to providing reliable and cost-effective flow measurement components for atmospheric sampling equipment manufacturers and environmental monitoring system integrators. We welcome sampling equipment manufacturers, monitoring station builders, and environmental instrument OEM partners to contact us for detailed data sheets, evaluation samples, or customized development discussions, to jointly improve the accuracy of environmental monitoring data and system reliability, and promote the advancement of atmospheric pollution prevention and control technology.