Tianhong THM-700 Series Air Quality Mass Flow Meter

Overview

The Tianhong THM-700 Series Air Quality Mass Flow Meter is a field-deployable, thermally based flow verification instrument engineered for metrological traceability in ambient air monitoring networks. It operates on a dual-stage principle: precision mechanical splitting of the main sample stream—minimizing pressure drop and flow disturbance—followed by high-stability thermal mass flow sensing calibrated specifically for dry air at atmospheric composition. Unlike volumetric displacement or differential pressure-based meters, the THM-700 series delivers direct mass flow measurement independent of ambient temperature and barometric pressure fluctuations, enabling accurate quantification of sample draw rates across regulatory-grade particulate and gaseous analyzers. Its modular design supports three distinct flow ranges (THM-701, THM-702, THM-703), each optimized for specific EPA-compliant monitoring configurations—making it suitable for routine calibration verification, QA/QC audits, and dynamic dilution system validation in fixed-site air quality stations.

Key Features

• Precision split-flow architecture ensures ≤150 Pa pressure drop at maximum rated flow, preserving upstream instrument performance during in-situ verification.
• Thermal mass flow sensor with NIST-traceable calibration for dry air (79% N₂, 21% O₂), supporting both standard condition (0 °C, 101.325 kPa) and user-selectable actual condition modes (20 °C or 25 °C).
• EPA-standard 1.25-inch (Φ32.7 mm) inlet/outlet interface enables plug-and-play replacement of PM₁₀/PM_2.5 cyclone cutters without adapter hardware or flow-path reconfiguration.
• Integrated environmental compensation: real-time temperature (±0.3 °C) and absolute pressure (±0.1 kPa) sensing for automatic density correction.
• Capacitive touch interface with auto-dimming OLED display; supports instantaneous flow readout, time-weighted averaging (1–60 min windows), and statistical summary (min/max/mean/std dev).
• Onboard wireless RF module (ISM band, 433 MHz) enables remote parameter configuration, firmware updates, and scheduled data pull via PC-based utility—no physical cable required.
• Rechargeable lithium-ion battery pack (7.4 V, 4400 mAh) sustains >12 hours of continuous logging at 5-minute intervals, including wireless transmission cycles.

Sample Compatibility & Compliance

The THM-700 series is validated for use with ambient air streams containing typical urban/rural particulate loadings (<100 µg/m³ PM_2.5) and common gaseous pollutants (SO₂, NO₂, CO, O₃) at concentrations within EPA Reference Method tolerances. It complies with mechanical interface requirements specified in U.S. EPA Guidance for PM Monitoring (40 CFR Part 53, Appendix L) and ISO 12103-1 for aerosol sampling system verification. While not certified to ISO/IEC 17025 as a standalone calibration standard, its factory calibration certificate includes uncertainty budgets (k=2) referenced to national standards. The device meets CE marking requirements for electromagnetic compatibility (EN 61326-1) and low-voltage safety (EN 61010-1). It supports GLP-aligned audit trails when used with Tianhong’s optional desktop software (v3.2+), which logs operator ID, timestamp, location metadata, and configuration changes.

Software & Data Management

The companion Windows-based THM-DataLink software provides secure local storage, visualization, and export functionality. Raw records include four synchronized parameters per interval: volumetric flow (L/min), mass flow (mg/s), ambient temperature (°C), and static pressure (kPa). Data files are saved in CSV and XML formats compliant with ASTM D6245-22 for air quality data interchange. Audit log entries capture all configuration modifications—including flow unit selection, compensation mode, and wireless session initiation—with SHA-256 hashing for integrity verification. Optional integration with LIMS platforms is supported via OPC UA server extension (license required). All firmware and software updates are digitally signed and delivered through Tianhong’s secure customer portal.

Applications

• Verification of sample flow rate accuracy in FRM/FEM PM₁₀ and PM_2.5 monitors operating at 16.7 L/min (THM-703).
• Calibration validation of gaseous pollutant analyzers (SO₂, NO₂, CO, O₃) requiring stable sub-3 L/min sample draw (THM-702).
• Performance testing of dynamic dilution calibrators—paired use of THM-701 (0–200 mL/min) and THM-703 enables ratio verification across two independent mass flow paths.
• Field QA/QC for mobile monitoring units where battery autonomy and rapid deployment are critical.
• Supporting ISO 17025-accredited laboratories conducting flow system validation per ISO/IEC 17025:2017 Clause 7.8.2 (Equipment Verification).

FAQ

Does the THM-700 series require annual recalibration?
Yes. Tianhong recommends recalibration every 12 months against a primary standard flowmeter traceable to NIST or equivalent national metrology institute. Calibration certificates include expanded uncertainty (k=2) and drift assessment over the full range.
Can the THM-700 be used with humid or contaminated air streams?
It is rated for ambient air with relative humidity ≤90% non-condensing and total suspended particulate ≤1 mg/m³. For high-humidity or oil-laden streams, an inline desiccant or coalescing filter is required upstream to prevent sensor fouling.
Is FDA 21 CFR Part 11 compliance supported?
The THM-700 itself does not implement electronic signatures or audit trail encryption. However, when paired with THM-DataLink v4.0+ and configured with role-based access control, it supports Part 11–aligned workflows for regulated environmental laboratories.
What is the measurement uncertainty at 16.7 L/min?
At 16.7 L/min (THM-703), the combined standard uncertainty is ±0.8% of reading (k=1), derived from sensor repeatability, temperature/pressure compensation residuals, and calibration transfer uncertainty.
How is traceability documented for regulatory submissions?
Each unit ships with a calibration certificate listing reference standard ID, environmental conditions during calibration, measurement points, and uncertainty budget. Digital copies are archived in Tianhong’s calibration management system with 10-year retention.