Thermal Mass Flow Meters
Direct Mass Flow, No T+P Stack
Accuracy of ±1.0% of rate
Turndown ratio of 1:1200
Low-flow detection of 0.1 Nm/s
- Line sizes DN10 to DN300 inline (insertion to DN1000+; TMF-MEMS micro version DN8 to DN25)
- Working pressure ≤ 1.6 MPa standard, up to 6.3 MPa on request
- 8 thermal-dispersion inline models plus 1 TMF-MEMS micro version on the TMF Series
The TMF Thermal Mass Flow Meter family covers industrial gas service across DN10 to DN300 pipe sizes, with insertion versions (TMFW) extending to stacks DN1000 and larger. The thermal-dispersion principle; operating in constant-temperature-difference (CTD) mode; reads mass flow directly from heater power, with no external T+P stack and no flow computer required.
Eight thermal-dispersion inline models cover compressed air, oxygen, hydrogen, nitrogen, natural gas, biogas, landfill gas, and flue gas service. The 0.1 Nm/s low-flow detection catches off-shift purge drift and idle leak signals that vortex meters miss. The 1:1200 velocity turndown spans idle through peak demand on a single meter, eliminating parallel-meter bypass piping. CNEX Ex d IIC T6 Gb hazardous-area protection ships on every order. For micro-bore service below DN50 (analytical lab, fuel-cell test rig, battery cell formation, semiconductor wafer, medical-gas applications) the TMF-MEMS version adds a MEMS-chip sensor in a DN8 to DN25 threaded body, 0.05 Nm/s low-flow detection, and mL/min lab-output capability. Lead time 5–7 business days from the factory.
Thermal mass flow meter models
Eight thermal-dispersion inline models plus the TMF-MEMS micro version on the TMF Series. Click through for spec, configurator, and pricing.
Compressed Air TMF
Factory plant-air mains, compressor-bench audits, and ISO 11011 leak-attribution loops. ISO 1217 Free Air Delivery output direct on the loop.
View configuration →Oxygen TMF
ASU outlet headers, oxygen lance feeds, oxy-fuel burners, and aeration mains. No T+P stack, no flow computer, no compressibility table.
View configuration →Hydrogen TMF
PEM and alkaline electrolyser feeds, refinery sub-meters, and fuel-cell test rigs. Direct mass flow with no AGA Z-factor table to maintain.
View configuration →Nitrogen TMF
Inerting headers, blanket-gas feeds, purge service, and bulk LN₂ vaporiser outlets. Sanitary Tri-clamp option for pharma and battery service.
View configuration →Natural Gas TMF
Pipeline natural gas on factory inlets, M&R stations, and CHP feed lines. On-board calorific log (MJ/Nm³ + kWh-equivalent) for boiler-fuel auditing.
View configuration →Biogas TMF
Raw digester gas on WWTP, agricultural digester, landfill, and CHP-feed lines. Hastelloy C-276 probe handles H₂S to 10,000 ppm continuous.
View configuration →Landfill Gas TMF
Flare-stack feeds, LFGTE collection headers, and RNG upgrade-skid outlets. PTFE-coated Hastelloy C-276 probe handles H₂S, siloxane, and condensate.
View configuration →Flue Gas TMF
Conditioned flue gas downstream of post-cooler boiler stacks, RTO outlets, and drying-oven exhausts. Insertion version for stacks DN1000+.
View configuration →MEMS Gas Flow Meter
MEMS-chip sensor for analytical lab, fuel-cell test rig, battery cell formation, semiconductor wafer, and medical-gas service. 100:1 turndown, mL/min to kg/h output, 8 factory gas curves plus mixture custom calibration.
View configuration →How thermal mass flow meters work
A thermal mass flow meter measures gas mass flow directly from the heater power required to maintain a fixed temperature difference between two RTDs in the flow path. One RTD is heated above the reference RTD; gas flow carries heat away, the meter increases heater power to hold the differential, and the heater-power signal converts directly to mass flow without external pressure or temperature compensation.
This is the thermal-dispersion principle, operating in constant-temperature-difference (CTD) mode. Because pressure and temperature factors cancel on both sides of the heat-balance equation, the TMF outputs Nm³/h or kg/h directly on the 4-20 mA loop with one instrument; no multivariable transmitter, no flow computer, no compressibility table. The 0.1 Nm/s low-flow detection catches idle drift below the vortex shedding velocity, and 1:1200 turndown spans the full operating range on one meter.
Thermal mass versus vortex versus swirl
Choose thermal mass when the medium is wet, low-density, or below the vortex floor. Choose vortex for steam-heavy duty. Choose swirl for tight straight-pipe installs.
| Service | Thermal Mass (TMF); pick when | Alternative meter type |
|---|---|---|
| Idle leak drift, off-shift trickle | 0.1 Nm/s low-flow detection | Vortex reads zero below 3-4 m/s |
| Wet biogas, landfill gas, flue gas | No bluff body, condensate-tolerant | Vortex noisy below 5 m/s wet |
| Compressed air audit, ISO 50001 logging | Direct FAD, on-board kWh log | Vortex for < 0.1 Nm/s blind |
| Hydrogen, low-density gas | Direct mass flow, no AGA correction | Coriolis above 6.3 MPa |
| Saturated & superheated steam | Below T-rating, condensate concerns | Vortex (LUGB) for full DN range |
| Custody-grade utility billing | Not approved for fiscal primary | AGA 9 ultrasonic or Coriolis |
| Stack & flare metering DN1000+ | Insertion (TMFW) version available | Vortex insertion at ±1.5 % |
| High-pressure pipeline > 6.3 MPa | Beyond TMF working range | Coriolis (ZLMFM) |
TMF model selection by gas service
Match the TMF build to the gas service. Eight models cover the full gas range where direct mass flow + low-flow detection matter.
| Service | Wetted-parts & differentiator | Model page |
|---|---|---|
| Anaerobic-digester biogas, agricultural / WWTP / LFG | Hastelloy C-276 sour-service standard, composition input | Biogas TMF |
| Plant compressed-air ISO 50001 / 11011 audit, leak survey | 316L wetted parts, 0.1 Nm/s low-flow detection (vortex blind zone) | Compressed Air TMF |
| Conditioned flue gas (post-cooler boiler stack, RTO outlet) | 316L below 150 °C / Hastelloy C above, EPA reporting | Flue Gas TMF |
| Hydrogen (PEM / alkaline electrolyser, refinery, fuel cell) | H₂-clean materials, gas-specific factory K-factor | Hydrogen TMF |
| Landfill gas (high H₂S, siloxane, variable composition) | Hastelloy C standard, composition input mandatory | Landfill Gas TMF |
| Natural gas (boiler fuel, CHP feed, kiln burner) | 316L wetted parts, fuel gas K-factor | Natural Gas TMF |
| Industrial nitrogen (blanketing, ASU outlet, semicon purge) | 316L wetted parts, sanitary option (PFA + Tri-clamp) | Nitrogen TMF |
| Industrial oxygen (ASU, oxy-fuel burner, aeration, ozone) | 316L wetted parts, oxy-clean factory prep | Oxygen TMF |
All eight models share the TMF Series: ±1.0 % of rate, 1:1200 velocity turndown, 0.1 Nm/s low-flow detection, direct mass-flow output (Nm³/h or kg/h on 4-20 mA), CNEX Ex d IIC T6 Gb option, 5–7 business days lead time.
Model specification comparison.
| model | DN range | Wetted parts | Composition input | Key positioning |
|---|---|---|---|---|
| Biogas | DN25–DN300 | Hastelloy C-276 | Live CH₄% input | Sour service, H₂S to 5,000 ppm |
| Compressed Air | DN25–DN300 | 316L | Optional N₂-blend | ISO 50001 + 11011 leak audit |
| Flue Gas | DN25–DN200 | 316L (Hastelloy C above 150 °C) | O₂ + CO₂ optional | EPA / Subpart reporting |
| Hydrogen | DN15–DN150 | H₂-clean materials | Refinery balance optional | PEM / alkaline / refinery / HRS |
| Landfill Gas | DN50–DN300 | Hastelloy C-276 | Live CH₄% mandatory | Variable composition, siloxane, LMOP |
| Natural Gas | DN25–DN300 | 316L | Stable composition | Boiler fuel, CHP feed, city-gate sub |
| Nitrogen | DN10–DN300 | 316L (PFA sanitary option) | None; pure N₂ | Blanketing, ASU, semicon, pharma |
| Oxygen | DN15–DN300 | 316L oxy-clean | None; pure O₂ | ASU outlet, oxy-fuel, aeration |
All models share the TMF Series: ±1.0 % of rate, 1:1200 velocity turndown, 0.1 Nm/s low-flow detection, direct mass-flow output, CNEX Ex d IIC T6 Gb option, 5–7 business days lead time.
Universal TMF install requirements
Five install rules shared across all 8 TMF models:
- Send the gas service and operating range at order timeFactory K-factor depends on medium (NG / N₂ / H₂ / O₂ / biogas / compressed air / flue gas) and operating pressure/temperature. Composition variance beyond ±5 % requires the live composition input option.
- Respect 10× DN upstream and 5× DN downstream straight pipe10× DN clean full-bore pipe upstream, 5× DN downstream from the last fitting. For tight-skid installs see the LUXB swirl sibling (3D / 2D rule).
- Wire only the loop you need; no external T+P transmittersT+P read on-board via the thermal-dispersion sensor pair. Field wiring runs only the 4-20 mA loop (or RS485, HART) back to the DCS.
- Follow the catalog Ex d flameproof wiring rulesDo not modify the Ex d circuit, components, or explosion-protection type. CNEX Ex d IIC T6 Gb ships standard for hazardous-area orders.
- Keep the meter clear of magnetic and dirty-power sourcesAvoid strong external magnetic fields (large motors, transformer banks); do not share power with VFDs or welders. The thermal-dispersion sensor is µV-noise-sensitive.
Frequently asked questions
Need help selecting a thermal mass flow meter?
Send the line size, design pressure, and process medium. The engineering team returns a sized model code, an estimated unit price, and a ship window within one business day. Lead time 5–7 business days from the factory.