Compressed Air Thermal Mass Flow Meter

Thermal mass is the only technology that reads mass flow (Nm³/h at ISO 1217 FAD) directly from the physics; heater power is proportional to mass flow rate, full stop. Vortex and swirl read volumetric flow at line conditions and compute mass through a flow computer that divides by the density derived from an external Pt100 and pressure transmitter; every added instrument is another failure surface and another source of calibration drift. Orifice plates are worse; square-root authority collapses below 1 bar ΔP and the sharp edge erodes on any high-velocity air. The TMF-CA fits the three cases where those alternatives struggle: (1) the audit needs true mass (Nm³) traceable without a compensation stack; (2) the application needs wide turndown (1:1200) to catch nighttime leakage AND peak workshop demand on one instrument; vortex typically gives 1:10, swirl 1:30; (3) the line has to run at near-zero pressure loss, which TMF delivers above DN80 because the sensor is in the wall, not across the stream. Specify vortex (LUGB) when capital cost per DN on clean, high-velocity dense air is the primary driver. Specify precession swirl (LUXB) when the retrofit has no room for 10D upstream; the 3D+2D straight-pipe advantage is decisive there.

Correct; for compressed-air service you eliminate four external components that a vortex-based measurement chain requires: the Pt100 temperature transmitter, the gauge-pressure transmitter, the separate flow computer, and the junction box wiring that ties them together. The TMF-CA transmitter computes Nm³/h directly from the heater-power signal on the sensing element, outputs it on the 4-20 mA loop, and writes it to the Modbus register; no math happens downstream. Typical savings: $1,800–$3,500 of integration cost per measurement point, plus the maintenance-interval reduction (one instrument to recalibrate per audit cycle instead of four). The only case where external correction is worth adding is high-pressure natural-gas service (≥ 2.5 MPa) where AGA 8 compressibility begins to matter; for compressed air at 7 bar gauge, compressibility is 0.998, so the correction is below the meter’s accuracy range and safely ignored.

One instrument covers the full operational range of a factory compressed-air header. At the low end, 0.1 Nm/s velocity is enough to detect and quantify the leak rate during a nighttime shutdown; a DN80 line with a 2 Nm/s steady leakage reads out at about 36 Nm³/h, well above the meter’s minimum. At the high end, 120 Nm/s handles peak workshop demand on the same DN80 line at about 2,200 Nm³/h. A vortex meter with 1:10 turndown on the same DN80 line would miss everything below 220 Nm³/h; so the nighttime leakage is invisible to it. A swirl meter with 1:30 turndown reads down to about 73 Nm³/h, which catches the leakage but not the slow nightly demand ramp. For ISO 11011 audits where you need the same meter to log baseline leakage AND peak demand AND the specific-power curve across the day, 1:1200 is the only technology that does it on one model. It is also the reason TMF-CA is the technology of choice for the “install one meter, get five years of useful data” philosophy of modern ISO 50001 rollouts.

Usually not. Clean compressed air is not a flammable atmosphere and the vast majority of factory installations are IP66 general-purpose with no hazardous-area classification; that’s the TMF-CA standard configuration and it covers 85 % of the units we ship. Three specific cases where Ex d (CNEX flameproof) becomes mandatory: (a) oil-flooded compressor rooms where the oil-mist zone drifts into Zone 2 during long compressor runtimes; most large industrial compressor houses carry a Zone 2 classification on the building perimeter; (b) paint shops and spray booths where the compressed-air header passes through solvent-vapor Zone 1 or Zone 2; (c) chemical-plant utility air where the header runs through a classified process area. For any of these, specify the Ex d (CNEX flameproof) option; same thermal sensor and electronics, flameproof housing / CNEX certification scope, works identically. The local display, USB audit-log export, and 4-20 mA output all pass through the flameproof window and Ex-rated entry without limitation.