Thermal Mass Gas Flowmeter

A thermal mass flowmeter has two temperature sensors in the gas stream; one is heated, and the power needed to hold a constant temperature difference between them is a direct function of the mass of gas passing. Because the measurement responds to mass rather than volume, no pressure or temperature compensation is required, and the meter keeps its accuracy at the low flows and low pressures where orifice plates and vortex meters give up.

Inline models from ¼" to 2" suit small lines such as burner fuel gas, purge and blanketing gas, dosing and sub-metering. Insertion models cover 2½" to 99" pipes and ducts with threaded, flanged, fixed-welded or retractable mounting, the last allowing removal under pressure. Ranges are model-dependent, from 0.01 to 950 Nm³/h and 0.07 to 305 Nm³/h, at pressures to 69 bar and temperatures from −40 to +454 °C. Wetted parts are 316 stainless steel or Hastelloy.

Communication options include 4–20 mA HART, RS-485, FOUNDATION Fieldbus H1, PROFIBUS PA, frequency or pulse, USB and Ethernet. A local LCD, flow conditioner, dual-element configuration for redundancy, data logger and in-situ calibration verification are available, the last documenting sensor health without removing the meter from the line.

Users are onshore and offshore oil and gas, refining, petrochemical, chemical, power, HVAC and emissions monitoring, including compressed-air audits and boiler air-fuel ratio control.