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Air and Gas Duct Flow Meters

Duct Flow Meters for Air & Gas

Rheotherm flow sensing probes for duct gases are easy to install and provide long-term service with little or no maintenance.  The output can be in mass, standard volume or velocity units.  Options for hazardous locations (intrinsically safe/explosion-proof) are available. 

Various line connections for air and gas flow sensorsWhat Can We Measure?
Air and most other non-condensing gases, including corrosive and explosive gases.  The stainless steel construction and lack of moving parts make it ideal for rugged industrial environments.  Common uses include vent air, stack gas and digester gas.  Contact Us about any application you have.

How Are They Installed?
These are insertion probe flow sensors that install through the pipe or duct wall.  Typical line connections are 1” NPT, but flange, hot tap and sanitary fittings are available.  The probes can be installed in horizontal or vertical pipes.  With some models the electronics are integral to the sensor, and other models have a separate electronics enclosure to install, up to 200 feet from the sensor. Electronics Options

What Is the Turndown Ratio?
Typical calibration ranges are 10:1 (options up to 200:1), with good accuracy over the entire range.  The sensors cannot be damaged by overranging.  
 

Probe flow sensor installationHow Do They Work?

Our insertion flow sensors have a shaft with two stainless steel flow sensing tips.  One tip has a heated RTD in it and the other an unheated RTD.  The temperature differential between the two RTDs provides the primary flow signal:  at high flow rates the differential is lower as flow removes more heat, and at low flow rates the differential is higher, as flow removes less heat.  Nothing touches the gas but the metal probe.  More on Method of Operation (PDF)

What If There Is Little to No Straight Run Available?
The historically reliable Rheotherm flow meter for duct flow measurement is now available with a revolutionary new sensor head which eliminates off axis error common to other sensors.  The new system measures true mass flow rate in turbulent ducts and pipes using Rheotherm flow sensors and the Rheovec transport velocity vector extractor.
U.S. Patent No. 4,942,763

How Do I Get One?

Submit your inquiry today to send us the application data to review, or visit our contact us page for telephone, fax and email information.

Insertion Probe Sensor Specifications:

Standard Options
Service Duct & pipe gases
Wetted Surface 316 SS Alloys 276 and 400
Flow Velocity Limits 5-25,000 SFPM
(0.025-127 meter/sec.)		 Consult factory
Turndown Ratio 10:1 200:1
Process Connection 1” MNPT Flange, hot tap, sanitary fitting
Max. Temperature 175ºF (80ºC) Up to 500ºF (260ºC)
Max. Pressure Depends on fitting 4,000 psi
Location General purpose Hazardous
(CL I, Div. 1, Grp BCD)
Pipe Sizes 1” and larger pipes Consult factory
Accuracy (with electronics) Up to +/- 1% of reading
Repeatability +/- 0.5%

Electronics Options   

More information about Rheotherm flow meters for gas mass flow (PDF)