The Dwyer 641B Air Velocity Transmitter employs heated mass flow sensor technology to deliver reliable airflow measurement in demanding industrial environments. Unlike traditional Pitot tubes or flow sensors that can clog or degrade in dirty air, the 641B features a rugged steel sensor that withstands particulate-laden airstreams and can be easily cleaned in the field with a simple cloth or pulse of compressed air—restoring performance without removal or recalibration.

The transmitter offers four user-selectable velocity ranges: 250, 500, 1000, and 2000 FPM (with corresponding metric ranges of 1.25, 2.5, 5, and 10 MPS), providing flexibility for a variety of duct sizes and airflow conditions. An isolated 4-20 mA output is proportional to the selected velocity range, and a selectable output filter (0.5 to 15 seconds) allows damping of signal fluctuations.

Housed in a NEMA 4X (IP66) enclosure, the 641B is protected against dust, water, and corrosion, making it suitable for outdoor and washdown environments. Electrical connections are made via screw terminals with 3- or 4-wire configuration. The transmitter operates over a wide process temperature range of -40 to 176°F and requires 12-35 VDC or 10-16 VAC power, with a 1.5A supply rating to accommodate initial power surge.

Typical applications include:

• Industrial HVAC systems with contaminated air streams
• Exhaust and ventilation monitoring in manufacturing facilities
• Process airflow measurement in non-combustible gas applications
• Dust collection system performance verification

Features

• Heated mass flow sensor technology with rugged steel construction
• Four user-selectable velocity ranges: 250 to 2000 FPM (1.25 to 10 MPS)
• Easily field-cleanable—wipe or air blast without removal
• Isolated 4-20 mA output proportional to velocity
• Selectable output filter (0.5 to 15 seconds)
• NEMA 4X (IP66) enclosure for harsh environments
• Process temperature range: -40 to 176°F (-40 to 80°C)
• 3- or 4-wire screw terminal connections
• For use with air and compatible non-combustible gases