The Dwyer 641 Air Velocity Transmitter is a versatile, high‑performance instrument designed for precise monitoring of air flow in industrial and commercial applications. Utilizing a heated mass flow sensor, it delivers accurate velocity measurements across a wide range of flow rates and temperatures, making it ideal for demanding environments such as exhaust stacks, HVAC systems, and clean rooms.

With 16 field‑selectable ranges covering velocities up to 15,000 FPM (75 MPS), the 641 can be easily configured to match specific application requirements. Its ±3% accuracy and 1.5‑second response time ensure reliable, real‑time data for process control and safety monitoring. An optional bright LED display provides local indication, while the 4‑20 mA output (with isolated 24 VDC excitation) allows seamless integration with PLCs, DCS, and building automation systems.

Designed for ease of use, the transmitter features push‑button setup and a digital filter for signal damping, reducing noise in turbulent flows. The compact, rugged housing houses screw terminal connections and a 1/2" male NPT process fitting, simplifying installation. It operates within a process temperature range of -40 to 212°F and withstands pressures up to 100 psi.

Typical applications include:

• Exhaust stack flow monitoring
• Air control in drying processes
• HVAC air velocity measurements
• Fan supply and exhaust tracking
• Clean room fresh air supply
• Lab hood exhaust flow verification

Features

• For use with clean air and compatible, non‑combustible gases
• Accurate up to ±3%
• 1.5 second response time
• Process temperature limit: -40 to 212°F
• Pressure limit: 100 psi (6.89 bar) maximum
• Ranges to 15,000 FPM or 75 MPS
• Optional bright LED display
• Easy push‑button setup
• Compact housing
• 4‑20 mA output, isolated 24V source, 3 or 4‑wire connection
• Digital filter for signal damping
• Screw terminal electrical connection
• 1/2" male NPT process connection