Dwyer 641 Series Offers

Features

• Heated mass flow sensor which allows for precise velocity measurements at various flow rates and temperatures
• 16 field selectable ranges provides it the versatility to be selected for several air flow applications
• The optional LED produces a complete, low-cost solution for local indication of air flow
• Easy Push Button Set-up
• Compact Housing
• 4-20 mA Output
• Digital Filter for Signal Damping

• Service: Clean air and compatible, non-combustible gases
• Accuracy: 3% FS Process gas: 32 to 122°F (0 to 50°C); 4% FS Process gas: -40 to 32°F & 122 to 212°F (-40 to 0°C & 50 to 100°C)
• Response Time: Flow: 1.5 seconds to 95% of final value (output filter set to minimum)
• Temperature Limits: Process: -40 to 212°F (-40 to 100°C). Ambient: 32 to 140°F (0 to 60°C)
• Pressure Limit: 100 psi (6.89 bar) maximum
• Humidity Limit: Non-condensing
• Power Requirements: 12-35 VDC, 10-16 VAC. 1.5 A rating required on supply due to initial power surge drawn by transmitter
• Output Signal: 4-20 mA, isolated 24V source, 3 or 4-wire connection
• Output Filter: Selectable 0.5-15 (seconds)
• Loop Resistance: 600 ohms max
• Current Consumption: 300 mA max
• Electrical Connections: Screw terminal
• Process Connections: 1/2" male NPT
• Enclosure Rating: Designed to meet NEMA 4X (IP66) for non LED models only
• Mounting Orientation: Unit not position sensitive. Probe must be aligned with airflow
• Weight: 12.6 oz (357.2 g)

• Exhaust Stack Flow Monitoring
• Air Control in Drying Processes
• HVAC/R Air Velocity Measurements
• Fan Supply and Exhaust Tracking
• Clean Room Fresh Air Supply
• Ensure Proper Lab Hood Exhaust Flow Rates

Anemometers are instruments used to measure wind speed or air velocity in meteorology and aerodynamics. The name is derived from the Greek root Anemos, meaning wind. There are many anemometer sensor types with one of the most popular being thermo, or hot-wire, anemometers for HVAC/R air velocity monitoring. Thermo-anemometers use a sensor element that is heated up beyond the ambient temperature. Airflow moving past the sensor will have a cooling effect that is directly proportional to the flow velocity.

Hot wire anemometers come in three basic types: constant current, constant voltage, and constant temperature. All three types have circuits that are based on trying to maintain a specific variable during the cooling effect based on Ohm's Law. Thermo-anemometers offer good low flow detection, fast response times, and high rangeability of measurements. They are omni-directional, making them good for turbulent flows and easier to use than pitot tubes, but are more fragile than pitot tubes.

Usually, a probe style sensor is made for insertion into ducts and pipes. For constant temperature thermo-anemometers, two temperature sensors are installed at the end of the probe, typically resistance temperature detectors (RTDs). One RTD measures the ambient temperature as a reference. The second RTD is continuously maintained at a constant temperature above ambient. The higher the air velocity, the more current is required to maintain the second RTD's temperature. Based on the current usage, the air velocity is calculated.

Like a pitot tube, thermo-anemometers are a single point sensing device that requires being in the center of the velocity profile or the use of traverse readings for accurate measurements.