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Model-641B
Heated Mass Flow Air Velocity Transmitter, 250-2000 FPM, HVAC/Exhaust
- SS sensor suitable for dirty air flow measurement
- Ranges from 250 FPM (1.25 MPS) to 2000 FPM (10 MPS)
- 4 to 20 mA output
- Digital filter for signal damping
Model-641B
From
SGD
1,374.04
Product Overview
- Accuracy ± 5 %
- Accuracy Detail 5% FS process gas: 32 to 122°F (0 to 50°C); 6% FS process gas: -40 to 32°F and 122 to 176°F (-40 to 0°C and 50 to 80°C)
- Air Velocity, Max 2000 FPM
- Air Velocity, Min 250 FPM
- Electrical Connection Screw Terminal
- Electrical Output 4 to 20 mA
- Filter 0.5 to 15 s (Selectable)
- Loop Resistance 600 Ω max
- Media Compatibility Clean dry air / inert gas, HVAC / room air, Inert / non-reactive gases, Helium, Nitrogen, Non-Corrosive Dry Gases
- Mounting Orientation None
- Number of Wires 4
- Operating Temperature, Max 140 °F
- Operating Temperature, Min 32 °F
- Output Detail 4 to 20 mA, isolated 24 V source, 3 or 4-wire connection
- Power Consumption 300 mA
- Probe Length 4 in
- Process Temperature, Max 176 °F
- Process Temperature, Min -40 °F
- Relative Humidity Non-Condensing
- Response Time 1.5 s to 95%
- Response Time Note Flow: 1.5 s to 95% of final value (output filter set to minimum)
- Series ID Model-641B
- Supply Power Note 12 to 35 Vdc, 10 to16 Vac. 1.5 A rating required on supply due to initial power surge drawn by transmitter
- Supply Power Type AC/DC
- Supply Voltage 10 to 16 Vac, 12 to 35 Vdc
- Weight 12.6 oz
Supported Applications
The Dwyer Series 641B is a heated mass flow air velocity transmitter designed for measuring air and compatible, non-combustible gases. The sensor technology is suitable for dirty air flow applications.
Operating Conditions & Performance
The series measures air velocity across user-selectable ranges from 250 FPM to 2000 FPM (1.25 MPS to 10 MPS). Accuracy is specified as 5% FS for process gas temperatures between 32 to 122°F (0 to 50°C) and 6% FS for process gas temperatures from -40 to 32°F & 122 to 176°F (-40 to 0°C & 50 to 80°C). The ambient operating temperature range is 32 to 140°F (0 to 60°C), with a process gas limit of -40 to 176°F (-40 to 80°C) in non-condensing humidity.
Response time for flow is 1.5 seconds to 95% of final value when the output filter is set to minimum. The transmitter provides an isolated 4-20 mA output with a maximum load resistance of 600 Ω max.
Output Filter Response
The series supports adjustable filtering via an adjust dial, affecting response time as follows:
- Min. setting (0.5): 7.5 seconds to reach 63% of full velocity.
- Mid. setting (1.1): 17.3 seconds to reach 90% of full velocity.
- Max. setting (2.3): 44.9 seconds to reach 95% of final value; 69.0 seconds for other metrics at this setting.
Configuration Options
The Series 641B is available in two primary configurations: the standard air velocity transmitter (Model 641B-4) and a version with an LED display (Model 641B-4-LED). The enclosure rating meets NEMA 4X for non-LED models only; the data sheet also notes IP66 compliance. Power is supplied via 12-35 VDC or 10-16 VAC, requiring a supply with a 1.5 A rating to accommodate an initial power surge exceeding 300 mA on startup.
Mounting and Accessories
The transmitter features a 1/2" NPT process connection (conduit). Optional accessories include:
- A-155: Mounting gland with 1/2" male NPT fitting.
- A-156: Flange mounting plate with 1/2" female NPT.
Sensor and Construction Details
The sheath material is stainless steel. The overall dimensions are 9-1/4" [235.0] in length, with a body length of 4-31/32" [126.21] and a diameter (height) of 1-23/32" [43.66]. The unit weighs 12.6 oz (357.2 g). Electrical connections are made via screw terminals.
Key Product Differences
The primary distinction between the enumerated variants is the presence of an LED display on Model 641B-4-LED versus the standard output-only configuration of Model 641B-4. This difference impacts the enclosure rating, which is specified as meeting NEMA 4X for non-LED models only.
Range selection (250 FPM through 2000 FPM or metric equivalents) and filter settings are user-configurable via internal jumpers or dials rather than fixed by model number. The series supports both 3-wire and 4-wire connection configurations for the isolated 4-20 mA output.
PDFs & Manuals
