Model 641B Air Velocity Transmitter

Dirty Air Flow Applications

The Model 641B Air Velocity Transmitter uses a heated mass flow sensor suitable for dirty air flow applications. It has user-selectable ranges from 250 FPM (1.25 MPS) to 2000 FPM (10 MPS).

Product Applications

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

Models & Ordering

Model Description Usually Ships Price Order
641B-4
Ships: Same Day
Price: $450.00
Air velocity transmitter. Same Day $450.00 Order
641B-4-LED
Ships: 1-2 Weeks
Price: $580.00
Air velocity transmitter with LED display. 1-2 Weeks $580.00 Order

Specifications

Service:
Air and compatible, non-combustible gases.
Accuracy:
5% FS process gas: 32 to 122°F (0 to 50°C); 6% FS process gas: -40 to 32°F & 122 to 212°F (-40 to 0°C & 50 to 100°C).
Response Time:
Flow: 1.5 s to 95% of final value (output filter set to min).
Temperature Limits:
Process: -40 to 176°F (-40 to 80°C). Ambient: 32 to 140°F (0 to 60°C).
Humidity Limit:
Non-condensing.
Power Requirements:
12 to 35 VDC, 10 to 16 VAC. 1.5 A rating required on supply due to initial power surge drawn by transmitter.
Output Signal:
4 to 20 mA, isolated 24 V source, 3 or 4-wire connection.
Output Filter:
Selectable 0.5-15 s.
Loop Resistance:
600 Ω max.
Current Consumption:
300 mA max*.
Electrical Connections:
Screw terminal.
Enclosure Rating:
Designed to meet NEMA 4X (IP66).
Mounting Orientation:
Unit not position sensitive.
Weight:
12.6 oz (357.2 g).

*A brief current transient exceeding 300 mA may be seen on startup.

Features

  • 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

Accessories

Model Number Description Usually Ships Price Order
Cable gland with 1/2 A-155 Cable gland with 1/2" male NPT fitting. Same Day $16.00 Order
Flange mounting plate with 1/2 A-156 Flange mounting plate with 1/2" female NPT. Same Day $16.25 Order

Videos

Product Literature

Manuals

Catalog Pages

Approvals

Drawings

Questions

Question
We have recently replaced a Dwyer air velocity transmitter (PFS1300204) with a Dwyer Series 641. The new sensor works fine for only a few days and then starts reading almost no flow. These devices are used in an Air Scrubber application (exhaust stack). Is this the right application for the Series 641? I suspect that moisture might be the issue, but I cannot confirm.
Answer
I do not think you are using the 641 series air velocity transmitter in an appropriate application. Any moisture or particulates in the exhaust could be causing damage to the hot wire sensor, leading to the failure. The difference in the sensors is probably why you got longer life out of the PFS series, which unfortunately, is no longer available. The PFS series used a glass filled polyester sensor, which is a little more robust and can with stand the elements a little better. In your specific application, you might take a look at our 641B series which uses a heated mass flow sensor which can be used in dirty air environments.

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