Series 641 Air Velocity Transmitter

High Accuracy, Field Selectable Ranges

The SERIES 641 Air Velocity Transmitter is the ideal instrument for monitoring air flow. This transmitter uses a heated mass flow sensor which allows for precise velocity measurements at various flow rates and temperatures. The 641’s 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.

Product Applications

  • Exhaust stack flow monitoring
  • Air control in drying processes
  • HVAC air velocity measurements
  • Fan supply and exhaust tracking
  • Clean room fresh air supply
  • Ensure proper lab hood exhaust flow rates

Models & Ordering

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Model Description Usually Ships Price Order
641-12
Ships: Same Day
Price: $450.00
Air velocity transmitter, 12" (304.8 mm) probe length. Same Day $450.00 Order
641-12-LED
Ships: Same Day
Price: $580.00
Air velocity transmitter, 12" (304.8 mm) probe length, with LED display. Same Day $580.00 Order
641-18
Ships: Same Day
Price: $450.00
Air velocity transmitter, 18" (457.2 mm) probe length. Same Day $450.00 Order
641-18-LED
Ships: Same Day
Price: $580.00
Air velocity transmitter, 18" (457.2 mm) probe length, with LED display. Same Day $580.00 Order
641-24
Ships: 1-2 Weeks
Price: $450.00
Air velocity transmitter, 24" (609.6 mm) probe length. 1-2 Weeks $450.00 Order
641-24-LED
Ships: 1-2 Weeks
Price: $580.00
Air velocity transmitter, 24" (609.6 mm) probe length, with LED display. 1-2 Weeks $580.00 Order
641-30
Ships: 1-2 Weeks
Price: $450.00
Air velocity transmitter, 30" (762 mm) probe length. 1-2 Weeks $450.00 Order
641-30-LED
Ships: 1-2 Weeks
Price: $580.00
Air velocity transmitter, 30" (762 mm) probe length, with LED display. 1-2 Weeks $580.00 Order
641-36
Ships: 1-2 Weeks
Price: $450.00
Air velocity transmitter, 36" (914 mm) probe length. 1-2 Weeks $450.00 Order
641-36-LED
Ships: 1-2 Weeks
Price: $580.00
Air velocity transmitter, 36" (914 mm) probe length, with LED display. 1-2 Weeks $580.00 Order
641-6
Ships: Same Day
Price: $450.00
Air velocity transmitter, 6" (152.4 mm) probe length. Same Day $450.00 Order
641-6-LED
Ships: Same Day
Price: $580.00
Air velocity transmitter, 6" (152.4 mm) probe length, with LED display. Same Day $580.00 Order

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Specifications

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 s to 95% of final value (output filter set to min.).
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 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.
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).
Agency Approvals:
CE.

OPTIONAL DISPLAY VERSION:
Display:
4-1/2 digit 1/2" red LED.
Resolution:
1 FPM, 0.01 MPS (10 FPM @ 10,000 and 15,000 FPM ranges).
Weight:
13.3 oz (377 g).

Features

  • Ranges from 250 FPM (1.25 MPS) to 15,000 FPM (75 MPS)
  • Optional bright LED display
  • Easy push button set-up
  • Compact housing
  • 4 to 20 mA output
  • Digital filter for signal damping

Accessories

Model Number Description Usually Ships Price Order
Flange mounting plate with 1/2 A-156 Flange mounting plate with 1/2" female NPT. Same Day $16.25 Order
Split flange. A-158 Split flange. Same Day $13.75 Order
Mounting gland with 1/2 A-159 Mounting gland with 1/2" male NPT. Same Day $28.00 Order
641-LED Field-upgradeable LED. Same Day $130.00 Order

Videos

Model Chart

EXAMPLE
641
6
LED
Series 641 Air Velocity Transmitter, 6" probe, with LED display.
SERIES
641
 
 
Air Velocity Transmitter
PROBE LENGTH
 
6
12
18
24
30
36
 
6"
12"
18"
24"
30"
36"
OPTIONS     AT
LED
NIST
ST
Aluminum Tag
LED Display
NIST Certificate of Calibration
Stainless Steel Tag

Product Literature

Manuals

Catalog Pages

Product Data Sheet

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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