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.

NIST CALIBRATION available in Product Configurator.

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

Shipping Information

All shipping times are dependent on product availability at time of shipment.

Although we make every effort to ensure a continuous supply of our products, occasional circumstances may force us to temporarily run out of a product, or have shipping delays. Should this occur, customers will be notified soon after placement of any orders for such products and, if applicable, items will be put on backorder. For orders requiring expedited shipment, our customer service team can be contacted to confirm product availability

COVID-19 Update: Due to high customer demand, lead time on some products may be up to two weeks. While this is a developing health situation, we are working continuously to take the necessary measures to ensure that the products you need are available with minimal interruption.

Build Your Custom Part. Use our Product Configurator

Model	Description	Usually Ships*	Price	Order
641-12 Ships: Same Day Price: $502.00	Air velocity transmitter, 12" (304.8 mm) probe length.	Same Day*	$502.00	Order
641-12-LED Ships: Same Day Price: $639.00	Air velocity transmitter, 12" (304.8 mm) probe length, with LED display.	Same Day*	$639.00	Order
641-18 Ships: Same Day Price: $502.00	Air velocity transmitter, 18" (457.2 mm) probe length.	Same Day*	$502.00	Order
641-18-LED Ships: Same Day Price: $639.00	Air velocity transmitter, 18" (457.2 mm) probe length, with LED display.	Same Day*	$639.00	Order
641-24 Ships: 1-2 Weeks Price: $502.00	Air velocity transmitter, 24" (609.6 mm) probe length.	1-2 Weeks*	$502.00	Order
641-24-LED Ships: 1-2 Weeks Price: $639.00	Air velocity transmitter, 24" (609.6 mm) probe length, with LED display.	1-2 Weeks*	$639.00	Order
641-30 Ships: 1-2 Weeks Price: $502.00	Air velocity transmitter, 30" (762 mm) probe length.	1-2 Weeks*	$502.00	Order
641-30-LED Ships: 1-2 Weeks Price: $639.00	Air velocity transmitter, 30" (762 mm) probe length, with LED display.	1-2 Weeks*	$639.00	Order
641-36 Ships: 1-2 Weeks Price: $502.00	Air velocity transmitter, 36" (914 mm) probe length.	1-2 Weeks*	$502.00	Order
641-36-LED Ships: 1-2 Weeks Price: $639.00	Air velocity transmitter, 36" (914 mm) probe length, with LED display.	1-2 Weeks*	$639.00	Order
641-6 Ships: Same Day Price: $502.00	Air velocity transmitter, 6" (152.4 mm) probe length.	Same Day*	$502.00	Order
641-6-LED Ships: Same Day Price: $639.00	Air velocity transmitter, 6" (152.4 mm) probe length, with LED display.	Same Day*	$639.00	Order

Can't find what you need? Build Your Custom Part. Use our Product Configurator

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
A-156	Flange mounting plate with 1/2" female NPT.	Same Day	$17.25	Order
A-158	Split flange.	Same Day	$14.75	Order
A-159	Mounting gland with 1/2" male NPT.	Same Day	$29.75	Order
641-LED	Field-upgradeable LED.	Same Day	$137.00	Order

Videos

Thermo-Anemometers

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

Instruction Manual

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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