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Dwyer DAFM User Manual

Dwyer instruments, inc, Series dafm duct air flow measuring probe

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Bulletin AV-2-DAFM

The DAFM Model Duct Air Flow Measuring Probe uses evenly
distributed total and static pressure measuring points to deliver an
accurate measurement of flows in a duct. The Air Flow Measuring Probe
can be completely installed from outside of the duct making it very easy to
install. With its lightweight and durable construction in addition to its ease
of installation, this product lends itself to being used in the HVAC industry.
These air flow measuring probes may be ordered to fit into either round or
rectangular duct installations.

INSTALLATION
When you unpack the Model DAFM Duct Air Flow Measurement Probe
ensure that there is no visible damage from shipping. Inspect each sensing
point on the probes to ensure that they are not filled with debris from
shipping. If there is obvious shipping damage, the probe must be replaced
prior to use in order to avoid inaccurate measurements. Please contact
Dwyer Instruments, Inc. if it is necessary to replace your air flow
measurement probe.

RECTANGULAR DUCT MODELS
Determining Probe Number and Placement for Rectangular Ducts

1. To determine the number of probes you need please consult the chart

below.

2. In order to determine where to place your probes, divide the short duct

dimension by number of probes.

3. Divide the result by two and this will be the distance from the side of

the duct to the first probe location.

4. The next probe will be placed two times the resulting distance from

step two from the first probe. So, if the first probe was placed 4˝ from
the side of the duct, your next probe would be placed 8” from the first
probe, or 12˝ from the side of the duct.

5. Continue this pattern until you have determined all probe locations.

DWYER INSTRUMENTS, INC.

Phone: 219/879-8000

www.dwyer-inst.com

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A.

Fax: 219/872-9057

e-mail: [email protected]

SPECIFICATIONS
Wetted Materials:
Aluminum with clear anodized finish.
Accuracy: ±2% (Note: Field Calibration May Be Required).
Max. Temperature: 400ºF (204ºC).
Minimum Design Flow: 400 fpm (2.03 m/sec).
Maximum Design Flow: 12,000 fpm (60.96 m/sec).
Process Connections: 1/4˝ barb.
Straight Run Requirements: 5 diameters or longest side dimensions.

Specifications - Installation and Operating Instructions

Series DAFM Duct Air Flow Measuring Probe

Example: You have a duct with a 24˝ side, and upon consulting the chart

determined that you needed 3 probes for this size duct.

24 / 3 = 8

8 / 2 = 4

Therefore, the first probe is placed 4˝ from the side of the duct.

The second probe is placed 4˝ + 8˝ = 12˝ from the side of the duct.

The third probe is placed 4˝ + (2 x 8˝) = 20˝ from the side of the duct.

OUTTER RADIUS TO MATCH
INNER RADIUS OF DUCT
1 INCH OUTER PERIMETER

INNER RADIUS TO MATCH
OUTTER RADIUS OF DUCT
4 INCH OUTER PERIMETER

1/4˝ BARB FITTINGS TO
BE CENTERED ON PLATE

1-7/19
[36.51]

L

1-1/16
[52.39]

6

[152.40]

Ø1/4

[6.35]

4X

1/2

[12.39]

1/2

[12.39]

Ø1/4

[6.35]

2X

5

[127.00]

3/8

[9.52]

1/2

[12.70]

1/8

[3.18]

1/8

[3.18]

1

[25.40]

1/8

[3.18]

1/8

[3.18]

2

[50.80]

4

[101.60]

1/2

[12.70]

1/2

[12.70]

Ø1/4

[6.35]

4X

6

[152.40]

1-7/16

[36.51]

L

2-1/16

[52.39]

5

[127.00]

Ø1/4

[6.35]

2X

1/2

[12.70]

3/8

[9.52]

Short Duct Dimension

Number of Probes

<12˝

1

12˝ - 23˝

2

24˝ - 35˝

3

36˝ - 59˝

4

60˝ - 89˝

5

>89˝

6

L = Smallest Duct Diameter

or Length

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