1) DETERMINE the OPEN AREA as follows: On RETURNS, the OPEN AREA is the 100% of the full measured area of the grille, as the air is flowing first through the 417 measuring vanes, then into the return duct. On SUPPLIES, the OPEN AREA is the fraction or percentage of the grille that the air passes through, before moving through the 417 measuring vanes. See grille manufacturers product info for open area data **. Then Multiply the Duct dimensions (Height and width) in inches by multiply of the OPEN AREA factor.
FOR EXAMPLE: We have a supply grille that is 6x10 inches with 65% open area. The open area is 6 x 10 x 0.65 = 39 sq inches open area
2) ENTER the OPEN AREA into the 417.Turn ON the 417, after a few seconds the display comes up. PRESS AND HOLD the RETURN ARROW (Hold/Max/Min Key) until a number appears on the display and the in2 label is blinking. Use the UP or DOWN arrows (VOL and MEAN keys) to adjust the number in the display your open area. IN THE EXAMPLE ABOVE adjust it to 39.0
3) EXIT to measuring mode by pressing the RETURN ARROW (Hold/Max/Min Key) 5 times
4) MEASURE: Place the 4" vane into the air stream in front of the grille position it at one corner of the grille, parallel to the grille surface. A) Press the MEAN key TWICE to enter the timed average mode. B) Press the RETURNkey (Hold/Max/Min Key) when you want to start collecting data. C) Keep the 417's measuring head about 1" away from the face of the grille. Move the 417 head across the grille at a rate of about 1 foot (12") over 4 seconds. (note the timer on the 417's screen) D) Be sure to "paint" the entire grille face with head of the 417 to account for total flow through the grille.DO NOT paint any area more than once! E) When you are done covering the entire grille area, press the RETURN key (Hold/Max/Min Key) again to pause the reading on the display.
OPTIONAL: You can measure again (re-paint the entire area) to improve the reading. Just start at step 4B.
5) DISPLAY the average values by pressing the MEAN key. The Timed MEAN icon will flash and the average Feet Per Minute (FPM) will be displayed. Tap the VOL key once to see the Average CFM for this test. Tap the VOL key again to see the Average Temperature for this test. Tapping the VOL key continues rotating thru these three results.
NOTE: BE SURE to record the data, as there is NO memory storage in the 417. Once you tap the MEAN key again, the data is gone.
6) CLEAR the data and prepare for another measurement by tapping the MEAN key
** One manufacturer's data books give open area factors of from 71% to 75% for one type of floor diffuser (depending on size), 66% to 75% for another model and 65% to 75% for another model. While a heavy duty, dual shutter floor grille from the same manufacturer has a range of 48% to 52% open area factor. Generally speaking, the larger the grille dimension, the small the open area factor.