Airflow Instruments ProHood PH731 - Backpressure Compensated Flow Measurement

56 ProHood Capture Hoods PH730/PH731
Running Average Measurements
In this mode, the instrument will measure continuously while displaying a running average of flow.
Pressing either the READ key on the meter or the red switch on the base will hold the current reading. To
restart the running average measurement, press the READ key or the red switch. The SAVE key can be
used at any time to log to memory.
To measure in this mode:
1. Select Capture Hood or Hood BP Comp in the Pressure Tool menu.
2. Set the Data Logging mode to Manual/Single.
3. Set the Time Constant to 5 seconds.
Capture Hood Measurements (non-backpressure compensated)
Non-OPEN
position. If the flap iOPEN THE FLAP
Backpressure Compensated Measurements
In the backpressure compensated, a correction is applied to account for the change in flow due to the
presence of the Capture Hood. In most cases, backpressure compensated measurements will provide
the most satisfactory flow measurement results, especially when the flow is greater than 500 ft
3
/min
(850 m
3
/hr, 235 l/s).
Make sure that Capture Hood Back with Pressure Compensation is selected from the Pressure Tools
menu.
Backpressure compensated measurement require two sequential measurements: first with the back
OPENCLOSED
Follow the sequence of operation as described below:
1. Place the Capture Hood over the diffuser, grill or other opening through which you wish to make a
measurement.
2. Open the backpressure flap. This is done by pressing up on the flap handle with your left hand as you
hold the hood in place. Press until the flap clicks into full open position.
3. OPEN as the meter takes the reading. (In very
low flows, this step and step 5 may take up to eight (8) seconds each. Higher flows will require
less time.)
4. CLOSE FLAP then close the flap by pulling down on the flap handle until it
clicks into the fully closed position.
5. CLOSED
reading.
6. The backpressure compensated measurement value will appear and remain on the display until
another reading is initiated, or other meter function is initiated. To log reading to memory,
press SAVE.