Retrotec DM32 - Manual (Page 75)

Page 75 of 94
©Retrotec Inc. 2014
2. Some newer versions of the Model 3 and 4 contain an additional Reference port. If available,
connect the green tube in the Umbilical cable from the green port on the gauge to the
Reference port on the fan.
3. The power and Control Cables included in a Retrotec Umbilical cannot be used when using a
3rd party fan. Make sure the batteries are fully charged, prior to beginning testing.
To conduct a basic pressure test and ensure your gauge is working
1. Turn the gauge on by pressing [On/Off].
2. Check the battery power before beginning a test to ensure the gauge has enough power to
complete the test. (Plug the gauge in, or recharge batteries if needed).
3. Select the appropriate device to which the gauge is connected by tapping
[Range/Device][ChangeDevice].
4. Select the Range Configuration installed in the fan by tapping on its picture.
5. Tap [Channel B] to select the required results to display. Note that the result displayed can be
changed at any point during the test.
6. Select an appropriate time averaging value for the test conditions by tapping [Settings][Time
Average] and choosing a value.
7. Tap [Settings][Baseline][Begin Capture] to begin acquiring a baseline pressure reading.
Tap [End Capture] after 60 seconds to set the baseline reading.
8. Either press [Set Speed] to set the fan speed to a particular percentage, OR press [Set
Pressure] to control the fan to a particular building pressure.
9. To view estimated flow at the exact target pressure, use the [@ Pressure] function.
10. Tap [Channel A] to “Hold” the results on the display to make them easier to copy down.
The gauge calculates Flow based on Pressure readings from the fan
The air flow being produced by the calibrated fan is a value that can be calculated based on the pressure
developed by the air moving across the inlet side of the fan towards the exhaust. Because the fan is
calibrated, there are known values describing the mathematical relationship between the fan pressure,
which is measured across the fan inlet, and the resulting air flow through the fan.
The Fan Pressure needed to calculate the fan flow is the difference between the pressure at the pickup and
the pressure in the vicinity of the inlet side of the fan. The fan pressure pickup is located inside the fan
near the inlet side of the fan. Self-referencing fans have the reference port built in, and it is placed to
measure the ambient pressure in the vicinity of the inlet side of the fan. Fan Pressure, FP, is determined
by setting the gauge to display pressure on [Channel B] and reading the resulting pressure on the gauge
when the room is at the test pressure.
Each fan and range combination has a different flow equation. For each fan and range combination
available, the variables needed to calculate flow are listed in Table 8.
The form of the flow equation depends on where the pickup for the Fan Pressure connected to the yellow
“ref B” port on the gauge is located with respect to the green “input B” port of the gauge.
Case 1: Flow Away from Operator