3. Signal Menu
to fast measuring mode. This can be ended with the C I/O key. The device
returns to the normal (battery-saving) measuring mode with the unit chosen
last.
Signal AUTO alternately displays pressure, temperature, and air humidity
values in the pressure and temperature units chosen last.
An overpressure at the socket marked with the + sign and an underpressure
at the socket marked with the – sign causes a positive differential pressure to
be displayed. When the differential pressure exceeds 125 hPa, the device au-
tomatically switches to the higher measuring range up to 2000.0 hPa. When
the value falls below 125 hPa in this measuring range, the display switches
back to a resolution of 1 Pa.
3.2 Flow rate measurements based on Prandtl
The flow rate of air in m/s can be measured with a Prandtl’s tube. This mea-
surement is activated when the ± key is repeatedly pressed in the Measuring
Mode menu until the text “Prandtl” appears with the unit of measurement
“m/s”. The total pressure of the tube is connected to the + overpressure so-
cket and the static pressure to the – underpressure socket on the DC 2000
PRO
(see Figure 3.2).
First of all the device must be “zeroed” in a medium at rest (
P=0
). Then the
probe is inserted into the gas or air flow, as parallel as possible and with the
tip facing the flow, and the measured values are read off. The current flow
rate v is automatically calculated with Equation (1). According to Equation (2)
the air density ρ in Equation (1) depends in turn on the absolute air pressure
p
cur
and the current temperature
T
.
whereby:
v
flow rate in m/s
Dp differential pressure in Pa, measured with the Prandtl’s tube
ρ air density in kg/m3
p
cur
absolute air pressure in hPa, manual entry in the Setup menu item
(default 1013 hPa)
T
air temperature in °C
The absolute air pressure
p
cur
can be set under the menu item Setup > Ab-
solute pressure. This setting is also used to determine leakage rates under
Section 6.
(T(°C) + 273 K) • 1013 hPa
ρ = 1,2 • kg/m
3
•
293 K • p
akt
(hPa)
(2)
2 x ∆p
√
ρ
v =
(1)
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