www.sensirion.com Version 2 – February 2013 5/7
3.3 Connecting Hose
Sensirion recommends a hose with an inner diameter
of 3.18 to 3.8mm (1/8 to 3/20 inch). Due to the dynamic
measurement principle, a small air flow is required
(Figure 3) which leads to a dependence on the length
of the hose (Table 4). Tubes up to 1 m show less than
2 % error of the measured value (Table 4).
Figure 3: Typical air flow through the SDP1108. Please note:
1 scc/min = 1 cm3/min at 0°C and 1013 mbar pressure
(1 sccm = 0.001 norm liter).
Table 4: Influence of the length of the connecting hose
the accuracy (using 4 mm inner diameter).
given in % of the measured value. Example SDP1108
500 Pa difference pressure is shown as 492.5 Pa when
using 1 m tube with 4 mm inner diameter.
Table 5: Maximum flow through the sensor element.
Mass flow through sensor element:
SDP1108-R SDP2108-R
123 sccm (@ 500 Pa) 66 sccm (@3500 Pa)
4 Electrical Specifications
4.1 Power Supply
The SDPx108 differential pressure sensors require a
stable voltage supply of 5.0 V. The requirements for the
electrical supply are specified in Table 5.
4.2 Voltage Output
The SDP1108 features a voltage output from 0.25 V to
4.0 V. An output voltage below 0.25 V indicates a
negative differential pressure (not calibrated).
The resistive load at the output pin should be larger
than 20 kOhm. The capacitive load at the output pin
must not be larger than 200 pF. If the design shows a
larger capacity at the output pin an additional resistor is
required in series at the output (e.g. 620 Ohm).
Table 6: SDPx108 electrical characteristics.
Parameter Conditions Min. Typ. Max. Units
Power Supply Voltage V
DD
4.75 5.0 5.25 VDC
Operating Current 5 V, no load, zero flow 5.1 6 mA
Output capacitive load C
load
20 200 pF
Recommended load R
load
20 100
∞
kΩ
Hose length SDP1108 SDP2108
@FS @0.5 FS @FS @0.5FS
0.5 m (20 inch) -0.75% -0.95% -0.06% -0.07%
1.0 m (40 inch) -1.5% -1.9% -0.12% -0.14%
2.0 m (80 inch) -3.0% -3.8% -0.24% -0.28%
