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v5 February 2013

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3.3 Connecting Hose

Sensirion recommends a hose with an inner diameter

of 1/8 to 3/20 inch (3.18 to 3.8mm). Due to the

dynamic measurement principle, a small air flow is

required (Figure 6) which

leads to a dependence on the length of the hose

(Figure 7). Tubes up to 1 m show less than 1 % error

of the measured value (Figure 7).

Figure 6: Typical air flow through the SDP1000 / SDP2000.

1013 mbar pressure (1 sccm = 0.001 norm liter).

Figure 7: Influence of the length of the connecting hose on

the accuracy (using 3/16 inch inner diameter).

Example: a 50 Pa difference pressure is shown as

49.8 Pa when using 0.5 m tube with 3/16 inch

diameter.

4

Application Example: A High End Differential Pressure Sensor

Example:

Range: 0…500 Pa, linear characteristics

Component

Value

LM78L12

LP2980

SDP

SDP1000

LMC6044

200 nF

2.2 uF

10 k

Ω (5%, 10 ppm)

18 k

Ω (5%, 10 ppm)

1 k

Ω (5%, 10 ppm)

100

Ω

6 k

Ω (3x18 kΩ 5%, 10 ppm in

parallel)

10 k

Ω (5%, 10 ppm)

Figure 8: Schematic of a high-end differential pressure transmitter using the SDP1000 / SDP2000. With only a few external

components and no additional calibration the transmitter features an accurate and temperature compensated 0…10 Vdc

output signal. (Component values not valid for SDP1000-L025.)

0

20

40

60

80

100

120

0

20

40

60

80

100

differential pressure [% full scale]

5V

+

-

+

-

+

-

5V

12V

SDP1000 / SDP2000

1

2

3

Length of the

connecting hose

Deviation of

Measured Value

0.5 m (20 inch)

- 0.4 %

1.0 m (40 inch)

- 0.8 %

2.0 m (80 inch)

- 1.6 %

4.0 m (160 inch)

- 3.2 %

1

2

3

12V

12V

12V