ASF1400 datasheet(4/9 Pages) ETC2

4 / 9 page

ASF1400 Bidirectional Mass Flow Meter

1.1 Gas Flow Characteristics

Figure 2 shows the applied gas flow vs. the digital

output of the ASF1400.

1.3 Gas Flow and Pressure Difference

-500

-250

250

500

-500

-250

250

500

Mass Flow [sccm]

The ASF1400 is calibrated for mass flow

measurements. However, there is a well defined

relation between mass flow and pressure drop. This

relation is shown in Figure 4. On request the

ASF1400 can also be calibrated for the pressure drop

at its output (for more details refer to the

documentation of the Sensirion Differential Pressure

Sensor ASP1400).

- 400

- 200

200

400

Massflow [sccm]

- 150

- 100

-50

100

150

Figure 2: ASF1400 transfer characteristics.

1.2 Sensor Principle and Gas Types

The ASF1400 device detects mass gas flow by

measuring heat transfer. A heating resistor on a

thermally insulated membrane is kept above ambient

temperature. In the presence of gas flow, the

temperature distribution up- and downstream is

disturbed. This asymmetry is then measured. Due to

the minimal thermal mass of the membrane,

symmetrical arrangement, and accurate temperature

measurement, the revolutionary specifications of the

ASF1400 devices are achieved.

Figure 4: Differential Pressure vs. Mass Flow of

ASF1400 Device.

1.4 Adjusting the Measurement Range

To adjust the measurement range, the ASF1400

device is used in conjunction with a bypass

configuration (see Figure 5). Only a sample of the

total flow actually gets directed through the bypass

channel and the sensor system. A tube with flow

restrictor and all required connection items are

included in the Mass Flow Meter Evaluation Kit EK-

F1, also available from SENSIRION AG.

The above mentioned thermal principle requires

information about the gas type to be measured. The

ASF1400 is available for air and nitrogen. Other gas

types are available on request.

In Figure 3 the repeatability of the ASF1400 devices

is compared with the repeatability of a typical Mass

Flow Controller (MFC). It emphasizes the superior

performance of the ASF1400 device.

Flow restrictor

100

200

300

400

Massflow [sccm]

0.1

0.2

0.3

0.4

0.5

200

Specs of typical MFC

Repeatability ASF 1400

Figure 5: Extending the measurement range of the

ASF1400 device using a bypass configuration. Only a

sample of the total flow actually gets directed through

the bypass channel and the sensor. Shown tube with

flow restrictor is included in the EK-F1 evaluation kit.

Figure 3: Comparison of the repeatability of the

CMOSens® ASF1400 device compared to a typical

Mass Flow Controller (MFC).

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