Type 8703

7 | 10

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6.

Product operation

6.1. Measuring principle

The mass flow sensor operates according to a thermal principle which has the advantage of providing the mass flow which is inde-

pendent on pressure and temperature.

A small part of the total gas stream is diverted into a small, specifically designed bypassing channel which ensures laminar flow

conditions. The sensor element is a chip immersed into the wall of this flow channel. The chip, produced in MEMS technology,

contains a heating resistor and two temperature sensors (thermopiles) which are arranged symmetrically upstream and downstream

of the heater. The differential voltage of the thermopiles is a measure of the mass flow rate passing the flow sensor. The calibration

procedure effectuates a unique assignment of the sensor signal to the total flow rate through the device.

6.2. Flow characteristic

Nominal flow range of typical gases

Note:

• Q(Gas) = f x Q(N

2)

• When using the gas factors, measurement errors may occur that are outside the data sheet specification. For applications

requiring high accuracy, calibration under field conditions is recommended.

• Furthermore, the media compatibility of the sealing materials of the MFM should be checked before use with another gas.

Gas

Min. Q

Nom

Max. Q

Nom

[l

N/min]

[l

N/min]

Argon

0.01

80

Helium

0.01

500

Carbon dioxide

0.02

40

Air

0.01

80

Methane

0.01

80

Oxygen

0.01

80

Nitrogen

0.01

80

Hydrogen

0.01

500