Bronkhorst EX-FLOW Mass Flow Manual de usuario descargar pdf (Pagina 7)

BRONKHORST HIGH-TECH B.V.

1 INTRINSIC SAFE SENSORS

1.1 General description

The Bronkhorst High-Tech B.V. series mass flow meter is an accurate

device for measuring gas flows up to 700bar, virtually independent

of pressure and temperature changes.

The system can be completed with a control valve and flexible readout

to measure and control gasflows from

0 5 ml / min

−

up to

1000 m / h

Model F-112AX

1.2 Principle of operation of flow sensor

The Bronkhorst High-Tech B.V. series flow sensor is operating on a principle of heat transfer by sensing the

∆T along a heated section of a capillary tube.

The ∆T is directly proportional to the gas mass flow. The heat transfer function between gas mass flow and

temperature difference can be described by the equation:

∆ ΦT K c

p m

= ⋅ ⋅

∆T = temperature difference

= specific heat

K = constant factor

= massflow

The temperature sensors are part of a bridge circuit and the unbalance is amplified to the right signal level.

1.3 Sensor and laminar flowdevice of flow sensor

The Bronkhorst High-Tech B.V. flow sensors have a small bore capillary.

Small bore sensors have a pressure drop at atmospheric conditions of approximately 35 mbar.

These sensors have a laminar flow device consisting of a number of discs with precision etched flow

channels.

Each flow channel represents approx.

10 ml / min

airflow at 35 mbar.

9.17.028 page 7

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Bronkhorst EX-FLOW Mass Flow Manual de usuario Pagina 7