Bronkhorst EX-FLOW Mass Flow - Manual (Page 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
n
− up to
1000 m / h 3
n
.
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:
∆ Φ T K c
p m
= ⋅ ⋅
∆T = temperature difference
c
p
= specific heat
K = constant factor
Φ
m
= 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
n
airflow at 35 mbar.
9.17.028 page 7