Sensor - The Electronic Nose Artificial Olfaction Technology - page 44

Flow Q is the volume flowing through a mathematically precise determined cross
section over a certain time unit.
Q ¼ Volume = Time ¼ V = t
A flow sensor is a device that measures the flow volume of water, pure water,
compressed air, gas, drugs, steam, and similar liquids or gases. Flow sensors are of
various types that each operates with different detection principles [ 6 ].
Flow sensors are used in many examining and control applications, to measure
both air and liquid flows [ 7 ]. There are many ways of defining flow (mass flow,
volume flow, laminar flow, turbulent flow). Usually the amount of a substance
flowing (mass flow) is the most important, and if the fluid's density is constant, a
volume flow measurement is a useful substitute that is generally easier to perform
[ 9 ]. Various types of flow sensors are shown in Fig. 2.9 and also summarized in
Table 2.6 .
Flow measurements include measuring of flow rate of solids, liquids, and gases.
There are two basic ways of measuring flow; one on volumetric basis and the other
on weight basis. Concrete materials are measured in terms of either weight per unit
time or mass per unit time. Very rarely hard quantity is measured in terms of
volume. Liquids are measured either in volume rate or in weight rate. Gases are
normally measured in volume rate.
For measurement of flow various methods are used, i.e., thermal anemometers,
differential pressure measurement systems, and vortex shedding sensors. Methods
used for measuring liquid flow are: differential pressure measurement systems,
vortex shedding sensors, positive displacement flow sensors, turbine-based flow
sensors, magnetic flow sensors, and ultrasonic flow sensors [ 9 ].
Flow Sensor:
• Electrical
- Electro magnetic sensors
• Mechanical
- Turbine meters
- Rotameters
- Karman vortex meters
- Coriolis meters
• Others
- Ultrasonic meters
- Thermal meters.
Units
The units used to describe the flow measured can be of several types depending
on how the specific process needs the information.