A hot wire anemometer is a temperature transducer used for measuring flow rate.
When the electrically heated temperature sensor is placed in a flowing fluid, heat is transferred from the sensor to the fluid. Hence the temperature of the sensor reduces resulting in a change in resistance of the wire. The amount of cooling of the wire depends on the flow velocity and hence the resistance variation can be used to measure the flow rate of the fluid.
Hot wire anemometer are connected in two methods for measuring flow rate.
- Constant current method
- Constant temperature method.
In the constant current method, the current of the wire is kept fixed and is exposed to flow velocity. Then the change in temperature of the wire becomes a measure of flow velocity.
In constant temperature method we maintain the temperature and resistance of the wire at a constant level. So the current through the wire is increased and it is a measure of flow velocity.
- Can be used for fluids with rapidly fluctuating velocity.
- Relatively low cost.