First of all, what is a flow meter? A flow meter is a device that is used to continuously measure how much air or liquid is present in a given area at a given time, in order to calculate the value of flow volume in a pipe or any channel. It is used in various industries such as engineering, water supply maintenance, and medicine (such as in peak flow meters which measure how much air a person exhales; used specially by those suffering from asthma).
There are so many different types of flow meters available-mechanical flow meters, optical flow meters, turbine flow meters, open channel flow measurement, thermal mass flow meters, vortex flow meters, and ultrasonic, electromagnetic and coriolis flow meters.
The kinds of flow meter used will determine the rate of accuracy, the equipment involved, the procedure, and the cost of purchase.
Generally, the calculations done by a flow meter follow a specific formula: the volume flow rate, multiplied by the energy content per unit volume. However, how a flow meter is able to come up with the necessary values depends largely on what type of flow meter is being used. If you're looking to purchase a flow meter or looking into flow meter rental, it's good to know which particular type would be most suited to your needs. Different features are available as well, such as flow meters with a flow switch and digital reading capabilities.
Here's a look at five types of flow meter and how they work:
- Mechanical flow meters. Mechanical flow meters are the simplest forms of flow meters, but this classification is broad so that there are varied and different processes involved in this category. Mechanical flow meters include piston meter, venturi meter, paddle wheel and the bucket-and-stopwatch meter. In general, mechanical flow meters work with controlled mechanisms that operate at known speeds, a measuring device (such as a pressure sensor) and a channel of known volume capacity. More recent mechanical flow meters developed have a digital meter and flow indicator to provide easier measurement.
- Optical flow meter. The main tool used in optical flow meters is light. How does it work? In the most basic terms, two illuminating optic beams are focused on different locations in a pipeline. Systems would be able to calculate the time that passes between one particle passing through one optic beam, and that same particle passing through the second optic beam. The velocity is then calculated using this formula: distance between the laser beams divided by the time interval.
- Thermal mass flow meters. These flow meters measure the heat transfer in a liquid and then calculate the energy flow, taking into consideration the fluid's density, specific heat and base temperature. Temperature sensors and heated elements are used for this process.
- Vortex flow meters. A liquid or gas flowing through a pipe, when obstructed by a bluff body, forms an eddy or a vortex; the frequency of these disturbances are measured by sensors, along with the velocity of flow over that obstruction. These values are then calculated (along with the length of the bluff body and a constant) to produce the flow rate.
- Ultrasonic sensor flow meter. The ultrasonic sensor is installed at the floor of a channel or pipe; it sends out pulses or ultrasonic beams through the water and then back again. The beams travel through the water at a consistent rate, and then how speedily it comes back up to the sensor (taking into consideration the speed of sound in water) will be the measurement of how deep the water level is. An installation of a down-looking sensor can be done in the case of turbulent waters.
There you have it! These are just some of the ways that a flow meter will work. Hopefully this information will help you understand the basic workings of this very simple but highly useful technology.