Flow measurement is an important process with diverse applications like measuring the flow rate of blood in human beings to measuring and controlling the flow rate in an oil well useful for extraction of oil. It forms an important part of several industries like chemical, wastewater treatment, pulp and paper, oil and gas, and several others. The scope of flow measurement extends far beyond that covered in the following sections. This exhaustive system spans several processes, techniques, and technologies. We have attempted to touch the tip of the iceberg that is flow measurement.

The accuracy of flow measurement determines the functioning of the system. A well-functioning system will provide highly accurate results. Several new technologies are being developed in this realm to support flow measurement systems. These systems as well as direct and indirect processes can help organizations achieve brilliant results.

As the name suggests, flow measurement is the process of measuring the flow rate and volume of a liquid or gas. This process can be employed to measure the liquid passing through an application (as seen in water purification systems), or stored in an application (as seen in fuel injectors). Flow measurement is a vital function used to monitor and control the rate of liquid flow in applications. This process is used to measure the flow of versatile substances like heavy oils, abrasive chemicals, and light gases. Hence, this process is utilized in applications across various industries.

Flow measurement is employed in critical applications where the flow rate or level of liquid stored needs to be administered regularly. The safe functioning of applications depends on flow meters. In terms of flow measurement, accuracy is of such importance that it can be the determining factor of a company making a profit or loss.

In some applications, the flow needs to be regulated within a specific range. This is achieved by using flow meters. A flow meter is a device used to facilitate flow measurement. Flow meters are broadly classified as:

1) Differential Pressure
2) Positive Displacement
3) Velocity
4) Mass
5) Open Channel

Flow meters can be used to measure the flow rate of liquids or gases. The unit is decided depending on the function and parameters of flow measurement. The unit used varies according to the system of measurement being followed, as well as the material being measured. Dissimilar media need to be measured under diverse conditions and using different units. Units Used to Measure Flow

The following units are used to measure liquid and gas flow:

1) Liquids are measured based on density: liters per second or gallons per minute
2) Steam is measured based on weight: Tonnes/ hour and kilograms/ minute
3) Gases are measured based on energy content: Joules/ hour and British Thermal Unit/ day

Gases are also measured according to STP (Standard Temperature and Pressure) and NTP (Normal Temperature and Pressure) in units like m3/hour and acm/ hour (actual cubic meters per hour). Depending on whether the gas is measured at NTP or STP, the units will include the details. Two examples of the symbol at STP and NTP, respectively are: Std m3/hour and Nm3/hour

The unit of measurement changes in accordance with the medium of material being measured. For example, the units of measurement of liquids, gases, and steam could vary. This is because the change in their density is dependent on different factors. The density of gases is dependent on pressure and temperature. On the other hand, the volume of liquid is independent of pressure. Hence, the units used to measure the different media change accordingly.