Flow gauge, flow indicator, liquid meter, flow meter – they’re all the same thing; depending on the industry they may have different names, but their function remains the same: to measure flow.

In the simplest of terms, a flow meter is a device which is used to measure the quantity and/or flow rate of a gas or liquid as it moves through a pipe. Some flow meters measure the amount of fluid that passes through the pipe in a given time, while others measure the total amount of fluid or gas that has passed through the flow meter. Sign up for FlowSight, the Litre Meter newsletter.

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**How do flow meters work?**

Flow meters consist of three parts: a primary device, a transducer, and a transmitter. As the fluid passes through the primary device, the transducer senses it; the raw signal from the transducer is then sent to the transmitter and turned into a usable flow signal.

Mathematically speaking, a flow meter typically uses the following equations:

**Q = A · v**– Where the volume of fluid passing through a flow meter is equal to the cross-sectional area of the pipe (A) multiplied by the average velocity of the fluid (v).**W = r · Q –**Where the mass flow of fluid passing through a flow meter (A) is equal to the fluid density (r) multiplied by the volume of the fluid (Q).

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**Different types of flow meter**

There are a number of different types of flow meter available, each one suited to a different purpose, but always with the same goal of measuring the flow of a fluid or gas through a pipe.

**Positive****displacement flow meters:**As the only meters to measure the actual volume, positive displacement meters work by repeatedly filling and discharging fluids from a chamber. Also known as volumetric flow meters, or rotary piston meters due to the way in which they operate.**Inferential flow meters:**These types of meters don’t measure volume, mass, or velocity. Instead they measure the flow of a fluid by inferring its value from other measured parameters such as differential pressure.**Velocity flow meters:**The flow of fluid through the pipe is measured by the velocity of the flowing stream in order to determine the volume of the flow.**Mass flow meters:**A mass flow meter, also known as an inertial flow meter, measures the flow rate of the mass of fluid as it travels past a fixed point during a specified unit of time.

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**What type of flow meter do I need?**

There is no one-size-fits-all solution when it comes to flow meters. It largely depends on the industry you’re in, and what the flow meter will be used for. Here at Litre Meter we’re the flow meter experts, so we can help you to choose which type will work best for your needs, but here are a few questions to ask yourself before looking into purchasing a flow meter for your company:

- What gas or liquid do I want to measure?
- What level of accuracy do I require?
- What is the temperature and viscosity of the fluid?
- Does the fluid flow continuously or intermittently?
- Will the meter be mounted in a safe or hazardous location?
- What are the minimum and maximum flow rates?
- What is the maximum pressure at the location?
- What level of pressure drop is allowable?
- Is the fluid compatible with the materials used in the flow meter?

Each type of flow meter has a different set of applications and constraints, so the best way to choose the right one is to use the application of the equipment, rather than the technology, to guide you in your choice. Once you know the answers to some or all of these questions speak to us and we can help you to determine which flow meter will best suit your needs.