What Is a Water Meter?
A water meter is an instrument used to measure the flow rate of a liquid, a body, or any other mass or volume.
Also called a flowmeter, when selecting an instrument, the purpose of use should be clearly defined, and the accuracy, measurement range, and required sensors should be selected. High accuracy is not necessary for monitoring or controlling water volume but is required for controlling the amount of application or spraying.
There are two types of measurement methods: volume flow rate, which measures the change in volume per hour, and mass flow rate, which measures the change in mass per hour. Water volume control is important from the viewpoint of quality control, early detection of equipment malfunctions, protection of equipment, and cost reduction through understanding of water volume.
Uses of Water Meters
Water meter is used at plants and manufacturing sites to control the amount of water in piping facilities such as water supply and drainage pipes, etc. When installed outdoors, select a device that is compatible with outdoor environments or a device with a large bore that can handle higher flow rates and higher pressures.
Flow control of cooling water and cleaning water at metal processing and semiconductor manufacturing sites has become important from the viewpoint of quality control, and equipment can be selected in consideration of clogging, maintainability, and accuracy.
In the case of coating liquids and lubricating oil other than water, models that enable more precise flow control are selected from the viewpoint of process control. Other applications include manufacturing in the food, chemical, and paper industries.
Principle of Water Meters
The principle of a water meter depends on the measurement method.
1. Ultrasonic Flowmeter
Ultrasonic waves are transmitted and received from two points on the pipe, and the difference in propagation time is measured.
2. Electromagnetic Flowmeter
The electromagnetic flowmeter measures the amount of water by measuring the electromotive force generated by the movement of a conductive liquid in a magnetic field. Faraday’s law of electromagnetic induction is used as the measurement principle.
3. Area Type Flowmeter/Floater Type Flowmeter
The water volume is measured by the position of the float that moves up and down.
4. Coriolis Flowmeter
Water flows through a U-shaped pipe and the amount of water flow is measured by comparing the amount of twist in the pipe.
5. Kalman Vortex Flowmeter
When water passes through a column-shaped vortex generator, a vortex is generated, and the number of vortices is detected to measure the amount of water.
6. Impeller Type Flowmeter
Pulses generated by the turning of the impeller are converted into a voltage signal to measure the amount of water.
7. Differential Pressure Flowmeter / Orifice Flowmeter
This meter measures the amount of water by detecting the difference in pressure between the front and back sides of the water as it passes through the throttle valve. The square root of the differential pressure between two points is taken according to Bernoulli’s theorem, so the amount of water can be calculated accurately.
Types of Water Meters
There are a wide variety of water meter types, depending on the principle of measurement. Each method has different features, advantages, and disadvantages.
1. Ultrasonic Flowmeter
Installed on the outside of piping, ultrasonic flowmeters are used to measure outdoor piping. Since there are no moving parts, maintenance is easy, and digital and analog flowmeters can be used. However, it is prone to errors due to air bubbles.
2. Electromagnetic Flowmeter
Low-pressure drop and can measure the direction of flow.
3. Area Flowmeter/Floater Flowmeter
Simple structure and low cost, but not very accurate.
4. Coriolis Flowmeter
It is insensitive to changes in viscosity and density and has a fast response speed. However, it is expensive and has a large pressure drop.
5. Karman Vortex Flowmeter
Simple structure with no moving parts, but vulnerable to vibration.
6. Impeller Type Flowmeter
Used in large water meters.
7. Differential Pressure Flowmeter or Orifice Flowmeter
Simple, inexpensive, and easy to install and remove. On the other hand, they cause pressure loss and are not suitable for measuring liquids mixed with solids or small flow rates.
How to Select Water Meters
Since there are many types of water meters, it is necessary to select the right product for your purpose. First, define the purpose of the measurement and determine the accuracy required of the water meter. For example, volumetric flow monitoring displays instantaneous flow rates and does not require high accuracy. And if the error that causes an alert is too fine, on the contrary, it is because it is not useful.
Next, consider the detailed conditions of the actual installation environment. Specifically, the power supply, output signal, and installation location are important.
Finally, the cost is compared to determine the best solution. Not only the price of the main unit but also the price of related equipment, installation costs, maintenance work costs, etc. must be compared in total to make a decision.