AWWA C751-2019: Magnetic Inductive Flowmeters (Magmeters)

AWWA C751-2019 – Magnetic Inductive Flowmeters, an American National Standard, reviews magmeter principles. This technology is one of the latest additions to the water industry, and it has been met with wide commercial acceptance.

What are Magmeters?

Magnetic inductive flowmeters, also known as magmeters (the two terms are used interchangeably in AWWA C751-2019), are able to function due to Faraday’s Law of Induction. According to this law of electromagnetism, when a conductor travels through a magnetic field of a given strength, a voltage is produced in the conductor that is dependent on and proportional to the relative velocity between the conductor and the magnetic field.

As covered in AWWA C751-2019, when the magnetic field is generated in a magmeter, it is configured to be mutually perpendicular to the axis of flow of the conductive liquid and the axis of the electrodes used to detect the induced voltage. The voltage induced within the liquid is mutually perpendicular to both the velocity of the liquid and the magnetic field. The simplest way to understand this technology is that an increase in velocity will cause an increase in the value of the voltage generated.

Magnetic inductive flowmeters are available in wafer style and threaded and flanged-end connection designs, and they generally consist of a primary device and a secondary device. The primary device is composed of more distinct parts, specifically the measurement flow tube, nonconductive liner, electrodes, and sensors. The secondary device is just the transmitter.

The glory of magmeters derives from the following qualities: they require less maintenance, contain no moving parts, and do not create any flow restrictions in the pipeline. Overall, they are more accurate than mechanical meters in use today. Magnetic inductive flowmeters currently have found use in a wide range of applications, including the measurement of wastewater, raw water, treated water, and revenue generation and in different stages of the treatment process.

Their perceptible advantages, however, do not mean that magmeters exist without potential issues. Obviously, performance issues, such as those associated with accuracy, rangeability, linearity, and repeatability when measuring a flow rate, can be present, affecting a magmeter’s results. The AWWA C751-2019 standard addresses these issues, detailing them and offering guidance on verification.

About AWWA C751-2019

In all, AWWA C751-2019 is focused on reviewing magnetic inductive flowmeter principles of operation, calibration, and selection. This encompasses a range of interests, including flowmeter components, performance issues, calibration methods, and markings, among many others.

Users of AWWA C751-2019 should note that all liners and other materials in contact with potable water in the United States, in accordance with the laws of most government agencies, must comply with NSF/ANSI 61-2022: Drinking water system components – Health effects. These materials must also meet the requirements of the Safe Drinking Water Act and other federal, state, and local requirements.

AWWA C751-2019 does not apply to the insertion type of magmeter. A separate standard or the inclusion in this standard for the insertion type of magmeters may be developed at a later date.

Changes to AWWA C751-2019

In 2016, AWWA C751 was published as an entirely new standard, being the first edition resulting from the Committee Report on Magnetic Inductive Flowmeters completed by the AWWA Standards Subcommittee on Magnetic Devices.

AWWA C751-2019 revises AWWA C751-2016. In addition to editorial updates, information on chlorine and chloramine degradation of elastomers was added to the foreword. Furthermore, obsolete references on evaluating the health effects of products and drinking water additives were removed.

AWWA C751-2019 – Magnetic Inductive Flowmeters is available on the ANSI Webstore.