Electromagnetic flow meters
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Learn about installing and maintaining an electromagnetic flow meter/magflow.
What’s an electromagnetic flow meter?
An electromagnetic flow meter is a device used to measure the flow of liquids through a pipe.
Electromagnetic flow meters measure trade waste effectively because they use magnetic parts, rather than mechanical parts. Magnetic parts give more accurate readings and are more durable than mechanical parts, which can easily break because of solids in the waste and chemical corrosion.
The device includes a pipe with electromagnetic coils around it and electrodes which sit in the liquid within the pipe.
The coils create a magnetic field across the flowing liquid.
The electrodes then detect the voltage generated by the charged particles in the magnetic field.
This voltage is sent to a transmitter that calculates the volumetric flow rate based on the pipe dimensions.
Do I need to install an electromagnetic flow meter?
You will need to install an electromagnetic flow meter if:
- you’re a trade waste customer discharging more than 25 kilolitres per day to the sewerage network
- the volume of your trade waste cannot be related to the volume of drinking water supplied to your site
- your business and/or quality of your trade waste requires it.
We will advise customers when electromagnetic flow meter installation is required.
We use the readings to:
- bill accurately
- establish current and forecast future trade waste contaminant loads discharged to sewage treatment plants
- assess sewerage network capacity.
Electromagnetic flow meters have a digital display and are often linked to a recorder for data collection. We will sometimes request that your flow meter is linked to a datalogger so we can see past flow data within a specific time or date range.
Installation
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You must employ a third-party supplier to assist in the sizing, design and installation of your flow meter.
You will need to provide a verification statement post installation.
| Consideration | Description |
|---|---|
| Location |
Flow meters must be located downstream of any on-site wastewater treatment system and before the connection to the sewer. No other trade waste connection or flow to sewer should be made beyond the flow meter other than domestic connections. Domestic contributions need to be plumbed with separation connections to the sewer and should not contribute to the liquid passing through the flow meter. If domestic liquids pass through the flow meter, we will apply a correction to the account. |
| Gradient |
The flow meter should be installed level with no gradient. It may be installed vertically if the flow passes in an upwards direction only. |
| Full pipe |
A flow meter can’t give accurate readings if the pipe is not full. You may need to put a downward bend in the pipe upstream of the flow meter and an upward bend beyond the flow meter so this can be achieved. The angle of these bends is not critical, but the nature of the wastewater (solids content) must be considered to avoid blockage or excessive pipe wear. It might also be necessary to add an air vent into the pipework near the flow meter to achieve a full pipe. Pressure differences over the flow meter can sometimes prevent a full pipe from being achieved. Vents also reduce the likelihood of siphon effects occurring. If a flow meter has been installed vertically, upstream of a lower-level pump, a non-return valve may be needed downstream to make sure the flow meter remains full of liquid. |
| Straight lengths | It is essential that a straight length of pipe is installed upstream and downstream of the flow meter, and that these sections of pipe hold water at all times. Instructions on how to achieve this, and the required minimum/maximum lengths will be included in your supplier’s installation manual. Please read this carefully and liaise with us before and during the install. |
| Meter size and flow rate | The size of your flow meter will depend on the size of your pipes. The velocity, or speed that the liquid moves through your meter, should be between 1 and 3 metres per second. Your third-party supplier will tell you what size flow meter is best for your set up. |
| Vibration | Support the pipelines on both sides of the flow meter, to avoid potential damage. |
| Clearance | Allow sufficient room next to the pipe flanges to install nuts and stud bolts. Flow meters should be installed so that quick and easy maintenance is possible. |
| Turbulence | If the flow meter has a smaller diameter than the pipework, tapered reducers should be used either side of the meter to reduce turbulence. |
| Foaming | If the flow meter has a smaller diameter than the pipework, tapered reducers should be used either side of the meter to reduce turbulence. |
| Static | Installation of earthing flanges must be in place to prevent the build-up of static electricity around the flow meter. |
| Submersion | A submersible flow meter can be used in liquid. This can allow a flow meter to be retrofitted into an existing trade waste pit rather than having to do additional excavation works downstream. |
| Isolating valves | Suitable isolating valves must be installed so that operations and maintenance activities can be performed. |
| Power supply | Hard wired 240v power supply must be provided to flow meters. All flow meters must have a back-up power supply in the event of a power failure (e.g., solar panel, battery back-up). |
| Electromagnetic fields | Avoid installing flow meters near strong electromagnetic fields, e.g., major power sources, power substations, high voltage power lines, switchboards, eddy current sorter machines as these can interfere with the flow meter's operation. |
| Pulse outs and signal strength | Spare pulse outputs must be available to allow a connection to a data logger and/or composite sampler. The strength of the signal/pulses must be strong enough to be recognised by composite samplers. |
| No reset to zero | The totaliser readings displayed on your flowmeter must not be reset to zero. |
| Measurement | Flow meters should be able to return instantaneous readings in litres per second and totalised volume in kilolitres. |
Further guidance is available from the Water Services Association of Australia Code of Practice WSA-15 (Trade Waste Metering Code of Practice) and WSA-12 (Metering Selection and Installation Code of Practice). Flow meter manufacturer's recommendations should also be considered.
Maintenance
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Flow meters must run within our required tolerance of +/-2.5%.
| Requirements | Description |
|---|---|
| Calibration certificates | Calibration certificates must be obtained by the customer upon installation of the flow meter. They provide a guarantee for one year that the flow accuracy is within 2.5% tolerance. Calibration is not typically performed in-situ. A copy of this certificate must be provided to us. |
| Verification certificate (post- installation) |
At the time of installation, a verification certificate needs to be obtained by the customer from the third-party supplier. During verification, checks are performed on the electronics (motherboard etc.), connections (cables, linking equipment), and magnetism (check for interference from electric motors etc.) to ensure the 2.5% accuracy tolerance can be maintained. If the accuracy is not within 2.5%, the technician will have to troubleshoot the installation as they should not be able to print out the certificate until it meets the tolerance. We require a copy of the verification report. |
| Verification certificate (annual) | Each year, customers are required to verify that the flow meter is reading within the 2.5% tolerance. This is done by a third-party supplier providing a verification certificate. We require copies of these verification certificates. |
It is important that customers notify us before removing a trade waste flow meter for repair. The time and date of removal, along with the totaliser reading, should also be provided.
We will adopt, in consultation with the customer, an alternative method for determining trade waste volumes for the purpose of billing whilst the flow meter is being repaired. Trade waste should not be discharged when appropriate metering is not available.
