The main function of a customer meter is to provide data that describes
the volume of water a particular consumer has used for billing purposes.
In many cases this data is also used to bill for sewage discharged into
the sewer network. Increasingly, utilities are becoming aware that this
data may also be used to better understand and manage their
distribution networks and helpcustomers conserve water.
There are a number of mechanical customer meters available. Rotary piston, single-jet and multi-jet are the most common.
Rotary Piston Meters
Piston meters are a pseudo positive displacement meter technology. As the name suggests, a piston rotates within a cylinder and discharges a known volume of water upon each rotation of the piston. Each rotation of the piston is then detected (usually via magnetic induction) and the volume of water associated with a single rotation recorded either on a mechanical register or more recently on an electronic register.
Single/Multi-Jet or Velocity Meters
Single-jet meters are the low cost option for measuring water for revenue purposes. The principle involves a jet of water impacting an impellor the rotation of which is proportional to the velocity of the water. The volume of water that passes through the meter is proportional to the rotation of the impellor. After installation, this technology can (depending on the consumption profile of the customer) slightly over record, but still within the stipulations of the MID. However, this is soon reversed with time, volume and water quality. Wear, damage and other influencers can also significantly affect the performance of these meters, causing them to under record volume over time.
A multiple jet or “multi-jet” meter is a velocity type meter which has an impeller which rotates horizontally on a vertical shaft. The impeller element houses multiple inlet ports which direct the fluid flow at the impeller causing it to rotate in a specific direction in proportion to the flow velocity. This meter works mechanically much like a single jet meter except that the ports direct the flow at the impeller equally from several points around the circumference of the element, not just one point. This reduces uneven wear on the impeller and thus extends the effective measurement period beyond that of a single jet meter.
Solid State Meters
The two most common types of solid state meters for revenue purposes are electromagnetic and ultrasonic. One of the biggest challenges of these technologies is the need for batteries to power the electronic primary elements. Both the measuring technologies and data storage systems and associated circuitry need to be energy-efficient to meet this challenge. Solid state meters maintain their initial measurement accuracy, but are not designed to be maintained or refurbished like mechanical meters.
Electromagnetic Flow Meters
Electromagnetic flow meters are based on Faraday’s law of induction. The potential difference between two electrodes generated by the liquid passing through a magnetic field is proportional to the flow rate. This method is widely used in water networks for monitoring water abstracted from the environment, within treatment processes and at the zonal or DMA level. The technology is now applied to small bore revenue metering bringing excellent low flow capabilities and continuous measurement.
Electromagnetic flow meters are characterised by free passage, no moving parts, no wear, a long lifetime, insensitivity to the presence of suspended particles (no need for strainers), and negligible pressure loss. However, the fluid needs to have some level of conductivity. Electronics associated with the flow sensor introduce features that support the concept of smart water networks, such as bi-directional volume measurement, flow rate monitoring, alarms (e.g. leak, backflow etc.), data logging, and wireless data transmission.
Ultrasonic Flow Meters
Ultrasonic flow meters are based on transit time measurement of an ultrasound wave crossing or traveling with and against the flowing media. The pulse is accelerated (with flow direction) or decelerated (opposing flow direction) by the flowing media and the time difference measured. The difference in time taken by the upstream and downstream waves and is proportional to the fluid velocity. The volume is then calculated from the known flow cell dimensions and the velocity measured.
As with electromagnetic devices, with ultrasonic devices, there are no moving parts, and negligible pressure losses. They can work on non-conductive liquids, but are more sensitive to the presence of solid particles. The same data capture and alarm capabilities can be embedded in ultrasonic flow meters along with wireless data transmission.
Some of the benefits of customer meters include:
Provide data to facilitate customer billing
Provide data to customers to promote water saving
Provide data to manage the water networks
Provide data for water efficiency initiatives
Monitor losses and leakages on customer assets to help customers control their water use and assist in the estimation of NRW
Unlike larger meters, small customer meters are designed to be able to operate with little or no straight run of pipe before and after the meter. On the whole, this makes them impervious to velocity profile configuration or variation.
Proper sizing of the flow sensor is fundamental for acceptable measurement and the best achievable uncertainty. The flow sensor should be sized in accordance with the flow range to be measured and, in particular, to the low flow regime in order to ensure the flow meter performance.