Click here to enlarge imageSurface water from Salt River Project (which includes the Salt and Verde Rivers) and the Central Arizona Project (from the Colorado River) account for nearly 75 percent of Mesa’s water supply. This water is treated at two plants with a combined capacity of nearly 270 mgd. The city’s 36 wells make up the remaining 25 percent. Well depth is between 800 and 1,000 feet and flows range from 700 to 3,000 gpm. Mesa’s water distribution system is divided into eight zones to control water pressure. Pressures within a zone can vary from 40 to 100 psi.
Magmeter Uses
Mesa has used magmeters for more than 20 years, including some Fischer & Porter meters bought before the company became a part of ABB Inc. Later, Mesa switched to the MagMaster line and currently has magmeters that range in size from 4 to 54 inches.
Typical uses include measuring and totalizing water being pumped into distribution mains from wells, influent and effluent flow at water treatment plants, effluent flow from wastewater treatment plants and measuring wholesale transfers and the sale of water.
Mesa had contracted with ABB to provide a specialist to verify and certify nine custodial magmeters every six months. The cost for this service was about $17,000 a year. When Mesa decided to replace the 12 inch meters at its well sites approximately two years ago, an evaluation confirmed that the city could realize substantial savings by purchasing its own calibration equipment and factory training for staff. All verifications are now done in-house.
Verifying Calibration
A MagMaster meter and its transmitter are calibrated as a matched pair at the ABB factory. They are shipped with a floppy disk that contains a “fingerprint” of all pertinent calibration data for this specific measuring system. These data also characterize the important, permanently installed, shielded cable that carries the small millivolt measuring signal from the primary to its transmitter.
To verify and re-certify calibrated accuracy of the installed magmeter, the operator needs only a laptop PC that contains the floppy disk and the CalMaster control box with its two cables to connect the transmitter to the control box and the box in turn to the PC.
The shielded cable connecting the transmitter with its primary is already there as a part of the measuring system. This cable is specially shielded to protect the small millivolt measuring signal coming from the primary. Flow measurement continues during the test.
The PC contains software to carry out a pre-programmed verification procedure. When the test is initiated at the PC it carries out a check of the entire system - the meter, the transmitter, and the connecting cable.
To confirm that the test results are within set standards, they are reviewed on a PC display. If the results are positive, a certificate of validation for the tested metering system can be printed out. Providing the customer with a copy of the certificate authenticates the billing.