Ultrasonics, Water Flow Measurement: Part 1

Since Sierra is a leading supplier of immersible thermal mass flow meters, I find myself heavily involved in the waste water treatment industry, where Sierra’s model 640S Steel-Trak® is the instrument of choice for measuring the low pressure air fed to the flocculation tanks, where oxygen-loving (aerobic) bacteria happily munch on the wastes. Over time, I fielded a growing number of enquiries along the lines of “Scott, we love your 640’s…what have you got to measure our water flows.” Well, I only had to get hit over the head a few dozen times before I realized we at Sierra were missing a golden opportunity to supply this industry, so in the early in about 2003, Sierra started investigating water measurement technologies.

Eventually, we narrowed it down to the two most innovative new technology meters: ultrasonic and magnetic. In a magnetic flow meter (commonly called a mag meter), a magnetic field is applied to the metering tube, electromagnetic induction then results in a potential difference proportional to the flow velocity perpendicular to the flux lines. In an ultrasonic flow meter, it is sound that provides the measurement basis.  Using ultrasonic transducers, a blast of ultrasound is transmitted into the fluid and the flow meter measures the average velocity along the path of the beam.  The difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow (Δt) is proportional to the fluid velocity.

Today,  many many years later, our Innova-Sonic family of ultrasonic flow meters is a huge success story supplying wastewater plants and dozens of other industries. You can even buy them from stock online from Sierra. In my next post, I will discuss one huge advantage of ultrasonic flow sensor technology that was a major reason Sierra chose ultrasonic over mag meters…what could it be, stay tuned?