When we think of flow metering for liquids, we rarely get past the industrial workhorses of the Magflow (Magnetic Flow Meter) or the turbine meter. I have no real beef with these; years of development has led to accurate and reliable meters and are still the meters of choice for countless applications.
However, lurking in the wings for many years has been the clamp on ultrasonic flowmeter. Often dismissed as being only for temporary installation and of dubious accuracy, this technology has advanced to the point that it is a viable alternative to "mainstream" metering, and when well installed can offer similar levels of accuracy.
Having worked with ultrasonic meters for over 20 years, I remember the difficulties of setting up and getting reliable metering values from the early units. I can also say that those days are gone, and with improvements in the metering technology as well as the interface, setting them up is more-or-less childs play (so long as the given child can use a screwdriver, measuring tape and keyboard).
The main advantage of the ultrasonic technology is that there is no need to break into the pipe to install the equipment. As well as offering higher integrity for hazardous materials or hygienic systems, they are ideal for retro-fit metering installations.
Here is an example of an ultrasonic meter Engineered Efficiency installed on a live fire water system at a Perth hospital.To install a more conventional flow meter would involve draining the line, cutting into the galvanised pipe (and compromising the galvanising), welding in flanges before fitting the meter and re-hydrotesting, with a likely project cost of over $5,000 and many hours downtime. We installed the ultrasonic flowmeter in less than half an hour with no system downtime, at a significantly lower project cost.
So what about the accuracy? This meter has an accuracy of around ±2% or better, which is fine for most practical purposes. Whilst not quite the accuracy of a magflow meter installed under ideal conditions, it is probably as good (if not better) than a poorly installed magflow meter done in haste as a retrofit.
So next time you are looking at a meter retrofit, or are metering a product where minimal pipe fittings is an advantage (hazardous materials, hygienic systems), run the ruler over an ultrasonic meter.