Instrumentation
a sweep frequency and it takes quite a bit of time to set those things up and put them on the pipe. Then you have to find a ‘sweet spot’ and even after you’ve found the spot, you still have to adjust the transducers to get an accurate measurement.” John O’Brien, general manager of Flexim Americas
Corporation, said: “There are many ways of getting a signal to a pipe. Many use multiple transducers which operate at different frequencies to overcome the various types of pipes and wall thicknesses and types of liquids. Flexim uses the same transducer for everything, but they filter the transmission pattern and either increase the power to the transducer or break up the pattern of transmissions to adapt to the real world conditions. Power to the transducer may go from 15 volts transmit to 90 volts transmit. The meter sends approximately 1000 pulses back a second in 500 pairs, and the system automatically realises a change in the consistency of the liquid. Not even coal slurries are a big challenge. The system automatically realises it’s losing signal and increases power to the transducers. It’s a combination of software, clever transducers, and signal processing. It can monitor anything from quarter-inch tubing to a 30-foot penstock. “I think we can safely say that ultrasonic flow meters
have finally met their potential. I have taken more than 600 readings with this portable meter and my success rate is 99.8 per cent, and that includes pipes containing acids, water, gasses, and slurries at several hundred degrees. At the end of the day, I collect all the data dumps from the built-in data logger and export it to my spread sheet program. “And our internal customers have gained faith in
Fig. 2. FLUXUS F601 portable ultrasonic flowmeter: It can be mounted directly on the pipe and measure flow non-invasively
difference and determines the average flow velocity of the medium. Since ultrasonic signals propagate in solids, the meter can be mounted directly on the pipe and measure flow non-invasively, eliminating any need to cut the pipe.
The tests Harper said: “One of my first tests for all the meters was in the parking lot where we have a 30-inch water line. Aside from accuracy, I was looking for ease of installation. After all, I have to go all over the plant measuring flow and I don’t want to waste time setting up. I was also looking for reliability, data logging capability, diagnostic tools, and a good battery life. The thing with the water line was that if it took too long to set up the meter or the accuracy wasn’t there on such an easy task, there was no point going into the other test sites.”
And the winner is … Harper continued: “I’m not going to name those meters or the others that didn’t make the cut because some were good products with good accuracy and I don’t want to make them look bad. But at the end of six months, one meter met all of my standards, but especially for ease of set up and accuracy. It was from Flexim. “They had two distinct advantages over the others. First,
they were a combination gas/fluid meter so I only had to buy one meter, not two. Second, their installation is a snap. The main problem with the others was installation. Flexim has a fixed frequency on their transducers. It doesn’t matter what they are measuring, they keep that frequency. The others use
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ultrasonics and have bought ultrasonics to replace their older meters. And the concerns about accuracy are a thing of the past. One of our clients was doing an addition process and having some problems with the feed rates. They had a plate flow meter on the line, but weren’t getting consistent measurements. I took the portable over there and spent three days with them. They liked the results, but weren’t sure about the accuracy. So I took the portable meter to our metrology group. They had a coriolis flowmeter set up and we bench tested the Flexim versus it and got a correlation of .9999.”
Next steps Harper continues: “We currently have five of the ultrasonic meters in our group. Four of the meters are the Fluxus F601 Liquid and one is the Fluxus G601 Gas unit. The G601 Gas meter is actually a multi-meter in that it has the capability of measuring liquids as well. Most of the applications we have are for liquid measurements but with a plant this size the ability to measure gas flows from outside the pipe is definitely a plus. The specifications of this meter states a minimum requirement of 100 psi to measure gas flows but the lowest pressure line that I have personally attempted to measure is 140 psi. That particular application was for a nitrogen header and the meter worked well. “At the present time our Flow Measurements Group
consists of three people (me and two Utility Operators). Our future plans are to possibly add addition people to the group but for now our model is working. As news of our having this ability spreads throughout the plant we are finding a need to do some ‘creative scheduling’ given that we are a small group, but that is a good problem to have. We are continually finding
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