Test & measurement In using the acoustic imager, the first-time

operator is impressed at the speed at which leaks can be detected and positively identified. The built- in video camera makes it easy to record a close-up still picture or video of the leak, which is stored on the device memory for later download. The imager software has the capability of automatically measuring the sound level in decibels, and the distance to the leak by triangulation. Using this information, and entered in pressure information for the leak, an estimate of the leakage flow can be calculated for the final report. Once the leakage flow is known, using the estimated efficiency of the compressed air system, and the site power costs, the total cost of all the leaks captured can be calculated in a final automatically generated output, called a “LeakQ report.”

Other acOustic imaging uses

The use of the imager is not limited only to compressed air; other items within a plant generate ultrasonic signals. Ultrasonic detectors are commonly used to detect nitrogen, bulk gas, steam and vacuum leakage. In addition, pump cavitation, noisy bearings and electrical discharge corona also can be detected using ultrasonic detectors. The ii900 has a tunable frequency range that can be used to better differentiate different types of emitters, depending on the sound signal characteristics. In evaluating an imager for the first time, Fluke

Corp. A leak detector instrument, called the ii900 Sonic Industrial Imager, uses a video camera to provide a live image, and an array of 64 different directional microphones to create a “heat map” of ultrasonic emissions on top of the visual display. This device brings new meaning to the old saying “a picture is worth a thousand words.” Having an image representing both visual and audible signatures emitted by a leak makes the detection exercise a much easier task. In using the Imager, the operator also “points and shoots,” but in this case the ultrasonic emission shows up as a live feed on the onboard video screen as a coloured spot, making the location identification much quicker. As the operator gets closer to the leak, the location becomes easier to identify, even when shooting through protective screens or pointing at locations out of reach without a ladder. When shooting among other ultrasonic emitters, like a bench full of active compressed air powered grinders, the leak shows up as a consistent spot on the screen, with the tools being intermittent, so it is easy to differentiate. Reflections, which can cause time consuming “wild goose chases” with typical audible only detectors, are easy to separate from the leakage, moving the camera from side-to-side moves the location of a reflection, but not the image of an actual leak.

Instrumentation Monthly April 2021

deployed the ii900 at a small 10 bay service shop as part of a compressed air efficiency survey. As a value-added service, the operator spent only 10 minutes locating 12 various compressed air leaks totaling about 10 cfm. This flow consumed about 35 per cent of the average facility flow. At the customer’s power rate, the total cost of these easily repairable leaks was estimated at $1,000 per year. If the customer repairs the leaks, it will save this cost and qualify for an extra $1,500 utility grant to help with the purchase a more efficient air compressor. This represents about $2,500 value in the first year through only 10 minutes of leak detector work, and roughly two hours of repair time.

A second survey was done at a small

fiberglass parts manufacturer during full production hours. This time, 51 compressed air leaks totaling about 50 cfm were identified in a one-hour survey. Two vacuum leaks were also identified. Total cost of these leaks is estimated at $6,300 annually. What became particularly striking is that a leak survey was previously done with a standard ultrasonic gun about a month earlier and repairs were made. About half of the leaks found during the acoustic imager survey had developed over a 30-day period or had been missed in the previous work with a standard detector gun. The survey found many quick connect

couplers and rubber hose leaks, which are common problem areas in a plant of this type. When presented with the visual results, the plant managers immediately recognised the problem and started investigating solutions. A wholesale change of connector and hose type is being considered. Throughout the surveys, the high value of the

acoustic imager output became obvious. For example, an operator found leakage of one pressure regulator in a bank of regulators - a configuration like this makes for difficult work in identifying the source of the leak if done with a standard ultrasonic gun; use of the imager found the leak immediately. In another area, the operator identified a leak in a pressure regulator behind a protective screen, something that would be difficult to do with a standard gun without shutting down the machine. Experience with the acoustic imagers shows it

makes leak detection quicker and more efficient. Once found, leaks can be clearly identified and recorded, and easily differentiated from background noise, reflections and interference. Leaks in overhead piping and behind screened barriers can be identified without incurring any safety risks. And a basic final report can be conveniently generated online at the Fluke website.

Fluke Corporation


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