Choosing an acoustic camera

Acoustic cameras are similar to ordinary cameras, but instead of making pictures with just light, they make pictures that combine light with sound. The acoustic ‘pictures’ are displayed on a screen, where they are overlayed on an ordinary optical picture of the same scene. This makes it easy to identify the sources of the sounds.

This is useful because sounds often point to problems. For example, in a process plant, the sound of gas escaping may indicate a costly leak, while in an electrical installation, the sound of an electrical discharge may indicate faulty insulation that could soon lead to a complete breakdown. Acoustic imaging can find these problems faster and more conveniently than any other diagnostic technique.

Acoustic cameras also enhance safety because they operate over considerable distances. This means it’s not necessary to approach potentially dangerous equipment and can eliminate the need to climb ladders to pinpoint a fault.

However, it's important to choose carefully when you’re looking for an acoustic camera to ensure it meets your needs. Here are some key points to consider:

Where you’ll be using it. Working in an industrial environment dictates a minimum IP54 environmental rating to stop water or dust ingress. If you’re going to use the acoustic imager to check for leaks in process plants where there are likely to be explosive or flammable gases, you will need an ATEX-approved camera – which, of course, is equally suitable for use in non- hazardous areas.

Number of microphones. The acoustic image is captured using an array of microphones. More microphones mean better frequency resolution and accuracy. The best balance of performance for modern instruments is usually over 120 microphones.

Resolution of optical camera. To help identify the sound source accurately when producing reports, having the ability to zoom in on the image makes pinpointing the sound source far easier. Having an optical camera with a resolution of at least 8 megapixels gives a very detailed image.

Detection range. It’s often more convenient - and safer - to stand some distance away from the plant or equipment you’re surveying. That way, you can scan large areas from the same location and stay well away from dangerous equipment. For this, you’ll need a good detection range. A good acoustic camera should work at 100 metres or more from the sound source.

Ultrasonic monitoring. Most sounds that indicate fault conditions are ultrasonic – that is, they are at frequencies too high to hear directly. To make fault location and pinpointing faults easier, the camera should be able to modulate the signal to an audible frequency band, so the user can monitor the signal using headphones.

Ease of use. Complicated setting up wastes time and negates the convenience of acoustic imaging. Fortunately, the latest models need only two simple settings for the majority of applications, although they can, of course, be fine-tuned to meet special requirements.

Acoustic focusing. If you’re working in a very noisy environment or have multiple fault signals, the provision for ‘focusing’ the operation of the microphone array is very useful. It minimises the effect of ambient noise on the acoustic image and allows a single fault to be measured.

Built-in analytical features. Acoustic imaging is fast, versatile and easy to use, but it’s even more useful if the acoustic camera not only visually displays the sounds but also analyses them. Look for instruments that can provide quantified leak rates and partial discharge categories in electrical systems on screen for immediate diagnosis.

There are many more technical features to consider when buying an acoustic camera – like the camera’s ability to run a self-check to ensure all the microphones are working correctly - but there’s one more very important thing to consider: the supplier. Are they a trusted brand with a local presence so that you can easily access technical support and advice, should you ever need it? Do they provide supporting documentation to help you get the best from your acoustic imager? Do they have a reputation for delivering reliable, high quality products? If you can answer ‘yes’ to these questions and choose an acoustic imager that meets all of your technical requirements, you can be sure that it will soon save you a lot of time, money and trouble.