Video: TC706

Video transcript

How a camera makes an invisible gas visible, what is inside it, and how to run a leak survey with it. SF₆ is colourless, odourless and heavier than air. A leak makes no sound and leaves no stain, and the first sign is often a low pressure alarm, months later. The camera works because of a coincidence of physics. SF₆ absorbs infrared strongly around 10 and a half micrometres, and the camera looks only at that band.

The gas blocks part of the radiation coming from the background, so where the gas is, the camera receives less energy. On screen, that shadow moves. This is the camera's own recording of a real leak: the gas drifts, it swirls, and it always comes from one point. In a still photograph it is a smudge. In two seconds of video it is unmistakable. To see something that faint, the detector is cooled. A cooled quantum well array of 320 by 256, tuned to the SF₆ band,

with a thermal sensitivity better than 25000ths of a degree. It was built to be carried. Three kilograms, one operator, 3 hours of battery, and a handle and viewfinder that rotate together so you can aim at an awkward angle without contorting yourself. And when there is no leak to chase, it is still a thermographic camera: the same instrument covers routine inspection of connections and terminals. And the palette is not decoration. The same escape, in a colour palette rather than grey,

separates the plume from the background by hue instead of by brightness. 11 palettes are built in, and on a difficult background changing it is often the whole trick. Everything you find can be proved later. Radiometric images keep the measurement inside the file, and a voice note records what you were looking at. And although it was bought for SF₆, the same band shows other gases: ammonia, ethylene, freon, chlorine dioxide and several more.

Start with what is under the housing, because it explains almost every rule that follows. That cooler is why the camera is not instant. Switch it on and it needs about 10 minutes before it is ready to measure. Plan for it: turn it on while you walk to the bay. The battery goes in the compartment under the eyepiece, curved side down. It will not fit the wrong way round, so never force it. Getting a good image is 3 moves: open the cap, aim, focus.

And then correct, because a camera that has just cooled down drifts. For gas work, switch to the detection mode and change how you move. Scan slowly, keep the background behind the leak, and watch for something that drifts rather than something that is simply warm. This is what you are looking for, at the speed you will see it. For temperature, the camera measures where you tell it to: at points, inside areas, or along a line. And it needs to know the emissivity of what

you are looking at, and how far away you are. Most of what the camera does is set from the menu, and 4 settings decide whether a measurement is right: the emissivity of the surface, the distance to it, the analysis you want, and the units you work in. Before a survey, decide where the files go. The camera can file them by day or by month on its own, or into folders you create and name yourself.

On a big site that decision saves an hour back at the office. Getting the work out of the camera can be done 4 ways, and all 4 are in the box. And then the report. The camera ships with a report analysis system, and it is worth understanding why it matters: a radiometric image is not a picture of a temperature, it carries the whole measurement, so you can move the points, change the emissivity and re-analyse the scene weeks later, at your desk. Everything worth keeping goes to the card,

and the card is what you take back to the office. And when something looks wrong, the cause is usually one of 4 things. Gas leak detection, from Amperis.