DIY thermograhics

[Steve Walker]

I don't know if it covers the right wavelengths, but you can certainly buy

35mm infra-red film for a good old fashioned SLR.

SteveW

[John Rumm]

The systems I have worked on used a polished tilting rotating polygon to scan the image over the detector (the rotation and angle synced to TV line and field rates). The detector being a cryo cooled linear strip detector. However for most applications there would be and additional "lens" (typically made from germanium) of some description on the front end of it. The most elaborate airborne systems have a thermal telescope (again all germanium). These beasties typically cost in excess of £100K just for the telescope.

[Owain]

I suppose a couple of them would do if you don't have any spare uniselectors :-)

Need a heck of a lot of uniselectors though :-)

How high-res does would it really need to be?

Owain

[Andy Dingley]

Easiest would be a polygonal mirror (laser printer or barcode scanner) that rotates continuously and generates a sync pulse. Especially so if you want to scan quickly.

[Harry Bloomfield]

These thing do not get a reading very quickly.

[Harry Bloomfield]

Owain presented the following explanation :

One foot square would be enough, but if it is only nine feet from the surface and looking at a house the angles would be acute to cover the entire house width and height. Moved parallel and by hand, with aiming points marked in chalk on the wall, it might produce some interesting data.

[Andy Dingley]

No, it doesn't. The first rule of IR film is that if you can store it at all conveniently, you can't do much useful with it! Also to focus it you needed to use an old plate camera with a single lens mounted far from the film plane (modern 35mm lenses performed wonderfully well in the visible, but not so well at IR) and also a glass plate back helps a lot (and an IR converter tube to watch it!). For years the best lenses available were WW2 German kit, developed for aerial recon in the IR. Germany led the way in near-IR imaging. These cameras, heavily adapted over the years, were fairly common in university labs into the '80s.

"IR thermographs" of vegetation (back in the film days) weren't usually anything of the sort, they were false-colour images of the state of leaf senescence (chlorophyll being present or absent changes their brightness considerably).

[Harry Bloomfield]

Andy Dingley brought next idea :

I had thought they used UV?

[Frank Erskine]

On Mon, 9 Nov 2009 12:19:08 -0800 (PST), Owain had this to say:

I have loads of uniselectors, and a few Ledex switches, which are very similar in principle.

In fact I have a few 2-motion selectors, which could replace several uniselectors, if one really could be arsed. :-)

Just do it analoguely - take a photo or two of the house with infra-red film or filters and look for the 'hot spots'.

In the winter and there's snow about, it's pretty obvious who has reasonable loft insulation (or has little heating!) by looking at roofs... Although most of you 'dahn sarf' don't know about this 'snow' thing :-)

[Adrian C]

Or, waaaay too much, a hotwired electic meter, permanently drawn curtains, a wiffy smell and no sign of residents. :-(

[Matty F]

I have removed the fliter on a video camera. It's the blue thing on the left:

really need to put a piece of plain glass in its place or it doesn't focus properly. The cameras are quite complicated inside. I'd say that it would never work again if you take it apart.

[Thomas Prufer]

Maybe not, if the hire is close to the price of having someone come in, as there are pitfalls that an experienced operator should be able avoid. My fist-hand experience:

In a similar situation, I borrowed an IR camera. The friend I borrowed it from said that they had two, but one was calibrated, and I'd have to pay for an operator to come with it, because they weren't letting it of their hands. ("Calibrated" meant that it had been compared to the Kelvin they keep locked in a basement in Paris, and they had the paperwork to prove it.)

So I got their "cheap" one for a few days, a FLIR costing about five grand. This makes the hire of such a camera expensive: it is a delicate, expensive piece of equipment, and the ham-fisted borrower has to be priced in. Also, I had install a bit of software to d/l the pictures, and that might beyond what a lender would trust a common-or-garden borrower to manage alone, simple as us usenetters might find it.

While it is easy to use -- turn on, point, and look at the screen -- interpreting the results can be tricky. First, it measures the radiation coming from somewhere, and interprets it as a surface temperature of that somewhere, coded as a color. (The absolute temperature isn't of particular interest in finding hotspots, so a whole load of trouble regarding emissivity calibration goes out the window.) Reflection happens, though it is easily recognizable on the screen as one moves: there will be hot or cold spots flashing up on the screen as flat surfaces reflect. This will throw off the scaling of the picture. (Generally, the screen is scaled to show hottest, coldest, and all between, though there are Options).

What is a real pain is that ideally, one would measure the outside of a building on a very cold night with no wind, and the house evenly heated from the inside. Once even diffuse sun hits the outside, a house with an outer insulation layer will heat up very quickly to surprising values, giving an uneven reading on a perfectly good wall. Wind will also suck heat from flat exposed surfaces, tending to leave it in inside corners. Reading from indoors, inside corners and edges will be cooler because convection is less there, dropping less heat there, without any deficit in the insulation.

These are not large problems, but someone who has done this often will be better able to spot what is a problem and what is "normal".

One other thing these cameras are used for is to check wiring: loose or corroded connections will heat up and show clearly, even under plaster if the connection is loaded for long enough for the heat to soak out. I think the unit could resolve to under 0.05 K or better -- this translates to leaving a thermal handprint on a wall for thirty seconds just by touching it. Should you borrow such a unit, look at the wiring as well, directly and under plaster; it'll only take a few minutes.

HTH,

Thomas Prufer

[Mark]

You can't be losing too much heat through your roof otherwise you would have already had a dawn raid from the drugs squad.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember dave saying something like:

Take a step back and do IR film, still available, still reasonably cheap. Time to dig that old SLR out of the cupboard.

[Owain]

Hadn't heard of them -

Switchporn!

Owain

[The Medway Handyman]

Even better idea. Ring the local nick anonymously & grass up your home address as a cannibis farm. Defend the case & they will have to produce the photos!

[Clot]

Latest ploy here , (though it could be old hat to some), "The HeatSeeker vehicle ahs recently visited your area and thermal imaging has identified your property as one which may benefit from improved insulation."

Fine, would not disagree, whilst we have DG and CWI and loft is done to a certain extent.

The letter could be true and all houses in the neighbourhood plastered with the bumpf!

We do not grow tomatoes or any other plants under heat and light indoors. ;)

[John Rumm]

Still no use for this application alas - wrong part of the spectrum.

[Adam Aglionby]

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Inventor of IR and UV photgraphy was Prof Robert W Wood :

name lives on as the glass on Blacklight (UV) effects lamps is called Woods Glass, great for finding dandruff, at lower wavelengths how good your hotel laundry is....

Cheers Adam

[Andy Dingley]

Roof space grow rooms are generally really well insulated. Thanks to nPower's sponsorship in particular - just watching the crowds buying up their subsidised rockwool rolls in Bristol was a laugh. If you take an IR camera though Easton, the growrooms are darker than the houses. I believe UV spillage is actually an easier way to spot them - many houses leak IR, few have full-spectrum lighting.