Author Topic: Cute little Electro Optical Industries Cavity Blackbody - a peek inside :)  (Read 554 times)

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Online Fraser

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A little while ago I stumbled upon a cavity type Blackbody on eBay.com. The unit looked to be in good condition and was equipped with a useful 1" diameter cavity. Such cavity type Blackbodies present a >99% emissivity source to a thermal camera when testing measurement accuracy etc.

The price of the EOI Blackbody made it very tempting, even though it was located in the USA. I pulled the trigger and bought the unit. It took an awful long time to arrive thanks to eBay's new budget shipping program. Well thankfully the parcel arrived today :)
My first thoughts were that the parcel was not the expected Blackbody as it was so small ! I opened it and sure enough the box contained a Blackbody :)

I am so pleased with my purchase.... first impressions were good and this thing is soooo dinky  ;D I thought the unit would be a lot larger than it actually turned out to be. Those who know me will already know that I like compact and well engineered products  :)

The Blackbody head came with its expensive umbilical cable but not the temperature controller. If it used the usual EOI 19" rack mount temperature controller, I would not have wanted it anyway. I will need to build a nice compact PID based controller to match the diminutive dimensions of the head unit. To do this I need to better understand the EOI Blackbody design so it was time to remove the cover  :-+

Once the cover had been removed, the very neat engineering within was revealed  :) This unit is a beautifully scaled down version of the other two (full size) Cavity Blackbodies that I own. There is the Cavity 'core' module that contains the metal cavity tube, helical heater, temperature sensor(s) and lots of high temperature ceramic wadding insulation. That 'core' module is solidly mounted on a pair of yokes that are, in turn, mounted on the thick aluminium base plate. The front and rear panels are made from the same thick aluminium plate so this unit is nice and solid. These units are made in relatively small numbers and are hand made rather than the product of a mass production automated assembly line. They are very expensive as a result.

My investigations into the technology within the head unit revealed that it contains a single heater of 10 Ohms resistance, a PT100 RTD and a Thermocouple. Why an RTD and Thermocouple ? Well the RTD is the sensor for the temperature controller feedback loop whilst the Thermocouple is used with a cold junction reference for either calibration of the temperature controller, or monitoring of the cavity temperature using an accurate meter. On high temperature cavity Blackbodies it is common to find an 'S' type Thermocouple in this role.

This unit will be very convenient due to its portability and I will make up a Tripod mount to fit to the base plate to increase its mounting versatility. There are already tapped screw holes in the base for just such an adaption.

Well enough from me on this dinky little unit.... to the pictures......

In the pictures you will see Bailey and Oskar examining the new arrival and a CD case is used for scale to show just how compact this cavity Blackbody is  :-+

Fraser

« Last Edit: October 01, 2020, 08:02:51 pm by Fraser »
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Online Fraser

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Under the cover.......
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Online Fraser

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The Umbilical cable is terminated in Amphenol MS3106A-16S-1S and MS3106A-16S-1P connectors. These connectors are available from Radio Spares for around £22 each. I am pleased that the Umbilical was provided with my head unit as that is a good saving and the Umbilical is often a hybrid screened RTD and unscreened heater supply cable. I will just need to buy a panel mount female connector part number MS3102A-16S-1S for the Temperature controller.

I suspect that this head unit was permanently mounted in some sort of Thermal FPA test jig as the many calibration labels refer to the unit as part of "FPA Eng/Test". This would explain its good condition and relatively clean interior. The unit appears to have been operated at a fixed temperature of 227 Degrees C as this is stated on the Calibration labels.

Fraser

« Last Edit: October 01, 2020, 07:35:57 pm by Fraser »
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Online Fraser

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I have cleaned the dust out of the Blackbody and studied it’s distribution around the chassis. This gives me a pretty clear idea about the orientation that the unit was operated in whilst serving its previous owner. It appears to have been mounted vertically with the emission aperture pointing upwards. The dust was limited in quantity, but what was present was sat on surfaces that would be uppermost if the Blackbody was positioned as I have suggested.

An FPA test rig with horizontally mounted FPA’s passing over the Blackbody aperture possibly ? Another possibility would be a vertically mounted Blackbody projecting onto a 45 degree angled 1st surface mirror system as used in some thermal camera test configurations.

The calibration labels sates that this unit is used as part of “Calibration Assurance” and it is marked as a “Special”. The calibration label also specified a four digit number that correlates with a reference output of 227C. This could be a software configurable value that is part of the test jigs control over the Blackbody.

If this is a custom product that formed part of a calibration and test bench, you can bet that it was seriously expensive to buy from EOI.

Fraser
« Last Edit: October 01, 2020, 10:06:44 pm by Fraser »
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Offline Ultrapurple

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In the pictures you will see Bailey and Oskar examining the new arrival and a CD case is used for scale to show just how compact this cavity Blackbody is  :-+
Fraser

Come off it, Fraser. That "CD" is clearly Photoshopped in and Bailey & Oskar are just badly re-sprayed leopards  :-DD
Rubber bands bridge the gap between WD40 and duct tape.
 

Online Fraser

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 :-DD

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Online Fraser

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I am currently trying to decide what power I should apply to the heater in this Blackbody. I know that it is of 10 Ohms resistance and is capable of operating at 227 Degrees C. Most EOI Cavity Blackbodies are capable of >1000C but I am minded that they have forced air cooling over the Cavity module to dissipate the heat being generated from its casing. My dinky little Blackbody is fanless and convection current cooled. The cavity module may be the same as that used in other EOI products but the cooling of its outer surface, or lack there-of, will determine its safe maximum cavity temperature.

I think some real World testing is in order. I will power the heater from a suitable lab power supply and monitor both cavity and module casing temperatures.

The DIAS temperature controller is not a bad ‘fit’ for the EOI head except the heater resistance is 10 Ohms as opposed to the DIAS heads ~15 Ohms. The 50 vac 4.5A drive may struggle with the current draw.

Fraser
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Online Fraser

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There has been a similar 'LS' model Electro Optical Industries Blackbody head on eBay for a while. The seller is asking over $800 for it without a controller  :scared:

That units pictures are attached. Note that this also appears to be a 'fixed installation' head as evidenced by its weird mounting bracket. Also note the small emission aperture that is less than optimal for camera calibration checks, though could still be used.
The unit is another 'special' that does not appear in the EOI catalogue. It is fitted with a 12 Watt Papst cooling fan and air duct connection to cool the cavity core module with forced air. This may well be to permit a higher operating temperature for the cavity.

From its ID label marking of LS400/025 it would appear that the head is an "LS" model with a 25mm diameter cavity, designed to operate up to 400C. Whether this requires the fan cooling or that was due to the specific, close cabinet ?, installation I do not know.

The ID label also shows the options: AM/S/TTL. I suspect the AM is for "Angled Mount", S is for "S type thermocouple" and TTL is ?
I would have expected an "option" entry for fan cooling  :-//

Fraser
« Last Edit: October 02, 2020, 01:56:38 pm by Fraser »
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Offline Bill W

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TTL might be a 'temperature ready' logic feedback line ?
Would be useful in a calibration checking scenario.

Odd that you say your body has a blackened metal tube, that may be a limit.  All the 'sausage cooker' styles that I have seen were ceramic. 

As background, it is the cavity shape as much as the materials that make them a black body, so white ceramic is just fine.

Bill

Online Fraser

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Bill,

There are two types of cavity in common use. The metal ones cover temperatures up to 1050C but anything higher appears to use specialist ceramics in the cavity construction. Both my Barnes and IR Systems 1050C Blackbodies use a steel cavity 'core' with a helical wound Mineral Insulated heater wound around it, along its length.

As you say, some cavity type Blackbodies have to use the ceramic cavity to cope with the very high temperatures that some units can produce. It was Mikron that detailed the materials that are used in various cavity type Blackbodies and they stated that the very high temperature Blackbodies were only made possible by the development of advanced ceramic materials and insulation.

In the case of the baby Blackbody that this thread covers, I think its maximum safe operating temperature will likely be around 400C, like the DIAS Blackbody that is rate at "intermittent 530C" due to the heat building up in the casing. I will do some tests to see how the Blackbody behaves running off a set DC supply and how much heat reaches the cavity module casing. I note that this cavity module does not have an over-temperature cutout visible on its outer casing which is a bit of a surprise considering it is a passively cooled unit.

Much of my work is below 400C so this unit will be useful for more portable usage.

Fraser
« Last Edit: October 02, 2020, 02:44:43 pm by Fraser »
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Offline rockwell

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--totaly off topic --

Fraser, what kind of race is your grey cat ?
We had for a long time a russian blue, unfortunately we lost him last year.
 

Online Fraser

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Oskar is a Pedigree British Short Hair Blue  :)

We have had him since he was a kitten. He us now 2 years old  :)

Fraser
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Offline Ultrapurple

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And here he is as a kitten, before the re-spray:



(Image borrowed from here)

 :-DD

I promise I'll behave from now on. At least for a while, anyway.
« Last Edit: October 03, 2020, 12:59:39 pm by Ultrapurple »
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Online Fraser

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 ;D
Cogito, ergo sum
 

Offline bap2703

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Looks like its made by Weller  ;D
 


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