EEVblog Electronics Community Forum
Products => Thermal Imaging => Topic started by: Fraser on January 31, 2020, 11:16:13 pm
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I use BlackBody calibration sources when testing and calibrating thermal imaging systems. These are not an essential accessory for users of a thermal camera, but they are very useful when wishing to check that a thermal measurement system is operating within its specification. Such thermal references are also needed when carrying out a cameras calibration routine. Some cameras, like my FLIR SC4000, are designed to be calibrated by the user to suit specific scenarios. Creating NUC tables requires large area plate type Blackbodies but temperature measurement calibration may be carried out using small aperture cavity type Blackbodies.
I own a number of Blackbody reference sources and have detailed the designs of some on this forum previously. My most recent low and mid temperature units are made by Mikron and cover the temperature range -5C to +400C between them. They have 4" x 4" Emission plates so are perfect for calibrating cameras and cores, including NUC table creation. I had thought about how I could generate reasonably accurate temperatures above +400C. I considered DIY designs using diesel engine Glow plug heaters, MCT heaters and ceramic Biomass igniters. Searches on eBay showed high temperature Blackbodies to be relatively uncommon in the UK auctions. They are more common in the USA but not exactly cheap. I did some searching of eBay.com in case anything affordable appeared. I found one high temperature head unit from Infrared Systems and providing a temperature range of +50C to +1000C within its 1" diameter high emissivity cavity. It was in nice condition and perfect for my needs. At less than £40 the price was right. Postage to the UK was painful at almost £100 but these units are not exactly light weight or small ! The fly in the ointment was that the PID controller for the Blackbody was missing. This was why the Head Unit was so reasonably priced. I intended to build my own controller using an OMEGA PID.
The Gods were smiling on me the week that I bought the Blackbody. Whilst researching my Infrared Systems 11-210 Blackbody I discovered a U.S. seller offering a used Infrared Systems PID controller unit for that exact Head unit model and with 80% discount being offered ! I bought it for $30 without hesitation :) The unit looks a little dirty but nothing that a good clean will not fix :) My Blackbody came with the umbilical cable and so it will be immediately useable with the controller when it arrives.
So in the period of just one week, I found, from two different sellers, an affordable high temperature Blackbody head unit and the correct model of high accuracy PID controller unit to drive it :)
As is to be expected, the U.S.A. sourced Blackbody units are designed to operate from 115V and some are not switchable to 240V due to the heaters used in them. This is no problem for me as I purchased a very neat compact 2kW 240V-110V torroidal step down transformer for my two 115V Mikron Blackbody units
As with most used equipment that I buy on eBay, I have semi-dismantled the high temperature Blackbody head to inspect it for damage, clean it and check safety etc.
Although this is a specialist piece of equipment, I have decided to upload some pictures of what I found inside the nice casing. I am pleased to report that the unit is well built and tests showed its heater, 'S' type thermocouple and fan to be in good working order. The unit was surprisingly clean inside considering that such units are normally left running for many hours in professional test and calibration environments. There is some discolouration on the stainless steel front panel that I first thought might be evidence of a burn up of some sort, but I can find no issues with the unit to concern me. Once the PID controller unit arrives I will hook it up for some live tests on the head unit.
Why no pictures of the innermost components of the cavity heater ?
Well I have been inside such units before and know how they are constructed. They are not designed to be disassembled and reassembled. They contain the cavity that either incorporates the heater in its casting, or is surrounded by a heater. Around that cavity there are layers of very high temperature ceramic wadding and bandage that is very fragile and does not take well to being unwrapped and re-wrapped. The outer stainless steel 'shell' compresses the thermal insulation layers around the heater and cavity. This forms a more resilient module that may be secured into an outer protective casing that has an air gap to help with thermal isolation to keep the outer casing cool during use at high temperatures.
UPDATE: I have now fully disassembled the cavity core module for inspection. It is fully documented later in this thread.
Some points of note about the Infrared Systems 11-210 high temperature cavity Blackbody:
Temperature Range : +50C to +1000C
Supply Voltage : 115V to PID. Head heaters are 115V
Wattage of Head Heater : 500W @115V
Cavity diameter : 1" with Conical end and High Emissivity coating.
The 11-210 Blackbody was originally designed in the 1980's and continued in production into the late 1990's. Over that period of time, the head unit remained virtually unchanged but three different PID Controller designs were used over the years. the MK1 controller was an analogue design. The Mk2 and Mk3 designs are both Digital PID's. The Blackbody was made by Barnes Engineering for Infrared Systems Inc. Both Barnes Engineering and Infrared Systems Inc rights to the designs were bought by Infrared Engineering Development in 1997.
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The 11-210 system with the Mk1 controller
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The Mk2 Digital PID controller that I found to match my 11-210 Blackbody...... she may look dirty, but this saves me an awful lot of work making my own and setting up the PID characteristics correctly :)
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The umbilical cable was supplied with the Blackbody head, which was fortunate as the ITT-Cannon connectors are very expensive at around £50 each in the UK :phew: That is the sort of nasty surprise that can ruin your day when you think you have bought a bargain but suddenly face huge expense for missing parts.
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The disassembly for inspection and cleaning begins.......
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Outer casing detail. The end caps are thick aluminium pressed into shape. The central section is cast aluminium.
The front end cap has the polished metal cavity aperture surround mounted in it. This insert also provides the front mounting point for the cavity & heater module. The rear end cap houses the 115V whisper quiet fan, umbilical connector and terminal strips to interconnections.
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The front end cap insert detail. Note the calibrated port formed by the metal aperture plate attached to the rear of the insert.
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A picture of what resides inside a typical high temperature cavity blackbody similar to the 11-210 head unit.
Mine does not have the multiple calibrated aperture wheel on the front or second thermocouple fitted.
In the provided plot, deduct 273.15K to obtain Degreees Celsius. 1000C is 1273.15K
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Just in case anyone else buys one of these Infrared Systems Inc/Barnes Engineering Blackbody head units and does not have the PID controller, here is the pinout of the ITT Cannon connector on the rear of the head viewed from the outside.
Top pair of pins : Heater / Heater (115V max from PID)
Middle row of pins : Chassis / Thermocouple / Thermocouple ('S' type)
Bottom pair of pins : Fan / Fan (115V)
The Connectors are ITT-Cannon 'Standard K' types with 7 pins. These are uncommon and expensive.
The fuse on the rear panel serves the fan supply input only.
Fraser
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For anyone interested in the challenges of creating a heater for a cavity type Blackbody that must achieve 1000C operating temperature, take a look at the Watlow catalogue. They specialise in high temperature heaters. Achieving 1000C+ operating temperature is not simple and many cartridge heaters max out at less than 800C. Specialist high temperature elements and insulators are needed, combined with clever encapsulation design.
https://transition.watlow.com/downloads/en/catalogs/high-temp.pdf
Fraser
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The Infrared Systems Inc. 11-210 digital temperature controller arrived today :)
It was the unit shown in the auction photograph and was as dirty as it looked !
On the cosmetic condition front, the unit is a little challenged but nothing too serious. It has clearly not been greatly cared for in its life ! However, given the option of this tatty unit or having to build my own from scratch.... I will take the tatty unit :D
Before switching the controller on I took it apart to inspect its safety, internal condition and identity of the PID controller.
So in that order......
1. The unit is made in the USA so should meet US electrical safety standards. It incorporates the expected fuses, mains filtering and MOV spike protection. The electronics are mounted on a removable chassis that is correctly earthed and safe to use. The outer casing is not connected to an earth cable so does breach modern best practice fro earthing. The rubber coated power cable has degraded at the equipment end. The outer insulation is cracking. The power cable is going to be replaced as part of the units renovation anyway. One fuse carrier cap was missing but thankfully that is a simple item to source and replace.
2. Internal condition is excellent with no corrosion or significant dirt present. Compared to the exterior condition it looks almost new !
3. The PID controller is a USA made ATHENA 6075. A custom front panel label by Infrared Systems Inc. has replaced the original ATHENA labeling. The PID drives the Blackbody 115V heater via an external Solid State Relay that is rated at a very healthy 25A.
The outer casing has been given a thorough clean with white spirit and soapy water. Whilst the dirty marks cleaned off, the casing paint is still in a pretty rough state. I will be sanding it before a repaint with a heard wearing cream enamel that is on order.
The PID controller front panel label is marked and the display section window is heavily dented. The PID button areas on the label are becoming worn/split. Thankfully they are real tactile buttons mounted behind the label so no membrane switches to sort out.
I purchased a used ATHENA 6075 PID from the USA for $10 today so I will have spare parts and a decent front panel label to replace the one on the 11-210 controller unit. I include a picture of that unit in the attached pictures.
To the pictures of the unit before and after cleaning ........
Fraser
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Chassis detail....
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The case after cleaning.....
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I have connected the 11-210 control unit to the 11-210 Blackbody head and applied power. The ATHENA PID booted correctly and began to drive the Blackbody heater but the indicated temperature was incorrect. It was showing a permanent 4C ! Some investigation is required. My K type thermocouple simulator proved the PID to be OK so the problem is in the head unit.
After I have given the control unit some more TLC in the cosmetics department and calibrated the PID to the heads sensor, I will be happy with the system.
Happy Days :)
Fraser
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When the head is connected to the controller, the PID starts to drive the heater but the cavity temperature shows as 4C on the PID. The result of this is that the heater in the head is being continuously powered as the PID thinks the cavity temperature is only 4C which is well below ambient. This results in a very hot thermal cavity! This would explain the discolouration found on the front of the stainless steel cavity module. The heater appears to have survived this ‘abuse’ but the cause is an issue with the temperature sensor. The temperature sensor in the head is a cartridge type thermocouple that slides into an orifice in the cavity module. It is held in place by a spring clip that applies axial pressure on the rod for a good thermal contact.
I suspect that the thermocouple has succumbed to high temperature fatigue in some way. This unit has likely spent a lot of time running at a high temperature. We shall see what it looks like once removed. Thankfully thermocouple extraction requires just the removal of three rear casing nuts, a spring clip retaining screw and the two sensor wires from the terminal block. Nice and simple :) Almost as though it is an expected and planned maintenance operation ;D
Fraser
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I forgot to say..... I hate mysteries and I am pleased to now know why the discolouration occurred at the front of the cavity module stainless steel casing. That did not look ‘normal’ to me and was niggling at the back of my mind.
Fraser
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You know when you think a job will be simple and then your pet Gremlin decides to make a job more exciting by throwing in a curve ball ? ...... well my Gremlin decided to introduce a seized thermocouple probe into the situation!
The probe is supposed to be a clearance fit into the cavity casting but mine would not budge in any direction. I could see that someone else had attempted mild leverage on the thermocouple probe from the witness marks around it on the aluminium back plate. A plan was needed as brute force could shear off the probe cartridge in the cavity core.
I know I said I was not going to do a teardown of the cavity core module and it’s associated heater as it can be a challenge to reassemble correctly, depending upon the insulation design. Well what I should have said is that I would not dismantle it for no good reason. The combination of a failed sensor causing thermal stress to the heater and potential thermal damage to the cavity module insulation is a good reason to dismantle the module.
I will upload pictures of the complete tear-down of the cavity module shortly. I dismantled it down to its component parts and inspected all parts for damage. The heater is, as I suspected, a helix would around the cavity core. There is no visible evidence of overheating on the heater helix. Blue patches on the grey heater element sleeve can indicate overheating no such discolouration was found.
I managed to extract the thermocouple cartridge using vibration and gentle twisting back and forth to break the metal to metal bond that appeared to have formed. After some careful manipulation I managed to remove the thermocouple. As part of the rebuild I cleaned all parts including screws, heater, cavity core and the thermocouple well.
Now to source a new thermocouple.
Fraser
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I have just ordered the parts to get my 11-210 Blackbody up and running again :)
All parts were available for next day delivery from Radio Spares and are of decent quality :-+
I purchased a dual thermocouple element high temperature K type thermocouple cartridge that will provide me with the signal for the PID controller plus another that comes out on the Blackbody heads rear panel for independent monitoring or logging. This was an upgrade option when the 11-210 was originally supplied.
Buying the dual thermocouple element cartridge was an extra £5 but will be a useful improvement to the unit.
To go with the additional thermocouple that he new cartridge provides, I purchased the correct round pin type K thermocouple socket as that will fit the ready made mounting hole intended for it in the heads rear panel. I only have to remove the blanking plate :) I do not normally use the round pin type thermocouple connectors so I had to buy one of those as well.
Pictures and data sheets for the parts attached. The thermocouple was a bit of a challenge to source as it has to be the correct length and rated to 1100C minimum. The Radio Spares part appears to be a “product” of decent quality. No point in penny pinching on such an important part :D It cost £30 including VAT.
All being well, the parts will arrive tomorrow :)
Fraser
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Dual, independent element & insulated Thermocouple RS Part No. 397-1359 - data sheet attached.
Fraser
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The pictures of the cavity core module teardown as promised.....
This will be followed by pictures of the rebuild.
As already stated, I tried to remove the thermocouple cartridge but it was stuck fast in the core. I considered the possibility that it had a threaded end into which a screw would be placed as a retainer. To check for this I had to remove the whole whole core, including insulation, from the stainless steel module casing. As it turned out, this was not the way that the core should be dismantled!
The core should should be disassembled from the rear but I had gained access to the front of the assembly and could see that there was no screw securing the thermocouple cartridge in place within its well. I could now apply suitable forces to extract the cartridge without fear of a hidden retaining screw fighting my efforts. I succeeded in removing the cartridge so disassembly could start on the core.
The cavity core is held centrally in the stainless steel outer casing by two sets of supports. One set at the front and one at the rear of the core. The core is surrounded with large ceramic fibre insulation blankets that are built up in layers. To remove the insulation, the rear supports have to be removed. They are secured to the core with brass screws. The high temperatures that the core has operated at made their removal a challenge ! All were seized into their threaded holes. The wonder fluid WD40 came to my rescue and after some effort I had removed all of the screws and brackets to enable disassembly to continue.
The ceramic fibre insulation layers were easily removed but it is pretty awful stuff to work with and very fragile. If you crush it, it does not bounce back ! Care must be taken when handling the insulation and respiratory protection is recommended.
Once all of the layers of insulation had been removed, the central cavity core was revealed. Would around the central core is a high temperature heating element. The heater is a friction fit and is not secured in place by any fastenings. The heater is marked with identification and is rated at 115V/600W. All of the WD40 that had migrated onto teh core sides and heating element was removed to avoid smoking when the unit is powered again.
Fraser
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Pictures continued....
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Pictures continued....
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Heater and core detail.......
The metal core is hollow with a conical end to the orifice to form a blackbody cavity. The inside of the cavity is coated with a high emissivity coating. The core is surrounded by a helically formed single ended heating element that is designed to withstand the 1000C + temperatures that it generates. This approach assists in providing even heating of the metal cavity core.
Note the reducing pitch of the heater helix as it approaches the open end of the core. This is deliberate and intended to help compensate for the thermal losses that occur at that end of the core due to the cavity opening and proximity to the outside world Ambient temperature. Clever design.
Fraser
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Pictures of the stainless steel and aluminium cavity module casing.
You can see that it bears witness to the high temperatures that have been present in this Blackbody unit. There is clear bluing of teh stainless steel at the top of the casing and severe discolouration around the cavity port.
The aluminium rear cover shows less thermal stress. The two thermocouple ports and guides are clearly visible. These protect the thermocouple cartridges. Note that only one thermocouple was deployed in this particular head unit.
Fraser
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The reassembly after cleaning.........
The process went smoothly and the cavity module is now ready to return to the head unit casing.
Fraser
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No chance of finding a 230VAC heater element, as the controller and SSR will work with 230VAC, so you will probably have to find a 600VA autotransformer to place in the controller case to keep the 115VAC one.
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SeanB,
Ah, but that is not a problem for me.......
A very nice chap gifted me a couple of professional Mikron Blackbodies recently. They are wonderful bits of kit with 19" rack mount controllers and separate Blackbody heads...... they are 115V though. I purchased a really nice 2KW 240V-110V step down transformer. It uses a torroidal transformer and is really compact :) I can power all three of the Blackbodies from that one transformer :) The transformer cost me just £44.
Fraser
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All of the required parts to return my 1000C blackbody to service have now arrived :-+
I will be fitting a new power switch, fuseholders and a mini Thermocouple socket to the controller and a new thermocouple and standard thermocouple socket in the head unit.
Note the size of the standard (non-mini) thermocouple connectors ! They are big beasts but the hole in the head unit is sized to take that type of connector as I have already said.
Fraser