Dahua Reference Blackbody - under the covers :) - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 11:15:24 am
content: I have seen a lot of Thermal Reference Blackbodies being sold for use with Fever Detection camera systems over the past couple of years. Blackbody thermal references used to be a relatively specialist piece of test equipment found mainly in calibration-check labs and thermal camera production environments. With the onslaught of Corona Virus it was quickly recognised that accurate measurement of humans face temperatures was challenging when using thermal imaging camera technology. An accurate temperature reference in the thermal scene was required in many cases where adequate measurement accuracy was needed. The standard to be met for fever detection measurements was commonly +/-0.3C which is far tighter than the more common Industrial specification of +/-2.0C or 2% (whichever is greater). Due to the need for stable temperature references for fever detection, a new industry in reference Blackbodies appeared in the market place. Suddenly thermal camera manufacturers were making, or having made, compact Blackbody thermal emitters that presented a very accurate temperature reference to a thermal camera observing a scene. The mini reference Blackbody was born !Sadly, Blackbody systems have always been expensive to buy new. This is because of the small market for such, virtually 100% hand built production techniques and the requirement for both temperature accuracy and stability over long periods of time. The new mini reference Blackbodies needed to be more easily manufactured and at lower cost to the end user. This was achieved during the Pandemic, but the units remain quite expensive to buy new. It is not uncommon to see such a reference Blackbody being sold new for >$1200. Accuracy costs money.So what resides inside these mini reference Blackbodies ? We will find out in this thread as I dismantle two examples that I have just received. From experience, I expect to find the following inside the casings….1. High quality PID temperature controller with Auto Tuning and either a RTD or carefully calibrated Thermocouple input2. A solid state relay to couple the PID heater control PWM signal to the heater.3. A thick Copper or Aluminium emission plate, coated on one side with high emissivity paint and with a foil type heater mounted on the other side to provide the required heating energy.4. A fan to maintain an acceptable ambient operating temperature for the PID temperature controller.Thermal Blackbody systems can come in various configurations when it comes to the temperature controller and the Emission head. Some operate as a separate controller unit connected to the emission head via an umbilical. This keeps the temperature controller electronics away from the localised heat of the emission plate within the head unit. Other designs integrate the temperature controller and emission plate into one casing. This immediately presents the designer with the challenge of maintaining the temperature within the casing at a level acceptable to the temperature controller electronics, whilst also not causing internal air movements that effect the emission plate thermal ‘flatness’. To build a decent performance, fully integrated controller + emission plate Blackbody is not as simple as some may think. This is the challenge faced by those manufacturing the mini Blackbodies for fever detection systems.I will be inspecting the two mini Blackbody units that I have just received and shall document my findings. They will likely be relatively simple in appearance but do not mistake that simple appearance for a lack of design effort ! I have already noted that the two units contain highly reputable ‘imported’ PID temperature controllers from FUJI Electric and Omron. It is vital that the temperature controller is of adequate quality and performance if an accurate reference Blackbody is to be achieved.I will attach some pictures of the units I have and also advertising images showing their intended use. The disassembly will have to wait until later.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 11:18:35 am
content: The two Danua units that I have just received. They are two different models, but perform the same role with equal effectiveness.Officially their temperature coverage is Ambient +5C to 50C but this is only constrained by the materials used in the emission head and configuration of the PID controller max limit setting. I may choose to increase that upper temperature limit.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 12:51:16 pm
content: An interesting article detailing how a School district misunderstood the significance of not buying the Reference Blackbody units for their Hikvision Fever Detection camera systems….. a rather large Ooooops !https://ipvm.com/reports/hik-fayeI should state that I also favour the use of a ‘known accurate’ temperature reference in a thermal scene where accuracy of the measurement system needs to be assured.These Reference Blackbodies are designed to be accurate and I will assess them in terms of their usefulness to hobbyists and professionals for thermal camera testing, calibration and accuracy checks.As time moves on we may see such Reference Blackbodies becoming available at hobbyist budget friendly prices. My two ‘used’ Danua units were less than £100 each.

author: Vipitis
author_rank: Frequent Contributor
timestamp: April 26, 2022, 02:44:53 pm
content: I saw some fever screening systems (camera, tripods, laptop, signs) being sold here as well. Not quite as cheap but it was the whole system. When we had the initial forum thread in like December 2019, we were already discussing if cheaper cameras would end up in the market for us hobbyists - but it didn't occur to me that reference black bodies might. If I had cores that supported the whole lens correction routine, having one of these would be really useful as I am still looking for new lenses to eventually use.

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 03:41:30 pm
content: Cover has been removed from the Dahua DH-TPC-HBBInside I have found……1. Thick Aluminium emission plate, coated with high emissivity paint on one side and with a foil heater clamped to its rear face.2. A ‘firewall’ between the emission plate/heater and the electronics package. Expanding foam has also been employed.3. Two PCB’s, one supporting a PCB mount self contained power supply :24V @ 1250mA and the other providing power to the heater and fan via control electronics. This PCB also provides mains input filtering for the unit.4. A small fan provides case ventilation5. A OMRON E5CC-QX2ASM-800 digital PID controller provides control over the temperature of the emission plate using its SSR output.There is no SSR module within the design. The heater switching function appears to be carried out by a MJE13007 power transistor on the control electronics PCB. This was presumably cheaper than buying in a SSR.Build quality is fine with no obvious issues.Pictures to follow

author: DaJMasta
author_rank: Super Contributor
timestamp: April 26, 2022, 04:04:46 pm
content: I had an Indigovision branded thermal blackbody that appears to just be a rebrand of the same (I think it's model 69671), there are likely quite a few branded ones out there.It took a bit to get to temperature and stabilize, but read consistent with the display and was quite uniform in a cursory inspection with an e60.

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:37:20 pm
content: Ok folks, time for the promised picturesModel : DH-TPC-HBB. Built April 2020I have also opened the second unit and that is different. Details to follow after these pictures.

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:38:39 pm
content: Pictures continued.....

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:40:12 pm
content: Pictures continued.....

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:52:54 pm
content: The second Thermal Reference Blackbody appears to be very similar from the exterior but opening its casing reveals a different design of electronics package.Model : JQ-D70Z. Built 30th January 2020The emission plate is very similar in design and used the same style of foil heater clamped to its rear. A MeanWell 24V / 1.5A caged SMPSU provides the power for the heater and the fan. The heater is controlled by a Fuji Electric PID controller that provides a SSR output to a PCB that accommodates the drive electronics, similar to that found in the other Blackbody..Both Blackbodies use a PT100 RTD as the temperature sensor that monitors the emission plate. This is good to see as an PT100 can be very accurate.To my eyes, this unit appears to be an earlier design than the first unit that I disassembled.Pictures follow .........

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:55:04 pm
content: Pictures continued...

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 07:56:54 pm
content: Pictures continued....

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 08:31:05 pm
content: So what do I think of these two Reference Blackbodies ?The units are actually better built than I had expected. The castings are excellent quality and the electronics packages are fit for purpose. The DH-TPC-HBB unit has a more refined design but that does not mean that its performance is superior to that of the JQ-D70Z unit as they both use high quality PID temperature controllers and a PT100 temperature sensor. The design of the emission plates in both units are almost the same. The emission plates are isolated from the surrounding metalwork and front casting by the use of nylon (PTFE ?) spacers. The construction of the electronics packages within the units is good, with the only concern being the implementation of the metal casing earthing.The two Thermal Reference Blackbodies have yet to be tested for accuracy but I do not foresee any issues on that front due to the use of quality temperature controllers and sensors.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 09:57:14 pm
content: Some research has confirmed that the Dahua JQ-D70Z is a Mk1 design from 2019 and the Dahua DH-TPC-HBB is the 2020 Mk2 version that replaced it.This tally's with the feel that I got for the two units designs whilst comparing the builds. The JQ-D70Z was a fast response to a need in the market and the DH-TPC-HBB was a more refined build, both in terms of the case design and the electronics package layout.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: April 26, 2022, 10:01:18 pm
content: Well that is all from me for now. Anyone who wondered what lived inside one of these Blackbodies can now satisfy their curiosity with this threadOne of these units would likely make a half decent calibration check source or even, potentially, a 2 point camera calibration reference source, if reconfigured for a higher temperature capability. If thinking of increasing the emission plate temperature beyond 50C, be aware that the emission plate insulators and expanding foam will limit the maximum safe temperature that the unit may produce. Upgrades to those temperature limiting parts is likely feasible, if desired.TTFN

author: Fraser
author_rank: Super Contributor
timestamp: April 27, 2022, 11:16:11 am
content: For anyone considering modification of these Fever Detection system Blackbodies for generic use, there is good news….The nylon insulators used around the emission plate should be good to at least 100C, if not higher. It depends upon the type of nylon that has been used. The melt point will be higher than 200C but that is not the service temperature.http://www.craftechind.com/app/uploads/nylon_final.pdfThe expanding foam ‘filler’/insulation is an unknown but similar products are useable in environments exposing them to 100C so some assumptions can be made about the ‘Service ceiling’ of the foam used in these Reference Blackbody’s.https://spsenvirowall.co.uk/assets/technical-resources/technical-data-sheets/2625_SPSenvirowall_Limited_Expanding_Foam_TDS.pdfhttps://docs.rs-online.com/d39a/0900766b8024ab13.pdfhttps://www.behlinginsulationsupplies.co.uk/wp-content/uploads/2014/09/Fire-Rated-PU-Expanding-Foam.pdfAll about spray polyurethane foams …….https://en.m.wikipedia.org/wiki/Spray_foamWith regard to the electronics package…. If the emission plate is operated above the original +50C limit set in the PID controller, temperature testing will be needed in the vicinity of the PID controller to ensure that the ambient temperature around it does not exceed its Operating environment specifications. A more powerful fan and increased ventilation port dimensions may be required to keep things cool

author: Fraser
author_rank: Super Contributor
timestamp: April 27, 2022, 11:49:00 am
content: For anyone concerned about the heaters ability to operate higher than the ‘standard’ 50C of the unit, I am pleased to advise that the Polyimide foil type heaters are happy up to temperatures around 200C (clamped) / 180C (3M Adhesive) This is well above where you should consider operating the emission plate in these units. My personal view of the maximum temperature at which these units emission plates should operate is 100C.

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2022, 02:34:54 pm
content: Thanks Fraser, very nice units there, will look out locally if there are any around, because I have seen none in actual use anywhere they do "screening" with thermal cameras. Then again, most use a IR thermometer, and aim it at your hand, arm, or anywhere but your face, and thus get by with having almost zero detection, which is what the retail stores want.Would say you can get to 150C with some PTFE retrofitting, and removing the foam and replace with some glass fibre wool batting, though I really think the foam will survive short term use at 100C, but the PT100 sensor they use will need new sleeving on it, in place of the heat shrink they put on. Or just remove it from the sensor to the insulation, and leave the bare PTFE wires exposed, or insulate with silicone sheathed glass fibre sleeve over the heatshrink, and accept the smell for the first month or so of use.I can DIY one, got the heaters and block, just need the Vantablack paint, or find a can of known emissivity black paint, or just use the existing flame applied ceramic coating. But probably will make a heated reflow bed out of it instead.

author: Bill W
author_rank: Super Contributor
timestamp: April 27, 2022, 03:09:07 pm
content: Quote from: Fraser on April 26, 2022, 10:01:18 pmA large span is not necessary, a lot of camera systems calibrate with 20 / 35 °C especially if mainly looking for ambient use. The difficulty is in stabilising the low(er) temperature with a heater-only system. It either has to come up very slowly or you rely on thermal losses to deal with overshoot.Obviously, depending on your climate, 20°C may be below ambient.So 'off' / 50 °C may be best operationally for these devices, but then not all camera factory calibration software has a variable input temperature pair either.Bill

author: Fraser
author_rank: Super Contributor
timestamp: April 27, 2022, 03:15:18 pm
content: SeanB,I think we will see more of these units appearing on eBay as companies scale back their COVID-19 defences. Operating a Fever Detection check point can become quite costly in staffing hours and the World seems to be rolling back on thermal detection methods these days. It never was a particularly effective approach and was commonly used incorrectly. Having just had COVID-19 I can say that I had no elevated temperature until I was knocked on my arse by the darned Virus. High temperature for 2 days and then back to normal temperature but feeling pretty rotten. I would certainly have been infectious before and after the fever stage.With regard to coatings for the emission plate of a DIY Blackbody, I was told about ultra flat camouflage paint produced by Krylon (thanks Bill_W) and did some research into its performance some time ago. It cannot be as good as the specialist coatings used by some Blackbody manufacturers but NASA were impressed with its Blackbody performance across a wide spectral range including MWIR and LWIRhttps://www.krylon.com/products/camouflage-paint/I bought plenty of the Ultra Flat Black camouflage paint for TIC related projects but have yet to fully test it in my applications. It does appear to offers excellent, predictable, emissivity across the LWIR band thoughPeople sometimes do not realise that the emissivity of a paint can vary greatly over the spectral range and so at differing emission plate temperatures. The paint will have a maximum service temperature that does limit its use on high temperature Blackbodies but, from memory, it will cope with 150C.Fraser

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2022, 03:25:19 pm
content: Ooh, camoflage paint, jobby brown and olive drab, along with flat black, but of course Krylon is not exactly common here by me, just will have to go with another brand, Aerolac, who at least does a matt black. But likely the spray ceramic will work well enough, it is old, but pretty much even, as I have measured it before, and you could barely see the heaters through the block heating up, with 500W cartridge heaters in the plate heating it up.

author: Fraser
author_rank: Super Contributor
timestamp: April 28, 2022, 11:04:02 am
content: Just tested my blackbody’s at 70C with no problems. It takes time to get up to that temperature due to the low wattage of the heater used. Not sure 100C will be achievable but will do some more tests to see. These Reference black bodies use a relatively low wattage heater and a very thick Aluminium emission plate. This means they are slow to get up to temperature and require a settling time. In their original deployment they are often on 24/7 in relatively stable ambient temperatures so this is not an issue. These are little different to the ‘heater only’ type commercial blackbody’s that I already own but some of those incorporate a cooling fan to help lower the emission plate temperature if a lower temperature set point is entered. The fan only gets used in this situation and is not running continuously. The relatively large thermal mass of the emission plate and low heater power helps to reduce temperature overshoot and facilitates accurate temperature control using the PID SSR drive + heater as thermal excitation of the emission plate whilst natural cooling through convection and radiation balances the process. All in a days work for a modern digital PID controllerTalking of PID controllers…. The two in my Reference Blackbody’s cost more than I paid for the complete used units ! Decent quality PID temperature controllers from name brands are anything but cheap ! Be warned if building a budget DIY Blackbody…. do buy a PID controller with SSR drive (not relay), preferably PWM, and do not buy cheap ‘no name’ units. Better to buy a well known brand PID controller ‘used’ than a cheap new one of unknown quality and performance. Some cheap units have truly tragic temperature stability !Fraser

author: SeanB
author_rank: Super Contributor
timestamp: April 28, 2022, 01:00:28 pm
content: True, but also remember that often the Omron and other PID controllers are multi output types, and have a menu selection for output type, that is set for the particular variant you have. Thus if the one you get is relay only, and you want SSR output, you just have to open the case, and remove the relay, and put the 2 screen printed wire links onto the board, to convert the 2 connections for the relay into the SSR drive, so it now will provide 24VDC at 20-30mA to drive the SSR directly.You can also install the optional second output relay, and get the alarm output, which can be used to turn off on sensor failure, or to switch a duel heater one into a high power mode for rapid warm up, putting both in parallel for rapid heating, then on approaching a temperature well under the set point it switches them to series operation, so that they then only put in slow controlled heat, or runs a phase angle controller to select a low part of the mains cycle to provide heating. Some also have a set of jumpers you install, to get a voltage proportional to difference, for driving a variable power input to the heater, so you drop power as you approach set point, and then the offset power stabilises at something just compensating for the losses.There is a lot of smarts in the supposedly simple PID controller that comes in a DIN cutout, often with hidden network ability as well, just need to use a cable to link them to a computer or PLC.

author: Fraser
author_rank: Super Contributor
timestamp: May 04, 2022, 10:35:09 pm
content: SeanB,I just bought a new CAL 9411 PID for a Blackbody that I am working on. It was very cheap on eBayAs you stated, the programming of the PID permits setting of the output interface type. The CAL 9411 is equipped with two relay outputs and I will remove them, bridge the required points on the PCB, and set it to SSR output mode in the output configuration menuThanks for getting me to think about PID controllers outputs as modifiable from their supplied configuration. I have previously just bought units with SSR outputs, but that limits what is available at reasonable cost on eBayI got lucky today and bought a complete Galai BB50 Peltier based Blackbody with its original 204-P temperature controller. Israeli kit like this is excellent quality and I already own a BB50 for which I had to convert a suitable Peltier element controller (the original controller was missing). The unit that I purchased today is Ex GEC Ferranti and looks to have been well cared for in its lifeThese Galai Blackbody units are crazy expensive new and not common on the used market. I got very lucky as the seller accepted my offer on itDetails of my other Galai BB50 Blackbody head unit are to be found here…..https://www.eevblog.com/forum/thermal-imaging/black-body-thermal-references-and-fraser_s-new-black-body-project-)/https://www.eevblog.com/forum/thermal-imaging/black-body-thermal-references-and-fraser_s-new-black-body-project-)/Fraser

author: f3d3r8
author_rank: Newbie
timestamp: May 16, 2022, 08:08:52 pm
content: I just bought a used DH-TPC-HBB. It's in reasonable shape, but the emissions plate is a bit worn...Would these defects cause any issues? I've checked it out with my Seek and I can't really see an effect...Are there any recommendations on how to repair the plate and what coating Dahua used?Cheers!

author: Fraser
author_rank: Super Contributor
timestamp: May 16, 2022, 08:41:13 pm
content: The high emissivity coating is fragile and all Blackbody manufacturers warn not to touch it or attempt cleaning with anything more ‘aggressive’ than a photographic lens blower brush. This is good advice as the surface is very Matt and easily takes up oils from fingers or scratches from ‘tools’. Many relatively gentle solvents will damage the coating so do not even think of using a solvent on it.As to the damage you have on your emission plate……. Well the good news is that what you see in the visible light domain is often not what is seen in the thermal energy domain. That is to say, a rub on the coating may look nasty, but it does not change the emissivity enough to make it visible at LWIR wavelengthsA scratch that gets through to the aluminium or copper plate is a different matter. That will be seen as bright metal or oxidised metal in the VL spectrum and sadly such damage will effect emissivity at that point. Such serious damage will be visible at LWIR but it may be possible to ignore it or touch-in the damage with some suitable very Matt paint. I use Krylon very Matt black camouflage paint but the solvent in it can attack the original high emissivity coating. Matt black enamel paint may also work well enough to cover a bright metal scratch and recover acceptable performance. The Krylon very Matt paint was tested by NASA and found to have excellent and predictable emissivity over a wide temperature range.https://www.krylon.com/products/camouflage-paint/In your case, I believe the ‘damage’ is limited to scuffing of the surface with possible light penetration to the aluminium plate. It is likely best left alone. You cannot restore that surface to factory state by any easy method and you will likely end up with a lower performance coating if you respray it. The original high emissivity paint coatings are both hard to source and expensive.Fraser

author: Bill W
author_rank: Super Contributor
timestamp: May 17, 2022, 09:35:48 am
content: Quote from: Fraser on May 16, 2022, 08:41:13 pmThere are two other saving factors here.Depending on the lens being used, the emission surface will be a (long/ very very long) way out of focus for a calibration routine, as the camera is failry close to the source.Some calibration routines take a large number of frames over several seconds, so a 'shaky hand' can be used to blur these effects too.Bill

author: f3d3r8
author_rank: Newbie
timestamp: May 17, 2022, 05:23:31 pm
content: Thanks Folks!Sounds like good news: I don't have another project to do... for nowI had a few other questions to finish out my thought process:* Could you recommend any good papers on the more advanced high emissivity paints? Are they using Vanta Black or some variant of it?* Would a DI water mist and a light brush do damage? (I'm not going to risk it now, just if it gets progressively worse...)* If I end up having to resurface the plate, would you just spray over the factory coating?Fun adventures in thermal imaging - this is a dangerous subject for my wallet

author: Fraser
author_rank: Super Contributor
timestamp: May 17, 2022, 06:20:14 pm
content: This thread should help you……..https://www.eevblog.com/forum/thermal-imaging/black-body-thermal-references-and-fraser_s-new-black-body-project-)/You will find discussion on coatings there.As to whether to strip the original coating to bare metal before repainting….. you will likely have to do that to avoid a reaction between the solvent in the new paint and the original coating.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 17, 2022, 06:32:47 pm
content: The NASA paint testing page appears to have moved/disappeared.The Wayback machine comes to the rescue thoughhttps://web.archive.org/web/20190412075821/https://masterweb.jpl.nasa.gov/reference/paints.htmFraser