Products > Thermal Imaging

Dahua Reference Blackbody - under the covers :)

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Fraser:
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 input
2. 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

Fraser:
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

Fraser:
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-faye

I 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.

Vipitis:
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.

Fraser:
Cover has been removed from the Dahua DH-TPC-HBB  :)

Inside 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 ventilation
5. 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

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