BX-350 portable Blackbody temperature reference teardown by Fraser

[Fraser]

Those of us familiar with the thermal imaging market will have seen the BX-350 Portable Blackbody temperature reference being sold under several brand names, including ATP and CEM. The BX-350 is a heater based Blackbody that can produce accurate(?) reference temperatures in the range Ambient +5C to 350C using its ~50mm diameter emission plate? Sounds useful but I have never seen inside one of these units and always wondered how well designed and built they are. I have yet to see a teardown of such a unit so when one came into my possesssion recently, it provided me with the opportunity to provide a teardown for members of this forum.

The teardown took place yesterday and will be shown in this thread later today.

Executive Summary: Relatively compact design, decent emission plate module design, otherwise of not great quality ! These units retail at significant prices and are, in my opinion, not a good investment. They need to be rebuilt from scratch. The unit is of poor design, uses cheap components and is poorly assembled. Every screw in my unit was either finger tight or loose ! Best Avoided !

Compared to the Dahua Blackbody temperature references that I previously dismantled for this forum, the BX-350 is of poor quality.

I will provide the teardown pictures later today but attach some exterior sales brochure images plus a teaser interior image taken when I first opened the units casing.

Fraser

[Fraser]

My unit arrived in a faulty condition. The cooling fan was not running. The fan is rather important in a Blackbody that operates at temperatures as high as 350C ! The cause of the failure was the cheap fan dismantling itself ! The brushless motor PCB separated from the fan chassis and the two fan bearings were loose in their mounts. Basically a cheap and nasty fan that likely failed due to an impact to the BX-350 unit at some point in its life. The previous owner does not recall ever hearing the fan running ! It is supposed to be running all the time and the PID controller works against its cooling effect. Without the fan, things around the emission plate module get very hot and the PID suffers initial temperature overshot. The overshoot activates an ‘out of permitted tolerance band’ error and the heater is disconnected by a relay until the emission plate drops back to a temperature within the permitted tolerance of the set temperature. The heater is then reconnected and the Blackbody operates normally (but without the fan obviously). A new fan with ball race bearings has been purchased and will be fitted as part of the reassembly process.

Pictures of faulty fan attached.

Fraser

[Fraser]

OK,

Time for the next part of this teardown thread.

Let me set the scene first though.......

I am fortunate enough to already own several Industrial/Lab grade BlackBody thermal references against which to test and calibrate thermal cameras. Some I bought as surplus, others were incomplete and needed controllers making for them, whilst my favourite Mikron "large area" Blackbody's were gifted to me by a very generous fellow forum member  You know who you are.... thank you  These high quality Blackbody's have given me a good understanding of what should be inside such a unit and how it should be designed and constructed. These are the baseline against which I compare other Blackbody units that I have found on the market.

A while back I was fortunate to discover a seller offering the Dahua Blackbody thermal references used in Fever Screening setups. Those thermal references provide the thermal camera image analysis software with a known accurate temperature against which to calibrate its Fever Detection algorithms. As a "medical" type device you would expect such a blackbody to be well designed and constructed. Well with me being both a perfectionist and a Pessimist by nature, I expected a pretty rough design and build in a pretty case from the Dahua unit. I was wrong ! Yes the Mk1 version that I have is a little rough around the edges but the Mk2 unit that I also have is a more refined design and impressed me. The Dahua units were designed to operate at around the temperature of human skin so ~35 Celcius and that could be set on the good quality OMRON or Fujitsu PID that is used in the dahua units. The maximum operating temperature of the Dahua reference is set only in the PID's configuration and constrained by the materials used to make the emission plate. I have run one of mine at 100C without incident.

To see my teardown of the Dahua Blackbody, go here......

https://www.eevblog.com/forum/thermal-imaging/danua-reference-blackbody-under-the-covers-)/msg4139053/#msg4139053

So why am I telling you about the Dahua Blackbody when this thread is about the BX-350 Blackbody that is sold under the brands ATP, CEM and others ? Well the BX-350 may look like a decent Blackbody and has an impressive +350C maximum temperature.....but it is actually everything that I so wrongly expected that the Dahua would be. To put it bluntly, the BX-350 is a turd ! (Excrement) So with that in mind, let us continue with the teardown description and pictures 

To be continued shortly .........

Fraser

[Fraser]

First Impressions upon arrival.....

The used BX-350 that I purchased was in well used condition. It had one of the temperature controller vinyl button covers missing due to numerous operations, plus the emission plate had some minor marking to the high emissivity paint. Neither of these issues was a problem to me as I was buying the unit as a bit of a restoration project anyway. I liked the idea of a compact, portable blackbody that could achieve +350 Celsius and I had seen this particular model for sale over many years so it could not be that awful.... right ? how wrong I was

Now it may be my memory tricking me, but I seen to remember the BX-350 being sold new for around £500 pre-pandemic. I now see them being offered at neared too £1000 ! Spoiler Alert..... the BX-350 is not even worth the lower £500 asking price. £200 would be pushing things for this unit, as supplied.

As many readers will know, Blackbody thermal reference units are not that common and are considered somewhat specialist items. This leads to higher retail prices and often high useed prices as well. I got lucky with this well used unit and was not disappointed with what I received for my money when it arrived. It would make a good basis for a restoration project and likely improvements to make it more useful to me. The Dahua BlackBody's are nice pieces of kit, but they cannot easily be made to operate above 100 Celcius and I wanted a portable blackbody that can produce at least +250 Celsius with acceptable accuracy, without it being a serious fire hazard !

Upon powering the BX-350 and setting a temperature of 40 Celsius, I was rewarded by the unit silently increasing the temperature of the emission plate towards the 40c target. Note that I said "silently" in that sentence... that is not right for this unit as it contains an 80mm fan that should be running ! So we had a dud fan to fix...what next ? Well the 40 Celsius target temperature was reached and then exceeded until the Temperature Controller went into over-temperature alarm mode and disconnected power to the heater. The PID had a tolerance band around the set temperature which, if exceeded, indicates a problem (excessive undershoot or overshoot) and this activates an alarm output that acts upon a relay to disconnect the heater from the Triac controller. So my Bx-350 was overshooting its target temperature enough to upset the PID controller. The good news was that once the emission plate temperature dropped back within the set temperature tolerance band, the temperature controller reconnected the heater and began to regulate the emission plate temperature correctly using PWM. I could see what was happening..... when first turned on and set to a target temperature, the Temperature controller applies 100% power to the heater to quickly raise the emission plate to a temperature close to that which the user set. Then the PWM drive to the heater triac brings the emission plate onto the target temperature with its variable duty pulse train.... or so it should. Not in my case though as the cooling fan was not running. The lack of a cooling fan has two significant implications in the BX-350.... firstly it is used to work against the heating action of the PID controller to assist in preventing significant temperature overshoot and reduce the time it takes for the emission plate to shed excess heat energy, secondly it is a safety system that blows cooling air around the emission plate heater module to create an air curtain between it and the surrounding environs within the casing. Without that air curtain, the emission plate module would introduce a significant temperature rise within the casing of the BX-350 when it was operating at high temperatures, such as its maximum of +350 Celsius. Indeed, the user manual warns that when operating the unit at such high temperatures, it must be set to a low temperature and the heater/emission plate allowed to cool before the unit is switched off and fan cooling lost. The manual warns that failure to do this could easily damage the BX-350. I had better fix that fan fault as a priority then 

Upon removing the top cover of the BX-350 I was met with a sight that was not pleasing to my eye. I immediately knew that I was working with a piece of equipment not dissimilar in build quality to a really inexpensive soldering or hot air rework station ! It had that cheap and nasty appearance that I know all too well. YUK ! A quick look at the fan that is positioned behind the heater and emission plate module quickly revealed the problem. The fan had dismantled itself this safety critical part had literally come apart and there was no RPM monitoring to activate an alarm or safety shut-down... classy, real classy 

I removed the fan and found its casing to have been distorted by over tightening of the vertical bracket screws. This did not cause the fan to fail though. Whilst there was no damage to the BX-350 casing, I suspect that it suffered a bump at some point in its life and the fan flew apart ! Yep, the fan rotor, two ball race bearings and the windings PCB all exited the chassis backwards and jammed into the supporting bracket. it was dead and burnt out when I reassembled and tested it. Upon contacting the previous owner, he was surprised but admitted that he had never heard a fan running when he used it and he had used it a lot over the years. He knew about the temperature overshoot alarm but as the unit settled and worked after some settling (cooling) time he thought that normal behaviour. Thankfully I see no evidence of overheating in or around the heater module  I think the unit was used at lower temperatures so the fan was less important for cooling.

A new, decent quality fan has been purchased in preparation for rebuilding the BX-350. I purchased a fan of the same air flow specification as the original as there may be a need for the air flow to balance with the PID programming that I cannot easily change.

So what next ? .... a teardown, that is what 

I did not trust this units build quality so a complete teardown was essential for my confidence in the units safety. My concerns were fully justified as we will see !

Let us break down the sections of the BX-350 that I disassembled and inspected.....

[Fraser]

1. The PID Temperature Controller

The PID temperature controller in a BlackBody reference is responsible for ensuring that the units emission plate is maintained at the desired temperature and well regulated in terms of drift and settling time. the quality of the PID controller can make or ruin a BlackBody's performance so we should expect a quality product, like that used in the Dahua blackbody that incorporated a "bought-in" expensive OMRON or FUJITSU PID temperature controller that inspires confidence in a design. No expense spared and all that.

In the BX-350 we find a typical cheap PID temperature controller that is commonly available from ASIA for around $30 ! It is what you commonly find in a cheap product that needs to regulate a temperature  but without any great precision ! A Eurotherm or OMRON it is not I immediately noted that the top casing of the Temperature controller had been modified. A large hole had been cut in the plastic using a soldering iron ! A user modification maybe ? .... Nope, that is a factory mod as we will see 
The hole provides access to a multi turn potentiometer that sits on a daughter board that has been added to the PID controller sensor input PCB. The function of that daughter board.... to trim the PT100 input and bring the unit onto calibration. Soft calibration ? not on this PID controller  The modification is ugly and says a lot about the PID Controller in its standard, as supplied, Ex factory, form. The Blackbody manufacturer clearly had problems getting the controller to supply the required  emission plate temperature for their product.

Note that I mentioned a PT100 input to the pid controller. That is correct, at least the BX-350 uses a PT100 RTD temperature sensor rather than a thermocouple. Whilst this is good, it only provides an accurate emission plate temperature of the PID Controller is of decent performance.

In the longer term, I will be fitting a high quality Eurotherm PID temperature controller to the BX-350. I have plenty of such pid controllers but sadly not in the short case 72mm x 72mm format  Good quality PID controllers are quite expensive so I will either wait for a 72mm x 72mm short-case PID to appear on eBay, or install a Eurotherm smaller case type. This is NOT something you want to have to do if you just bought the BX-350 for almost £1000 ! Nothing about the PID controllers PCB's inspires confidence in the unit from me. Cheap and cheerful generic no name kit.

Of note is that the BlackBody manufacturer has removed all identifying labels including the rear terminal designations ! The PCB's are marked as "ECT" but I think that is the PCB fabricator and not the temperature controllers brand. If anyone knows the manufacturer of this PID controller, I would be interested to hear from you 

Fraser   

[Fraser]

2. The PID Controller to Heater interface

A small custom PCB is used to interface the PIC temperature controller to the heater that drives the emission plate.
The PCB is nothing particularly interesting but I will detail it here for completeness. The PCB provides a regulated 12V DC supply, TRIAC driver for the heater and a relay that can disconnect the heater drive if the PID goes into over temperature alarm.

The regulated 12v power supply comprises an external transformer, a bridge rectifier, smoothing capacitor and 7812 linear regulator. Note that the pcb doe not provide the normally recommended decoupling capacitors at the input and output of the 7812 regulator. That is poor practice and unacceptable in a commercial product. The 12v dc supply provides power to the 80mm fan.

There is a triac mounted on the PCB that provides the PWM drive to the heater using the PWM output of the PID controller. the PID Controller drives the TRIAC via an opto isolator. The supply to the heater may be disconnected using a relay that is mounted on the pcb. this relay is controlled by the PD controller. The normally closed contacts are used but may be opened under the alarm output control of the pid controller. 

A final comment on this little PCB .... just look at the standard of soldering on the wires to it ! I shall say no more !

Fraser

[Fraser]

3. The Heater and Emission plate module

The BX-350 uses a self contained heater and emission plate module that actually looks to be fit for purpose ! There is a heater core that supplies the thermal energy to the emission plate "core". The temperature sensor attached to the emission plate is a PT100 RTD that uses ceramic insulators due to the high temperature that the cores can achieve. The heater core and emission late are surround with a metal shell that sits inside the modules outer casing. Conduction of thermal energy from the heated core to the outer module casing is minimised by maintaining small points of contact. Air is free to move around the heated core.

I could find no issues with the design of the heater and emission plate module design but would have liked to see a high temperature safety thermostat or thermal fuse to prevent serious over temperature events leading to fire. The current safety systems within the BX-350 appear to just rely upon correct operation of the PID temperature Controller. There could be a thermal fuse buried in the heater itself but I cannot verify this as it is a sealed unit.

Fraser

[Fraser]

4. The wiring and interconnects !

What can I say..... the wiring in the BX-350 is quite frankly rubbish ! 

Where to start ?

1. The insulated wire used is stiff and of too large a gauge to fit through the TRIAC interface PCB wiring holes
2. The wire does not appear to take solder well. Could it be plated aluminium wire  I wonder ?
3. The wire ends were tinned before being clamped in the interconnect terminal block which is not good practice as solder flows under physical pressure and the wires can come loose over time. This was the case here as all of the interconnect terminal screws were loose ! This was because the wires collapsed due to solder flow and took the tension off of the screw clamps. I was amazed that the unit even worked when I first tested it.
4. The soldering of the wires to the TRIAC interface PCB was of very poor quality and, due to over-size were soldered to just the top of the PCB through holes.
5. The soldering of all wires to the mains input socket, two fuse carriers and main switch was poor and some were dry joints that allowed the stiff wires to rotate inside a solder collar ! The Earthing wire on the mains input socket was very poorly soldered.

Not impressed and I will have to completely rewire the BX-350. I will use high quality wire and will also replace the mains input socket and mains switch as both are cheap junk.

Fraser

[Fraser]

So what do you do when faced with this pile of 

You tear it down and rebuild it as it should have been built, that's what 

I have torn it down and will make a project of it to rewire everything, likely ditching the rubbish connector block in the process. There really is no need to use that connector block, it appears to have just made assembly easier in the factory.

In the pictures below, you will see that the unit has been stripped down. Take a close look at the small transformer primary wiring. The transformer uses a dual primary winding for 115V/230V compatibility and the manufacturer soldered the windings in series. No problem with that, but look at the quality of the solder joint ! It just pulled apart in my fingers 

Fraser

[Fraser]

So there we have it, the BX-350 BlackBody thermal reference. 

Please do not buy one of these units as I honestly believe that they are a piece of junk, built in some sweat shop of a factory, just like cheap soldering stations and the build quality is simply tragic. Cheap parts put into a reasonable casing and connected together with suspect wire and terrible soldering ! I suppose I should be thankful that they even included fuses in this design.

There seems little point in a performance test of the unit when it is already highly suspect due to build quality. I will test and calibrate this unit once I have rebuilt it properly and maybe fitted a better PID controller.

Fraser

If I have just saved you from buying one of these pieces of questionable quality kit, good  Do not waste your hard earned money on it.