EEVblog Electronics Community Forum
Products => Thermal Imaging => Topic started by: Fraser on August 25, 2020, 02:00:54 pm
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OK, a bit of fun. A Seek Reveal is showing an interesting fault symptom and you have to decide the likely cause without opening its case. I will show the fault symptoms in the attached pictures but the fault description is that part of the thermal scene is missing on the displayed scene. The whole bottom left area of the displayed image is missing. You are the tech and need to assess the provided images and suggest what the cause of the symptoms might be. Look closely at the information that the images present to you. Everything you need is there ;) The pictures are not mine and I would image a flat thermal scene provided by a large area blackbody operating at 40C. Such a scene is more helpful than those attached.
In your answer provide your reasoning as that can help others to understand how you came to your diagnosis.
This is a simple fault but I thought it might be fun to diagnose using the pictures.
And yes, I do know what the fault is and in the not too distant future I may document this cameras repair.
One hint : 74F = 23.3C
Enjoy
Fraser
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FCC flag failure. It doesn't open all the way and therefore shadows the sensor, giving you a reading of a temperature close to the sensor flag/sensor itself. It will let in a sliver of radiation on the bottom left of the sensor as the image is inverted.
The third image shows ghosting artifacts because the camera corrects(subtracts) information it though was the flat field, but still partially showed the scene. The resulting image is an offset(useful for some applications, but unwanted here).
To confirm this hypothesis one needs to take off the lens and observe the shutter and it's operation. It might still move but the resting position is not completely clearing the sensor.
I had this issue myself and was able to fix it by carefully cleaning the flags and adjusting some screws. It took me several attempts to get right, but I recorded video of the malfunction and correct function. Having no shadows on he sensor allows for much better AGC and generally feels less claustrophobic.
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Well done Vipitis,
You have described the fault cause and symptoms associated with such perfectly :-+
The next step for me will be to investigate the cause of the FFC shutter failure. It is an interesting design with the flag attached to a small bar magnet thar pivots inside the FFC drive coil. Likely points of failure are the coil drive and flag pivot. If the camera is dropped, it is possible that the flag pivot has become displaced. Whether the fault is an easy fix or something more complex will have wait until I receive the patient in a week or so.
Fraser
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Some of pictures for those not familiar with the Seek Reveal FFC solenoid design and flag. The two images are of a standard Reveal core and a Pro core. The principle of operation is the same in both but the flag is smaller in the non Pro core as the microbolometer is Physically smaller.
Fraser
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For anyone interested, the scene measurement shown in One of the pictures just added to the evidence that the FFC shutter was sitting across the Microbolometer in a semi deployed position. The microbolometer is measuring the temperature of the plastic FFC flag and the reading is sensible. As such the microbolometer is working as it should. There is a shape to the ‘blank’ area that if you study it, matches the shape of a partially deployed Seek Reveal FFC shutter ;)
If the microbolometer had been the cause of the fault we would have seen different symptoms that can include, but are not limited to :
Dead pixels scattered around the area of failure
Dead rows and/or columns in the area of damage
An area of differing thermal response where damage has occurred, but not not total ‘blindness’
Incorrect temperature measurements when the spot temperature cross hair enters the area of damage.
An area of high noise and digital garbage where damage has occurred
A whole section of the microbolometer not functioning at all. It would correlate with rows and columns and have straight edges as a result. No meaningful measurements would come from within that ‘dead’ area.
A relatively small area of ‘blindness’ caused by a damage event or contamination on the microbolometer window.
Complete microbolometer or ROIC failure resulting in no thermal image displayed.
Fraser
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With regard to potential FFC flag pivot failure due to a drop event, it may just be a case of popping the Pivot pin back into its receptacle. If the pin or receptacle have been damaged, life becomes more complex ;D
If the failure was due to FFC coil drive loss, I would check the continuity of the coil and it’s wiring back to the drive chip. I would use an oscilloscope or multimeter to monitor the drive coming from the FFC solenoid driver. If the wiring was OK but no drive was present from the coil driver chip, I would need to delve deeper into the FFC drive design. From memory the command for FFC comes over an SPi data link in the Seek Pro core but I would need to check if the standard core differs in this respect.
My patient does not look to be suffering from drive failure as the FFC shutter appears to be stuck in its current partially deployed position. It is more likely a mechanical problem.
Fraser
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Also to be borne in mind when working on any Seek Thermal cores microbolometer area is that the microbolometer is connected to the PCB using thin and very fragile bond wires. One wrong move or slip can damage the bond wires or, at best, bend them, causing adjacent wire shorts. Steady hands, magnification and care is needed when doing any work on the Microbolometer PCBA.
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I might create this sort of post again if I find a suitable candidate to diagnose. Most of my patients do not have such simple faults however and it would be unfair to expect readers to identify the cause of a fault without access to the patient and the ability to carry out testing. I will see what I can find though. I may even be able to create some faults on cameras that are diagnosable from images and a basic fault description. I could always chuck in a few test measurements or DSO waveforms to aid diagnosis ;) We shall see. I will only do it if people enjoy such ‘for fun only’ posts.
Fraser
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The poorly Seek Reveal has just arrived :)
A quick operational check confirmed the fault. When switched on I can see the classic FFC flag shape and hear the FFC flag solenoid trying to operate so we can deduce from this that the solenoid is being driven :-+ I am expecting a FFC flag that has a mispositioned pivot or the bar magnet may have shifted in its holder and jammed against the solenoid coil ? We shall see later when I remove the core. Sadly this unit has the awful ‘Pentagon shape + centre pin’ security screws fitted :( I will need to deal with their extraction first.
https://www.fastenright.com/brand/pin-pentagon-security-screws (https://www.fastenright.com/brand/pin-pentagon-security-screws)
https://www.fastenright.com/general-fixings/pin-pentagon-button-self-tapping-security-screw/PP05 (https://www.fastenright.com/general-fixings/pin-pentagon-button-self-tapping-security-screw/PP05)
Fraser
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Can you guess what it is yet ? ;D
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Answer.....
Thick wall copper tube to make a Pentagon screwdriver pattern :-+
The loo roll ? Just a hint that the copper rods are in fact tubes ;D
How do you make the pattern ? You select a thick wall soft copper tube of roughly the diameter of the pentagon extremities and open the centre diameter to fit over the screw heads centre pin. The copper tube is then pressed into the pentagon screw head to press the pentagon shape into the tube end face and leading edge. A fine file is then used to create the correct pentagon shape along the tube, using the press-fit impressions as a guide.
The result is a pattern of the pentagon screwdriver tip for the creation of a a suitable tool in steel.
I just completed a first draft of the copper pattern to check the process effectiveness and it worked perfectly.
Sadly copper is too soft to use as the screwdriver so I cannot use the pattern directly to remove the screw. I could try hardening the copper but it is not the right material. Brass would have been a possibility but I do not think I have brass tube of the correct dimensions.
Once you have a pattern, be it made of copper, plastic, hot melt glue or whatever, you can use it to create an accurately dimensioned tool by offering the tool up to the pattern for Demi Simon all checks. This process is well proven and avoids involving the security screw in the equipment too much....and so lowers the risk of damage etc.
Fraser
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Fraser + Bosch PSB-10.8 LI2 + Drill bit : 2 for 2
Pentagon Security Screws Qty 2 : NIL. 8)
Sometimes, just sometimes, you have to show a screw who is boss and bring out the ‘big guns’ ;D
Those Pentagon Security screws must be made of the softest steel as the rounded out at the application of the driver. Maybe deliberate ? The threads are locked hard into the cameras casing.
My advice on removing these nasty screws...... forget the delicate approach ..... go straight to the drill and replace the screws with something sensible afterwards :-+
Apart from the screws, there was no damage and the camera is well enough sealed against swarf ingress to permit a relatively relaxed approach.
Fraser
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Spoiler Alert.......
The FFC shutter was jammed in its partially engaged position...... but not for the reasons I suspected !
More later, with teardown pictures and detailed images of the failure cause :) It‘s a shocker !
The Patient is doing well and recovering nicely ;)
Fraser
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First let us look at the disassembly of the front section and removal of the screw stubs......
The Pentagon socket security screws were a Royal PITA and, as I have already revealed, I had to resort to a power tool to remove the screw heads. The steel used seems very soft so the drilling process was easy and there was very little vibration :)
Drilling off a screw head leaves a stub that will need to be removed after the front section has been pulled forwards. Note that the front section is a tight fit on the weather seal so just gently press on the top and bottom sides of the metal front piece to wiggle it off. You will see two protruding screw stems that provide plenty of material to grip for removal. The Imaging core should be removed from the camera to avoid damage to it and to provide better access to the screw stem on that side. It is now that I would like to introduce a useful tool that readers should consider as an addition to their tool box..... the screw removal pliers :-+ These pliers are special in that they have hardened jaws designed to grip screw heads, stems or any cylindrical item that needs to be twisted without slipping off. These pliers are simple superb for removing drilled screw stems :) You will see the design in the pictures and they worked perfectly for this task. I was very surprised at just how tight the screw threads were in the cameras chassis. No wonder the heads rounded out when i tried to unscrew them. Of interest to me was the differences in these screws to those used in the later PRO model. The Pro model uses a far better screw system and includes water resistant gaskets on each screw. I will be adding such gaskets to this camera. The standard model uses long self tapping screws that are not covered in screw locking fluid but do seem to be overly tight in their holes. I will source new self tapping screws of the appropriate dimensions and possibly open the holes slightly.
OK, to the pictures that are pretty much self explanatory ........
Fraser
P.S. Fault detail will follow shortly.
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First correct image after the fault was diagnosed and corrected.......
All working as it should :)
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Time to reveal the cause of the fault and it was not what I had expected. It was a design and manufacturing error !
First a description of the core and its mounting in the Seek Reveal camera......
The Seek Reveal core is a self contained module comprising the Microbolometer PCBA mounted on a diecast aluminium chassis that contains the lens assembly. The core is mounted in a neoprene girdle and has a neoprene boot over its front section. The neoprene girdle acts as a means of mounting the core and as a shock absorber.
The Microbolometer PCBA has the FFC flag solenoid mounted on it using barbed 'arrow head' fixings that also provide the electrical connection between the solenoid coil and the solenoid drive from the PCB. As already stated, I could hear the FFC solenoid truing to operate but failing to move completely out of the normally closed position. The issue was therefore unlikely to be drive related.
Upon inspecting the the core installation I discovered what was causing the problem....... that will be revealed a bit later. See if you can spot the issue before reading the next post :)
Fraser
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The reveal (forgive the pun ;D ) .....
Once the core was dismantled, and the Microbolometer PCBA removed from the chassis, the FFC flag was tested and was found to work normally. The cores aluminium chassis and FFC solenoid were inspected for loose debris or possible contact points where the flag could become stuck. No debris or contact points could be found. Attention then moved onto the FFC solenoid design and possible causes of such malfunctioning. It was quickly clear that the design is flawed. The rear of the solenoid pivot assembly has a protruding spigot that comes very close to the edge of the PCBA and extends just beyond the Solenoid coil housing. This looked ripe for a contact point induced failure. The neoprene girdle surrounds the core at the level of the FFC Flag solenoid so its interior surface was examined. There is a cut away area in the girdle to allow the FFC Flag pivot assembly to move. This is not a great design when a neoprene girdle is flexible and can easily move. A clearance check with the girdle fitted showed that the cut away area did permit FFC flag operation BUT, there was an issue when it is installed in the camera !
The neoprene girdle normally has three mounting points but in the Reveal camera the mounting point adjacent to the FFC Solenoid has been chopped off. That side of the neoprene girdle now butts up against one of the front assembly screw mounts. If everything was perfect with the design, this might work OK. However this particular Reveal camera highlighted that the removal of the unwanted neoprene mounting lug and moulding of the front assemble screw mount is defective. It was a recipe for disaster and in this camera it caused the fault.
So what was the cause of the fault ? ..... The poorly modified neoprene girdle was pressed against the rear of the FFC solenoid by the poorly moulded front assembly screw mount. The result was the FFC flag pivot arm rear spigot contacting the neoprene girdle and failing to correctly withdraw the flag from the optical path. Removing the girdle from the core released the FFC flag and enabled it to operate normally.
The remedy to this situation will be to reshape the front assembly screw mount plastic and possibly the neoprene girdle mounting lug stump to remove pressure on, and contact with, the FFC flag pivot..... Simple ;D
Fraser
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For anyone who needs the information....
Front assembly retaining screw physical dimensions:
Head type : Socket Head Half Dome
Head diameter : 3.91mm
Head Depth : 1.45mm
Total shaft length (Plain + Threaded) : 19mm
Of which: Plain section length = 9mm, Threaded Section = 10mm
Thread Type : self tapping for plastic, blunt tip.
Thread Major Diameter = 2.14mm
Thread Minor Diameter = 1.72mm
Plain Shaft diameter= 1.84mm
I believe a fully threaded screw of the same dimensions will be a suitable replacement if one with a Partial plain shank cannot be sourced.
Fraser
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The later Seek Reveal Pro is fitted with a different neoprene girdle and not one that has been chopped about.
Note the totally open area in the girdle where the FFC flag solenoid is located. This removes the risk of interference with the flag pivot action. I will likely modify the standard Reveal neoprene girdle in a similar way.
Fraser
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For those unaware, there is a Teardown of the Reveal camera available here.....
https://www.allaboutcircuits.com/news/teardown-tuesday-thermal-camera/ (https://www.allaboutcircuits.com/news/teardown-tuesday-thermal-camera/)
Fraser
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My two Seek Reveal XR cameras arrived today. The thread detailing their fault and my work on them is to be found here.......
https://www.eevblog.com/forum/thermal-imaging/a-calculated-risk-risk-purchase-two-faulty-seek-reveal-xr-cameras-] [url]https://www.eevblog.com/forum/thermal-imaging/a-calculated-risk-risk-purchase-two-faulty-seek-reveal-xr-cameras- (http://[url))/[/url]
Note on the Pentagon Socket head security screws on the Reveal XR.....
Note that the Seek Reveal XR units both had silicone gaskets On the front assembly securing security screws. I found the screws to be much easier to remove than on the standard Seek Reveal detailed in this thread. My custom Pentagon tip screwdrivers removed three without trouble but was worn out by the fourth so a suitably sized torx bit was used to finish the job. 4 complete screws removed :-+
Fraser
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I have just completed the teardown of the Seek Reveal in order to clean it
I am uploading the pictures to this thread but may also produce a dedicated teardown Post for ease of location in the future for those looking for such.
Of note in the teardown, I thought this Seek Reveal was likely an early model due to the lack of seals under the screw heads securing the front assembly in place. Well it seems this may not be the case as the USB socket on this particular Seek Reveal is a heavily reinforced type that is found on the later Seek Reveal PRO models. The case gasket sealing design remains that of the standard Reveal and not the PRO however.
To the Pictures.......
Fraser
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Of interest during the teardown of two Seek Reveal XR cameras today, was the different case design and neoprene girdle in the front of the unit. The USB connector was not heavily reinforced however. The XR series have also had Ferrite filters added that are not present on the standard Reveal camera that I dismantled.
The Revision number of the standard Reveal Main pcb (Pt No. 368) is Rev 9 whilst that of the XR models is Rev 5. So I have to wonder why the inferior girdle design is present on the core of the later generation Seek Reveal (Standard) unit and no filters. Weird :-//
I attach selected pictures of the XR units.
Fraser
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The Seek Reveal that features in this thread was built in 2016. The Seek Reveal XR units that I dismantled today were built in 2015. So it is confirmed, the seek Reveal in this thread is a later revision that differs to the earlier versions in the following ways....
1. The USB socket is fitted with a reinforcement bracket, as found on the PRO versions.
2. The ferrite filters on the core to main board, and LED to main board cables, are not fitted.
3. The neoprene girdle that holds the core in position and its associated chassis mount points have been changed. The girdle no longer has a cut out area for the FFC shutter pivot assembly spigot.
Fraser
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I have decided to use M2x20 or M2x16 socket head machine screws to replace the two front assembly securing self tapping security screws. It may be possible to use them without first tapping the holes, but I will use a tap just to be safe.
Fraser
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It's remarkable just how much processing power we're getting per milliwatt these days in consumer electronics.
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Power consumption related issues in thermal cameras can extend beyond battery run time as a processor or other VLSI that generates too much heat can be a challenge for the camera designer. Too much internal heating is the enemy of the designer because that heat either has to be transferred outside the cameras casing by some means or tolerated within the casing. Internal temperature changes and elevated temperatures around the microbolometer core can adversely effect measurement accuracy. Whilst radiometric thermal imaging cores take account of the temperature around the core, and sometimes the lens, it is better to avoid generating too much heat in the same space that the core occupies.
So how do you avoid excessive self heating and it’s negative effects on the core ? That is really a question for thermal camera designers but in my experience there are a few options......
1. Use the most efficient processor and VLSI technology available that can still provide the processing capability required, but is not excessively powerful for the task. The ultra low power, more thermally efficient processors can be more expensive than older, less power efficient processor designs though. Some manufactures will want to make that cost saving at the expense of thermal management !
2. Incorporate thermal transfer systems into the physical design to sink heat away from components that are generating heat and passing to an area of less thermal sensitivity, such as the outside of the cameras casing. Heat pipes, heat sink plates and even ducted fans may be used. It is just necessary to move the thermal energy away from the cores local environment.
3. Incorporate thermal storage into the design such that the thermal energy produced by the components within the camera is accumulated in a thermal reservoir that has adequate capacity to aid thermal compensation within the core. The thermal reservoir does not remove the energy within the casing, it just absorbs it, slowing any temperature variance experienced by the core to acceptable levels that may be compensated within the cores software.
4. Active temperature stabilisation of the microbolometer. This approach has fallen out of favour in some modern microbolometer designs due to the relatively high power consumption of the Peltier element incorporated within the cores design and the additional thermal energy produced But the Peltier element that must be dissipated within the case design.
5. The mainly software approach to internal heating within a thermal camera. This approach can include a combination of clever case design separating the core from the heat producing PCB’s, thermal throttling of the processor to manage its heat production, especially when full processing capability is not needed and temperature compensation tables that are used to correct errors in radiometric measurements.
6. No effort made to manage heat production within the cameras casing and only radiometric measurement correction tables used. This is a not uncommon approach by some manufacturers of budget thermal imaging cameras and can explain their somewhat less accurate radiometric measurement capabilities.
The Seek Reveal Pro contains a significantly more powerful processor chip and It’s casing gets noticeable warm during use. It is a sealed unit to provide weather resistance so the core and measurement software must cope with the elevated case internal temperature and heat produced by the powerful LED positioned next to it in the metal front assembly. It manages this task admirable :-+. The standard Seek Reveal cameras (non Pro) use a less powerful processor and do not suffer the same level of self heating found in the PRO model. It should be noted that handheld equipment can take up thermal energy from the users hand so this is also to be considered where internal temperature is concerned. A handheld device that relies upon its case for thermal dissipation can see that thermal path compromised by a human hand wrapped around said casing. Such effectively becomes a ~30C thermal blanket around the camera ! This is especially the case with the seek a Reveal design.
The environmental operating temperature of a thermal camera sold into the World market must also be considered. There are some very warm countries in the world and a design that can self cool and cope in a 25C environment using thermal radiation from its case, may not cope so well in 40C+ temperatures in the UAE, Australia or similar environs. Getting rid of excess thermal energy from a very temperature sensitive device can be a real challenge.
Fraser