The fix here, which has the negative downside of costing a lot more money and rendering the equipment useless once it gets too old (because parts would no longer be available) would be to have built the heater with a proprietary sized-and-threaded hole for the thermocouple, or some other way that only a vendor-approved part could be used for replacement. But where would the fun be in that?
I hear alarm bells when someone talks about "proprietary parts". We shy away from vendors who do too much of this. I had a vendor once admit to me that they used a custom made feed chain for carrying lumber through their machine because it made for good parts business. They did the same thing with their cutterhead spindle motors: completely custom motors. Needless to say, we ran away from them screaming. Being tied to the OEM too tightly is a sure fire way to spend way too much on replacement parts.
In the case where buying wrong sized replacements and people with no knowlege modify the spares, well, tough crap. Consider the servicemans visit a training excercise. Buy the spares (overpriced) from the OEM if you don't know what you are doing.
Pretty hilarious that they were trimming that thermocouple and still having it work. I made a themocouple tip welder from three 10,000 microfarad capacitors in parallel, charged up from a 12 volt source through a 330 ohm 1-watt resistor. I connect one side of the charged capacitor bank to the twisted thermocouple wires (both together, with an alligator clip an inch from the end), and touch the tip to the other side of the capacitors. Typically 1mm or so of material disappears in the resulting flash (use eye protection!) and the themocouple is welded and ready to go. Then I discharge whatever's left in the capacitors through the resistor for safety.
This reminds me of the sign in an auto repair shop stating the job will cost you double if you tried to work on it first. Be careful of the Mickey Mouse fix that isn't a fix.
The amazing thing is that they were able to form a working thermocouple junction - multiple times! - using nothing but a set of shears. I think these people are more skilled than we give them credit for.
The other amazing thing on this fix is that the operator took the time to change the heater but stopped short of changing the thermocouple before calling in outside help. A quick resistance would have shown the failure.
The flaw was in not having a means for adjusting the thermocouple penetration. Designing in proprietary parts in order to assure that only the "right" part gets used should always cause a manufacturer grief! The solution that we used was to provide repair parts that were easier to install than the generic ones, or were already calibrated, or sometimes even less costly. Of course, we needed to be able to ship repair parts overnight, or faster, for some customers.
The fact that anybody cut off the end of the thermocouple shows that they had no idea what they were doing.
One more thing, which is that many thermocouple-based controllers have an option called "upscale-burnout", or "downscale burnout", and, using a combination of upscale burnout and an overtemperature alarm contact output, it would be simple to have an "open thermocouple" warning light.
1) The machine was made in Germany; the original thermocouples were German and given thet the machine was down and there were no remaining spares, I had to find a fast (and reasonably priced) solution. Which was to use a standard TC probe from Omega Engieering. The original probe was (apparently) a standard Off-The-Shelf probe, with a probe length of about a foot, coupled to a 5 foot cable with a DIN connector to mate with the control box. The entire assembly appeared to be a standard, stock item (these machines are not made in huge quantities, so custom TC probes were probably not on the designer's hot list.
2) The probe was mounted to the heater (at the cold end!) with a cable tie. The end of the probe - the last 2 inches or so was bent (by the machine operator) at right angles to fit into the hole in the side of the heater just below the heating element. The tip was inserted into the hole until it was in the heated air stream and locked (gently) in place by a setscrew. If the PID controller was set to (say) 450C and the temp. readout also read 450C, then you had it right, and got back into prodution - otherwise, you would adjust the probe in or out until things worked properly. Not exactly rocket science....
3) The operator, while certainly capable as a mechanic, was not familir with these sort of controls. The shop manager was also not really familiar with these details either. This was a small company without electronic personnel on board; I had done some work for them, so they called me in. Unfortunately, when I asked if they had any spare probes, they handed me a plastic bag with half a dozen of them - all defunct. They had just burned out the last one. The only good thing about this, is that all the dead probes had connectors, which can be used to make the new Omega OTS probes compatible with the control box.
4) The advantage of the design is that it uses OTS thermocouples and with the long probe, keeps the low-temp cable away from the hot zone, so ordinary cable can be used, thus keeping the cost down. Given that the TC probe is basically a consumable, that's not a bad idea, both from a cost and logistical point of view. The logistical issue is paticularly inportant, given the cost of downtime and the time involved (even using Fedex, etc.) of getting probes from Germany.
5) The PID Controller was a somewht older design, and while there was a safety relay to shut the machine don in the event of a TC failure, there were no diagnostics in the system.
By refining topologies and using new fluid technology, Moog's new peak sine drive controller increases available power without increasing controller volume.
Lantronix Inc. has expanded its line of controllers for sensor networks with the release of a rugged controller that improves management of automation systems used in a number of industries, including manufacturing, oil and gas, and chemicals.
Inspired by the hooks a parasitic worm uses to penetrate its host's intestines, the Karp Lab has invented a flexible adhesive patch covered with microneedles that adheres well to wet, soft tissues, but doesn't cause damage when removed.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
7 
