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Maxim Integrated - Integration Nation
Dennis Feucht

Thermocouple Nodules, Cold Junctions & Integration Opportunities

Dennis Feucht
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Brad Albing
Brad Albing
5/28/2013 5:49:32 PM
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Blogger
Re: Error propagation
I hadn't thought about the implications of selling a piece of test equipment with regard to the possibility of needing to get it certified by a testing agency. Good point. But beyond that, good observations on techniques to evaluate error sources as part of the design process.

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DirceuRodriguesJr
DirceuRodriguesJr
5/28/2013 12:59:41 PM
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Artist
Re: Error propagation
Good question,

    when you launch a measuring device on the market, regulatory agencies require that Certificate of Calibration includes the measurement uncertainty or other statistical values. But it does not provide much information on how the product was engineered from the beginning, in order to reach the final specifications. I'm referring to the mathematical tools (Total Differential, Taylor Series, Mean Square Error, etc. ..) used to evaluate the error propagation, select components (eg tolerance, ADC resolution,...) and write the software (int32, int64, ...). I'm not talking here about significant figures - which is something that physicists like, but engineers seem do not to pay much attention. For example, some engineering students often ask me why the LCD is showing 1.22, 1.24, 1.26, ... I wonder if the classic courses are teaching this kind of thing to our future professionals. I also think there is little literature specifically for the filed of electronics.

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Brad Albing
Brad Albing
5/28/2013 9:05:42 AM
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Re: Error propagation
Dirceu - did you mean that you are concerned that many engineers designing products don't go thru this sort of analysis?

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Brad Albing
Brad Albing
5/23/2013 10:41:03 AM
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Re: TCs are key
Yep - I knew that - but you're right - lots of folks get that one wrong. That'd be a good question to give on a job interview.

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Brad Albing
Brad Albing
5/23/2013 10:38:10 AM
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Blogger
Re: Thermodynamics
DK - that's related to Heisenberg, isn't it? Or maybe it's the observer effect. You can't measure something without changing what you thought you just measured.

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DirceuRodriguesJr
DirceuRodriguesJr
5/22/2013 2:14:45 PM
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Artist
Error propagation
   I worry if developers involved with temperature related instruments, especially the low cost ones, actually do all that end to end error propagation analysis (sensitivity, mean square, derivatives,...) - from the sensor, conditioning circuits, ADC (oC/bit) and the impact on the final equation (fixed point Q format or floating). Or a more direct way: Post-design statistical measures in order to attain the desired specifications.

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TheMeasurementBlues
TheMeasurementBlues
5/21/2013 10:12:23 PM
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Teacher
Re: TCs are key
Brad, you'd be surprised how few people even get the basic concept of a thermocouple. It's a case of how wrong information, repeated enough, becomes accepted. Simple, but Misunderstood.

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Brad Albing
Brad Albing
5/21/2013 4:28:21 PM
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Re: TCs are key
I would hope that the engineers and technicians working in and around the clean room would have a complete and thorough understanding of thermocouples - else the company fabricating the microchips will be in big trouble in a hurry.

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DEREK.KOONCE
DEREK.KOONCE
5/21/2013 11:48:29 AM
User Rank
Master
Thermodynamics
One other improvement thought is to think of the heat-sink capability of a thermocouple. Though in most cases the thermocouple is very small compared to the object being measured, but if the masses are similar, then the thermocouple can act like a heatsink with the leads being fins. Furthermore, if any air flow exists, the leads can further act as heat sinks.

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analoging
analoging
5/20/2013 8:42:51 PM
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Blogger
TCs are key
Having a good fundamental understanding of thermocouples is critical for work in clean rooms for the fabrication of microchips. Nearly all process tools have some sort of Tc for temp measurement and their accuracy often dictates the performance of a particular process. Occassionally, the wrong specified type is inserted into a system such as a non-oxygen compatible type which leads to quick degradation and failure. 

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