TUS Sensors in AMS2750 Calibration Requirements

robanbieber

Starting to get Involved
#1
The AMS 2750E Pryometry is quite complex and convoluted when it comes to sensor requirements and calibration do's and don't's . I am using some type K expendable sensors for my TUS and despite all the references to not being able to recalibrate them I do not see a requirement that they would need to be recalibrated after initial calibration unless they are damaged or the user has taken action after "ensuring that excessive drift has not occurred under the particular conditions (environment, time, and temperature) of exposure." section 3.1.2.3
From section 3.1.3.4
Any base metal TUS thermocouple that is (1) used exclusively under 1200 F (650 ?C), (2) identified, and (3) preserved/protected from damage (i.e., crimping, excessive moisture contact, corrosion, etc.) between tests orremains installed on a rack that is protected between tests,) shall be limited to no more than 90 uses or 3 years, whichever comes first and may be reused subject only to the limitations of 3.1.3.1 to 3.1.3.2.

It appears that I can use and reuse my type K expendable sensors for TUS at 500F or less as long as they are not damaged (3.1.3.1 and 3.1.3.2) and according to Fig 1 in the reuse column that I need to follow the U-formula at 3.1.3.3 and 3.1.3.4
So as I see it I can use my K expendable sensors for 30 uses (3.1.3.3 is the 30 restriction for expendable sensors) or "3 years, whichever comes first.." .
So if I have one oven that requires a TUS quarterly (one "use") I can pretty much expect my TUS sensors to last 3 years without having to be replaced OR recalibrated... and since they cannot be recalibrated I would just replace them.. of course if they are damaged per 3.1.3.2 before then they would have to be replaced before the time or use limit comes into effect.
Am I correct? This seems that I can actually justify that I do not have to or am not allowed to check/calibrate these sensors ever for 3 years!

I have attached the Fig 1 and the sensor cal table 1 with its accompanying notes...
 

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BradM

Staff member
Admin
#2
Basically, the wires have very short lifespan; with increased temperatures and frequent uses degrading them even quicker.

So what exactly are you trying to determine? How often to replace wire?

And yes. :) It can all be quite confusing. :D
 

robanbieber

Starting to get Involved
#3
Well it makes sense that if I only use the probes for less than 30 uses at less than 500F that I should easily be able to get 3 years out of them before having to "recalibrate" or scrap them!
What I do not understand is what is the reference for recalibration at 3 months in the base nonexpendable row in Figure 1? I guess it covers the fact that if you use these at higher temperatures than you are expected to make sure that the heat does not damage and degrade their performance and you are pretty much penalized for wanting to use a nonexpendable sensor. Unless you do the calibration of the sensor inhouse the costs and time associated with sending out the sensors for a cal every 3 months would be cost prohibitive and it would make more sense to buy the expendable ones at the start. According to the document I would have to start the 3 month cal cycle on a base nonexpendable J sensor used at under 1200F right after the first 3 months of its use irregardless that section 3.1.3.4 grants 90 uses or 3 years! Had it been a base expendable J sensor I would not have to worry about the 3 month cal and instead take the 30 use or 3 years only as the requirement!

Do you read section 3.1.3.4 as stating that the sensor after 90 uses or 3 years is to be discarded , OR do you read section 3.1.3.4 as stating that after 90 uses or 3 years the sensor may be reused if not damaged per section 3.1.3.1 to 3.1.3.2. Section 3.1.3.1.2 seems to nullify this as even if you "salvage" the sensor you still need to include the number of uses prior to the salvage to the total number of uses (which tends to say a "salvage" does not even save the whole sensor wire from being scrapped!)... or does this only apply to expendable sensors as referenced in 3.1.3.3 from 3.1.3.1.2? ARRRGH. :frust:this seems really messed up.. I attached the sections in question in case anyone has the answer, to this convoluted doc... Thanks.
BTW I really have learned a lot from this forum in my short time here .... hope it can remain active...
 

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BradM

Staff member
Admin
#4
I know it can be confusing. Ok... if you don't mind, let's approach this from a different angle.

Let's identify your needs.
  • How many ovens/chambers do you map?
  • How many survey temperatures for each chamber?
  • How often is that performed a year?
Then, for each of these, break them into different components for the temperature break points (500?F; 1200?F; 1800?F) if that applies.
Are you purchasing calibrated rolls of wire? Special limits of error?
Are you purchasing teflon for below 500F? Or is it all a fiberglass based wire?
One more question (I think:D)... how does your wire physically appear over time? Does it appear to get pretty worn/ pretty quick? Is a door closing on them, wearing them out?
Sorry for all the questions, and you can ignore if you wish. I just think it would be much more helpful to determine what your needs are, then develop a use-approach based on the procedure.
 

robanbieber

Starting to get Involved
#5
Thanks.
I have only one oven currently with minimum 9 sensors for TUS. I will probably add an another oven to the TUS schedule for a backup.
I have a single temp of 302F and that is what I have my TUS dataloggers and sensors all calibrated for to keep it very simple and inexpensive, we only have one process temperature for the only 3 parts we dry film!
My TUS is obviously also for this one temp... to keep it simple and fast as I only have to ramp the oven up and down once!
I have purchased the TUS expendable k thermocouples in a 6 inch probe configuration because that really makes it easy to clip them on my oven rack and position them exactly toward my zone extremities. This makes clipping the ends off and reusing them impossible as compared to a straight wire one but reading into the 2750 spec i did not seem to need this as long as the probe/wire was not damaged plus getting 3 years for my purchase seemed like a good ROI. These sensors/wire are PFA coated and have special limits of error to meet the 1.1C of the spec. but they are considered expendable due to the PFA wire sheathing at least that is how I interpret their definition of "expendable".

With a class 5 oven with Intrument D, we are currently required to do a quarterly TUS but can drop it to semiannual after a year of consecutive TUS reports. This will enable me to add my second oven with the same set of probes, as it currently stands if we stay quarterly TUS with two ovens that would be 32 uses for 3 years which is a bit over the allowed 30 but if we went semi annual then I have extra uses available.
 

BradM

Staff member
Admin
#6
Thanks for the writeup! So you have non-expendable TCs.

What about keeping a log of use?. At 30 uses, carry your data logger to a local, competent lab and have them calibrate the probes and the data logger as a loop?

To me that sounds like the least expensive and the easiest.
 

robanbieber

Starting to get Involved
#7
Why do you say I have nonexpendable TCs?

Screen Shot 09-29-14 at 12.09 PM.jpg

Screen Shot 09-29-14 at 12.10 PM.jpg

I believe my PFA coated TC wires fit the definition of expendable in the document..

There seems to be a minor conflict in the documents of Fig 1 and table 1. Table 1 seems to say that no matter whether the E or K sensors are expendable or non expendable the "types E&K not permitted" for recalibration. But Fig 1 seems to give more detail based on whether it is a TUS, resident SAT or non resident SAT and whether it is expendable or not. Figure 1 seems to allow recalibration of E&K NONEXPENDABLE as long as they are never used above 500F. So if I go with Figure 1 detailed rules and determine my sensors are nonexpendable then I could justify a recalibration on a 3 month schedule forever as long as we meet 3.1.3.4, and 3.1.3.1.2 only refers to expendable sensors as pointed to in section 3.1.3.3.
It is not cost effective to recalibrate a non expendable K every 3 months for 3 years with an external cal service as compared to using an expendable one for 3 years with only an initial calibration and then throwing it away and buying a new one! That is how I read Figure 1!
 

BradM

Staff member
Admin
#10
OK. So I would recommend buying a 1000' roll of wire. That way, the cost of calibration is then spread across the roll.

Make t/c's , keep track of their use; and when they're done, toss them.
 
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