Load Thermocouple requirement for TUS (Temperature Uniformity Survey)

[Nmark78]

Good Afternoon,

I'm hoping that someone here might be able to provide a litte help understanding AMS 2750. We recently had our NADCAP and received a finding for not using a load TC during TUS's. As a little background we are a type D instrumentation, however, we do occationally use a load TC when requruired by the customer. The Load TC is not used as a controlling TC. It is a recorded monitor TC only that is used for product acceptace. For our TUS's we use 9 thermocouples. The 8 corners and the center. All TC's are placed in heat sinks. The TUS rack is empty.

The NADCAP auditor did not explain why this is a finding only that it is required. The only thing I can think of is that although we are a type D instrumention, when we use a load TC we change to a type B and that is where the requirement is coming from. Any thoughts or ideas?

It is difficult to come up with a Root Cause when you are not even sure where you went wrong.

Thank you for any thoughts or guidance.

 

[MTProcessing]

Re: Load Thermocouple requirement for TUS

Instrument types A, B, C, D relate only to the frequency of TUS and SAT. I can't see occasional use of a load thermocouple justifying the TUS and SAT frequency reductions that accompany type B, and don't think instrument type has any relation to your finding. I know this doesn't seem to match with paragraph 3.5.13.3.2 (Data from frunace sensors required by the applicable instrumentation type shall be recorded.). I read through the current FAQs in the Nadcap Pyrometry Guide and didn't find anything directly applicable to your situation.

Lacking any definite answer (maybe after your finding is resolved you could suggest that this situation be added to the Pyrometry Guide's FAQs), I would guess the finding is against AMS 2750 paragraph 3.5.8:
During each survey... all parameters shall reflect the normal operation of the equipment in production.

"Normal operation" from the AMS 2750 paragraph is a very vague term for any shop that runs a variety of parts. I can see the point of view that if some aerospace customers require a load thermocouple, then the setup of that load thermocouple should be verified as part of the temperature survey. It's possible to interpret "normal operation" broadly enough that it includes the occasional use of load thermocouples.

 

[Tom W]

Re: Load Thermocouple requirement for TUS

I would guess the finding is against AMS 2750 paragraph 3.5.8:
During each survey... all parameters shall reflect the normal operation of the equipment in production.

"Normal operation" from the AMS 2750 paragraph is a very vague term for any shop that runs a variety of parts. I can see the point of view that if some aerospace customers require a load thermocouple, then the setup of that load thermocouple should be verified as part of the temperature survey. It's possible to interpret "normal operation" broadly enough that it includes the occasional use of load thermocouples.

If memory serves me well this is spot on. If you occasionally have the requirement to run a load TC then you must replicate this for your TUS to make sure the channel for the load TC is within limits. This issue is even more clear if the load TC is controlling the furnace vs your control TC.

 

[robanbieber]

Re: Load Thermocouple requirement for TUS

Well that is interesting. We run a type D furnace for dry film lubricant curing and we use a load sensor on a part just because the MIL-PRF-46010 spec for the dry film requires that the cure time starts after the part gets up to temperature. I did not have my TUS run a load TC during the test. We received an initial NADCAP audit and it was not a finding on it.
We only need a type D all the time.
So did the auditor miss that we ran no load sensor during the TUS?
It is a not a temperature controlling load sensor. It is only used to manually verify that the load has gotten up to temp and at that point as long as we get the cure time fullfilled from that point in time we are good for the batch.

If a load sensor was required would I need to attach it to a dummy load?
I do not run loads during my TUS because I have no need to do it and it would make my TUS harder to do in my setup.

 

[robanbieber]

Re: Load Thermocouple requirement for TUS

I would like to hear what your PRI review engineer has to say about this. I would be sure to ask him/her why this was a finding and provide some clarity on this especially in regards to actual, dummy or no loads during the TUS....

 

[MTProcessing]

robanbieber - How to do a TUS without a load but with a load thermocouple is addressed in the Nadcap Pyrometry Guide: where it comments on AMS 2750 paragraph 3.5.13.3.2 (FAQ #43 in the current edition). The Pyrometry Guide is available as a download on eAuditNet.

 

[robanbieber]

thanks for the document tips. Fortunately my load sensor is not a requirement for my class of oven (D) so I am not needing to run a load sensor for my TUS. the load sensor I am using is not controlling temperature but is monitoring that my part gets up to temperature which is a requirement for the dry film lubricant spec mil-prf-46010, so I do not need to use one in my TUS.

 

[MTProcessing]

robanbieber - I'd recommend running that interpretation by a staff engineer. It sounds like exactly the situation the OP had a finding for.

 

[robanbieber]

I think it has everything to do with the fact he has a process that uses a type B furnace. Part of the requirement of a type B furnace is to have at least 1 recording load sensor. This is not a requirement for type D....The fact that is a requirement for class B operation makes it a requirement for the TUS. But that should not really be a problem for the TUS as having a load on the sensor stabilizes the reading which should make that sensor easily pass the TUS. It makes sense that my audit did not have a finding with our type D oven not using a load sensor for our TUS but our process does use a noncontrolling nonrecording load sensor to meet the mil spec requirement and not because it is a requirement for the AMS2750E spec....