AMS 2750E Heat Treat Furnace System Accuracy Test SAT Report question

S

sshaubrich

I have a question on the allowed correction factors for the AMS 2750E heat treat furnace System Accuracy Tests. The pertinent section, 3.4.5.3, is still confusing to me with how to handle all the corrections.
There are 5 examples of how to handle offsets and corrections, but I don't feel any of them adequately address what exactly gets subtracted/added when filling out the SAT report.

According to Figure 6, you are supposed to subtract any:
- manual correction factor from calibration of the instrument (Binst)
- manual thermocouple calibration correction factor (Btc)
- correction factor from TUS offset of control or recording instrument (Btus)
- Test thermocouple correction factor (E)
- Test instrument correction factor (F)

We already actively subtract the test instrument and resident SAT thermocouple correction factors from the test instrument reading, but I have questions about the controller calibration correction factor and the control thermocouple calibration correction factors. We are using SSI 9205 and old Dual Pro controllers on our furnaces, and I don't believe these are capable of programming these 2 factor into the instruments. And I don't believe trying to get the heat treaters to add in a manual adjustment to the setpoint (which would be different for every setpoint) is feasible. So I want to put forth another example SAT and hope for an answer:

example: The furnace has an offset of -5 (meaning a correction factor of +5, and we use the same offset for both TUS and SAT). If an SAT is run at 500 DegF (displayed on the controller), where The K control T/C calibration correction factor is +3.3 DegF, the SSI 9205 controller calibration correction factor was 1 DegF, the type N Resident SAT test T/C was -2.5DegF, the Fluke multimeter used to perform the test had an error of 0.2DegF, and this test instrument gave a reading of 505 DegF, should the math be:

Instrument Reading (A): 500 DegF
Furnace Offset (Btus): +5 DegF
Corrected Control Instrument Reading (C): 505 DegF
Indicated Test Instrument Reading (D): 505 DegF
Test T/C correction Factor (E): -2.5 DegF
Test Instrument correction factor (F): 0.2 DegF
True Test Temperature (G=D+E+F): 502.7 DegF
SAT Difference (C-G): 2.3 DegF = PASS

Or should the math be:

Instrument Reading (A): 500 DegF
Furnace Offset (Btus): +5 DegF
Correction Factor from instrument cal (Binst): 1 DegF
Correction Factor from control K T/C (Btc): 3.3 DegF
Corrected Control Instrument Reading (C): 509.3 DegF
Indicated Test Instrument Reading (D): 505 DegF
Test T/C correction Factor (E): -2.5 DegF
Test Instrument correction factor (F): 0.2 DegF
True Test Temperature (G=D+E+F): 502.7 DegF
SAT Difference (C-G): 6.6 DegF = FAIL

As you can see, this is the difference between passing and failing the TUS on a class 5 furnace. So are you supposed to include Binst and Btc in the calculations if they aren't programmed into the controller or you didn't manually adjust the setpoint to run at 504.3 DegF?
 
M

MTProcessing

We do not use manual offsets; any offsets are programmed into our controllers. Given that restriction, we track three types of correction factors for each furnace:
1. Instrument calibration (whatever our calibration contractor needs to get the control instrument in calibration, no limits)
2. SAT offset (limited by table 6 of 2750)
3. TUS offset (again, limited by table 6, but this is tracked separately from #2 per footnote 3 of the table)

The total instrument offset - the amount actually programmed into the instrument - is #1 + #2 + #3.

When we do an SAT, we adjust for the correction factors of the SAT instrument and SAT thermocouple (just as you do). For the control, we remove #3 (TUS offset); that's it.

Your second example is wrong; there is no need to do anything with the control instrument or control thermocouple correction factors.

Your first example would be right if you decided the -5 offset (+5 correction) was a TUS offset. If you labeled that offset as an SAT offset, you wouldn't need to correct for it (and I think you'd still pass, with the instrument reading of 500?F making the difference 2.7?).
 
P

prichy

That post help me with the furnace. Thanks for sharing your thoughts with us.
 
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