AMS 2750F pyrometric requirements for heat treatments: calibrating process instrumentation

In the previous article we introduced the type of process instrumentation required by AMS 2750 revision F depending on the type of the required process.

The 4 new AMS 2750F requirements for process instrumentation

What are the new requirements of the AMS (Aerospace Material Specifications) 2750F for process instrumentation?

1. All process instruments (control, recording, over-temperature) must be digital from June 2022.
2. Furthermore, as of June 2022, all recording instruments in addition to being digital must have a readability of 0.1 °C or 0.1 °F.
3. The sensitivity test it is no longer required for digital instruments, but attention must be paid to additional customer requirements.
4. The recording tools used on heat treatment plants should not be used to record TUS or SAT sensor temperatures unless it can be demonstrated that the recording channels of the TUS and/or SAT sensors of an integrated system are separated from the recording system of the heat treatment furnace and also meet the requirements of the field test instrument.

The last point is an important change.

From this point it follows that in a process recorder set up with separate groups/systems, they can be associated, individually, for two different purposes:

• process registration and
• field test instrument for SAT and/or TUS tests.

However, it is necessary to establish the hierarchy between the two systems, defining accuracy and calibration frequencies.

Calibration

The process instrumentation must allow to detect the temperature values by measuring the electromotive force (emf).
In the case of multi-channel instruments (e.g. recorders), all used channels will have to undergo periodic calibrations; those not used must be suitably identified and inhibited from use.
The calibration of the instruments must be carried out periodically according to the manufacturer's and internal instructions with reference to the AMS 2750 Table 7.

At least three checkpoints must be carried out choosing the temperature minimum, average (1/3 average) and maximum in the qualified operating temperature range, for each type of input.

Let's see an example.

In a vacuum furnace qualified in the operating temperature range of 600-1200 °C, calibration must be performed at 600-900 and 1200 °C.
The intermediate calibration point can be performed in the range 800-1000 °C (1/3 average), while the minimum and maximum points must correspond exactly to the minimum and maximum qualified operating temperatures.

The 18 information to always report on the calibration certificate

Which are the the minimum information to be reported on the calibration certificate?

1. Unique identification of the instrument.
2. Make and model of the calibrated instrument.
3. Identification of the test tool used during calibration.
4. Identification of the type of sensor in use (example, type K, N, etc.) and shape (example, V, mA, etc.), if the instrument is used for these scales.
5. Identification of the position from where the signal was simulated (only required for the measurement system involving the alternate SAT).
6. Requested accuracy requirement.
7. Data of each calibration point (as found and as left) and data if any adjustments were made including:
   1. Nominal test temperature.
   2. Test tool error (optional or when requested by customer).
   3. Error of the instrument under test (corrected or incorrect for the error of the test instrument, when applied).
8. Offset correction and modification as found and as left.
9. Sensitivity, compliant/non-compliant (applicable to analog instruments only).
10. Result of the calibration of the instrument, compliant or non-compliant.
11. Any limitations or restrictions of the calibration.
12. Date of execution of the calibration.
13. Calibration due date.
14. A traceability statement to NIST or other internationally recognized standards organizations.
15. Identification of the technician who performed the calibration.
16. Identification of the agency that performed the calibration, if not done internally.
17. Approval of the laboratory manager who performed the calibration, if performed by a third party source.
18. User quality organization approval.

In the next article we will deepen the requirements of the AMS 2750 on calibration instruments, going to illustrate for example the offsets, their classification, their amount and the necessary training.