QA_FCP_SOL.docx

QUESTIONS

Section 1.1

The third sentence refers to operation with "current Navy load cell calibration standards".

Are the load cells calibrated with a stand-alone indicator or are they calibrated using a generic indicator with recorded mV/V readings with different loads being applied to them? (as per ASTM E74-13a)

Is there an overall system accuracy that is required and if so, what is it?

This may be defined as percentage of applied load or in terms of an "uncertainty budget" which takes into account other factors effecting accuracy such as perpendicularity of the cylinder, stability of readings under load, and levelness of the test surface under load.

Furthermore, please advise the accuracy Navy supplied standard load cells so we can apply their tolerance to our uncertainty budget in order to source the proper components and configuration to meet required system accuracy.

Section 3.9.2.2

The third sentence says "shall be manually operated". This appears to be the governing aspect of the section's requirement. However, ambiguity is introduced by the last sentence which states "Manual operation, motor assisted operation or a combination of operation methods is acceptable". Please clarify the ambiguity by defining manual and motor assisted operation. By our "industry" terminology, manual operation would imply the operator uses a hand pump to apply loads and motor assisted operation would imply the operator using automated controls, which are usually computer driven, load can be applied by.

Does this section require the calibration system to be manually operated apart from controls and/or computer system?

Does this section allow the operator to control the calibration system through computer interface?

ANSWERS

1.1 General

The current Navy load cell calibration standards are used with a DC power supply and a nanovolt meter. The nanovolt meter is used to indicate mV/V output of the load cells. This equipment is calibrated together as a system. Per ASTM E74-13a, force loads generated by dead weight primary standards are used to generate polynomial equations relating standard load to mV/V load cell output. The target uncertainty of the load cell calibration standards is +/-0.025% of indicated value (iv) or better, test platform scales having an accuracy of is +/-0.1% iv or larger. We do not have an uncertainty budget that takes to account the FCP cylinder perpendicularity, stability of readings, and levelness of test surface under load.

There are three dead weight primary standards used to calibrate the load cell standards. The first has a range of 20 to 1,220 lbs with an uncertainty of +/-0.0037% iv. The second has a range of 100 to 12,200 lbs with an uncertainty of +/-0.0038% iv. The third has a range of 2000 to 102,000 lbs with an uncertainty of +/-0.0015% iv.

3.9.2.2 Hydraulic pump

Manual operated means a calibration technician will operate the FCP and control the rate and magnitude of the applied load. The calibration process involves the technician adjusting the load to obtain a near nominal load indication on the unit under test. The mV/V indication of the nanovolt meter/load cell standard will be entered into an Excel spreadsheet to convert to force units. The unit under test indication will also be entered into the spreadsheet to compare its indication to the standard force indication. Also, manual operation indicates that we do not expect automatic control of the calibration process, since will be no feedback between the unit under test, the load cell standards and the FCP that would allow automated control of load application and data recording.

The last sentences of 3.9.2.2 states manual operation, motor assisted operation, or combination of operation methods is acceptable. To clarify this sentence manual means hand driven pump and motor assisted mean electrical motor driven pump. Combination means an electrical motor driven pump could be used for course/rapid force adjustment and a hand drive pump could be used for fine/slow force adjustment. The intent was to provide the technician with course and fine control.