Downloaded from https://www.everyspec.com MIL-STD-1312B I Strain gaged dynamometers (load cells) of appropriate size may be used for alignment adjustment (Figures 3a and 4). o a. b. A bridge amplifier (or equivalent) ia used to condition and amplify the load (strain) signal (Figure 3b). c. A multichannel switch and balance is used for strain gage element selection and basis signal balance (Figure 3c). d. A high quality oscilloscope or light beam galvonometer recording device is used to display the load (strain) signal. 70.2 Alignment cells. Static alignment cells should be designed to operate between 15 and 60 ksi at the verification load.
The verification load shall be at least 10 percent of the maximum machine capacity. Typical alignment cells, the material from which they were mxde, and verification loads that cover mxximum machine capacities from 440 pounde to 250,000 pounds are shown in Figure 4. Tubular cells or actual test bolts of appropriate load range mxy be used. 70.3 Procedure. Four strain gages shall be bonded 90 degrees apart around the circumference on a common plane perpendicular to the axia of the cell. Sach active strain gage shall be wired into a separate channel of the switch and balance unit so it can be individually balanced and switched f.ntothe strain indicator. 70.4 Alignment example. a.
’10check the alignment on a 24,000 pound take 10 percent of 24,000 = 2400 pounds. select cell no. 7, rated for use between pounds. fatigue machine, From Figure 4 2400 and 9600 b. Assemble the alignment cell into the test machine using equipment that meets the apecified fixture requirements. c. strain in order from gages 1, 2, 3 and 4. Unload the machine, and rotate the alignment cell 45 degreea; load Load the alignment cell to 2400 pounds and record the the cell again to 2400 pounds and record the readings > from gagea 1, 2, 3 and 4. d. Sample calculations of strain gage results from the 2400 pound test loadings; 14