Balances, analytical mounting

Force-Coil Analytical Balances. The most precise modern analytical balances use a "force coil," mounted in a magnetic field the current needed to counterbalance the weight placed is measured (electromagnetic force restoration balance) or an optical system measures displacement these can be sensitive to 1 part in 3 x 106. Some "window comparators" yield a precision of 1 part in 109. 

A 30-tooth 20 DP steel gear, -in. bore, required for the magnetic pickup Steel box for mounting tachometer and speed control equipment Analytical balance, 0.002 g readability Stop watch... 

Wear tests are conducted with a thrust-washer test apparatus. A sample thrust washer is mounted in an antifriction bearing equipped with a torque arm (see Fig. 3-105) [323]. The test-specimen holder is drilled to accept a thermocouple temperature probe. The raised portion of the thrust washer bears against a dry, cold-rolled, carbon-steel wear ring with a 12- to 16-microinch finish at an 18 to 22 Rockwell C scale hardness at room temperature. Each evaluation is conducted with a new wear ring that has been cleaned and weighed on an analytical balance. The bearing temperature and friction torque are continuously monitored. 

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