SERVO-OPERATED MICROBALANCE FOR THE MEASUREMENT OF MAGNETIC SUSCEPTIBILITY.
FRANKLIN INST RESEARCH LABS PHILADELPHIA PA
Pagination or Media Count:
A semi-microbalance, which had been successfully used in previous susceptibility experiments 1,2 was improved by the addition of an electro-optical servo-system. The servo circuit, which follows closely the design of Garber et al 3 and Hurd 4 is essentially a Wheatstone bridge with a pair of CdSe photocells occupying two of the arms. A D.C. power supply is connected across two ends of the bridge while the orthogonal ends are connected together through a solenoid suspended from one end of the balance beam. The position of the light spot on the CdSe cells is influenced by the position of the balance beam and the suspended coilinteracts with a stationary pot magnet to keep the balance always counterqoised. As it was desired to servo-couple the balance with the minimum amount of structural modification, beam movement is indicated simply through the optically-uagnified movement of a spot of light formed by condensing light onto a lmm hole on a piece of aluminum foil glued to one end of the beam. Adequate velocity damping is achieved through the movement of the aluminum coil former in the fairly strong 400 oe field of the pot magnet. The gain of the system confers sufficient stiffness to the movement to make vejtical motion of the sample practically negligible during measurement. Author
- Test Facilities, Equipment and Methods