The Fielden Servograph is operated by a servo motorized mechanism which is controlled by a moving coil, moving iron, dynamometer or electrostatic movement, the pointer of the normal movement being replaced by a small light vane which acts as one plate of a variable condenser. Another similar vane arranged to be turned by the servo mechanism moves in the same are as the meter operated vane, and the two are maintained at a constant spacing by an electronic capacity relay which controls the servo motor. It is only necessary to provide enough energy to deflect a normal indicating meter movement, and the servo mechanism locates the pen arm with precision, being positionally controlled by this movement. The electronic relay circuit is present at works and needs no re‐adjustment.
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