Automatically controlled crystal growth

Claim 1

Apparatus for the controlled growth of a crystal comprising a container for containing a charge of material from which said crystal is grown; an electrical heater arranged adjacent to said charge to form a melt of said charge; means for pulling a crystal from said melt; a feedback loop for controlling the growth of said crystal by controlling energization of said heater, said feedback loop including: a weight function signal generator arranged so as to measure the weight of said melt and to provide an output signal representative of a function of said weight, a comparator, and means for supplying electrical current to said heater; means for providing a reference signal representative of the expected value of said generator output signal to said comparator for comparing said generator output signal with said reference signal and for providing for any difference between said signals a control signal for controlling the current supplied to said heater by said means for supplying current; and wherein the improvement comprises an error correction loop for cancelling an error in the weight measured by said weight function signal generator, said error correction loop including: means for monitoring the output of said means for supplying electrical current, means for deriving from said monitored current a correction signal proportional to said current and equal in magnitude to said error, and means for applying said correction signal to said feedback loop at a point in said feedback loop before said means for supplying current, in order to cancel said error.