Importance

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Abstract

A safety circuit for a lifting device extensible boom is presented wherein the boom angle of elevation and boom length are each converted into a parallel coded word. The two coded words, one representing boom angle and the other boom length, are processed in a digital logic network which provides inhibit functions that prevent boom extension or boom lowering when either of the two boom actions will place the boom in a position which will damage the boom or topple the machine. A plurality of switches are associated with the boom to generate and apply the boom length code word to a monitoring circuit, which responds thereto to provide a switch malfunction signal when one of the switches is defective, whereby boom extension or lowering are inhibited.

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First Claim