Drum rotation indicator

Claim 1

A drum rotation indicator for indicating the speed of raising and lowering a load by a rotatable winch drum mounted on a crane, said indicator being adapted for use with a plurality of standard electrical battery voltages used in crane batteries, said crane including a battery, said indicator comprising: a switch assembly coupled to said winch drum for developing signals having a frequency proportional to the rate of rotation of said winch drum, a pulse forming circuit coupled to said switch assembly for receiving said signals and for developing output pulses having a frequency proportional to the frequency of said signals; means for coupling said pulse forming circuit to a crane battery for operating said pulse forming circuit; a solenoid having a movable plunger; means for coupling said pulse forming circuit to said solenoid to operate said plunger in response to said output pulses; and a voltage sensing circuit coupled to said crane battery and to said pulse forming circuit, said sensing circuit including means for sensing the value of said crane battery voltage and adjusting the time duration of said output pulses according to the value of said crane battery voltage to provide a predetermined value of electrical drive to said solenoid for a variety of crane battery voltages.