Patent ID: 8607856

Claim:
A cable head for petroleum logging, comprising a first connector and a second connector which are fixedly connected with two ends of a tension rod respectively, wherein a first piston, a second piston and a third piston are provided sequentially at an upper portion, a middle portion and a lower portion of the first connector, a diameter of the second piston is larger than diameters of the first piston and the third piston; the first piston and the second piston of the first connector are disposed in a first cylinder which has inner cavities slidably fitted with the first piston and the second piston respectively; the third piston of the first connector is disposed in a second cylinder, and a lower portion of the second cylinder is fixedly connected with the second connector; a balance cavity is formed between a lower end face of the second piston of the first connector and an upper end face of the second cylinder when a lower end face of the first cylinder abuts against the upper end face of the second cylinder; an axial projected area of the lower end face of the second piston of the first connector is equal to a cross section area of the first piston; and wherein either the first cylinder or the second cylinder comprises a passage to the balance cavity.