Automatic depth control system

A hydraulic system for use with a farm implement having a frame and tool, including:

• a. a hydraulic cylinder for mounting to the frame and having a main piston to effectuate the raising and lowering of said tool and a floating stop piston for limiting the travel of said main piston within the cylinder, the position of said stop piston being adjustable by admitting and draining fluid from a region of said cylinder;
• b. depth sensing means for sensing the actual depth of the implement tool and providing a depth signal indicative thereof;
• and
• c. piston position control means for receiving said depth signal and controlling the positions of said piston, said piston position control means including:
• a. means adjustable to provide a first signal corresponding to the desired minimum depth penetration of said implement tool and a second signal corresponding to the desired maximum depth penetration of said implement tool;
• b. comparator means receiving said depth signal and said first and second signals for causing the position of said floating stop piston to be adjusted, and thereby the position of said main piston, to lower said implement tool when said depth signal indicates that the tool is higher than the desired minimum depth penetration and to raise said implement tool when said depth signal indicates that the tool is lower than the desired maximum depth penetration;
• and
• c. jog control means operative when activated to cause said main piston to travel in said cylinder to raise the implement tool without substantially altering the position of said stop piston.