Self-monitoring dual-spool servovalve

In a servovalve having first and second members mounted for independent sliding movement relative to a body along parallel axes, having a first driver operatively arranged to cause a desired motion of said first member, and having a second driver operatively arranged to cause a simultaneous motion of said second member, the improvement which comprises:

• a differential position sensing mechanism arranged to sense the relative positions of said first and second members and operative to produce an output position related to the differential position therebetween, said mechanism including a first part operatively associated with each member and mounted for movement therewith pivotally about an axis arranged in a plane substantially perpendicular to the axis of one of said members, and including a second part operatively associated with said first part and mounted for pivotal movement about an axis substantially perpendicular to said first part pivotal axis and arranged in a plane substantially perpendicular to said one member axis;
• and
• an indicating device supplied with said output and operative to indicate dissimilar relative positions of said first and second members.