Internal diameter measuring apparatus

Claim 1

Measuring apparatus for internally measuring tubes comprising: a flexible supporting member capable of being inserted into a tube; flexible centering devices disposed on said flexible supporting member at various locations along said flexible supporting member for centering said flexible supporting member with respect to the inside surface of said tube while being capable of negotiating constricted portions of said tube; electromagnetic means disposed in said flexible supporting member for detecting metal members through which said tubes are disposed thereby indicating the longitudinal location of said measuring apparatus in said tube; a linear variable differential transformer disposed in said flexible supporting member for transforming the force exerted on said linear variable differential transformer into a reading corresponding to the internal diameter of said tube; a slotted member disposed in said flexible supporting member; a first and a second link pivotally connected at their first ends through said slotted member and capable of sliding along said slotted member; a third link and a fourth link pivotally connected at their first ends to said linear variable differential transformer with the second end of said third link pivotally connected to the second end of said first link and with the second end of said fourth link pivotally connected to the second end of said second link; and a first roller attached to the connection of said first and third links and a second roller attached to the connection of said second and fourth links, said rollers contacting said inside surface of said tube and causing said third and fourth links to exert force on said linear variable differential transformer when either of said rollers encounters a constriction in said tube with said linear variable differential transformer transforming the so monitored force into readings indicating the internal diameter of said tube.