Patent ID: 8405926

Claim:
A method of operating a magnetic tape drive, said magnetic tape drive having a plurality of DC motors, each DC motor having a plurality of Hall sensors, said DC motors each arranged to longitudinally move a magnetic tape mounted on tape reels rotated by said DC motors under the control of a servo system, said servo system configured to read location information from said magnetic tape, to compute a primary tape velocity from said location information, to sense a secondary velocity signal based on a back-EMF voltage of at least one of said DC motors, and a tertiary velocity signal based on a signal of at least one of said Hall sensors and compute a tape velocity based on one of the sensed secondary velocity signal and tertiary velocity signal the method comprising: detecting if said primary velocity location information is available; employing said primary velocity to control said servo system in response to detecting that said primary velocity location information is available; and employing one of said secondary velocity signal and said tertiary velocity signal to control said servo system in response to detecting said primary velocity location information is unavailable and wherein said secondary velocity signal is employed when an absolute value of a term related to tape velocity is less than a predetermined value and said tertiary velocity signal is employed when an absolute value of said term related to tape velocity is greater than said predetermined value.