Patent ID: 8689868

Claim:
A method of switching wireline voltage between a tractor motor or the tractor output in a downhole tool string including a tractor comprising the steps of: sending a signal to a control unit on the tractor from a surface controller; processing the signal with a state machine on board the tractor for controlling the position of one or more switches located in one or more circuits connecting the wireline to either the tractor motor or a through wire that connects to the tool string wherein the state machine is adapted to identify the state of each said control unit and one or more valid signals for each state of the control unit; if the command is not valid for the state of the control unit, sending an error message from the control unit to the surface controller; if the command is valid for the state of the control unit, performing the command and sending an uplink message comprising the state of the control unit to the surface controller; identifying the relative position of the devices within the tool string by tracking the commands and uplink messages; removing power to the control units if the surface controller receives an error message; and removing power to the control units if the surface controller does not receive an uplink message after the command is sent.