An instrument carriage provides control of a surgical instrument coupled to the instrument carriage. The instrument carriage includes a control surface that is coupled to the surgical instrument to provide the control. A detection pin having a first distal end that extends from the control surface is coupled to the instrument carriage. A magnet is fixed to a proximal end of the detection pin. A carriage controller provides an indication that the surgical instrument is present on the instrument carriage when movement of the detection pin causes an output signal from a Hall effect sensor to exceed a presence threshold value that is stored in the carriage controller as part of a calibration procedure during the assembly of the instrument carriage. Surgical instrument removal may be indicated when detection pin movement causes the output signal to be less than a removal threshold value of less than the presence threshold value.