A vending machine apparatus comprising a housing defining an internal cavity and an article storage compartment positioned inside the cavity. The method further includes identifying locations within the region at which the wave is blocked from flowing and estimating confidence levels with respect to a blockage of the wave at the locations in response to the signals and the parameters. The signals from the read head are combined to produce output signals having improved signal to noise ratios from which the locations of spatial and thermal defects can be identified and distinguished. The second connection unit includes a second electrode that engages with the first connection unit, and, when engaged with the first connection unit, is statically coupled with the first electrode. Objects of interest may be qualified andor disqualified based at least in part on object motion in the field of view of the imaging sensor. The present invention also provides methods for preparing said salt form.