Final answer:
The rank required to perform as an on-scene supervisor for every consent to search incident is typically a sergeant or higher, depending on the department's policy.
Step-by-step explanation:
The rank required to perform the functions of the on-scene supervisor for every consent to search incident varies with department policy. However, general practice would normally allow a sergeant or higher to perform these functions. This is because a sergeant often has the experience and authority to make sure that searches are conducted legally and in accordance with the department's standard operating procedures. Though specifics may vary, it is unlikely that just any sworn officer would have this authorization, without prior designation or rank.