How often does android system scan wifi -

how android system scan wi-fi?

in following 2 cases:

when device connected network

or

when device not connected network. different android os version?

is there 1 know information?

android system scans wifi :

1. if device has wifi enabled , device not connected network, scans available network

2. if device connected network system scan available network on request user (i.e. when user clicks scan button)