There is one simple way to determine the difference: if the sentence could meaningfully/sensibly be transformed into a corresponding active sentence, then the verb phrase is passive. If not, it is a simple 'be' + participial adjective combination.
 The machine is needed on a daily basis.
is equivalent to
[1a] People need the machine on a daily basis.
thus 'is needed' is a true passive VP, whereas
 As you can see, the machine is plugged in at present.
does not correspond to
[2a] ?As you can see, people plug in the machine in at present.
showing 'plugged in' here to be purely adjectival.
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