On a FL, an OOB load will create a varying current draw.
On a TL, since the load won't go against gravity during one part of a drum rotation and with it during the other, the current will be consistently higher for a given load.
But, once the machine reaches a certain rpm, since the load weight won't matter (it already has a certain needed inertia, keeping it at a certain speed dosen't really need much different energy input depending on load weight) it will probably just go depending on total current draw and not actual variation in current draw.
A TL like a VMW also isn't the same kind of suspension as a FL - it's really just free floating and not dampened per se.
As long as it can spin up, the actual amount of unbalance dosen't matter, it just swings freely.
So, a FL will probably just look at maximum current draw secondarily and mainly check what the difference between maximum and minimum of the current draw is.
A TL will check if maximum current draw isn't exceeded until a certain rpm is reached, and once that is reached, it will just check if current draw is below a certain level.
Current sensing is usually done with a shunt resistor and with a known voltage across it.
It is done at several points for several functions in several specific ways - most kinds of power supplies from USB power supplies you use to charge your phone to what supplies the processors in these appliances all kind of rely on such stuff.
For example, certain components only start conducting once a certain voltage is applied.
So once a certain current runs through a certain resistance a certain volatge is seen across that resistance which in turn means these components then start conducting and thus switch other components.
