Re: In early elevators how did the power source know the required level

Hi, Steve:

Elevators – well, hoists – date from at least the third century BC.  The 
earliest ones were powered by muscle, either animal or human, turning a 
windlass.  Control of this was easy:  The passenger simply hollered “Take 
me Up!”  and “Stop here!  Couple more inches—That’s it!”  They didn’t go 
very high, making this practical.
 http://www.columbia-elevator.com/info/history.html http://www.elevatorloadtest.com/elevator_history.html

In the early 19th Century, mechanical power began to be applied.  Usually 
this was either a drum winding up a cable, turned by a steam engine, or a 
piston under the elevator raised by a steam powered hydraulic pump.  These 
were operated valves, operated by a rope that ran vertically through the 
elevator shaft.  One tugged on the rope, opening the valve.  The elevator 
moved, while the stationary rope slid through a hole in the floor.  
Tugging on the rope again stopped the elevator.  This took skill in order 
to not lose fingers, and a control system was added.  Later, when electric 
motors provided the propulsion, electric controls were installed.

As late as the 1970’s, elevators required a human operator riding in the 
car to work.  They manually lined up the floor of the car with the 
destination floor and worked the doors.  To see this in action, watch the 
classic movie “The Apartment” 

One piece of trivia:  When Mr. Cooper built the Cooper Union building, he 
was so confident that a safe effgicient elevator would be invented, he 
constructed an elevator shaft.  Sure enough, four years later Mr. Otis 
invented the safety elevator!