PLC elevator program
This is a PLC program for a traction elevator serving 4 floors, designed for educational purpose.
The position of the elevator is detected by two proximity switches, mounted on the top of the car, and
two dump switches mounted in the shaft on the first and top floor.
When the elevator moves through the middle floors, the count proximity switch senses a set of magnets
placed on the rails and sends a signal to the PLC. This signal drives the program instructions
K00, K01, K02, K03, KL1, K2, KL3. Due to these instructions the elevator takes the right direction and
decreases its speed when the car comes close to the requested floor.
The dump switches are activated by a cam mounted on the car, when the elevator comes close to the first
and top floor; they are supposed to reset the program instructions once the control panel is supplied. In
this condition the PLC does not know where the elevator is (unless a dump switch is activated) and any
request would turn on both direction instructions: for that reason one of them (RS) features a small delay.
The stop proximity switch lets the PLC know when the elevator is exactly on the floor; it stops the car
if it is moving at low speed.
The ST relay is supposed to reset all the run instructions when the stop button is pressed; it has a
normally closed contact connected to the ST input of the PLC.
If a request button is pressed and the elevator does not start moving within a certain time (set by RMP),
the request is reset due to the SFB input, which is connected to the feedback switches of the direction contactors (S, D).
The door operator contactors are controlled by the AP and CP outputs. The door operator limit switches are
connected to the FAP and FCP inputs.
The RCE timer is supposed to set the exterior requests delay; when the elevator is not in use that timer is
activated and the door is closed.
Once the PLC is supplied, it doesn't know the position of the elevator; when any request button is pressed the
car moves to the first floor (due to the delay on the RS instruction). During this stage the count program
instructions do not work and a reset light turns on.
This program has been simulated, but not tested on a real elevator model, so there may be some errors.
Ladder diagram (pdf)