Measuring the position of an installation platform in an elevator shaft using laser transmitters and light detectors

An arrangement for measuring the position of an installation platform in an elevator shaft, comprising:

• the installation platform arranged to be movable upwards and downwards in a first direction in the elevator shaft;
• two laser transmitters arranged at a bottom of the elevator shaft, each of said two laser transmitters producing a vertical upwards directed laser plane in the elevator shaft, said laser planes being perpendicular to each other;
• and
• at least four primary light sensitive detectors attached to the installation platform so that the at least four primary light sensitive detectors are visible to the laser transmitters, each of the at least four primary light sensitive detectors being positioned on a respective side of a rectangle,
• wherein the position of the installation platform in relation to the elevator shaft can be measured from hitting points of the laser planes on the at least four primary light sensitive detectors.