Safety
Presense Sensing Devices
Light Curtains
How to Calculate Safety Distances
When reflective surfaces (shiny/polished metals, foils, glossy painted surfaces, etc.) are in close proximity to opto-electronic devices such as light curtains, the system is susceptible to faultsdue to deflection of the optical beams. A situation such as this can result in the light curtain not detecting an object or personnel in the sensing field.
When installing light curtains, the potential for interference can be calculated to determine the minimum distance that the light curtain must be mounted from the reflective surface in question. As a general rule, no reflective surfaces should be contained within the beam angle of the light curtain emitter or receiver with misalignment taken into account. Using the following formula:
D = R/2 (tan 2a)
| Where | |
|---|---|
| D | Distance to the reflective surface (worst case) |
| R | Distance between the light curtain emitter and reciever |
| a | The angle of acceptable misalignment (angle of divergence) as determined from the light curtain specifications |
It is also necessary to take into account other opto-electronic devices near the safety light curtain. It is quite possible for light curtains to interfere with each other or “crosstalk.”
