In: Electrical Engineering
Explain the operation of the safety (Light) Curtain?
Safety light curtains are an advanced method of safeguarding
personnel around many hazardous machines. Safety light curtains
offer freedom, flexibility and reduced operator fatigue when
compared with traditional guarding methods such as mechanical
barriers, sliding gates and pull-back restraints. By reducing the
need, where applicable, for solid guards, safety light curtains
simplify routine tasks like machine setup, maintenance and
repair.
How They Work
A photoelectric transmitter projects an array of synchronized,
parallel infrared light beams to a receiver unit. When an opaque
object interrupts one or more beams in the sensing field, the
control logic of the light curtain sends a stop signal to the
guarded machine.
The transmitter unit contains light emitting diodes (LEDs) that
emit pulses of invisible infrared light when energized by the light
curtain’s timing and logic circuitry. The light pulses are both
sequenced – one LED is energized after another – and modulated –
pulsed at a specific frequency. Corresponding phototransistors and
supporting circuitry in the receiving unit are designed to detect
only the specific pulse and frequency designated for it. These
techniques offer enhanced safety and rejection of external light
sources. The control logic, user controls and diagnostic indicators
may be contained in a separate enclosure or be enclosed in the same
housing as the receiver electronics.