As per Ramayana, the great epic when Sita asks Laxman to go and search Ram in forest, Laxman draws a line which was meant to protect her from any intruders. In modern times powerful machines when unintentionally intruded wrongly may result is loss of lives and Laxmans, the management, whose job is to provide safety and protect lives of people may do so by providing light curtains at right places on most machines. The cost is very small compared to the cost of machine but the saving is enormous, as it involves human beings. Many old machines do not have these in-built because of various reasons but this can be easily fitted to make them safer today.

Light Curtains are opto-electronic devices, in form of invisible wall, which detect any unintentional movement across it and give signal to be used for activation of protective circuits. These are mainly used for safety of persons in moving machinery which has potential to cause harm. Light Curtains can be used as an alternative or addition to mechanical safety system and other form of traditional machine guards. The safety curtain is placed between a machine operator and dangerous machinery so, if operator puts any part of his body into machine then some of the optical beams are interrupted and receiver generates trigger signal for controller section and machine gets stopped.

Some technical data:
Light Curtains are used to detect penetration of curtain by human or other objects. Light Curtains have a two sections 1) Transmitter Section & 2) Receiver Section.
Light Curtains are available with different beam combination i.e. 8,16,24,32,40 etc. ( to fit the height of curtain wall)
-with various beam pitch i.e. 20 mm, 40 mm, etc. and in different safety categories i.e. hand safety, human part safety, head safety, finger safety,
-With 2 mtr, 5 mtr, 10 mtr. Sensing range (The width of curtain wall).

Transmitter Section:
Transmitter section consists of an array of Infrared beams, which are sequentially transmitted, one after another towards Receiver with appropriate transmission code and pulsed at a specific frequency. Infrared beams are modulated and have a wavelength that varies between 880nm to 940 nm.

Receiver Section:
Receiver section is designed to accept specific frequency & pulse from its transmitter. In receiver special filters are used to reject any spurious light pulses, which are generated from florescent light etc. It triggers output stage when any object / human come between transmitter and receiver. Output of Each beam is logically processed in controller section so that any beam out of 8,16,24,40, when interrupted will trigger the output for machine control.

Controller Section:
Controller section generates sequential pulse train for transmitter section and control pulse for receiver section. Control pulse keeps transmitter and receiver synchronized. Controller section on receipt of a trigger pulse from receiver section energizes the output relay for removal of motive power from Hazardous area.

Some traditional applications :
• Elevators
• Injection molding machinery
• Pharmaceutical machinery
• Safety mat
• CNC, Lathe, Shearing Machines & Power Presses
• Image processing