User Manual

SAFETY
Safety handbook page - 32 -
PNSPO
7. Light curtains
Light curtains are a part of the electrical equipment used in machines which present
risk of personal injury. It provides protection by causing the machine to go to a safe
condition before a person can be placed in a hazardous situation.
7.1 EN 61496, EN 999
Light curtains or barriers are named ESPE (Electro Sensitive Protective Equipment)
and AOPD (Active Opto-electronic Protective Device) due to using sensing function
with emitter and receiver based on optical system in the relevant norms EN 61496-1
and EN 61496-2.
ESPE are assemblies of
• a sensing device
• controlling/monitoring devices
• output signal switching device (OSSD)
The OSSD is the component of the light curtain that is connected to the control system
of the machine. When the sensing device is actuated by interruption of the beams in
normal operation it responds by going to the OFF-state. OSSD can be safety relays
with mechanical contacts or solid state outputs such as PNP-transistors.
The overall system stopping performance is the time occurring from actuating the
sensor to the cessation of a hazardous motion. This time T consists of min. two parts
where t
1
is the response time of the sensor and t
2
is the max. response time of the
machine: T = t
1
+ t
2
Because of this delay the distance between the sensor and the dangerous zone has to
be wide enough that personal injury is prevented.
EN 999 defines the minimum distance from the dangerous zone being calculated by a
general formula
Where:
S is the minimum distance in mm
K is a parameter in mm/s , derived from data on approach speed of the body or
parts of the body
T the overall system stopping performance in s
C is an additional distance in mm, based on intrusion towards the danger zone
prior to actuation of the protective equipment
S = ( K x T ) + C