Safety Inductive Loop Controllers


The safety inductive loop controller options SLC2 and SLC4 are comprise of the control box and 2 mute connection cables that link between the 8000 or 8000 Plus Series safety light and the inductive loop control box. The box provides connection for the inputs from the light curtain and inductive loops and output to the machine control panel.

Smartscan loop controller SLC4 uses two evaluation units (LD21) in conjunction with a Smartscan 8000 Plus Series safety light curtain to provide a control system integrity up to Category 4, as defined in European Standard EN954-1. Smartscan loop controller SLC2 uses a single evaluation unit (LD40) that monitors two inductive loops.

When used in conjunction with a Smartscan 8000 or 8000 Plus Series safety light curtain the unit provides Category 2, control system integrity as defined in European Standard EN 954-1. Smartscan dual loop controllers are used in a number of machine safety applications wherever the presence of fork lift trucks or other industrial vehicles needs to be detected, for example, when entering safe-guarded access-ways or, at pallet conveyors for loading and unloading.

The evaluation unit principle of operation is based on a change in the inductance within the loop that is created by the metallic components of, for example, a passing forklift truck. The changes are picked up and evaluated by a microprocessor within the unit.

Loop evaluation units have the following outstanding features:

Typical applications include conveyor systems where forklift truck access is required to load and unload pallets. px.gif (818 bytes) Smartscan loop controllers are normally used for detecting the presence of a forklift truck when entering and leaving a safeguarded area. The system provides safe operation of fully automatic end-of-line packaging machines and the infeed and outfeed zones of automated warehouses

The two output signals from the dual loop controller are used for muting a Smartscan safety light-curtain.

As a loaded pallet moves along the conveyor away from the dangerous machinery it enters the load / unload area at which point the conveyor stops. This load/unload area is safe guarded by a Smartscan light curtain that is positioned to detect personnel accessing the potentially dangerous machinery.

As the forklift truck enters the area it passes over the underfloor mounted dual inductive loops which detects it’s presence and provides output signals via the inductive loop controller to mute the light curtain. After inserting or unloading the loaded pallet, from the conveyor the forklift truck moves out of the area and therefore off the inductive loops. At this point the muting signals are removed and the light curtain becomes fully active again, thus providing fully automatic control of the machine and safety system.

The inductive loop and it’s associated capacitance is linked to the evaluation unit to form a LC oscillator. The frequency of the resonance circuit is determined by the capacitor and the magnitude of the loop inductance. The capacity of the capacitor and thus the resonance frequency can be modified using an internal switch. This prevents interference between two adjacent inductive loops or detectors. General Rule: The higher the inductance, the lower the resonant frequency.

If a current is present in the loop, an alternative magnetic field is generated around it. The magnetic field lines close to form loops. When a vehicle moves onto the inductive loop, the alternating field of the loop induces currents in the metallic parts of the vehicle (chassis, axles). These currents generate a magnetic field which opposes the loop field. This results in a change in the loop inductance and thus the frequency.

The loop detector detects this change in frequency. Such a change, beyond a pre-determined threshold, activates the loop controller’s output relay contacts.

Important Note: Ensure the loop evaluation units are protected from moisture.



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