The PIAB Load Guard is intended for use as an overload guard in cranes and lifts, for the automatic tensioning of belt conveyors and for other automatic power-sensing/load control.
PIAB Load Guard function:
The movement of the pull rod operates the micro switches through spring loaded contact points. The power absorbing element consists of specially made Belleville washers dimensioned to resist fatigue. The spring washers cannot be overloaded.
PIAB Load Guary safety:
Safety factor 5:1 stands for guaranteed strength against breakage at least 5 times the max. capacity. The load guard can be overloaded by 100% without interfering with the switch setting. As the transmission parts between the pull rod and the micro switch are spring-loaded, the load guard can withstand severe shock loads and sudden unloading. The pull rod and upper bracket of the load guards types IMB-IG are made of drop forged steel SIS 2174 (St 52-3N acc. to DIN 17100, 50 D acc. to BS 4360) which have guaranteed impact strength down to -20 C The setting of the micro switch is sealed by an Aluminium plate over the switch, on which the set value is engraved. The plate is screwed and glued to the housing with a 2-component adhesive. This plate cannot be removed without torch heating to about +80C.
PIAB Load Guard contact function:
The PIAB load guard with one or two micro switches is supplied with alternative contact connections for each micro switch. PIAB Load Guards with three, four or five micro switches have either one breaking or closing function on each switch. These are normally set for the breaking function (closed contacts at rest) and for rising loads, unless you order otherwise. When set for falling load, e.g. control on the slack line, the micro switch is connected for the closing function (open contact at rest). If the PIAB Load Guard will be used for a safety application, the breaking function should always be used.
The micro switches have gold-plated contacts, which make them suitable for operation on low current/voltage (under 10 V and/or 60 mA). The difference between the switching value on rising and falling loads is approximately 3% of the max. capacity of the instrument. This hysteresis is somewhat reduced at lower loads and slightly increased at higher load values. To avoid "chattering" of the contacts and contactors if the load should start to sway, a time relay to delay the reclosing of the hoisting circuit may be installed. When set for falling loads, special micro switches with a reduced hysteresis are used. The switch values are set by the factory to the required level.
