· Not all crane hoist ropes can be used with dynamometers; dynamometers can abuse and damage some types of hoist ropes.
· Dynamometers fitted with articulated arms swing around during crane operation. They also require suitable landing pads on the boom lacings to prevent direct collision with the boom during rigging and/or when there is no load on the hook which slacks the rope and drop the dynamometer on the boom lacings.
· Depending on application, tension-based systems require more fabrication and welding work on mounting brackets for the load sensors.
· Tension-based systems cost more on twin winch cranes.
· Dynamometers and dyno sheaves wear out over time.
· Stays very accurate as it is a direct measurement of the hoist rope tension.
· Fast, simple, one-time-only calibration
· Easily understood and serviced by local mechanics and technician
Advantages
Disadvantages
Tension-Based (Using Dynamometers):
· Non-intrusive to crane rigging and hoist cables.
· Neat and easier installation.
· In most cases, load sensors need not be removed during crane setup or de-rigging.
· Provides better safety against tipping as it monitors the forward moment (total moment) of the crane.
· Non-intrusive to crane rigging and hoist cables.
· Neat and easier installation.
· In most cases, load sensors need not be removed during crane setup or de-rigging.
· Provides better safety against tipping as it monitors the forward moment (total moment) of the crane.
Advantages
Disadvantages
News & Articles
What is Rated Capacity Indicator?
A Rated Capacity Indicator (RCI) or Safe Load Indicator (SLI) is an electronic device that monitors the working state of the crane and warns of overloading; provides working information to the crane operator; and may also deactivate crane controls if required.
Why do cranes require Rated Capacity Indicators
Cranes require Rated Capacity Indicators because:
Today’s cranes are worked harder.
Today’s crane load charts are more complex.
Today’s cranes are structurally maximized and overloading can happen without warning.
Accidents are reduced with safety systems.
Operator stress is reduced with available information provided by the RCI.
Today’s litigation actions demand the security of one.
Crane owners can protect their investment and save money on repair and maintenance of Cranes.
More safety regulations on cranes are being implemented and enforced on work sites.
Methods of Load Sensing
There are two basic methods or “load sensing” that can be used to monitor the crane load, the SDS following is a brief overview of these methods.
TENSION-BASED SYSTEMS
Tension based systems directly sense the line-pull generated in the hoist rope to lift the load. A range of sensor types are available, sensors can be Tension Plate load-cells, Dynamometers (Line-Riders), Load Pins, Compression Cells, Beam Cells or a combination of these depending on the number of winches to be monitored in the application.
Telescopic Cranes:
Dynamometers are the most common method, and are usually rigidly mounted on the top of the boom base section towards the other end.
Strut or Lattice Boom Cranes:
A variety of methods can be used as per the following description:
A Tension Plate cell can be fitted to the Hoist rope dead-end termination point at the boom tip.
Dynamometers can be fitted to the Hoist rope at the top or bottom of the boom either rigidly mounted or on an articulated arm, depending on which best suits the application.
Single-sheave Load Pins and other methods can also be used.
LOAD MOMENT-BASED SYSTEMS
As opposed to direct load line sensing, the lifted load can be calculated by monitoring other forces in the crane structure, this is known as Load Moment. The calculated load is derived from a combination of the boom angle, boom length and the force required to hold the boom up (load sensor fitted to the structure of the crane).
Telescopic Cranes:
The most common method is by the use of two Pressure Transducers used to monitor the hydraulic pressure in the Luff cylinder on both t he Force (piston) side and the Annular (rod) side. The se Transducers must be installed so as to DIRECTLY read the internal pressure of the cylinder and not affected by such devices as check valves, etc.
Strut or Lattice Boom Cranes:
Tension Plate cells or Load Pins can be fitted into the crane Luff rigging at various locations, i.e. between the pendants and the boom, the dead-end of the luff rope reeving back hitch pins of the A-frame, the equalizing sheave of the luffing bridle and other locations.
COMPARISON BETWEEN LOAD MOMENT AND TENSION-BASED SYSTEMS
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Robway has developed and produced the world’s first retro-fit weightless calibration technique in the crane safety systems industry.
The Big Advantage of Robway Load Moment Systems
Weightless Calibration
Robway has developed and produced the world’s first retro-fit weightless calibration technique in the crane safety systems industry.
One of the most difficult tasks to complete an installation and commissioning of RCI load moment systems is the procurement and availability of sufficient test weights to accurately calibrate the system. There never seems to be t he right known weights on site and the transport cost of getting these weights to site can be very expensive, so shortcuts are taken which results in less than perfect calibrations. Robway’s weightless calibration of load moment systems utilises no test weight or just the weight of the empty hook block to complete the calibration procedure. A known weight (of any weight) is only required after calibration to verify accuracy of the load readout.
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