One of our regular customers had a requirement for two compression load cells that would be installed in the jib extension hooks of an A-frame floating crane. The crane has a lifting capacity of up to 400 tonnes at a height of 45m, but with the jib extended it can achieve a lifting height of up to 76m with a lifting capacity of 200 tonnes. The crane is operated by a Norwegian specialist crane rental company who hire it out for general marine lifting operations along the Norwegian coast as far as Bergen in the north down to Germany in the south.
The load cells were required to monitor the loads on the jib when it is extended to protect against overload situations that could result in it being over-stressed and consequently susceptible to damage. The load cells are used to sense the force of the load during a lift, and when the load exceeds a pre-set percentage of the cranes rated capacity, an overload device temporarily stops the crane from lifting and only permits the lowering of the load.
Due to limited space, the load cells had height and width dimensional restrictions, so a custom design solution was required. With a height of 265mm and an 88mm maximum diameter, the load cells had a rated capacity of 35 tonnes. For suitability of use in a marine environment they also had environmental sealing to IP67, featured an integral amplifier to provide 4-20mA output for simple integration into the vessels PLC, and were supplied with 10m of armoured cable. Additionally, the load cells incorporated M42 x 2 load buttons on the top and bottom to assure more precise loading and hence more accurate and repeatable measurements.
The main criteria we were given was as follows:
- 2 x 35te compression load cells
- Must be suitable for use in a marine environment
- Integral amplifiers required to give 4-20mA output
- Dimensional restrictions
- Heavy duty cable required
- Calibration certificate traceable to UK National Standards
- 10m heavy duty armoured cable
- 35te Compression Load Cell
- 4-20mA integral amplifier
- Crane overload monitoring
- Environmentally sealed to IP67
- Manufactured from 17-4PH stainless steel
- Supplied with integral load buttons
The dimensions were a restricting factor with this load cell design, however our engineers had no problem designing a suitable load cell that exactly met the customers requirements. The load cells had be be rugged enough to cope with the harsh marine environment, but LCM Systems have many years experience in designing load cells for tough operating conditions.
LCM Systems manufacture a large and varied range of custom design and standard product variant compression load cells. These have been supplied as 1 off products, or as part of an instrumentation system. Many of these products are supplied with built in analogue signal conditioning, digital outputs or with wireless telemetry.