This article is meant to answer some of the more simple questions we get when first talking to customers about load cells for cranes and hoists. Having worked with numerous end-users and crane service companies, we think this will be helpful to others.
Firstly we will cover the reasons someone may want to measure the load on the hook. Either they want to know the actual weight of the pick or to prevent overload of the crane, or both. Knowing the actual load on the hook (especially while lifting unfamiliar objects) can prevent catastrophic damage to your hoist or crane or even worse, injury or death.
Crane Load Cell Type Selection
Let’s start with the easiest install, which is a load cell below the hook. This could be a S-type load cell with eye-bolts on either end, or a tension link load cell using shackles. You’ll need to decide if you can use a load cell with a cable that connects to the electronics, or if you’ll need a wireless load cell solution. The advantage of weighing the load below the hook with a load cell is accuracy, this is the most accurate way to obtain the load on the crane’s hook. Accuracy using this method can be as close as 0.025% of the load cell’s capacity. Also this type of load cell can be calibrated at the factory so no calibration is necessary in the field. The most common disadvantage is that you lose headroom which is some cases is not an option.
An alternative is if the crane or hoist has a dead end of the cable, is to use a clamp-on load cell. This type of load cell clamps on to a static wire rope and puts a slight bend in the cable. After installed and calibrated with a known weight, this method typically can achieve an accuracy of 0.7-2% of the capacity.
If your setup has an equalizer sheave, the pin can be replaced with a load pin. A load pin load cell is custom machined to the customer’s specifications to replace the original. This method produces roughly the same accuracy as the clamp-on load cell (0.7-2% of the capacity). Load pins are fairly easy to install but need to be calibrated after installation with test weights.
Another option is replacing the pin in the upper or lower block, this would be the hardest install of all the methods listed. Load Cell Systems can have the load pin manufactured with grease ports so the system can still be lubricated. These load pins typically achieve an accuracy, once installed, of 1-3% of the capacity.
Crane & Hoist Load Cell Electronics Selection
There are just as many options when it comes to the correct load cell electronics for the hoist or crane. First off, start by choosing the purpose of the load cell system. Do you want to just prevent overload or slack conditions using the system as a load limiter? Is it necessary for the operator to view the weight on the hook? Do you need to send the weight data from crane to the control system?
If the only purpose of the load cell is as a load limiting device (no display for the operator) all you need is the LCD1/2 crane load limiter and a load cell. The LCD1/2 can be used on cranes that have multiple hoists on one bridge. For example, if the bridge is rated at 10 ton and it has a main hoist rated at 10 ton and an auxiliary hoist rated at 2 ton, the LCD1/2 can be configured to stop the uplift if the combined weight on the hooks exceeds 10 ton (the capacity of the bridge).
Let’s say the goal is to do both, have a load limiter for your crane and display the weight. We can achieve this in several ways but the simplest is using the LCD1/2 load limiter electronics. It’s easy to connect a scoreboard to the serial communications port and the large LED display can be mounted on the bridge or wall and be seen from far away.
Hoist & Crane Load Cell Systems Conclusion
There are a lot of options when it comes to the load cell electronics for cranes and hoists. Sometimes a printer is needed to record the weights, or wireless load cells and receivers are required. As always, Load Cell Systems recommends talking to a knowledgeable sales person for assistance in choosing the correct load cell and instrumentation for your application.