Most SP loadcells utilise 2.4 GHz direct sequence spread spectrum (DSSS) radio technology which offers high integrity, error free communications that can co-exist with other wireless technologies such as Wi-Fi, Bluetooth® and Zigbee®.
Some applications however require a cabled solution, a great example of this is a subsea application where a loadcell could be mounted many hundreds of metres below the ocean and wireless technology would not work.
Choosing between wired or wireless load cells
The choice between wired or wireless load cells depends on a number of factors but the main ones are application, capacity, convenience and budget.
Wired load cells suit simple applications. A typical setup is where one load cell is connected to one handheld display (1:1) for a basic readout of the weight. Popular examples would be single-point weighing or when using a load cell in a test bed. But in below the hook applications a loadcell fitted to a crane hook can be cumbersome, easily broken and inhibit the movement of the hook on a crane, Davit or hoist.
More complex applications involving several load cells and showing individual and total loads are more suited to wireless systems. Each wireless load cell transmits a unique ID allowing data to be logged from each cell and alarms can be set if certain maximum or minimum limits are reached. Data logging can be done at speeds up to 200 times per second (200Hz) which suits dynamic testing such as destructive or drop tests.
The SP wireless system uses a proprietary hexadecimal addressing system so other wireless devices in the same location can never cause an incorrect (and dangerous) reading. It can operate on any one of 15 channels offering a solution in rare cases where radio frequency interference (RFI) is experienced.
Capacity and convenience:
Wireless systems allow the user to be a safe distance from the load or from the test being conducted. The higher the capacity involved the more likely the user wants to be away from the load for safety reasons.
Similarly, for convenience, the larger and more awkward an object is the more cables become messy, heavy and obtrusive. They can get snagged, damaged and are a trip hazard – wireless systems not only remove those obstructions but also allow centre of gravity of calculation of an object during weighing – a crucial piece of information when planning a safe lift. Typical structures to be weighed include large fabrications such as pipes, steel plates, precast concrete and offshore jackets for offshore use.
The reliability and convenience of wireless systems has led to those systems being favoured by customers. Around 90% of the systems we sell at Straightpoint are now wireless as customers upgrade from wired systems.
OEM and integrated systems often remain as wired systems. Load information is relayed to a PLC (often via current 4-20mA or voltage 0-5Vdc output). In this scenario, the PLC or Scada system may be monitoring or summing several load cells at one time.
Safety critical applications are usually cabled systems. For example, an entertainment rigging set up with loads transferred above the heads of performers. In this case it is vital high-speed data can transfer to controllers with no possibility of missing wireless data packets or local interference.