We thought it would be helpful to summarize important topics when evaluating a scale for a front end loader garbage truck. These points are based on comparing scale systems in the market in the USA, in other countries there are most likely differences.
In order to get the weight of a bin (also called container or dumpster depending who you ask) the scale takes the weight of the bin (filled with garbage) when lifting the bin up. After dumping the garbage the scale takes another weight of the empty bin when lowering the bin back to the ground. The difference of these two weights equal the weight of the garbage just collected.
There are different methods to actually measure the weight. One is to have load cells integrated in the fork assembly. These load cells measure the (minimal) bend which happens when the fork picks up the load of the bin. The other method is to install a device called strain gauge on the arm and measure how much the arm gets bend and translate that into a weight.
While this was already discussed here, real quick to recap: Dynamic means that the lifter does not have to be stopped to take the weight (up or down). A static scale means you need to stop the scale to take the weight. Obviously stopping to get the weight takes time and therefore causes decreased productivity.
When talking about accuracy it is important to define what accuracy is exactly referenced. Often accuracy is expressed in per cent. The next question should be per cent of what? For example, the per cent of the actual weight or per cent of the maximal capacity of the scale? To give an example, if the max. capacity of the scale is 8000lbs and you claim to have 1% accuracy based on max capacity that would be +/- 80lbs error across all weights you are picking up. If you use the definition based on the actual weight you are picking up, lets say 800lbs, that error would only be +/- 8lbs.
The other consideration when talking about accuracy is when weighing dynamically there is the human factor of the operator involved who controls the lifter when emptying the can (except if the lifting procedure is fully automated). Think about when the operator stops the lifter (for whatever reason) and starts again while the scale is measuring. Such a change would most likely influence the weight (compare it to jumping up and down on your bathroom scale and try to get an accurate weight). There are ways to minimize the error a driver can induce but it is good to distinguish between weighing results under optimal conditions and the results which are on average achieved under “field” conditions.
In the US dynamic scales are used to audit the weights of each single customer. As the waste hauler gets charged for the garbage he delivers to the landfill by the ton it makes sense to ensure the profitability of the operation by monitoring the weights picked up. How can you match a weight pick up with a customer? One approach is to record via GPS the location where the weight was picked up and match that location in a software with a customer name. The GPS functionality can also be used to run fleet management functions, like recording current speed, location, time and driver behavior like strong braking or acceleration. The data will be sent via a cell (GPRS) modem to the office in real time.
One aspect to note is that the driver in the cab should not have to do anything to operate the scale, but is free to fully focus on his job of collecting each single bin safely and efficiently.
If the scale should not be connected to a software platform with the described functionality it needs to be explored how the data could be collected and handed over to a 3rd party management system as just the weight of the bin by itself (not connected to the customer name) does only add very little value to the waste hauler operation.
If the scale has a functionality to add up the single weights you can also use the scale to prevent the truck from getting overloaded. Safety, maintenance costs, liability are just a few reasons why overload is an important factor to consider and a front loader scale with add up functionality can help with this. On the flip side you can also ensure to load the truck up to full capacity to avoid going too early to the landfill and losing money in the process.
Please add to this list anything you might miss or want to elaborate on, thank you!