Load Cells and Digital Technology
The Digital Divide – Are You on the Right Side?
Access to the latest digital technology can make as big a difference in your weighing operation as it does in other areas of business. To understand the benefits of digital weighing, look at how advanced digital technology stacks up against analog systems.
While most electronic technologies have been quick to convert to digital, much of the weighing industry has lagged. Many of the vehicle scales being sold today still use the same basic analog technology that was developed in the 1960’s. No business that hopes to gain an edge over its competition can afford to rely on technology that is 50 years old
Analog limitations
How big a difference can digital technology make in a vehicle scale? To find out, look at how analog load cells work. Load cells are the sensors that measure the weight of a load on a scale. In an analog scale, the load cells transmit weight readings to a scale terminal by means of an electrical voltage signal that varies as the load increases or decreases.
The first thing to notice about an analog signal is that it is relatively weak. A 30-ton load cell has a full capacity range of only 0.03 to 0.04 volts. As a result, very small changes in voltage have a big impact on a weight reading. Changing the signal by as little as 0.00002 volts can mean a difference of 20 kilograms (44 pounds). Maintaining accuracy is a tall order when you consider how temperature, humidity, electrical interference, and other environmental forces affect analog signals.
An analog signal is just an electrical voltage. It transmits no data, so it tells you nothing about how a scale is performing. Not only is an analog signal easy to disrupt, but weighing errors often go undetected until the next time the scale is serviced. There can be months of expensive errors before a problem is even noticed.
Digital innovations
POWERCELL® PDX® load cells also use electrical voltage to measure weight, but they convert the voltage to a digital signal before transmitting it. Because the digital signal consists of binary data, it is more stable and resists environmental forces.
The signals that POWERCELL® PDX® load cells transmit carry more than just weight data. They contain a wealth of information about how each load cell is performing. While analog systems tend to hide problems, this “smart” technology recognizes the effects of environmental forces and compensates for them. A built-in microprocessor uses digital compensation to maintain accuracy in hostile environments that cause weighing errors in analog scales.
Real-world errors
How well do these two technologies perform in the real world? To find out, we tested the accuracy of more than 2,700 vehicle scales of various types and ages. Figure 1 shows the accuracy results for scales that use POWERCELL® load cells. Figure 2 shows the results for scales that use analog load cells from a variety of manufacturers.
The vast majority of the POWERCELL® scales weighed within a few increments of zero error. More analog scales produced errors, and the errors tended to be larger. According to the statistics, the errors that you get from an analog scale are likely to be more than three times larger.
Those errors are just the tip of the iceberg. They were measured using typical calibration test loads of approximately 10 tons. When you weigh fully loaded trucks, you can expect significantly larger errors from an analog scale.
To demonstrate the difference between analog and POWERCELL® technology, we tested several scales with 10 tons and 40 tons of test weight. While POWERCELL® PDX® load cells maintained their accuracy, analog errors increased as test weight was added. An analog scale that showed 10 kilograms (22 pounds) of error for a 10-ton load jumped to 40 kilograms (88 pounds) of error for a 40-ton load.
The cost of errors
Keep in mind that we are talking about your money. Weighing errors that look small on a graph can have a big impact on your bottom line. Because weighing errors affect your business every time a truck drives across a scale, they add up quickly. Figure 3 shows how much money you stand to lose if your scale weighs 100 trucks per day and displays weight readings that are 36 kilograms (80 pounds) too low.
Greater reliability
Higher accuracy is just one of the benefits of POWERCELL® PDX® load cells. They also provide greater reliability and simpler maintenance. Junction boxes are the biggest maintenance problem for analog scales. These hard-to-seal boxes contain sensitive electronics that are easily damaged by moisture.
A POWERCELL® PDX® network has no junction boxes. This design innovation is just one of the reasons for the network’s greater reliability. Scale owners who have replaced analog load cells with POWERCELL® PDX® technology have been able to cut their annual maintenance costs by thousands of dollars.
The digital advantage
Although analog load cells offer a lower purchase price, any initial savings are more than offset by the ongoing cost of low accuracy and reliability. When all the factors are considered, the advanced digital technology of POWERCELL® PDX® load cells provides the best return on investment for vehicle weighing.
