Comparing POWERCELL Technology with Analog

Mettler Toledo's new POWERCELL® technology continuously monitors load cell performance, detecting changes that occur before they impact productivity. This technology enables manufacturers to maintain process control and avoid errors before material damage occurs. Without the continuous monitoring that POWERCELL® provides, load cell overloading, incorrect weighing and out-of-tolerance temperatures—problems that may go undetected for extended periods—can result. When this occurs, out-of-specification and lower-quality products emerge. This can lead to serious costs and reputational damage to the company. Equipped with internal microprocessors, POWERCELL® load cells not only alert operators to performance degradation but also compensate for environmental changes. This enables POWERCELL® load cells to deliver accurate weighing results independent of temperature, linearity and hysteresis effects. Should load cell failure occur, the POWERCELL® design also simplifies replacement of individual load cells. Global approvals for POWERCELL® load cells include OIML, C3, NTEP 5K, OIML C6 and NTEP 10K standards. Measurement errors stemming from temperature, non-linearity and hysteresis are digitally corrected in POWERCELL® technology, providing better accuracy and resolution values than analog load cells.

1. Load Cell Types

Analog System Architecture: In an analog system, cables and junction boxes have a significant effect on very low-level signals, and the system must be calibrated as a whole. Any component changes require complete system recalibration. Additionally, the low analog signal is sensitive to RFI/EMI and moisture-induced disturbance, affecting system performance. POWERCELL® System Architecture: The POWERCELL® system has no junction box. This reduces a component within the system that would otherwise affect system performance and reliability. Since weighing information is provided digitally, cables have no effect on system performance. This allows cables to be changed at any time without affecting system performance.

2. Performance Differences

Signal Content: Analog systems evaluate only the combined signal of all load cells. The POWERCELL® network receives weighing information separately from each load cell. This allows the terminal to monitor each load cell individually and make decisions about load cell and system status. Signal Strength: The strength of an analog signal is very low. Such low signals are easily affected by proximity to mobile phones, electric motors, moisture and other factors. POWERCELL® uses the CAN Bus data path for data transfer. CAN Bus is a robust +/- 5V digital signal commonly used in the automotive industry. Cable Effect: Analog cables have a significant effect on system performance. Cable length, cross-sectional area, quality, shielding, 4- or 6-wire configurations and other factors affect performance, but POWERCELL® system performance is completely independent of cable effects. EMI Protection: A measure of a system's capacity to withstand the effects of external electromagnetic fields such as mobile phones and high-current lines on itself.

Analog systems with low signal strength are highly sensitive, while POWERCELL® is far more robust (10 V/m field strength system).

Accuracy: Another important difference between analog and POWERCELL® load cells is the method of correcting errors inherent in each load cell. Analog load cells use passive components that can be used only within limited value ranges to correct temperature effects and adjust calibration. For this reason, passive components limit the precision of corrections that can be made. POWERCELL® uses internal microprocessors, advanced sensors and algorithms to balance performance errors. All major error sources are automatically corrected. It is possible to achieve high accuracy capable of reaching a unique OIML class C 10000e performance level three times above the standard. POWERCELL® load cell outputs are 100% interchangeable in production because they match exactly.

3. Calibration Differences

Analog CalFree™ and POWERCELL® CalFree™ Plus Comparison: CalFree™ is the latest technology offering weight-free calibration for larger systems where calibration with test weights or other methods is impractical. Essentially, the internal calibration of load cells is manually transferred to the final system. In analog load cell systems where cable effects are uncertain, interference in communication between junction box and load cells can adversely affect transfer accuracy. Additionally, calibration accuracy depends on the technician's calculations. In this case, a completely unsuitable calibration may go undetected. POWERCELL® CalFree™ Plus eliminates many potential error sources. There is no cable effect, no junction box and communication interference, and the technician needs no calculations. Thus, calibration performed with POWERCELL® using CalFree™ Plus is far more reliable.

4. Diagnostic and Maintenance Differences

What happens if the signal from an analog load cell due to deterioration or other reasons is incorrect? If the error is significant, the operator may detect it and investigate the cause. However, this requires the operator to be experienced and the weighing module to be completely "failed." Otherwise, the operator has no way of knowing that the weighing is inaccurate. Depending on the equipment's importance to the final product quality, the consequences can be very serious. Every POWERCELL® system is equipped with sensors that monitor the performance of each load cell. Should a problem become unavoidable, a message is generated at the weighing terminal indicating that a specific load cell is affected and a problem is expected. Weighing can continue normally until the cell is replaced at the scheduled time. Monitoring the integrity of each load cell ultimately eliminates "hidden" problems that could lead to unexpected weighing errors.

5. Conclusions

POWERCELL® helps avoid hidden errors that can have significant consequences for final product quality and cost. It allows repairs to be made before an error actually occurs. Additionally, because it eliminates the need for recalibration after service, weighing can resume more quickly. This table summarizes the benefits of POWERCELL®.     Uğur Tuncer Industrial Division Business Unit Manager METTLER TOLEDO Turkey