Ensuring Measurement Accuracy – Your Load Cell Needs TLC too!

Weighing scales and measuring devices are pieces of equipment, just like a wheelbarrow, an automobile or a luxury boat. As such, they all need care and attention to deliver optimum performance – from the simple ball bearing in your wheelbarrow, to the engine transmission system of your car. It’s the same with measurement systems large and small.

One component that deserve special TLC in these measuring devises is the load cells (or force transducers). These small, yet all important, components of weight-assessment devices face numerous challenges as they continue to operate. In return, to ensure optimal performance, they too deserve some TLC.

COMMON PROBLEMS and CHALLENGES

Measurement facility operators and device owners often have much on their plates to worry about. As a result, they may sometimes overlook some common situations that create load cell issues. Here is just a sampling of such conditions that might lead to measurement inaccuracies:

• Capacity Overload

Weighing scales and measurement platforms can’t withstand unlimited amounts of loads. They have a rated capacity, and the most common problem with faulty measurement readings is the result of overloading the scales (frequently) beyond that capacity.

• Extended Exposure to Moisture

Exposure to moisture, especially for scales and measurement structures not designed for such exposure, can wreak havoc on measuring precision – not just on the measurement device, but also on the force transducers that support them. This is especially true for older devices that have been in service close to their rated life.

• Chemical Leaks

Like other moisture exposure, chemicals that evaporate and enter the containers and structures where cells operate are a huge challenge to measurement accuracy. Corrosive chemicals are especially more dangerous, and do significant harm to weighing equipment.

• Watch for Damaged Connections

Environments that use more than a single load cell to measure loads are especially susceptible to situations where damaged connections, between cells and the measuring instrument, cause measurement inaccuracies. Watch for such occurrences where cells operate in corrosive environments. Moisture, acidity and salt may lead to corrosion of the connections, thereby disrupting the measurement signal.

• Electrical Damage

Direct exposure to electrical impulses and currents, like lightning strikes or electro-magnetic frequency interference, is a cause for concern to load cell performance. The situation might not only cause physical damage, but also lead to measurement disruption even in seemingly “un damaged” weighing systems.

• Temperature Changes

Strain gauge-based cells are especially susceptible to the warped metal casing that house them. Metal warps as a result of dramatic temperature changes, leading to measurement anomalies. Prolonged bursts of heat, like direct exposure to sun, and then extended cooling, like leaving the device out during cold nights, is a common reason for warping too.

• Load Cell Response

Cells used in a measurement device require a specific amount of time to return to zero prior to accurately measuring another load. The cells have an error tolerance built into them. If, for instance, the container requiring measurement starts filling-up too quickly, before the cell’s measurement returns to zero, the measurement will be inaccurate.

• Well-balanced Loads

For the cells to perform at their optimal levels, it is important to use well-balanced loads. Either balance the loads evenly on the cell, or put appropriate measures in place to accommodate situations where you use unbalanced loads. This is especially important in environments supporting multiple load-bearing receptacles. In these situations, make sure to evenly distribute containers or vessels so no single cell bears an undue portion of the load.

CARE, MAINTENANCE and TLC

So, is there anything that you can do to protect yourself from these and other load cell problems and challenges? And, if so, then what might those measures be?

The cells are typically a self-contained “system” in themselves. So, although the cells themselves do not require any major maintenance (one exception noted in point#7 below) perse, here are some recommendations to consider that’ll ensure optimal cell performance:

1. 1. Avoid lifting strain-gauge or cable-tethered cells by their cables
2. 2. Where possible, mount cells away from situations that might interfere with performance, such as excess heat, noise or vibrations
3. 3. When using cells in “aggressive” environments, take additional precautions, such a guarding the cells with steel coverings or mesh, or using rubber buffers to protect them
4. 4. Before performing any major maintenance on the measuring devices, such as scales and platforms, make sure the load cell is properly disconnected and protected from maintenance-related shocks or vibration
5. 5. As part of your regular maintenance routine, make sure you remove dirt, grime and spilled materials – especially liquids – from the cells and surrounding components
6. 6. Use a low-pressure air blower to disperse dust and moisture from cells and their vicinity
7. 7. Regular cell calibration ensures the accuracy of the measurements they deliver
8. 8. One cause of measurement anomalies that’s typically ignored (or underestimated) is air currents and wind force. This might be from outdoor conditions, or internally generated, such as from turbines and wind tunnels. For accurate measurements, make sure to appropriately protect the measuring devices from these forces
9. 9. Before transporting or relocating measurement systems, such as scales and weighing platforms, make sure you protect the cells to withstand shock and vibration during uninstallation, relocation and re-installation
10. 10. Beware of signal jitter. For optimal performance, cells require a steady signal. The “smoothness” of the signal aids the signal controller in averaging out fluctuations and variations of the measurement. Wobbling platforms, vibrating hoppers, overly shaky conveyor belts and instable surfaces aid and abet signal jitter which causes measurement disruptions

BETTER MEASUREMENT ASSURED

Although they are relatively small, in terms of their physical dimensions compared to the overall measuring structures they support, like weighing platforms and storage silos, the force transducer is a critical component of any weighing or load measurement system. And, just as one carefully maintains and cares for other components of those systems, so too should they care for the load cells that support those systems.

Being aware of the possible problems and challenges that can cause weight and measurement anomalies is the first step in assuring better measurement. Implementing proper care, maintenance and TLC of the cells and related components is the next important step.

Tags: Load Cell, Load Cells, force transducers, transducer techniques, transducer, transducer sensing elements