Recently updated on August 21st, 2024 at 07:36 am

Load cells are critical components in weighing systems, providing precise measurements across a wide range of industrial applications. However, like any piece of equipment, load cells can encounter issues that affect their accuracy and performance. Troubleshooting these issues is essential to ensure that your systems continue to operate efficiently and reliably.

In this article, we’ll guide you through the process of diagnosing and resolving common load cell problems. Whether you’re a technician, an engineer, or someone responsible for maintaining weighing systems, this guide will help you identify issues early and take the necessary steps to fix them.

Common Symptoms of Load Cell Issues

Understanding the symptoms of load cell malfunctions is the first step in troubleshooting. Here are some of the most common signs that a load cell may not be functioning properly:

Step-by-Step Guide to Troubleshooting Load Cells

1. Visual Checks

Before diving into more complex troubleshooting techniques, start with the initial visual checks.

• Ensure mechanical supports and load cell are secure, aligned, correctly oriented per manufacturer’s guidelines, with clean, level mounting surfaces, and check for uneven loading to prevent inaccuracies or damage. (see Load Cell Installation & Maintenance: 2024 Best Practices Guide.)
• Examine the load cell for dents, cracks, corrosion, wear, bending, or buckling; use a straightedge for deformation and ensure it’s free from contaminants like dust, oil, or debris.
• Inspect interconnecting cables for cuts, crimps, exposed wires, and secure connections, especially at the summing box; replace any damaged cables to prevent faults.
• Ensure the summing box is securely connected to the digital indicator and inspect for internal damage or corrosion.
• Ensure excitation voltage connections are secure and stable; measure to confirm it’s within the manufacturer’s recommended range to avoid erratic behavior.
• Immediately address any issues found during visual checks; secure connections, replace cables, clean surfaces, and recheck for faults before further troubleshooting.

Correct any issues found during visual checks; if faults persist, continue troubleshooting the load cell.

2. Gather Required Test Equipment

The remainder of the troubleshooting steps require the following test equipment:

• A high-quality digital multimeter capable of measuring voltage, current, and resistance within the ranges of 0–50 mV and 4–20 mA, with an accuracy of ±0.1 mV and ±0.5 mA.
• A screwdriver set.
• A mega-ohmmeter capable of reading up to 5000 ohms (or the insulation resistance specified on the load cell data sheet, whichever is higher) with an accuracy of 500 ohms at 50 V. Ensure the mega-ohmmeter does not supply more than 50 V, as higher voltages can cause permanent damage to the load cell.

3. Determine the Zero Balance

Accurate measurement with a strain gauge load cell begins with correctly setting its zero balance. The zero balance is the output of the load cell when no load is applied, and it’s crucial for ensuring precision in subsequent measurements. Here’s how you can quickly and effectively determine the zero balance:

1. Power and Connection: Connect the load cell’s input terminals to a reliable and stable excitation voltage source. The quality of this voltage is critical—it should be low-noise and consistent to prevent fluctuations in your readings.
2. Measure the Baseline Output: With no load applied, use a millivolt meter to measure the voltage across the load cell’s output terminals. This voltage represents the load cell’s baseline output, which will be used to calculate the zero balance.
3. Calculate the Zero Balance: To find the zero balance, divide the measured output voltage by the excitation voltage. This will give you a value in millivolts per volt (mV/V), which is a standard way to express the zero balance.
4. Verification: compare the calculated zero balance with the value specified in the load cell’s data sheet. If the values align, your load cell is properly balanced and ready for use. If not, adjustments may be necessary to bring the zero balance within the acceptable range.

If zero balance issues have been ruled out, performing an insulation resistance check is a crucial next step to further determine if moisture has entered the load cell.

4. Insulation Resistance Check

An Insulation Resistance Test is a procedure used to measure the electrical resistance between the load cell’s conductive elements (such as the strain gauges and wiring) and the load cell’s body or housing, which is typically grounded. This test is crucial for ensuring that there is no unintended electrical leakage or short circuit that could affect the accuracy and reliability of the load cell’s measurements.

1. Ensure the load cell is disconnected from its power source and measurement system.
2. Attach one end of the insulation resistance tester to the load cell’s signal wires and the other end to the load cell’s metal casing or grounding point.
3. Start the tester and perform the insulation resistance measurement. Record the readings, which are usually in megohms (MΩ). If the measured insulation resistance is lower than the manufacturer’s specified minimum (usually above 500MΩ), it may indicate moisture or contamination inside the load cell.
4. Repeat the measurement to ensure consistent results. If the insulation resistance remains consistently low, further inspection of the load cell’s sealing and protective measures is recommended.

If the insulation resistance is not the problem, proceed to the next tests.

5. Perform a Bridge Integrity Test

Performing a bridge resistance check is a critical step in diagnosing potential short circuits within a load cell after ruling out insulation resistance issues. This procedure helps ensure that the load cell’s bridge circuit is functioning correctly, maintaining the accuracy and reliability of your measurements.

1. Power off the load cell and disconnect it from external systems.
2. Use an ohmmeter to measure the resistance across the excitation (input) terminals and the signal (output) terminals.
3. Optionally, measure the diagonal resistances across excitation and signal terminals to check bridge integrity.
4. Compare the measured resistance values with the specifications in the load cell’s datasheet.
5. Identify any potential short circuits if the measured resistance is significantly lower than the specified values.

Please note: The difference between the two test readings (e.g., the resistance from the negative output lead to the negative input lead compared to the resistance from the negative output lead to the positive input lead) should be less than or equal to 1%.

When to Seek Professional Help

While many load cell issues can be resolved through the steps outlined above, there are times when professional assistance is necessary. Here’s when to consider reaching out to a specialist:

Persistent or Unresolved Issues

If you’ve tried the troubleshooting steps and the issue persists, it’s time to consult with a professional. Persistent problems could indicate deeper issues that require specialized equipment or expertise to diagnose and fix.

Calibration and Certification

If your load cells are part of a critical system where accuracy is paramount, professional calibration and certification may be required. This ensures compliance with industry standards and maintains the integrity of your measurements.

Load Cell Repair and Replacement

In cases where a load cell is physically damaged or consistently underperforming, it may need repair or replacement. Professional services can assess whether the load cell can be repaired or if it’s more cost-effective to replace it.

Conclusion

Troubleshooting load cells doesn’t have to be a daunting task. By understanding the common symptoms of load cell issues and following a structured approach to diagnosis and repair, you can keep your weighing systems running smoothly. Remember, regular maintenance and environmental controls are key to preventing problems before they occur. For a complete resource, visit our load cell guide.

Contact us today to learn more about how we can help optimize your load cell performance!