How to Check a Load Cell

Load cells are essential components in weighing systems, converting mechanical force into electrical signals for accurate measurements of weight and force. However, like any precision instrument, load cells can experience issues over time, such as drifting calibration, electrical malfunctions, or physical damage. To ensure they continue to function properly, it's important to periodically check their condition. Here's a guide on how to check a load cell and diagnose common issues.

 

1. Visual Inspection

 

Start with a basic visual inspection to check for any obvious physical damage. Look for:

 

Cracks or Deformation: Any visible cracks or bends in the load cell housing could indicate physical damage, which may affect its accuracy.

 

Corrosion: If the load cell has been exposed to harsh environments, check for rust or corrosion, especially on the strain gauges and wiring.

 

Loose Wires or Connections: Ensure all wires and connections are secure, without fraying or loose terminals. Improper connections can lead to erratic readings or failure.

 

2. Check the Wiring and Electrical Connections

 

Load cells are often equipped with electrical components, including strain gauges and amplifiers, that can wear out or malfunction. To check the wiring:

 

Test for Continuity: Use a multimeter to check for continuity in the load cell's wiring. This ensures there are no broken wires or disconnected circuits.

 

Inspect for Shorts: Using the multimeter, check for any shorts between wires. A short circuit can prevent the load cell from functioning correctly.

 

Verify Input and Output Signals: Measure the output of the load cell when it is subjected to a known load. Compare the signal to the expected output to see if the readings match.

 

3. Calibrate the Load Cell

 

Calibration is a crucial part of maintaining accurate readings. Over time, a load cell may lose its calibration due to environmental factors or prolonged use. To check the calibration:

 

Use a Known Calibration Weight: Apply a weight that is known and consistent, and observe the output signal from the load cell. Compare the output signal to the expected value for that weight.

 

Check for Drift: If the load cell reading drifts significantly from the known weight, it may need to be recalibrated or repaired.

 

Apply Different Loads: Test the load cell with a range of known weights, from low to high, to ensure it is responding correctly across its full range.

 

4. Check for Zero Balance

 

Before any testing, ensure that the load cell is correctly zeroed. This is important because even small deviations can affect the accuracy of the measurements. To check the zero balance:

 

Empty Load: With no weight applied, the load cell should show a reading of zero. Any significant deviation indicates a need for recalibration.

 

Tare Function: Many load cells or weighing systems allow for a tare function, which helps reset the load cell to zero after a container or additional equipment is added. Use this function and verify the results.

 

5. Perform a Load Test

 

To evaluate the load cell's performance under typical operating conditions:

 

Apply Gradual Loads: Gradually apply increasing loads to the load cell and observe the output signal. The load cell should produce a linear response with no sudden jumps or drops in the signal.

 

Test the Full Load Range: Ensure the load cell responds correctly at both its minimum and maximum rated load capacity. This will help determine if the load cell is still within its operational limits.

 

6. Check for Environmental Factors

 

Environmental factors such as temperature, humidity, and vibration can affect the performance of a load cell. To check for environmental effects:

 

Temperature Sensitivity: Load cells are sensitive to temperature changes. If possible, test the load cell in different temperature conditions to see if the readings change.

 

Vibration Effects: Excessive vibration can cause instability in the readings. Make sure the load cell is mounted securely and that vibration isolation is in place if necessary.

 

7. Check the Output Signal

 

Finally, check the load cell’s output signal using an indicator or controller connected to the load cell. The output should be consistent and smooth. Any fluctuations in the signal may indicate a malfunction. If your load cell is equipped with a digital output, ensure the readings are stable and match the applied load.

 

In conclusion, regular checks and maintenance of load cells are essential for ensuring their long-term reliability and accuracy. By performing visual inspections, checking wiring, calibrating, and running load tests, you can identify any issues early and prevent costly errors or downtime. If the load cell shows signs of malfunction that cannot be resolved through simple checks or recalibration, it may be time to replace or repair the unit. Properly maintained load cells ensure accurate weight measurements, making them crucial in various applications, from industrial processes to medical devices.