Testing Load Cells

Overview

• Importance of proper functioning of electrical scales
• Load cells are essential yet vulnerable components in weighing systems
• Aim: To test load cells quickly and easily

Preparation Before Testing

• Ensure possession of the specific load cell calibration certificate.
• Pay attention to the following:
  • Wiring diagram with cable color codes
  • Output and input impedance
  • Any other necessary details for testing

Testing Steps

1. Compare Measurements

   • After each test, compare the measured values with the manufacturer's calibration certificate.

2. Setup Multimeter

   • Use a multimeter to measure resistance across input and output of the load cell.
   • Identify Wires:
     • Positive Signal Wire: Green
     • Negative Signal Wire: White
   • Connect the multimeter:
     • Red probe to Green wire
     • Black probe to White wire
   • Expected Output Resistance:
     • Should be close to 350 ohms
     • Example Reading: 353 ohms (acceptable)

3. Check Input Resistance

   • Measure between positive excitation wire (Red) and negative excitation wire (Black).
   • Expected Input Resistance:
     • Should be around 435 ohms
     • Example Reading: 439.7 ohms (acceptable)

4. Test for Accuracy

   • Measure millivolt signal from input leads.
   • Equipment Needed:
     • Multimeter
     • Voltage Source (Load Cell Controller)
   • Procedure:
     • Plug controller into AC source (220 volts)
     • Supply 10 volts DC excitation voltage across input leads.
     • Measure millivolt signal across signal wires (Gray and White).
     • Expected Reading with no force applied: 0 mV
   • Apply a calibrated weight:
     • Compare measured output voltage with specified value in the calibration certificate.
     • If they match, the load cell is functioning correctly.

Conclusion

• Follow the steps to ensure accurate load cell testing.
• For more information on load cell testing, visit the provided website.
• Links for budget-friendly load cells are available in the video description.