Notes: Testing a Load Cell with Wheatstone Bridge Circuit

Introduction

• A load cell is an electronic device used to measure weight or force.
• The load cell operates using a Wheatstone bridge circuit.
• The strain gauge is the sensing element that converts pressure or weight into resistance.

Components of a Four-Wire Load Cell

• Wire 1 & 2: Connected to the strain gauge.
• Wire 3 & 4: Connected to the opposite resistance in the circuit.

Testing Procedure

1. Set Up: Ensure the load cell is connected correctly with the four wires.
2. Use a Multimeter:
   • Measure the resistance of the strain gauge.
   • Check the resistance value against the load cell datasheet.
   • The expected resistance without any load should be 350 ohms.
3. Measure Opposite Resistance:
   • Similar procedure to the strain gauge measurement.
   • Expected value is also 350 ohms for no load condition.
4. Check for Balanced Circuit:
   • When the circuit is balanced, the output voltage between wires 1 and 3 should be zero.

Load Application

• Refer to the datasheet for load application results.
• When a load of 2500 pounds (1134 kg) is applied:
  • The expected output is 30 millivolts.

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Conclusion

• Proper testing of a load cell involves checking resistance values with a multimeter to ensure the Wheatstone bridge is balanced and operational according to specifications.