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How to Test a Load Cell: A Step-by-Step Guide

  • Cody
  • 3 days ago
  • 4 min read

If your scale is displaying unstable readings, won't zero correctly, or is showing an error, the load cell is often one of the first components that should be tested.

Fortunately, you can perform several basic electrical tests with a digital multimeter before replacing the load cell.

This guide explains the same troubleshooting steps our technicians use to evaluate load cells in the field.

Multi meter for testing a load cell

Tools You'll Need

  • Digital multimeter capable of measuring DC volts and resistance (Ohms)

  • Load cell wiring diagram or datasheet

  • Access to the load cell cable or junction box

  • Known test weight (if available)



Step 1: Check Excitation Voltage

Before testing the load cell itself, verify that the indicator is supplying excitation voltage.

  1. Turn the indicator on.

  2. Measure DC voltage between +EXC and -EXC.

  3. Most indicators supply between 5 and 15 VDC (refer to your indicator specifications).

If there is no excitation voltage, the problem may be the indicator, wiring, or power supply rather than the load cell.


Step 2: Check the Load Cell Output (Millivolts)

Next, measure the load cell's output signal.

  1. Set your multimeter to DC millivolts (mV).

  2. Measure between the +SIG and -SIG wires.

  3. With no additional weight applied, record the output reading.


A new load cell is typically adjusted at the factory so the no-load output (zero balance) is very close to 0 mV. However, once installed in a scale, the load cell is supporting the system's dead load—the weight that is always present, such as the scale deck, hopper, tank, or weighing platform.


Because of this, it's common to see a reading between 0 and 5 mV, depending on the amount of dead load and the excitation voltage supplied by the indicator.


What to Look For

  • ✅ A stable reading that does not drift significantly.

  • ✅ A millivolt output that increases smoothly when weight is applied.

  • ⚠️ A reading greater than 10 mV with no additional load often indicates the load cell has been overloaded or damaged.

  • ⚠️ A negative millivolt reading under normal installation conditions is also a strong indication that the load cell or wiring has been compromised..


Step 3: Apply Weight and Watch the Millivolt Output

Now apply weight to the scale. The millivolt reading should increase smoothly as weight is added.


If the millivolt output does not change—or changes erratically—the load cell, wiring, or mechanical installation may be faulty.


Step 4: Compare Resistance to the Manufacturer's Specifications


Resistance testing is one of the most effective ways to identify internal damage.

Locate the manufacturer's datasheet and compare your measurements to the published specifications.


Before performing any resistance (Ohm) tests, disconnect the load cell from the indicator or junction box and remove power from the system. Resistance measurements should never be taken on an energized circuit.


Measure the following:

Excitation Resistance

Measure between:

  • +EXC and -EXC

Compare the reading to the specified input resistance.


Signal Resistance

Measure between:

  • +SIG and -SIG

Compare the reading to the specified output resistance.


Step 5: Cross-Check the Bridge

Measure the resistance between these terminals:

  • +EXC to +SIG

  • +EXC to -SIG

  • -EXC to +SIG

  • -EXC to -SIG

A healthy Wheatstone bridge should produce balanced readings. If one measurement is significantly different from the others or outside the manufacturer's specifications, the load cell may have an internal bridge failure.


Step 6: Inspect the Cable

Electrical problems are often caused by damaged wiring rather than a failed load cell.

Check for:

  • Cuts in the cable jacket

  • Pinched wires

  • Moisture intrusion

  • Corrosion

  • Loose terminals

  • Rodent damage

A damaged cable can produce the same symptoms as a failed load cell.


Common Testing Mistakes

Avoid these common mistakes:

  • Measuring resistance while the load cell is connected to the indicator.

  • Testing with power applied when measuring resistance.

  • Ignoring the manufacturer's datasheet.

  • Assuming every load cell has the same resistance values.

  • Forgetting to inspect the cable and connectors.

  • Measuring the load cell through the junction box without isolating it.


Frequently Asked Questions

  • Can I test a load cell with a standard multimeter?

Yes. A quality digital multimeter can perform most basic voltage and resistance checks. However, advanced testing may require specialized equipment.

  • Why is my load cell showing millivolts but the scale still won't weigh correctly?

The load cell may not be the problem. Indicators, junction boxes, damaged cables, mechanical binding, or calibration issues can all produce similar symptoms.

  • What if my resistance readings don't match the datasheet?

Significant differences often indicate internal damage or a failed strain gauge. Compare all measurements to the manufacturer's published specifications before replacing the load cell.

  • Can lightning damage a load cell?

Yes. Lightning strikes and power surges can damage the internal Wheatstone bridge, resulting in incorrect resistance readings or unstable output.


Need Help Testing a Load Cell?

If your measurements don't match the manufacturer's specifications—or you're unsure how to interpret the results—our technicians can help.

Whether you're troubleshooting a truck scale, floor scale, tank scale, or industrial weighing system, we can help determine whether the issue is the load cell, wiring, or another component.




 
 
 

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