Are you experiencing any of the below signs with your load cell measuring system? It could indicate that your load cell might be broken. Use our guide below to tell if your load cell is broken.
Signs that your load cell may be broken
Inconsistent Display Readings- The Display Readings Keep Fluctuating Up and Down
- The Display Will Not Return to Zero When the Load Has Been Removed
- The Zero Balance Has Changed Dramatically
- The Display Incorrectly Reads an Overload
- The Display Reads No Load When a Load is Applied
- The Display Readings do Not Change When Load is Applied
Inconsistent Display ReadingsThere are several reasons why your load cell may be showing signs of the above. These could be due to:
- Shock Overload
- Lightning or Electrical Surges
- Mishandling
- Moisture or Water Ingress
- Corrosion
- Broken Cable Connections
- Short Circuit
There are several checks you could do on-site to determine if your load cell is faulty before sending your load cell back to the supplier for repair. Only carry out the following on-site checks if it is safe to do so. Do not attempt them in an ATEX hazardous area.
Visual Check
A visual check of not only the load cell but the overall measuring system will determine the possible location of the fault. Things to look out for are:
- Damage to the Load Cell – Corrosion or Wear, Deformation, Cracks
- Cable Connections and Cable Assembly – Cuts or Wear from the Load Cell to the Connected Measuring Devices
- Obstructions – Anything Between the Load Cell and the Unit to be Measured
- Mounting Surfaces – Level or Uneven, Mechanical Supports Correctly Placed
Note: For multi-load cell applications, you must disconnect all other load cells from the individual load cell you are testing.
Zero Balance Check
To test a load cells zero balance you need to carry out the following.
- Disconnect individual load cells from multi load cell systems.
- Remove all weight from the load cells
- Connect load cell to a stable 10Vdc supply (use an outside source)
- Measure the load cell’s output voltage between +ve signal and –ve signal
- Divide this figure by the supply voltage (in this case 10Vdc)
- Check this figure to the zero balance of the calibration certificate provided by your supplier.
If the zero balance figure is significantly different to the calibration certificate this could indicate that the load cell has been subjected to an overload. A moderate overload would result in the permanent deformation of the strain gauges and would need to be sent back to the supplier for repair, while a severe overload will usually physically deform the load cell itself, meaning that it need to be replaced.
Insulation Resistance Check
- Disconnect the load cell from the junction box, indicator or display.
- Connect all the leads together
- Using a megohmmeter, measure the insulation resistance between the leads and the load cell body
- Using a megohmmeter, measure the insulation resistance between the leads and the cable shield.
- Lastly, measure the insulation resistance between the load cell housing and the cable shield.
- Compare this figure to the insulation resistance figure on the calibration certificate or datasheet.
If the insulation resistance is significantly different this could be the result of moisture getting inside the load cell.
Input, Output and Bridge Resistance Check
For the Input and Output Resistance:
- Disconnect the load cell from the junction box, indicator or display.
- Using an ohmmeter, measure the input resistance between the excitation leads.
- Using an ohmmeter, measure the output resistance between the signal leads.
For the Bridge Resistance:
- Using an ohmmeter, measure the resistance from the –ve signal lead and –ve excitation lead.
- Using an ohmmeter, measure the resistance from the +ve signal lead and +ve excitation lead.
In most cases, the difference between these two figures must be ≤1 ohm.
Compare these figures to the calibration certificate or datasheet.
If the bridge resistance figure is significantly different to the calibration certificate this would indicate a short circuit within the load cell. This could be due to a shock overload, lightning or electrical surge.
What do I do now?
After carrying out the load cell tests above and you think that it is your load cell is faulty, we recommend sending it back to your original supplier.
Our load cell testing experts here at Applied Measurements will repair any strain gauge load cells even if the product was not originally provided by us, see our repair services page.
Think your load cell is broken? Let us call you…
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