From time to time, load cells may confront many faults that may hamper with their performance. This article enlists some of the most common strain gauge load cell faults and how to address them.
Common faults in load cells
- A very sudden change displayed in the zero balance value of the load cells
- The readings are unstable and there are arbitrary changes in the zero balance point of the load cell
- Wrong or overload readings displayed for a known weight
- No weight recorded at all
- Wrong output load cell displays when a load is subjected or after it has been removed
For addressing each of these cases, a different test can be conducted.
When these or other faults are found, it is essential to verify the integrity of the weighing equipment and system before you apply any troubleshooting steps for the load cell.
This may include the steps listed below:
- Inspect the mechanical support, load cell orientation and mounting surface for levelness, cleanliness and alignment.
- Inspect the interconnecting cables in the summing box.
- Inspect the connection of the summing box to the connection with the digital indicator panel.
Once these steps are done in order to verify the integrity of the weighing system, you can troubleshoot the load cells for its faults.
And this may call for the test equipment listed below:
- A high quality digital voltmeter and ohmmeter that can read from 0 – 50mV and 4 – 20mA.
- A screw driver set.
- A mega-ohmmeter of 5000 ohms. Know that it shouldn’t supply more than 50 volts to the load cell as exceeding this value can damage the load cell permanently.
When you use these tools, you can further carry out the fault evaluations like this:
- Inspect the zero balance reading.
- Connect the load cell input terminals to an input voltage.
- Calculate the voltage across the load cell output terminals with the help of a millivolt meter and then divide the result by the excitation voltage for getting zero balance in the mV/V.
- Then compare the value obtained in the zero balance with the value in the datasheet of the product. If you want to know about Load Cell Signal Conditioning, visit here.
Then further three types of testing are done:
- Bridge integrity test
This is done when the weighing scales are overloaded, gives away wrong reading or doesn’t give any reading at all. It is accomplished by measuring the output resistance, input resistance and bridge balance.
- Shock resistance test
This is done when the load cell gives a weird output when the load is applied or after it is removed.