How to Calibrate Load Cells in Weighing Applications?

Load cells are special force transducers used for measuring weight or force in various applications. These are integral to weighing systems in various industries, including aerospace, marine, automotive. The reason being they produce highly accurate load measurement data. That is why it is essential to inspect and calibrate them routinely.

Weighing scale calibration services ensure accurate load cell readings and help identify operational issues so that negative consequences can be prevented.

How to Calibrate Load Cells

Why You Should Calibrate Load Cells

Load cells show signs of wear and tear over a period of years. Frequency of use, environmental causes such as temperature, and aging are some of the contributing factors to the deterioration of load cells.

Faulty cables and instruments, particle accumulation and matter buildup, mechanical defects, incorrect installation, and the influence of electricity can also lead to inefficiency.

That is why routine calibrations should be performed to ensure the efficiency and accuracy of load cells. In the absence of frequent calibrations, load cells can give incorrect readings and produce erroneous data.

Routine calibration of load cells can help achieve accuracies of around 0.03 to 1%. As part of product liability, safety, and compliance in a Quality Management System, load cells are required to be calibrated to National standards.

Steps to Calibrate Load Cells in Weighing Applications

Before calibrating load cells, inspect whether the machine is giving correct measurement data.

We have mentioned three key indicators to evaluate whether the load cells and transducers are functioning correctly, these are:

• When the system is unloaded or empty, the weight indication should return to zero.
• The indicated weight must be double when the weight is doubled.
• Irrespective of where the load is placed, the weight indicator should give equal readings.

Provided that all the conditions are met, it is safe to conclude that the load cells and transducers are working.

If you notice otherwise, follow the next steps.

• Load cells can give inaccurate readings due to faulty cables and incorrect installation. Therefore, check the following before calibrating load cells:
• Inspect the electrical cables and wires
• Remember to place dummy cells in place of operational load cells until construction and welding work is finished.

After performing the preliminary tests, if you find that load cells are causing problems, conduct the following tests:

Physical Inspection:

This involves inspection for any physical damage in the load cell. Also, check for dents and cracks on all sides.

Note that if the load cell is not in its original shape and is altered- compressed, bent, or stretched, you need to replace the cell.

Bridge Resistance:

This test should be done when there is no load and the system is disconnected from the weight controller. Now measure the excitation leads for input resistance, and signal leads for output resistance.

Compare the readings with the load cell specifications. out-of-tolerance readings are often caused by power fluctuation.

Zero Balance:

Residual stress in the sensing area can often cause a shift in zero balance. If a load cell is overloaded repeatedly over multiple operational cycles, residual stress builds up.

Check the output of a load cell with a voltmeter when the system is empty. It must be within 0.1% of the mentioned zero output signal. If it exceeds the zero balance tolerance band, the cell might be damaged.

Resistance to Ground:

Connect the input, output, and ground leads. With the help of an ohmmeter, check the resistance between the load cell body and the leads. If the reading does not reach 5,000 megaohms, separate the ground wire, and repeat the test. If it fails again, the cell could be damaged.

By following these steps, you would not only ensure load cells are functioning correctly but would also be able to prevent and take precautions against any potential damages.

Author Bio:

Kevin Hill heads the marketing efforts at Quality Scales Unlimited in Byron, CA. Besides his day job, he loves to write about the different types of scales and their importance in various industries. He also writes about how to care for and get optimized performance from different scales in different situations. He enjoys spending time with family and going on camping trips.