Load cell failure can appear with indications such as unstable weighing values, inability to return to zero, non-linear results as the load increases, or the indicator not receiving any signal at all. However, similar issues can also be caused by mechanical sticking, indicator calibration, junction box, cable, and electrical interference. Therefore, it is not correct to replace the load cell based solely on the indication on the screen.
The following steps are for field pre-checks. Working on a live circuit, cable insulation testing, and loading on capacity are dangerous; manufacturer instructions and workplace safety procedures must be followed.
Common indications of load cell failure
- Continuous zero drift on an empty platform
- Different readings for the same load
- Large differences occurring between the corners of the platform
- The indicator not returning to zero after the load is removed
- The value suddenly reaching the maximum or moving in the negative direction
- Deviation starting after rain, washing, or temperature changes
Mechanical check before starting the test
Check that the platform does not rub against the surroundings, that the load is freely transmitted through the mounting elements, and that there are no welds, bends, cracks, or impact marks on the load cell. Cable crushing, rodent damage, and moisture in the junction box are particularly common causes. Electrical measurement performed while there is mechanical contact may be misleading.
How to measure the load cell with a multimeter?
1. Determine the cable and connection layout
Identify the excitation, signal, and, if present, sense terminals according to the color code in the product datasheet. Colors are not standardized across brands; do not make connections by guessing. Before measurement, isolate the load cell from the indicator and from other parallel-connected cells.
2. Measure the input and output resistance
Set the multimeter to the ohm range. Measure the input resistance between the excitation terminals and the output resistance between the signal terminals and compare with the datasheet tolerances. Open circuit, short circuit, or deviation far from the nominal value indicates bridge circuit or cable damage.
3. Evaluate the insulation condition
No low resistance should be seen between the bridge ends and the load cell body. An appropriate device and the test voltage specified by the manufacturer should be used for insulation measurement. Uncontrolled high test voltage can damage the electronic circuit.
4. Check the zero signal
When a correct and stable excitation voltage is applied, the no-load output signal is measured at millivolt level. If the zero balance exceeds the datasheet limits, there is suspicion of overload, plastic deformation, moisture, or bridge damage. In this test, polarity and the resolution of the measuring instrument are important.
5. Perform signal testing under load
The known load is applied in steps. The output is expected to increase proportionally and steadily with the load. For example, a load cell with a nominal output of 2 mV/V produces approximately 20 mV at full capacity with 10 V excitation. This value is theoretical; an accurate assessment should be made using capacity, sensitivity, and calibration information.
Difference between four-wire and six-wire load cells
In a four-wire connection, there are excitation and signal pairs. In six-wire models, additional sense wires allow the indicator to compensate for voltage drops in the cable. Connecting the sense wires incorrectly can lead to gain and stability issues.
Is it a single load cell or the junction box that is faulty?
In a multi-cell system, the corner test is performed first. If the problem follows a specific corner, the relevant load cell or its cable is examined. If the problem occurs at all corners, the indicator, power supply, junction box, and mechanical structure are evaluated. Measuring the cells individually can help identify the faulty channel; however, the connection sequence must be recorded.
Other causes of unstable measurement
- Signal cable near motor, inverter, and power cables
- Incorrect shielding or shielding from multiple points
- Loose terminal and oxidized connection
- Insufficient or fluctuating excitation voltage
- Vibration, wind, liquid movement, and process effects
- Incorrect filter, fraction, or calibration setting
Can a load cell be repaired?
Minor damage at the cable end and connection point can be fixed with the proper procedure. However, if the measurement body, strain gauge bridge, or hermetic structure is damaged, reliable repair is usually not possible. In critical weighing applications, the faulty cell should be replaced with a model that has the same capacity, sensitivity, output, and mounting characteristics.
Frequently asked questions
What should be the resistance value of a load cell?
There is no single universal value. The input and output resistance is specified in the model’s datasheet; the measurement should be compared with this value and its tolerance.
Are load cell cable colors the same?
No. The same color can perform different functions in different manufacturers. The product label and wiring diagram should be taken as a basis.
Does a faulty cell completely stop the scale?
Not always. In a multi-cell system, the scale may appear to work, while severe errors may occur only in certain corners.
Right product and technical support
Suitable for the application You can examine load cell and force cell options for fault detection, equivalent product selection, and system verification You can contact the Kobastar technical team.