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Load cell working and wiring explaination


Load Cell Basics: Working Principle and How to Test One



What Is a Load Cell?






A load cell is a force-sensing device used to measure weight or mechanical load. It can respond to force applied in tension (pulling) or compression (pushing), and its job is to translate that mechanical force into an electrical signal — typically in the millivolt range.

That raw millivolt signal isn't useful on its own, so supporting electronics amplify and condition it, converting it into a readable weight value (kilograms or tons) on a display, or into a standardized industrial signal such as 4–20 mA or 0–5 V for transmission to a control system.

 

How Load Cells Work



Most load cells are built around a strain gauge. When force is applied to the strain gauge, its electrical resistance shifts slightly. This tiny resistance change is measured using a Wheatstone bridge circuit, which converts it into a proportional electrical output representing the applied force.






 

While strain-gauge load cells are by far the most common type in industrial use, pneumatic and hydraulic load cells also exist and are used in specific applications where their particular characteristics are advantageous.
 

How to Check If a Load Cell Is Working



Method 1: Using a Display Meter or Transmitter



The simplest way to verify a load cell is functioning correctly is to wire it to its associated display meter or transmitter, apply a known weight, and confirm the reading matches the expected value. If the displayed weight tracks accurately with the applied load, the load cell is healthy.



 

This method is common in real-world settings like weigh bridges, hoppers, storage bins, and belt weigh feeders, where load cells are routinely used to monitor weight and load.
 

Method 2: Using a Digital Multimeter (No Meter or Transmitter Available)



If a display unit isn't on hand, a load cell can still be tested directly with a digital multimeter. The process involves two steps:
Apply excitation voltage to the load cell's input wires (this is usually 10V, though it varies by device).
Measure the output voltage in millivolts across the output wires using the multimeter.


 

Every load cell has a rated capacity and sensitivity value stamped on its body or listed on an attached specification tag — commonly expressed as millivolts per volt (mV/V).

Worked example: Suppose a load cell is rated for 50 kg capacity with a sensitivity of 2 mV/V, and it's being excited with 10V.
At full rated capacity (50 kg), expected output = 2 mV/V × 10V = 20 mV
At half load (25 kg), expected output = 10 mV

By comparing the multimeter's actual reading against the expected value for a given applied load, a technician can quickly determine whether the load cell is responding correctly — if the output scales proportionally with load as expected, the cell is functioning properly.
 

Load Cell Wiring

Four-Wire Configuration






A standard four-wire load cell has two wires dedicated to supplying excitation voltage (commonly color-coded red and black) and two wires that carry the millivolt output signal (commonly green and yellow).


 

Six-Wire Configuration



Six-wire load cells include everything found in the four-wire setup, plus two additional "sense" wires. These extra wires monitor the actual voltage arriving at the load cell, allowing the controller to detect and compensate for any voltage drop caused by long cable runs or resistance in the wiring — resulting in a more accurate weight measurement, especially over longer cable distances.


 

Understanding these fundamentals — how a load cell converts force to signal, and how to verify it's reading correctly with either a display unit or a simple multimeter — covers the core skill needed for basic field troubleshooting of load cell-based weighing systems.


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