How does a load cell work?

Load Cell is a device that converts force into electrical signal.

A strain gauge based load cell is made of a specially engineered mechanical component called as an element. Four strain gauges are positioned precisely and bonded on to the element using a special adhesive. (strain gauge is a device that changes resistance when it is deformed or stressed).


The force-electrical signal conversion happens in two stages-

• force applied deforms the element which in turn deforms the strain gauges
• strain gauges converts the deformation to electrical signals

The strain gauges are wired in Wheatstone bridge configuration. The bridge is connected to a power supply unit and a signal conditioner through a 4-core cable. When an input voltage (10VDC) is applied to the bridge, the output is a voltage in the range of few millivolts.


The load cell output is proportional to the load applied to the element.


Basic specifications of a load cell-

• Capacity (kg)
• Full scale Output (mV)
• Sensitivity (mV/V)
• Excitation Voltage (VDC)
  
• Input resistance (ohms)
• Output resistance (ohms)

Below are the commonly used standard values-

• Excitation voltage: 10V or 12V DC
• Full scale output: 10mV, 20mV and 30mV
• Load cell sensitivity: 1mV/V, 2mV/V and 3mV/V
• Input resistance: 350Ω and 700Ω
• Output resistance: 350Ω and 700Ω

Sensitivity = full scale output/excitation voltage
Example: 20mV/10V = 2mV/V

Two articles to you can read-
Introduction to Load Cells
How Does a Load Cell Work?

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