Load Cell to PLC Basics

Load Cell to PLC Basics

“What options do we have to communicate to our PLC with your load cell weighing system?”

One of the most common questions we get from end-users and system integrators.


You can interface your new or existing PLC to a weighing / scale system using an analog or digital signal. It can be as basic as sending a 4-20mA signal that can be scaled in the programmable logic controller to any engineering units such as pounds, kilograms, or tons. Your application may require control as well as monitoring of the weight or force, in this case digital communications is the solution. Having a number of load cell transmitters in a fieldbus network, allows a single PLC to monitor the weight readings, as well as control the load cell transmitter’s functions such as ‘Zero’, ‘Tare’, Print’, or even configure or calibrate the device(s) remotely.


Common Digital Communication Options to a PLC from a Load Cell Transmitter

  • RS232 – RS485 Modbus RTU / ASCII
  • CANopen
  • DeviceNet
  • CC-LINK
  • Profibus DP
  • Modbus/TCP
  • Ethernet IP
  • Profinet IO
  • PROFINET IO
  • POWERLINK
  • SERCOS III

Advantages of a Digital Signal to a PLC

There a many, distance you can transmit the signal, the capability to create a network connecting several load cell transmitters together. Your facility more than likely has a preferred protocol for example Ethernet IP or DeviceNet. If you want to call it a downfall, digital communications can be more complex to setup. With that being said is it a downfall? You get much more control over your load cell transmitter and can utilize it’s full capability.


Analog Communication Options to a PLC from a Load Cell Amplifier

  • 4-20mA / 0-20mA
  • 0-10VDC / +/-10VDC
  • 0-5VDC / +/-5VDC

Advantages of an Analog Signal to a PLC

It is simple using a shielded 2 conductor cable sending a current or voltage signal to a PLC analog input module. A current signal (4-20mA) is best suited for industrial applications because if it’s immunity to noise in the signal and the distance it can travel. A 4-20mA signal can be run 1,000 or more feet, where as a voltage signal (0-10V or +/-10V) is only recommended for distances up to 50 feet. Really the only main advantage of using the voltage output is for applications that require both tension and compression measurements, the bipolar output +/-10V can accomplish this as long as you have an input module cable of accepting it.


Load Cell to PLC Communication Conclusion

It boils down to how much control you want or need the PLC to have with your weighing or force measurement system.
Let a technical load cell application specialist from Load Cell Systems to help you choose the right interface option for your needs.

You can view Load Cell Systems entire line of load cell electronics to interface with your PLC on our load cell electronics page.

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