When working with various electronic systems, Electromagnetic Interference (EMI) issues are not uncommon and can adversely affect nearby electronic devices, leading to problems such as serial communication loss, disturbances in output signals, and cross-talk. 

Electromagnetic Interference (EMI) is a widespread issue with diverse sources, posing potential challenges to the reliable functionality of electronic devices. Common sources of EMI include devices with switching power supplies, Variable Frequency Drives (VFDs), electric motors, and voltage converters, as well as transmitters, power lines, motors, generators, and other sources of Radio Frequency Interference (RFI). Additionally, switching devices, digital electronics with rapid voltage changes, and wireless communication devices all contribute to EMI. [1]

Some of these are present in a large number of manufacturing, transformation and transport processes commonly used in industrial applications.

1. How does EMI affect Rheonics sensors?

Rheonics sensors employ proprietary technology to achieve extremely high immunity from EMI. A properly connected Rheonics inline process density meter and viscometer can easily operate without performance degradation in high EMI environments like with large electric motors provided that the sensor probe and electronics are properly grounded following recommended procedure.

The table below gives general guidance on what symptoms a user would find when the sensor might be affected by EMI from computers and power lines - here the causes and mitigation strategies are discussed. These are items to take into consideration when doing a Root Cause Analysis (RCA) on sensor where performance degradation is taking place. Rheonics sensors employ real-time detection technology that can highlight possible measurement issues, these are shown as error codes on the sensor output. When using the Rheonics Control Panel (RCP) software, these codes are often accompanied with descriptive text that highlight possible cause and solution.


SymptomCauseDescription
Solutions or checks

  • E10 and E12 errors (Low Accuracy Error and Sensor Locked Error). 


  1. This can be triggered if user uses serial communication and try to control a VFD through a single Laptop.

  2. Running the sensor along power lines/noisy data/motor starters.


Due to EMI, sensor performance could be compromised and it may not provide reliable readings. 

  1. It is recommended to try Ethernet communication in these scenarios.

  2. We recommend connecting the motor or VFD controller to a different Laptops that the one used  for communication with the sensor electronics over USB

  3. Avoid usage of USB communication as those are heavily affected by EMI.

  4. Verify wiring and ground loops. Do not run sensor cable along power lines.

  5. Ensure the shield of the sensor cable is grounded properly - this ensures the signal is not affected by EMI between the probe and the sensor electronics (in particular when there is a long run length of cable between the probe and electronics)



2. How to reduce the EMI effects?

To reduce the impact of EMI we recommend the following:

  • Ensure the proper grounding of the panel (where sensor electronics is mounted) to the equipment ground (where sensor probe is mounted). 

  • Ensure that the sensor (probe and transmitter) are properly grounded.

  • Ensure the sensor cable shield is properly connected to ground.

  • Connect all ground connections to a metallic common ground block. 

  • Verify that all electronic components are adequately earth-grounded. 

  • Maintain separation between power lines and sensor cable to prevent interference. 

  • In extreme cases, an EMI filter is also recommended.

3. Resources

Introduction to Electromagnetic Interference (EMI) with VFDs 

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