Root Cause Analysis 1 min read

Root Cause Analysis of Encoder Signal Loss: Cable Protection, EMI and Connector Damage

Technical analysis: LADN22

Root Cause Analysis of Encoder Signal Loss: Cable Protection, EMI and Connector Damage

Introduction

Loss of encoder signal in the control system may lead to production stoppage or incorrect display of the status of mechanical processes. In this case, the failure occurred in the Telemecanique LADN22 equipment, which is used in the control system of the production line. The symptom of signal loss was detected during regular checking of the automatic control system on the production line in Ukraine.

Component Overview

Encoder Telemecanique LADN22 performs the function of measuring angular displacement and rotational speed of a shaft. It is mounted on a motor or drive shaft, and its output signal is used for controlling position and speed in the PLC system. Operating conditions include temperature from 0 to 60 °C, pressure 0.5–1.5 bar, as well as explosive atmosphere according to the standard EN 500144.

Defects

The technician identified the following signs of encoder signal loss:

  • Incorrect display of rotational speed on the system display;
  • Sparks and signal breaks on the oscilloscope;
  • Increase in encoder shaft vibration;
  • Increased cable temperature rating (up to 65 °C under load).

The connection cable between the encoder and the controller was found to have a damaged shielded layer, and the connector was found to be damaged and dusty.

Root Cause Analysis

The analysis used the 5 Whys method and an Ishikawa diagram. It was found that the signal loss is related to cable shielding damage, EMP influence, and connector damage.

Root Cause Analysis

The following is the definition of root causes in order of probability:

  1. Cable shielding damage – 45% probability. Evidence: shielding breaks, high EMP level, cable temperature above allowable.
  2. Electromagnetic Interference – 30% probability. Evidence: high level of EMP from adjacent electric motors and power lines.
  3. Damaged connector – 20% probability. Evidence: physical damage, dusty contacts, high vibration.
  4. Incorrect installation – 5% probability. Evidence: absence of cable fixation, vibration on shafts.

Correction Methods

The following are the corrections for each root cause:

  1. Screening damage – use a cable with high level of screening (for example, series EN 50284-2-23), install a cable terminal with screened contact and use an additional EMP filter.
  2. Вплив ЕМП – встановити екранировання на кабелях, використовувати фільтри сигналів, відокремити кабелі від живлення та приводів.
  3. Damaged connector – clean the connector contacts, install a new connector with high conformity to standard EN 50284-2-23 and use a shielded cable.
  4. Incorrect installation – install cable with fixation, use cable clamps and perform vibration check.

Quick diagnostic checklist

The following is a check-list for technicians on the tablet:

  1. Check the condition of the cable shielding for the presence of breaks.
  2. Measure the level of EMI in the environment using an EMI meter (for example, Fluke 9000).
  3. Measure the cable temperature and compare it with the allowable level (up to 60 °C).
  4. Clean the contacts of the connector from dust and corrosion.
  5. Perform vibration measurements on the encoder shaft using an accelerometer.
  6. Check the cable fixation and absence of vibration.
  7. Check cable grounding and compliance with standard EN 50284-2-23.
  8. Perform the signal measurement on the oscilloscope.
  9. Check signal stability during operation.
  10. Perform the EMP influence check using production certification.
  11. Perform the encoder grounding check.
  12. Use an additional signal filter for remote measurement.

Preventive strategy

For prevention of signal loss from the encoder:

  • Perform regular checks of cables for shielding and signal stability (interval 6 months).
  • Use vibration sensors and temperature sensors to monitor deviations from normal.
  • Install the EMP measurement system on the production line.
  • Perform periodic cleaning of connectors and cables.
  • Use cables that comply with standard EN 50284-2-23.
  • Install cable clamping and use mounting to reduce vibration.

Conclusion

Loss of encoder signal may have serious consequences for production. Performing the recommended actions and using components that meet the standards will ensure the reliability of the control system. For replacing damaged components or obtaining recommendations for selecting appropriate elements, visit UNITEC-D E-Catalog.

Sources

  • EN 50284-2-23:2014 – Cables for control and management;
  • ISO 11898-1:2016 – Cables for control systems;
  • EN 500144:1998 – Environmental Monitoring;
  • DSТУ 3045-98 – Requirements for electrical devices;
  • User Manual for Defect Analysis, Production and Technical Means.

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