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Signal Integrity

Do you understand the impact of signal integrity "noise" on your industrial network?

Signal integrity noise

"Noise," or other disturbances to the network digital signal, is one of the greatest causes of industrial network interruptions. Industrial networks are designed to be impervious to noise in general, but signal integrity deviations can still cause network problems.

The signal deviations are often a by-product of the electrical and environmental operating extremes found in industrial facilities.

Signal integrity deviation can be viewed from two aspects/perspectives/dimensions

  • Δ amplitude
  • Δ time

Always baseline segments at installation. Any change in waveform characteristics is usually an indicator of a problem's root cause.

Impact of noise on industrial networks:

  • Deviations in the signal integrity can cause the receiving device to generate a framing error code (CRC or FCS errors). The electrical signaling failures cause miscommunications in the digital protocol.
  • These errors can cause excessive re-transmission, creating excessive network traffic and delays.
  • Errors may occur continuously or periodically.

Analyzing signal integrity:

  • A typical network analyzer only indicates that errors are occurring; rarely will it diagnose the root cause of problems stemming from signal integrity issues.
  • Use an oscilloscope to visually inspect the signal waveform for Δ amplitude or Δ time noise errors.
  • Use the peak detect and waveform envelope/persistence mode to capture and display the full / extent of signal integrity deviations.
  • Some oscilloscopes offer an "eye pattern" mode that highlights the full extent of amplitude and time related deviations.

Examples of signal integrity deviations displayed on an oscilloscope.

"Scope" mode





"Scope" mode

Eye Pattern Mode

"Eye-Pattern" mode

        

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For More In-depth Information, Reference Fluke Application Notes:

Checking Voltage-frequency Ratio on Variable-speed Drives with a Fluke Scopemeter 190 Series (.pdf) »
A first look at oscilloscopes (.pdf) »
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