How noise affects the fieldbus segment
The fieldbus segment can function properly with large amounts of low-frequency noise,
small amounts of in-band noise, or moderate amounts of high-frequency noise. In-band
noise is most likely to directly impact fieldbus communications. Bursts of in-band noise
can cause the fieldbus network to slow down due to the messages being resent multiple
times. Devices may also disconnect from the network if the in-band noise becomes too
high/frequent.
High-frequency noise seldom impacts fieldbus communications, but it may cause
measurement errors or the device may restart.
Related information
Troubleshooting Fieldbus Diagnostics
5.11.1 View a spectrum of the noise measurement
You can view the noise spectrum that displays the levels of low frequency (870 Hz - 9 KHz),
in-band (9 KHz - 39 KHz), and high frequency noise (39 - KHz - 100 KHz).
Note
Before taking a noise measurement, remove the AC adapter from the Trex unit, if it is
connected. This isolates the Trex unit from the local power grid.
Note
The spectrum measurement will fail if the noise amplitude exceeds 1.5 V (peak-to-peak). If
you see multiple high-amplitude noise peaks, look for an unattached wire that may cause
high noise and saturate the noise detection.
Procedure
1. Connect to the FOUNDATION fieldbus device or segment.
2. On the Fieldbus Diagnostics Overview screen, tap Spectrum.
A spectrum displays the noise measurements. The highest peaks are outlined in
black.
Fieldbus Diagnostics application User Guide
September 2021
166 User Guide
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