Good, Bad, And Check Measurements In Fieldbus Diagnostics - Emerson AMS Trex User Manual

Note
The Fieldbus Diagnostics application does not show which device is the LAS on the fieldbus segment.
The Trex unit will become the LAS if no other LAS is on the fieldbus segment.
CAUTION!
The Trex unit draws approximately 12 mA from the fieldbus segment when it is online. (The
Trex unit draws 0 mA when it is offline.) Ensure the power supply or barrier on the fieldbus
segment has the capacity to provide this additional current when the Trex unit is online. If a
heavily loaded fieldbus segment is drawing near the capacity of the segment's power supply,
connecting the Trex unit may result in loss of communication.
5.3 GOOD, BAD, and CHECK measurements in
Fieldbus Diagnostics
The Fieldbus Diagnostics application uses labels of GOOD, BAD, and CHECK to indicate the
status of a measurement. The label is applied based on the measurement being within a
set of ranges that you can adjust. By default, the range of values includes typical operating
levels of DC voltage, noise, and signal-level based on the Fieldbus standard.
You can set the range of measurement values that are labeled GOOD, BAD, or CHECK in the
Settings. (Tap Settings > Measurement criteria.) You may want to increase or decrease the
range of values based on where the Trex unit is connected on the fieldbus segment.
Status
GOOD
BAD
CHECK
INACTIVE
User Guide
Description
The measurement is within the minimum and maximum values set
in the measurement criteria.
The measurement is below the minimum value set in the
measurement criteria. The BAD status is used for the DC voltage and
signal measurements.
The measurement is greater than the maximum value or less than
the minimum value defined the measurement criteria.
The CHECK status is used for the noise and signal measurements
because the measurements may be GOOD or BAD depending on
the location of where the measurement is taken and on the fieldbus
segment's tolerance to noise.
For example, if the device's signal measurement is 400 mV (peak-to-
peak) and the Trex unit was connected near the device, the
measurement is low and may be considered BAD. However, if the
Trex unit was connected to the fieldbus segment far away from the
device, the lower signal measurement is expected due to the length
of the cable and it can be considered GOOD.
The Trex unit is detecting no fieldbus communication. Tap Go Online
to communicate with the device.
Fieldbus Diagnostics application
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