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OPERATION
The FBT-6-PA is connected to the segment using the clip-on probes at
the end of the cable. The red probe is connected to the fi
wire, the black probe to the – wire and the green probe to the shield
wire. The + and – test leads are polarity sensitive and the Monitor
will not operate if they are reversed.
When first connected to a fieldbus, a version number is displayed
for several seconds. The Monitor then performs a Segment Check
providing a quick indication of segment health.
The “FUNCTION” and “SELECT” buttons are used to choose from
segment parameters that can be examined with the Monitor. When
a function is selected, the data portion of the LCD display is blank
until the Monitor has collected and processed the data. After that,
the measured value is shown. The indication “OK” is shown if the
measured value is within the acceptable range. The indication “BAD”
is shown if the measured value is outside of the acceptable range.
The rotating symbol in the lower right corner of the display indicates
that there is segment activity. A horizontal bar (underscore) under the
rotating symbol indicates that a frame was detected, but could not be
decoded. This is not a maintained function, so if a single “bad” frame
is detected, the underscore will only display for a short time. Periodic
“bad” frames will cause the underscore to blink. The following are
more detailed explanations of each of the Monitor’s functions.
Segment Check
When first connected, the FBT-6-PA gathers data for all of its
monitoring functions. If all measured data is within acceptable range,
the Monitor displays “ALL MEASUREMENTS OK”.
Voltage
The DC voltage on the segment is shown. By default, measurements
over 9 volts are OK. The maximum input voltage is 32.0 volts.
Device Count
If Profibus PA devices are active on the segment, the Monitor counts
them. If the count has remained the same since the initial segment
check was performed, the display shows “OK”. Note, on Profibus PA
segments, the Master is considered a device and, as such, is included
in the count.
The FBT-6-PA is more sensitive to missed communications than most
PC monitoring software. As a result, a device may still show up on
PC monitoring software, even though the FBT-6-PA has removed
the device from its internal list of active devices. Devices having
communication difficulties may show up on the FBT-6-PA as repeatedly
being added or dropped.
If a device leaves the segment, the display shows “-”; if a new device
is added it shows “+”.
Device
The address (in decimal and hexadecimal) and signal level of each
device on the segment is displayed in turn by pushing the “SELECT”
button. The first device shown will be the Master. By default,
measurements greater than 150mV are OK. If a device leaves the
segment, a “-” is displayed; if a device is added it shows “+”.
Average Noise
Displays the average of the most recent 100 noise measurements.
Noise levels are measured and displayed in 3 frequency bands:
frequencies in the fieldbus signalling band (Fieldbus Frequency, FF),
frequencies below the fieldbus signalling band (Low Frequency, LF)
and frequencies above the fieldbus signalling band (High Frequency,
HF). The particular frequency band displayed is selected by pushing
the “SELECT” button.
Peak Noise
Displays the peak noise recorded since the Monitor was connected.
The value displayed is the highest noise level measured since the last
reset. Peak noise levels are measured and displayed in the same
three frequency bands as average noise.
Retransmit
If a device does not respond to a request frame or a token frame, the
frame is retransmitted. The FBT-6-PA indicates the address (decimal
and hexadecimal) of the last device that failed to respond, together
with the number of retransmits since the function was reset. If more
than 250 retransmits are detected, the display will read “250+”.
Pressing the “SELECT” button cycles through screens indicating the
number of detected retransmits for each device.
Shield Short
If a short circuit between the + fieldbus wire and the cable shield
is detected, “(+) TO SHIELD SHORT” is displayed. If the short is
between the – wire and the shield, “(–) TO SHIELD SHORT” is
displayed. If a detected shield short goes away the Monitor indicates
an INTERMITTENT SHIELD SHORT to (+) or (-).
Add–Drop
If a new device is added to the segment, the Monitor will display
its address and signal level. If a frame is retransmitted to a device,
the device is considered “dropped” by the FBT-6-PA and the Monitor
will display the address and last known signal level of the dropped
device. A Master device that is sent an FDL Status Request frame is
also considered dropped.
Low
The signal level of the device with the weakest signal is shown. The
device’s address (in decimal and hexadecimal) is also displayed. This
will be the lowest signal level reading from a device since the Monitor
was connected to the fieldbus. By default, measurements greater than
150mV are OK.
F
OUNDATION
fieldbus
TM
is a trademark of Fieldbus Foundation
TM
, Austin, Texas
Specification subject to change without notice
EPS FBT-6-PA-1
Oct 2007
