Eaton The FBT-6 is connected to the network

Operation

The FBT-6 is connected to the network using the clip-on probes at the

end of the cable. The red probe is connected to the fieldbus + 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 an Overall Network

Check to give the user a quick indication of network health.

The “FUNCTION” and “SELECT” buttons are used to select from

network 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 network 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.

Here follows a more detailed explanation of each of the Monitor’s

functions.

Segment Check

When first connected, the FBT-6 gathers data for all of its monitoring

functions. If all the measured data is within an acceptable range, the

Monitor displays “ALL MEASUREMENTS OK”.

Voltage

The DC voltage on the network is shown. Measurements over 9 volts

are OK. The maximum input voltage is 32.0 volts.

Device Count

If there are fieldbus devices active on the network, the Monitor counts

them. If the count has remained the same since the initial network

check was performed, the display shows “OK”.

Note: on Foundation™ fieldbus networks, the Link Active Scheduler

(LAS) is considered a device and, as such, is included in the count.

The FBT-6 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 has removed the device

from its internal list of active devices. Devices having communication

difficulties may show up on the FBT-6 as repeatedly being added or

dropped. If a device leaves the network, the display shows “–”; if a

new device is added it shows “+”.

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. Measurements greater than 150mV

are OK.

Device

The address (in decimal and hexadecimal) and signal level of each

device on the network is displayed in turn by pushing the “SELECT”

button. On Foundation fieldbus™ networks, the first device shown

will be the LAS. Measurements greater than 150mV are OK.

Average Noise

Displays the average noise based on the average of the last 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. Measurements of less

than 75mV are OK.

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. Measurements of less than 75mV

are OK.