Fluke 125
Users Manual
A-2
Caution
Fieldbusses often are controlling delicate processes
that must not be disturbed. It is strongly
recommended to contact the system manager before
any connections are made.
Use of Probes and Accessories
Use of Probes: refer to page 0-2 and 0-3 of this Manual
for an overview of accessories as suplied with Fluke 125.
For most measurements the Shielded Test Leads
STL120 (1:1) are used. To hook up the ScopeMeter’s
COM terminal to a Bus System you can use the Black
Test Lead. In noisy environments however it is advised to
use the shorter ground lead with alligator clip (supplied
with STL120) instead of the Black Test Lead.
To hook up to bus line nodes you can use the Alligator
Clips or Hook Clips that fit on to the STL120 tip. TP88
Back Probe Pins (optional) can be used to probe screw
terminals at the wire entry point.
Alligator Clips, Hook Clips, and the optional Back Probe
Pins also fit on the tip of the VPS40 Probe (10:1) that is
used to test some of the Fieldbus types. VPS40 is used
on bus systems that are sensitive to the capacitive load of
STL120 (225 pF against 15.5 pF for VPS40). When using
a 10:1 probe other than VPS40, it must be adjusted for a
good pulse response! A poorly calibrated probe can
introduce measurement errors or the measurement may
not be possible. How to adjust is explained in chapter 2.
The Banana-to-BNC Adapter BB120 may be used when
testing systems with coaxial connection cables. If the
system requires so you must add a coaxial 50 or 75 Ω
termination at the BB120. As an alternative you may
connect the VPS40 10:1 probe across a terminator in the
system under test.
You can use the optional BHT190 Bushealth Test adapter
to connect the probe tip in an easy way to busses that
use a DB9, RJ-45 or a M12 connector.
In some bus systems (AS-i for instance) the protocol uses
continuous polling of all devices in a fixed time schedule
so that there is continuous data traffic. Other systems
such as RS-232 only carry data when settings are
changed. Bushealth requires continuous data traffic to
perform its measurements. In case of very low data
repetition rates, the banner ‘NO DATA’ is displayed. In
systems with low data rates, it is recommended to
increase the data rate by e.g. knob operation. Contact the
system manager for this.
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