Tektronix TDS3000 Serie Guide Rapide

Operating the TDS3000 Series Safely with Battery Power
Introduction
"Floating" a ground-referenced oscilloscope is the technique of
defeating or not utilizing the oscilloscope's protective grounding
system. It is done to make measurements when a ground connection
has an adverse affect on the measurement. However, this causes
accessible metal parts of the instrument to be at the potential of the
probe ground lead connection point. This is dangerous, not only
from the standpoint of elevated voltages present on the oscilloscope
(a shock hazard to the operator), but also due to cumulative stresses
on the oscilloscope's power transformer insulation and other
components. This stress may not cause immediate failure, but may
lead to future dangerous failures (a shock and fire hazard), even after
returning the oscilloscope to properly grounded operation! Not only
is floating a ground referenced oscilloscope dangerous, but the
measurements are often inaccurate. This results from the total
capacitance of the oscilloscope chassis being directly connected to
the circuit under test at the point where the common lead is
connected.
WARNING. Historically, floating measurements have been made
by knowingly defeating the built-in safety ground features of
oscilloscopes. THIS IS AN UNSAFE AND DANGEROUS
PRACTICE AND SHOULD NEVER BE DONE!
Battery-Powered Oscilloscopes
The TDS3000 Series, when operated from AC line power using its
standard power cord, is connected to earth ground via the third-wire
ground in the AC power cord. However, AC power is not always
available where you want to make oscilloscope measurements. The
TDS3000 Series optional battery pack (TDS3BATC) allows you
to operate the oscilloscope without the need for AC power. When
operating the TDS3000 Series from the optional battery pack, the
AC power cord is not used and the oscilloscope will not be
grounded and will be in a floating condition unless a grounding wire
is connected between the oscilloscope and earth ground. Observing
the following precautions will provide safe operation of the
TDS3000 Series oscilloscopes when battery powered. Figure 1
shows the warning that is displayed on the TDS3000 Series screen
when in battery operation mode. This warning applies to circuits that
have voltages of greater than 30 V
under test has voltages that exceed 30 V
TDS3000 Series chassis needs to be connected to earth ground using
the grounding wire provided with the instrument (Battery Pack) to
prevent electrical shock to the operator. See the product user manual
for instructions on connecting the grounding wire. If you do not
attach the grounding wire, you are floating the oscilloscope and you
are not protected against electrical shock if you connect the
oscilloscope to a hazardous voltage.
*P061423501*
061-4235-01
(>42 V ). If the circuit
RMS pk
(>42 V ), the
RMS pk
WARNING. Such electrical shock could result in serious personal
injury or loss of life.
While in battery operation and following environmental
specification limits for the TDS3000 Series, it is safe to "float" the
"signal common" for making measurements provided you do not
connect a signal greater than 30 V
to either the probe tip or common lead. For measurements where
higher voltages (>30 V , >42 V
RMS
chassis must be connected to earth ground using the supplied
grounding wire to prevent electrical shock to the operator.
WARNING. If there is any doubt whether more than 30 V
present or not, the supplied grounding wire should always be used
and floating measurements SHOULD NOT BE ATTEMPTED! Be
aware that hazardous voltages may exist in unexpected places due
to faulty circuitry in the device-under-test.
It's important to remember that the " signal commons" for all
channels are connected together and are at the same potential.
Ensure that all probe common leads are connected to the same
voltage or common point.
Do not connect a grounded device, such as a printer or computer, to
the oscilloscope unless the oscilloscope's grounding wire is
connected to earth ground!
WARNING. Whenever making measurements on instruments or
circuits which are capable of delivering dangerously high voltage,
current, or power, measurement technicians should always treat
exposed circuits, bus-bars, etc., as being potentially "live," even
when circuits have been shut off or disconnected. This is
particularly true when connecting or disconnecting probes or test
leads.
Figure 1. Warning displayed by TDS3000 Series when operated in
battery mode.
(>42 V ) from earth ground
RMS pk
) are present, the instrument's
pk
is
RMS

Copyright Tektronix, Inc.