LeCroy ADP300, Инструкция по эксплуатации, Страница: 16 / 39

ADP300/305 Probe
10
ADP30X-OM-E Rev B
OPERATION
Connecting the Probe to the Test Instrument
The ADP30X series of probes has been designed for use with LeCroy oscilloscopes equipped
with the ProBus interface. When you attach the probe output connector to the scope’s input
connector, the scope will recognize the probe, set the scope input termination to 1 M
Ω,
and
activate the probe control functions in the user interface.
Connecting the Probe to the Test Circuit
The ADP30X series of probes is ideally suited for applications where no ground is available or
where the location of a ground connection is unknown.
Two inputs are available at the probe tip to connect the probe to a circuit under test. For accurate
measurements, the
+ and – inputs both must always be connected to the test circuit. Positive
voltages applied to the + input (red) relative to the – input (blue) will deflect the oscilloscope trace
toward the top of the screen.
To maintain the high performance capability of the probe in measurement applications, care must
be exercised in connecting the probe to the test circuit. Increasing the parasitic capacitance or
inductance in the input paths may introduce a “ring” or may slow the rise time of fast signals.
Input leads that form a large loop area will pick up any radiated electromagnetic field that passes
through the loop and may induce noise into the probe inputs. Because this signal will appear as a
differential mode signal, the probe’s common mode rejection will not remove it. This effect can be
greatly reduced by twisting the input leads together to minimize the loop area.
High common mode rejection requires precise matching of the relative gain or attenuation in the +
and – input signal paths. Mismatches in additional parasitic capacitance, inductance, delay, and a
source impedance difference between the
+ and – signals will lower the common mode rejection
ratio. Therefore, it is desirable to use the same length and type of wire and connectors for both
input connections. When possible, try to connect the inputs to points in the circuit with
approximately the same source impedance.
Operation with a LeCroy Oscilloscope
When the ADP30X is connected to a LeCroy oscilloscope, the displayed scale factor and
measurement values will be adjusted to account for the effective gain of the probe.
Through the oscilloscope software, the probe’s internal attenuation and offset can be
conveniently controlled through the oscilloscope’s user interface.
Turning the V
OLTS
/D
IV
knob will control the oscilloscope’s scale factor and the probe’s internal
attenuation to give full available dynamic range from 1 V/div to 350 V/div for the ADP300, and
from 200 mV/div to 350 V/div for the ADP305. Some of the transition of the scale factor will result
in a change of attenuation.