Teledyne LeCroy ADP300_305 - Manual (Page 15)

Operator’s Manual
Operation
Connecting the Probe to the Test Instrument
The ADP30x series of probes has been designed for use with Teledyne 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 MΩ, 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.
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