Teledyne LeCroy AP034 - Manual (Page 18)

AP034 Active Differential Probe
12 922261-00 Rev A
When using a differential probe or amplifier, be careful to avoid exceeding the common mode
range. Because the common mode signal is rejected by the differential probe, and is not displayed,
changes in the amplitude of the common mode component are not apparent to the user.
Exceeding the common mode range may introduce distortion into the AP034 output.
Circuitry in the probe detects the presence of either attenuator, and displays the effective gain of
the probe on the probe front panel.
Operation with Teledyne LeCroy Oscilloscopes
When the AP034 probe is connected to a Teledyne LeCroy oscilloscope equipped with ProBus
interface, the displayed scale factor will be adjusted to account for the effective gain of the probe.
The channel OFFSET
knob will control the probe offset, rather than the offset at the oscilloscope
input. The probe control menu can be activated by pressing the COUPLING button (if available)
while the channel to which the probe is attached is selected.
When the AP034 Active Differential Probe is first connected to the oscilloscope, the following
message will appear: “WARNING: Probe offset buttons are locked.” This alerts you that offset
control must be made through the oscilloscope, rather than through the buttons located on the
probe. It does not indicate a failure in the probe or oscilloscope.
NOTE: Correct display of scale factor with the ÷20 attenuator installed and correct operation of
probe offset require that software version 8.1 or higher be loaded. Refer to “Oscilloscope Software
Compatibility” for additional information.
Using AP034 with the APPPS Power Supply
The optional ADPPS Power Supply allows the AP034 Active Differential Probe to be used with
instruments that are not equipped with the ProBus interface. When used with the ADPPS, the
AP034 must be terminated into 50Ω . If the test instrument input impedance is not 50Ω insert a
50Ω in-line terminator between the ADPPS and the instrument input. If a coaxial extension cable is
used, the terminator should be located at the instrument end of the cable. Note that the additional
parasitic losses of extension cables may reduce the usable bandwidth of the system below the
AP034 specification.
To prevent signal distortion, it is necessary to keep the AP034 output less than 400 mV at all times.
With the ProBus interface (see note on following page), the oscilloscope OFFSET control actually
controls the AP034 offset. Without the ProBus, it is acceptable to use the oscilloscope to position
the waveform at high sensitivities, but it is a practice that can lead to erroneous measurements
when the probe output exceeds ±400 mV. Therefore, when the ADPPS is used, it is preferable to
use the AP034 offset function to perform all waveform positioning.