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AP031/AP032 Differential Probe
Operating Instructions

Revision B - November 1996
I. Application
a. Overview
The AP031 / AP032 are fully differential active probes designed for applications where
electrical signals must be measured relative to a floating voltage different to the oscilloscope
ground potential.

These probes are specifically designed for situations where:
- The reference voltage may be several hundreds volts above or below ground.
- Measurements require the rejection of common mode signals.
- Ground loops and currents produce to excessive signal interference.

The use of these probes ensures safe operation of the oscilloscope and maintains high signal
fidelity with good common mode rejection and dynamic range.

b. Fully Differential Inputs
The probe is a fully differential active device. The differential capability allows measurements
to be made between two points in a circuit without reference to ground. The two input signals
are processed inside the probe (see figure 1) and the resulting single-ended signal may be
measured by any grounded oscilloscope. Because the differential voltage is calculated within
the probe, with only the resultant difference signal being passed to the oscilloscope, a large
dynamic range can be achieved with excellent rejection of common mode signals.
Figure 1

c. Making Measurements
Ensure the probe is fitted with four high-quality, AA cells. These should be cells that are
protected from leakage which could damage the power supply contacts in the probes.

Before making any measurements or connections refer to the safety information contained in
this document.

Connect the probe to one of the oscilloscope input channels ensuring the BNC connector is
fully mated, and the safety ground lead to the oscilloscope CAL BNC connection.
Select the proper range setting on the probe using the slide-switch on the probe body.
Figure 2
Adjust the input coupling impedance and attenuation of the oscilloscope
channel to which the probe is connected using the input coupling menu as
shown in Figure 2.

Ensure 1 M input impedance ( `DC1M ' or `AC1M ' ) is selected. The
use of 50 input impedance will unduly load the output of the differential
probe resulting in reduced amplitude output and incorrect scaling.

To ensure the oscilloscope correctly interprets the vertical waveform scale
be sure to adjust the probe attenuation setting using the `Probe Atten'
menu controls. The example shown, x100 probe attenuation, would
achieve correct vertical scaling AP031 operating with a maximum range of