Precision Measurements Start At The Probe Tip; What Is A Probe - Tektronix PRIMER P6101B Manual

Primer
Precision Measurements Start at the
Probe Tip
Probes are vital to oscilloscope measurements. To understand
how vital, disconnect the probes from an oscilloscope and
try to make a measurement. It can't be done. There has to
be some kind of electrical connection, a probe of some sort
between the signal to be measured and the oscilloscope's
input channel.
In addition to being vital to oscilloscope measurements,
probes are also critical to measurement quality. Connecting a
probe to a circuit can affect the operation of the circuit, and an
oscilloscope can only display and measure the signal that the
probe delivers to the oscilloscope input.
Thus, it is imperative that the probe have
minimum impact on the probed circuit and
that it maintain adequate signal fidelity for
the desired measurements.
If the probe doesn't maintain signal fidelity, if it changes the
signal in any way or changes the way a circuit operates, the
oscilloscope sees a distorted version of the actual signal. The
result can be wrong or misleading measurements.
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Figure 1.1. A probe is a device that makes a physical and electrical connection between
the oscilloscope and test point.
In essence, the probe is the first link in the oscilloscope
measurement chain. And the strength of this measurement
chain relies as much on the probe as the oscilloscope.
Weaken that first link with an inadequate probe or poor
probing methods, and the entire chain is weakened.
In this and following sections, you'll learn what contributes to
the strengths and weaknesses of probes and how to select
the right probe for your application. You'll also learn some
important tips for using probes properly.

What Is a Probe?

As a first step, let's establish what an oscilloscope probe is.
Basically, a probe makes a physical and electrical connection
between a test point or signal source and an oscilloscope.
Depending on your measurement needs, this connection can
be made with something as simple as a length of wire or with
something as sophisticated as an active differential probe.
At this point, it's enough to say that an oscilloscope probe
is some sort of device or network that connects the signal
source to the input of the oscilloscope. This is illustrated in
Figure 1.1, where the probe is indicated as an undefined box
in the measurement diagram.