Probe Grounding - Tektronix P6246 Mode D'emploi

Operating Basics

Probe Grounding

Differential measurements are not the same as "floating" measure-
ments. In addition to the (+) and (- - ) inputs on the probe head, there
is also a ground (common) input. (See Figures 2 and 3.)
CAUTION. To avoid damaging the circuitry under test, connect the
probe ground (common) to a ground-reference point only.
You can use the probe to take a differential measurement regardless
of whether or not the ground (common) is connected.
There are some applications that may require a ground reference
connection to maintain measurement accuracy. Generally this is
necessary when probing circuits which are fully isolated from ground
such as battery operated devices. In most applications, however, the
common-mode impedance to ground is greater than the differential
impedance. Hence, adding the probe ground lead does not improve
the high-frequency performance of the measurement.
In addition to the 6-inch ground lead, there are other ground lead
accessories that are useful in certain applications. Figure 2 on page
17 shows how to use the short ground contact. Figure 4 on page 19
shows the spring-loaded ground pin.
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P6246 & P6247 Instructions