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Fluke 192/196/199
Users Manual
68
Using the Independently Floating
Isolated Inputs
You can use the independently floating isolated inputs to
measure signals that are independently floating from
each other.
Independently floating isolated inputs offer additional
safety and measurement capabilities compared to inputs
with common references or grounds.
Measuring Using Independently Floating
Isolated Inputs
The test tool has independently floating isolated inputs.
Each input section (A, B, External Trigger / DMM) has its
own signal input and its own reference input. The
reference input of each input section is electrically
isolated from the reference inputs of the other input
sections. The isolated input architecture makes the test
tool about as versatile as having three independent
instruments. The advantages of having independently
floating isolated inputs are:
• It allows simultaneous measurement of
independently floating signals.
• Additional safety. Since the commons are not directly
connected, the chance of causing short circuit when
measuring multiple signals is greatly reduced.
• Additional safety. When measuring in systems with
multiple grounds, the ground currents induced are
kept to a minimum.
Because the references are not connected together
inside the test tool, each reference of the used inputs
must be connected to a reference voltage.
Independently floating isolated inputs are still coupled by
parasitic capacitance. This can occur between the input
references and the environment, and between the input
references mutually (see Figure 44). For this reason, you
should connect the references to a system ground or
another stable voltage. If the reference of an input is
connected to a high speed and / or high voltage signal,
you should be aware of parasitic capacitance.
(See Figures 45, 46, 47 and 48.)