(a) Probe
(b) PROBE compensation by Correction Square-Wave
Abb. 2.2 Probe compensation
2.2.2 Signal
Connections
There are three methods of connecting an oscilloscope to the signal you wish to observe. They are: a simple
wire lead, coaxial cable, and scope probes.
A simple lead wire may be sufficient when the signal level is high and the source impedance low (such as
TTL circuitry), but is not often used. Unshielded wire picks up hum and noise; this distorts the observed
signal when the signal level is low.
Also, there is the problem of making secure mechanical connection to the input connectors. A binding post to
BNC adapter is advisable in this case.
Coaxial cable is the most popular method of connecting an oscilloscope to signal sources and equipment
having output connectors. The outer conductor of the cable shields the central signal conductor from hum
and noise pickup. These cables are usually fitted with BNC connectors of each end, and specialized cable
and adaptors are readily available for mating with other kinds of connectors.
Scope probes are the most popular method of connecting the oscilloscope to circuitry. These probes are
available with 1 X attenuation (direct connection) and 10 X attenuation. The 10 X attenuator probes increase
the effective input impedance of the probe/scope combination to 10 M
Ω
shunted by a few picofarads, the
reduction in input capacitance is the most important reason for using attenuator probes at high frequencies,
where capacitance is the major factor in loading down a circuit and distorting the signal. When 10 X
attenuator probes are used, the scale factor (VOLTS/DIV switch setting) must be multiplied by ten.
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