EZ Digital OS-3060D Betriebsanleitung PDF herunterladen (Seite 15)

2.2.2 Cable connections (signal leads)

Three types of signal leads can be connected to

the oscilloscope:

- a single measurement ribbon cable, insulated

conductor

- a coaxial cable

- or a probe.

A single lead may be sufficient for higher signal

levels of low impedance, such as those of TTL

circuits. This type of signal feed, however, is not

used very often in case of low-level signals

because of the unacceptable distortion it intro-

duces. Unacceptable distortion is caused because

the single lead is not screened.

If signal sources having BNC outputs are to be

connected to the oscilloscope, a coaxial cable

should be used for such connections as a rule.

These cables are screened, i.e. the inner conduc-

tor that carries the signal is screened against

spurious external signals by braided copper

wires or braided tinned copper wires. This

"screen" is connected to the frame earth of the

power source or the oscilloscope.

If signals are to be measured on components or

subassemblies of circuits, probes are used for

this purpose. These are available in various

designs. Some probes have a switch that can be

used to change over to 1:10 attenuation (= cali-

bration setting). Roughly 1/10th of the ampli-

tude of the available measuring signal is displayed

in this switch position.

Example:

Indicated values = 5 mV pp, probe set to 1:10

position ==> actual value = 50 mV pp.

Warning!

Do not exceed the maximum input values.

If the source resistance or the line capacitance

are not known in the case of direct connection

between the device under test and the oscillo-

scope, especially at relatively high frequencies,

use a 1:10 low-capacitance probe.

One method of minimising the measuring error

at high frequencies in the case of coaxial cables

is to use a terminating resistor. The impedance

of this resistor which is connected directly to the

oscilloscope must match the impedance of the

signal source or the lead.

i) If the edges of the rectangular-pulse signal

are over or under modulated, the probe must

be matched to the input capacitance of the

oscilloscope. See ﬁgure on the next page.

j) Set the V-MODE switch (18) to channel 2 (CH

2) and repeat steps h) and i) for the other

probe.

h) Set any probe that has a selectable attenu-

ation ratio to 1:10, connect it to the channel

1 input (CH-1) and connect the probe tip to

the CAL output (35). A rectangular-pulse

signal, having an amplitude of 0.5 Vpp

divided by 10 (=Volt peak/peak=ss), should

then appear on the screen.

Probe body

Shielding

Compensation trimmer

Earth terminal

Tip

Optimum

compensation

Capacitance

too high

Capacitance

too low

Fig. 6. Probe compensation

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 43 44

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