A&D Series 57ZZ Uživatelský manuál stáhnout pdf (Strana 18)

can display a waveform on the screen. Multiple

channels are handy for comparing waveforms.

Some oscilloscopes have an AUTOSET or PRESET

button that sets up the controls in one step to accom-

modate a signal. If your oscilloscope does not have

this feature, it is helpful to set the controls to stan-

dard positions before taking measurements.

Standard positions include the following:

• Set the oscilloscope to display channel 1

• Set the volts/division scale to a mid-range posi-

tion

• Turn off the variable volts/division

• Turn off all magnification settings

• Set the channel 1 input coupling to DC

• Set the trigger mode to auto

• Set the trigger source to channel 1

• Turn trigger holdoff to minimum or off

• Set the intensity control to a nominal viewing

level

• Adjust the focus control for a sharp display

These are general instructions for setting up your

oscilloscope. If you are not sure how to do any of

these steps, refer to the manual that came with your

oscilloscope. The Controls section describes the

controls in more detail.

Probes

Now you are ready to connect a probe to your oscil-

loscope. It’s important to use a probe designed to

work with your oscilloscope. A probe is more than a

cable with a clip-on tip. It’s a high-quality connector,

carefully designed not to pick up stray radio and

power-line noise.

Probes are designed not to influence the behavior of

the circuit you are testing. However, no measure-

ment device can act as a perfectly invisible observer.

The unintentional interaction of the probe and oscil-

loscope with the circuit being tested is called circuit

loading. To minimize circuit loading, you will prob-

ably use a 10X attenuator (passive) probe.

Your oscilloscope probably arrived with a passive

probe as a standard accessory. Passive probes

provide you with an excellent tool for general-

purpose testing and troubleshooting. For more

specific measurements or tests, many other types of

probes exist. Two examples are active and current

probes.

Descriptions of these probes follow, with more

emphasis given to the passive probe since this is the

probe type that allows the most flexibility of use.

“Intelligent” Probe Interfaces

Many modern oscilloscopes provide special auto-

mated features built into the input and mating probe

connectors. The act of connecting the probe to the

instrument notifies the oscilloscope about the

probe’s attenuation factor, which in turn scales the

display so that the probe’s attenuation is figured into

the readout on the screen.

Some probe interfaces also recognize the type of

probe; that is, passive, active, or current. Lastly, the

interface may act as a DC power source for probes.

Active probes have their own amplifier and buffer

circuitry that requires DC power.

Using Passive Probes

Most passive probes have some attenuation factor,

such as 10X, 100X, and so on. By convention, attenu-

ation factors, such as for the 10X attenuator probe,

have the X after the factor. In contrast, magnification

factors like X10 have the X first.

The 10X (read as “ten times”) attenuator probe mini-

mizes circuit loading and is an excellent general-

purpose passive probe. Circuit loading becomes

more pronounced at higher frequencies, so be sure to

use this type of probe when measuring signals above

5 kHz. The 10X attenuator probe improves the accu-

racy of your measurements, but it also reduces the

amplitude of the signal seen on the screen by a factor

of 10.

Because it attenuates the signal, the 10X attenuator

probe makes it difficult to look at signals less than 10

millivolts. The 1X probe is similar to the 10X attenu-

ator probe but lacks the attenuation circuitry.

Without this circuitry, more interference is intro-

duced into the circuit being tested. Use the 10X

attenuator probe as your standard probe, but keep

the 1X probe handy for measuring weak signals.

Some probes have a convenient feature for switching

between 1X and 10X attenuation at the probe tip. If

your probe has this feature, make sure you are using

the correct setting before taking measurements.

Many oscilloscopes can detect whether you are using

a 1X or 10X probe and adjust their screen readouts

accordingly. However with some oscilloscopes, you

must set the type of probe you are using or read from

the proper 1X or 10X marking on the volts/div

control.

The 10X attenuator probe works by balancing the

probe’s electrical properties against the oscillo-

scope’s electrical properties. Before using a 10X

attenuator probe, you need to adjust this balance for

your particular oscilloscope. This adjustment is

called compensating the probe and is further

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