Specifications

Analog oscilloscopes

An analog scope is an oscilloscope constructed with analog circuit technology and signals are

displayed on a cathode ray tube (CRT), a type of vacuum tube using an electron beam (see the section

below on CRTs). Such technology has been evolving since the 1930's when the first commercial

oscilloscopes were available. While digital scopes constitute the majority of new oscilloscopes sold, this

does not mean there is no demand for analog oscilloscopes. Analog oscilloscopes don't have the

feature sets that digital scopes do, but can provide some benefits that digital scopes don't offer. We'll

first look at a typical analog scope, the B&K 2125A, and its controls. Then we'll examine an analog

scope's theory of operation and look at the operation of the 2125A scope.

Analog scope controls

Figure 5

Figure 5 shows the front panel of the 2125A scope. The controls are keyed to the numbers in the

following table:

Button

Number

Button label Function

1 Intensity

Changes the brightness of the trace on the screen. This is done by

changing the electron beam current in the CRT.

Focus

Focuses the electron beam, leading to a thinner trace on the screen.

3 Trig Level

Trigger level. This sets the voltage that the trigger circuit must see in

order for a trigger event to occur and, thus, a trace to go across the

screen.

4 Coupling

Trigger coupling. The choices are Auto, Normal, TV-V (TV vertical), and

TV-H (TV horizontal).

5 Source

Chooses where the triggering signal comes from. The choices are

channel 1, channel 2, line (i.e., the AC line), and external.

6 Hold off

Sets the time delay after the electron beam has swept across the screen

before the trigger is armed again. This is useful to help with triggering on

more complex waveforms.

Copying/reprinting/republishing without express written consent prohibited.