B&K Precision 2125A Specifikace

10 Experimentally, it has been established that the heating power of a waveform can be related to a DC situation by the use of RMS measures. Thus, a 1

11 Analog oscilloscopes An analog scope is an oscilloscope constructed with analog circuit technology and signals are displayed on a cathode ray tube

12 7 -- This switch chooses the display type. The choices are Main, Mix, Delay, and X-Y. We'll discuss each in more detail below. 8 Position Con

13 The rear panel has two BNC connectors: • Y-Axis Output Jack - a buffered signal of one of the channels (channel 2 on the 2125A) is available with

14 intensity control adjusts the magnitude of the electron beam current -- the more current, the brighter the spot the beam makes on the screen. The a

15 Horizontal and trigger circuits A block diagram for the horizontal and trigger circuitry is: Figure 9 The horizontal and trigger circuits are r

16 The rising edge of the sawtooth sweeps the beam across the screen (this voltage is on the plates in the CRT that deflect the electron beam horizont

17 Delayed sweep Some analog oscilloscopes come with a delayed sweep feature that allows a section of the displayed waveform to be magnified in the h

18 Operation of an analog scope We'll use the B&K 2125A as an example analog scope. It is a popular two-channel 30 MHz scope. A special feat

19 Vertical coupling Control 14 in Figure 5 sets the type of coupling to use with the channel 1 signal. It is AC coupling in the up position. This is

2 TABLE OF CONTENTS Introduction ...

20 If you have an external synchronization signal from the circuit being tested, it can be used to trigger the scope in the external trigger mode. On

21 two signals. For example, on a 2125A, two 1 MHz sine waves can differ in frequency by 1 part in 107 and the Lissajous pattern will move on the scre

22 The 2125A's measurement capabilities are: Quantity Useful measurement range If outside range, looks like Resistance 10 Ω to about 10 kΩ <

23 Digital oscilloscopes We'll use the B&K 2542B-GEN as an example scope. This scope is a two-channel 100 MHz digital scope with a built-in

24 Figure 16 All content Copyright © B&K Precision Corporation, except where otherwise noted. Copying/reprinting/republishin

25 Number Button label Function F None Soft keys. Their function is shown at the right side of the screen. The button 27 (MENU ON/OFF) can be used to

26 24 50% Sets the trigger level to 50% of the amplitude of the waveform being used to trigger the scope. This is useful when NORMAL trigger mode is

27 A 1 kHz sine wave is displayed on the oscilloscope's screen in the following figure: Figure 17 The various display elements are keyed by le

28 E The yellow 1 indicates the vertical position of 0 volts for channel 1. A similar cyan 2 indicator shows 0 volts for channel 2 when it is displaye

29 scope counterparts. Some offer isolated and floating inputs, which are advantages in industrial environments because it means the scope can be used

3 Vertical gain ... 36 Vertical cou

30 Sampling Because the idea of sampling is so fundamental to the operation of a digital oscilloscope, let's look at it in more detail. An anal

31 The next plot shows the waveform reconstructions using linear interpolation (i.e., drawing a straight line between each point): Figure 20 The &qu

32 In order to accurately reconstruct a signal and avoid aliasing, Nyquist theorem says that the signal must be sampled at least twice as fast as its

33 Since this measured waveform will be a high frequency, thousands of sampling windows can be used to generate thousands of sample points per period

34 The acquisition time  is determined by the sampling rate, memory depth, and the details of how the scope works. The scope takes a fixed amount of

35 The AUTO button One of the biggest time-saving features of a digital oscilloscope is the AUTO button 22. This button tells the oscilloscope to mea

36 Vertical gain This adjustment controls the volts per division setting on the vertical scale of the oscilloscope. The settings change in a 1-2-5 se

37 Figure 23 The center of the upper display is the main trace with a narrow black window around the section of the main trace that is expanded in t

38 The ability to press a button and store a captured waveform or screen image is valuable for documenting investigative and development work. With an

39 The buttons on the control panel mirror the buttons on the scope and you can operate the scope remotely. This is a powerful tool, as the scope can

4 Introduction This document is a primer on the use and application of analog and digital oscilloscopes (we'll also call them "scopes"

40 Recording transient events One of the most important advantages of a digital oscilloscope over an analog oscilloscope is the ability of the digita

41 The following picture demonstrates the ability of the scope to average out random noise: Figure 27 The signal at A was a 200 mV square wave with

42 Automatic Measurements An advantage of the digital oscilloscope is its ability to make measurements on the displayed waveforms. This provides thre

43 Figure 30 The three displayed measurements at the bottom of the screen are the RMS voltage of the channel 1 signal (yellow) and its frequency. Th

44 Figure 31 The white trace is the reference waveform that was saved to internal memory (a reference waveform can also be saved to a flash drive).

45 waveform w2. Each recorded waveform is called a frame. The B&K 2542B scope lets you set Δ t to values between 1 ms and 1000 s and record from 1

46 The scope's digital filter was set to be a low-pass filter with a cutoff frequency of 1.2 kHz. This effectively removed the higher signal comp

47 WaveXpress® Since a digital oscilloscope can have an interface to allow a computer to communicate with it, a program running on a computer can be

48 Probes Probes are the most common methods for connecting the oscilloscope to the circuit of interest. There are two basic types of probes availab

49 1M(9 + 1)M= 0.1 This is why the probe is called a 10X probe as it attenuates the signal by 10 times. You'll also see them called X10 probe

5 We will look at these pictures in more detail, but two observations are: • The peak-to-peak voltage of the waveform can be measured along the vert

50 = You can calculate the scope's rise time in ns from: =350 where B is the scope's bandwidth in MHz. Probe compensation

51 A passive probe and its accessories Let's look at a typical passive probe. The following picture shows a B&K Precision PR37AG 150 MHz 1X

52 The device at a is called a bayonet-mount spring tip. It is used on high frequency circuits because it eliminates the long ground lead inductance a

53 Position 1X: Attenuation ratio 1X (1:1) Bandwidth DC to 6 MHz (-3 dB) Rise time 58 ns Input resistance 1 MΏ (oscilloscope input resistance) Inp

54 Floating a scope Some people choose to "float" a scope so they can make a differential measurement with a probe. This is done to remove

55 Good measurement practices These are provided as guidelines of good practice, but may not be true in all situations. 1. Divide the bandwidth by

56 Oscilloscope safety Remember that your safety (and often the safety of others working near you) is ultimately your responsibility. Take this respo

57 Glossary AC Alternating current. It refers to a voltage or current that is periodically changing over time. It can also refer to the type of elect

58 bandwidth In the context of oscilloscopes, this is the upper frequency rating of the oscilloscope's vertical amplifier(s) (the scope's lo

59 CRT Cathode ray tube. It is the vacuum tube with a thermionic emitter and electrostatic deflection plates (some may also contain deflection coils)

6 Notation References to sections and figures can be clicked as hyperlinks. The bookmarks contain links to all of the chapters and subsections. The f

60 glitch An unexpected signal or portion of a repetitive waveform that is unlike the other parts of the waveform. Glitches tend to be of short durati

61 phosphor A chemical used to coat the inside of a CRT. When struck by fast-moving electrons, the orbital electrons of the phosphor are excited to hi

62 screen The visual display area of an oscilloscope. It can be a CRT (a phosphor-coated electron beam tube), an LCD (liquid crystal display), or an L

63 TV sync See video sync. unarmed In referring to an oscilloscope's trigger section, an unarmed trigger is when the trigger is not armed. The sc

64 References WaveXpress® is a registered trademark of B&K Precision Corporation. To contact B&K Precision, please visit http://www.bkpreci

7 Signals With regard to the oscilloscope, the term signal means a voltage that may vary in value as a function of time. One distinction is whether t

8 The sine wave's amplitude in Figure 2 is shown as the distance ‘A’. The mathematical expression for the sine wave, expressing the voltage as a

9 While the amplitude A shown in Figure 2 is used in the mathematical expression of the sine wave, it's rarely used in practical measurements.