The Basics Of Oscilloscopes – What Is An Oscilloscope – Part 2

Instek GDS-2000

What other factors should be considered when purchasing a digital storage oscilloscope?

Beyond the basic four specifications, it is common to consider:

  • Number of channels (typically two or four). If you need to record multiple high-speed signals beyond four, you might want to look at a dedicated recorder.
  • Size of the display is often a consideration. Larger, clearer screens make it easier to see multiple signals at once. Luckily today’s digital storage oscilloscope also has different color lines for each signal.
  • How you capture a signal is also important. This is where triggers come into play. It is often important to see only signals with specific characteristics among the many captured. With most digital storage oscilloscopes, a variety of different trigger types are available to find particular events that happen during signal analysis.
  • If you are looking at packets of serial data, you may also find it useful to decode the signal to make sure that the correct instructions are being sent. Protocols such as I2C, SPI, CAN, LIN, RS232 are commonly used to communicate between devices. It is important to make sure that the right commands are communicated when a specific event happens.

When graphing a signal, what do you want to find out?

  • The time and voltage value of a signal
  • The frequency of an oscillating signal
  • How much of a signal is direct current (DC) or alternating current (AC)
  • How much of the signal is noise and if the noise is changing over time
  • To see the “moving parts” of a circuit represented by the signal
  • To tell if a malfunctioning component is distracting the signal

Oscilloscopes come in many different versions

  • Digital
  • Analog
  • Mixed signal
  • Portable
  • PC based versions

If the recording of a waveform is required, a digital scope will be applicable. If you need to see the waveform in real time, or to see the original intensity an analog scope would better suit that requirement.  The higher the input signal frequency is, the higher the bandwidth that will be required. If you do not have the appropriate amount of bandwidth, you risk the possibility of not getting accurate results.

If there is doubt about the amount of bandwidth that is required, then you should go the next step up. The bandwidth can usually be calculated by this formula: BANDWIDTH = (0.35 / rise time of the signal)

The higher the sampling rate, the more accurate and precise the captured waveform is. As the sampling rate increases, it allows for more samples a captured waveform has, for any given period of time.

In almost every electric application, including lab use, research and development, and product development there is a need for an oscilloscope to provide waveform analysis.

Mixed Signal Oscilloscopes (MSO)

Mixed Signal Oscilloscopes (MSO) can capture both analog and digital signals at once. A mixed signal scope usually combines 2 or 4 analog channels with either 8 or 16 digital ones. This is useful when looking at logic signals after a specific input has occurred when developing a system that combines physical input and computer controls.

There are both digital and analog channels that provide the ability to accurately time-correlate both signals. The measurements are compiled by using a single time base on a single display. Any combination of these measurements can be used to trigger the scope.

The key advantage of the MSO is that only one unit is required for conducting tests that you would normally need two units for.

An oscilloscope is a test and measurement instrument used primarily to measure voltage over time. The input signal is converted from an analog wave to a series of digital signals. Once it is digitized, oscilloscope can then store the information in memory and display it on the screen. The faster the signal is processed, the better the display will be.

Refer to the above general and digital oscilloscopes discussions that cover the common features of an MSO with a DSO.

Applications for Mixed Signal Oscilloscopes

  • Aerospace
  • Defense
  • Industrial Electronics
  • Communications
  • Research and Development

The MSO treats the oscilloscope and logic channels in different ways

  • Logic Channels: These channels are converted to digital format, where no analog information is shown
  • Oscilloscope Channels: These channels use an analog to digital converter to allow the analog input to show in digital format

MSO scope vs. Logic Analyzer factors to consider

  • State Analysis

o             MSO- Yes. Separate channels for clocks

o             Logic Analyzer- No. No provision for clock input

  • Triggering

o             MSO- Single events on both the analog and digital channels

o             Logic Analyzer- Advanced sequential capabilities

  • Channel Count

o             MSO- 16 / 32

o             Logic Analyzer- 64 – 204 +

  • Timing Analysis

o             MSO- Yes

o             Logic Analyzer- Yes

What other factors should be considered when purchasing a mixed signal oscilloscope?

Beyond the basic four specifications, it is common to consider:

  • Number of analog channels (typically two or four). If you need to record multiple high-speed signals beyond four, you might want to look at a dedicated recorder.
  • Number of digital channels, usually 8 or 16
  • Size of the display is often a consideration. Larger, clearer screens make it easier to see multiple signals at once. Luckily today’s digital storage oscilloscope also has different color lines for each signal.
  • How you capture a signal is also important. This is where triggers come into play. It is often important to see only signals with specific characteristics among the many captured. With most digital storage oscilloscopes, a variety of different trigger types are available to find particular events that happen during signal analysis.
  • If you are looking at packets of serial data, you may also find it useful to decode the signal to make sure that the correct instructions are being sent. Protocols such as I2C, SPI, CAN, LIN, and RS232 are commonly used to communicate between devices. It is important to make sure that the right commands are communicated when a specific event happens.

PC Based Oscilloscopes

PC based oscilloscopes are the modern alternative to the traditional bench top oscilloscope. All data and configurations measured on these oscilloscopes can be saved into a PC for further data analysis.

One of the key factors involved is the USB connection. The USB (universal serial bus) is intended for communications between interfaces, such as the oscilloscope and the PC in this instance.

PC based oscilloscopes come in either internal or external versions.

The external version(s) is a small unit that connects to a PC, usually by a USB. They can be used by a laptop or a desktop computer.

The internal version(s) usually come with a plug in card that is PCI format. This does not allow for portability and being that the card is placed in the actual PC, there is a lot of noise which could interfere with the results that are being measured.

Advantages of PC Based Oscilloscopes:

  • Easy to Use
  • Portable
  • Cost Effective
  • Large Display
  • Uses already “off-the-shelf” equipment- USB and PC

Portable Oscilloscopes

Portable Oscilloscopes are otherwise known as handheld oscilloscopes. They are typically used for on- site contractor maintenance and either in the industrial or electronic field.

If you need to move your oscilloscope around to many locations or from bench to bench in your lab, then the portable oscilloscope would be ideal for you.

Advantages of a Portable Oscilloscope

  • Lightweight
  • Easy to Use
  • Turn On and Off Quickly

To read Part 1 – click here:  http://wp.me/p42MUZ-6Z

Use the contact form below to contact NorthTree Associates with any questions you may have on this article or about oscilloscopes in general.

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