9 Factors to Consider When Choosing an Oscilloscope

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If you’re involved in electronics, you’ll probably have an oscilloscope on your bench. As electronics become more complex almost daily, sooner or later a new oscilloscope will be in order. How to choose the right one for your applications?

Factors to consider:

Remember that the bandwidth specification of an oscilloscope is the frequency of the “-3 dB point” of a sine-wave signal of a particular amplitude, e.g. 1 Vpp. As the frequency of your sinewave goes up (while keeping the amplitude constant), the measured amplitude goes down. The frequency at which this amplitude is -3 dB lower, is the instrument’s bandwidth. This means that an oscilloscope of 100MHz would measure a 1Vpp sinewave of 100MHz at only (approx.) 0.7Vpp. That is an error of about 30%! In order to measure more correctly, use this rule of thumb: BW/3 equals about 5% error; BW/5 equals about 3% error. In other words: if the highest frequency you want to measure is 100 MHz, choose an oscilloscope of at least 300MHz, a better bet would be 500MHz. Unfortunately, this has the most influence on the price…

Understand that today’s signals are no longer pure sine waves, but most of the time square waves. These are built by “adding” the odd harmonics of the fundamental sine wave together. So a 10 MHz square wave is “built” by adding a 10MHz sine wave + a 30MHz sine wave + a 50MHz sine wave and so on. Rule of thumb: get a scope that has a bandwidth of at least the 9th harmonic. So if you’re going for square waves, it’s better to get a scope with a bandwidth of at least 10x the frequency of your square wave. For 100MHz square waves, get a 1GHz scope… and a bigger budget…

Consider rise (fall) time. Square waves have steep rise and fall times. There’s an easy rule of thumb to get to know what bandwidth your scope needs to be if these times are important to you. For oscilloscopes with bandwidths below 2.5GHz, calculate the steepest rise (fall) time it can measure as 0.35/BW. So an oscilloscope of 100MHz can measure rise times up to 3.5ns. For oscilloscopes above 2.5GHz up to about 8GHz, use 0.40/BW, and for scopes above 8GHz use 0.42/BW. Is your risetime the starting point? Use the inverse: if you need to measure rise times of 100ps, you’ll need a scope of at least 0.4/100ps = 4 GHz.

Choose your sample speed. Today’s oscilloscopes are almost all digital. The above steps involved the analog part of the instrument, before it gets to the A/D converters to get “digitized”. Here the bandwidth-to-rise time calculation can help you out: an oscilloscope of 500MHz has a calculated rise time of 700ps. To reconstruct this, you need at least 2 sample points on this edge, so at least a sample each 350ps, or 2.8Gsa/s (gigasamples per second). Scopes don’t come in this flavor, so choose a model with a faster sampling speed, e.g. 5Gsa/s (resulting in 200ps “time resolution”).

Decide on the number of channels. This is easy: most scopes come with 2ch or 4ch configurations, so you can choose what you need. Fortunately prices don’t double from 2ch to 4ch, but it does have a big impact on the price of the instrument. High-end scopes (>=1GHz) have always 4ch.

Calculate how much memory you’ll need. Depending on how much of your signal you want to see in a “single shot acquisition”, get your math right: at 5Gsa/s, you have a sample each 200ps. A scope with a memory of 10.000 sample points, can store 2µs of your signal. A scope with 100M samples (they do exist!) can store 20 seconds! Looking at repetitive signals or “eye-diagrams”, memory is less important.

Think about repetition rate. A digital oscilloscope uses a lot of time calculating. Between the moment of triggering (see next step), having the captured signal on the display, and capturing the next triggered event, most digital scopes “consume” several milliseconds. This results in only a few “photos” of your signal each second (waveforms per second), typically about 100-500. One vendor solved this problem with so called “Digital Phosphor” (from about 4.000 wfms/s to >400.000 wfms/s for the top models), others followed with similar-like technologies (but not always sustained/continuous, rather in bursts). This repetition rate is important because those rare errors and faults in your signal might occur just then when the scope is not acquiring, but busy calculating the last taken acquisition. The higher the repetition rate (wfms/s rate), the higher your chances are of capturing that rare event.

Check what kind of errors you expect to be looking for. All digital scopes have some sort of intelligent triggers on board, meaning you can trigger on more than just the rising or falling edge of your signal. If your repetition rate is high enough, you’ve probably seen that rare glitch every other second. Then it’s nice to have a Glitch trigger.

Think about resolution of LCD display. Small screens with poor resolution can make your life miserable if you cannot see results easily. Buy the largest screen with the best definition your budget will allow.

Some Final Tips

  • Triggering, repetition rate and memory: once you found the rare event with a high wfms/s rate, having the right trigger available is more important than repetition rate, as your scope will trigger only on the (rare) event, which occurs… right: rarely. So you don’t need high rep-rate anymore. Memory can become more important, as to be able to analyze what happened before or after the event.
  • Remember: garbage in is garbage out, so get the bandwidth and rise time issue sorted out first!

Established in 2004, NorthTree Associates (Cologne, MN) is a North American distributor that specializes in providing unique Electronic Test & Measurement tools for design engineers, test engineers and production engineers. You can visit our website at http://www.northtreeassociates.com

10 Reasons Why You Need A PC Oscilloscope

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PC Oscilloscopes (PCOs) are rapidly replacing traditional digital storage oscilloscopes (DSOs) as the essential item for your test equipment arsenal. Here are 10 reasons why:

  1. Compact and portable units
  2. Uses your PC monitor to provide a large and detailed color display
  3. Signal storage is limited only by your PC’s storage capability
  4. Captured waveforms and instrument settings can easily be shared with others
  5. New functionality through free software updates
  6. Can be used with desktop or laptop PCs
  7. High-speed USB 3.0 connection (parallel port oscilloscopes are also available)
  8. Hardware and software in one package
  9. Use your PC Oscilloscope for data acquisition
  10. A complete test and measurement lab in one unit

1.  Compact and portable units

By integrating several instruments into one small unit, PC Oscilloscopes (PCOs) are lighter and more portable than traditional test equipment. When used with a laptop computer, you can carry a complete electronics lab in the same bag as your PC.

2.  Uses your PC monitor to provide a large and detailed color display

The display of a traditional oscilloscope is limited by the physical size of the oscilloscope, and may only be a single color. With a PC Oscilloscope your computer controls the display, so not only do you get a full color display, but the display can be the size of your monitor, projector or plasma display.

3.  Signal storage is limited only by your PC’s storage capability

PC Oscilloscopes store the signals that you are measuring directly on your PC. With the power of today’s modern PCs this gives you vast storage capabilities. Along with allowing you to record lengthy signals this also lets you save signals for reviewing at a later date.

4.  Captured waveforms and instrument settings can easily be shared with others

Need to show your customer or colleague the signal you have captured? Just save the waveform and email them a copy. They don’t have a copy of the oscilloscope software? No problem – just export it as text, an image or in a binary format for use with third-party software. (If they want to set up their equipment to run the same test, simply send them the oscilloscope settings too.)

5.  New functionality through free software updates

If you’re lucky you can return a traditional DSO to the supplier for a firmware upgrade and maybe get improved functionality. With a PC-based oscilloscope new features and improved functionality can be added at any time with a simple software update. Free software updates means that a PC Oscilloscope is one of the few things that can actually become more powerful and useful with age.

6.  Can be used with desktop or laptop PCs

PC Oscilloscopes are external devices that are connected to your PC using the ubiquitous Universal Serial Bus (USB). Virtually every laptop or desktop PC sold comes with multiple USB ports so there’s no problem using your PC Oscilloscope with either a desktop or a laptop PC.

7.  High-speed USB 3.0 connection

USB 3.0 can transfer data at speeds of up to 1 GS/s. Using powerful PC Oscilloscope software it give you incredible performance with fast screen updates and the ability to stream data.

8.  Hardware and software in one package

Choose PC Oscilloscopes that come complete with the hardware and software in one package.

9.  Use your PC Oscilloscope for data acquisition

Using the sw, you can transform your PC Oscilloscope into a data logger that can log data over extended periods of time.

10.  A complete test and measurement lab in one unit

When you buy a PC-based oscilloscope make sure you don’t just get an oscilloscope: make sure you also get a spectrum analyzer, meter and data logger rolled into your PC-Oscilloscope choice. Some models even include a built–in signal generator or arbitrary waveform generator. So with a PC Oscilloscope you really do get a complete test and measurement lab in one cost–effective unit.

NorthTree Associates is a distributor and supplier of Electronic Test & Measurement Equipment. Companies represented include ITIC USB 2.0 Protocol Analyzers, LabNation SmartScopes, Micsig Oscilloscopes, Oscium iOS Test Tools, OWON Oscilloscopes.

Micsig MS510S 2 Channel Handheld Oscilloscope Review

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The Micsig MS510S 2 Channel Handheld Multifunctional Oscilloscope is portable unit has two fully isolated 100MHz scope inputs, a built-in isolated multimeter, 14.5cm (5.7”) color touch-screen, up to 190k waveform updates per second, 240k points memory and a battery life of up to 7 hours. It’s supplied with a pair of isolated probes for measuring up to 600V (Cat II).

As portable scopes go, this handheld oscilloscope offering from Micsig has a lot of good features and reasonably priced. One of the reasons this review was written was that we recognized how useful it is to have a scope with two fully isolated channels; this makes it much easier to make measurements at two different points in a circuit which may not necessarily have the same ground reference.

However, you do have to be a bit careful using an isolated scope because you can possibly have a high voltage not only between the input signal and ground but between those grounds and from each ground to earth. So the probes and inputs need to be well-insulated to prevent accidental shocks.

The Micsig MS510S unit does not disappoint as it is supplied with two insulated probes that shroud the BNC connector shields, earth clips and test probes (to the extent possible). These are 500MHz, 10:1 types rated for 300V CAT III and 600V CAT II.

First impressions of the overall user interface are good. The screen has good contrast and color and is easy to read indoors; it has an outdoor color scheme which helps for reading in sunlight. However the lack of an anti-reflective coating on the display means it would work a lot better with a hood or under shade. The unit boots up fast – in just a couple of seconds – and responds to button presses pretty quickly. So it doesn’t feel sluggish to use.

While the touch-screen can be used to perform many functions such as moving along the timebase, moving traces up and down, zooming into portions of the waveform and selecting measurements to display, virtually all functions can also be performed using the front panel buttons and side jog wheel. The operation of this unit is quite different to most benchtop scopes but users will quickly figure out the controls and get used to them. Like most digital scopes, it has soft buttons (F1-F4) which drive the on-screen menus.

The control layout below these buttons is pretty simple and the function of most buttons is self-evident. This oscilloscope is 165mm wide, 255mm tall, 62mm deep (not including side carry strap) and weighs 1.7kg. It has a tilting stand at the back to prop it up on a flat surface. Supplied accessories include the two probes, a set of multimeter leads, mains charger, user manual and PC software on CD and warranty card.

Oscilloscope Functions

Each channel of the Micsig MS510S oscilloscope has a selectable sensitivity of 5mV-50V/division so with the supplied 10:1 probes, that gives a range of 50mV-500V per division. The sampling rate is 1GS/s with one channel active and 500MS/s with two. As stated earlier, storage is 240Kpoints total so with both channels active it can store 120K samples. Channel bandwidth can be restricted to 20MHz if required and each channel can be AC or DC coupled.

This oscilloscope uses a 9-bit ADC which is slightly better than bargain basement oscilloscopes (including desktop models) which typically use an 8-bit ADC. As such, when the bandwidth is set to 20MHz, the traces are quite clean, however there is still a fair bit of noise evident with 100MHz bandwidth (this setting affects both channels simultaneously). You can of course enable averaging to reduce noise with repetitive signals; this is also enabled for both channels at once. By default, the oscilloscope has trace persistence, which can be handy in some circumstances as it allows you to see the ‘spread’ of the signal, i.e. – to get an idea of jitter in a digital signal or amplitude stability in an analog signal.

But sometimes you want to turn it off to get a ‘cleaner’ looking trace – unfortunately, we can’t figure out how to do that with this unit. The minimum persistence setting is 100ms. This isn’t a huge problem but it does seem to be an oversight in the software. (As of this posting, Micsig is working on a solution for this issue).

You can display up to four measurements in oscilloscope mode, selected from a large list and these appear at the top of the screen, overlapping the graticule. They’re updated a couple of times a second. The unit also has basic X/Y cursors that can be enabled and moved around in the usual way. Typical trigger options are available, including Edge, Pulse, Logic (ie, high/high, high/low, etc), Video (including high definition) and Serial Bus. The hold-off time is adjustable as is the trigger coupling (AC/DC).

Serial Bus Decoding

While this is not a mixed signal oscilloscope, it does have an option to decode various serial buses and trigger on the contents of the packets. This includes serial, LIN, CAN, SPI and I2C although given the fact that there are only two channels, it’s more suitable for I2C than say SPI.

Multimeter Functions

The built-in multimeter of the Micsig MS510S is easy to use because of the large touch-screen. It’s easy to switch modes by pressing on their icons and the numeric display is large. One aspect we particularly like is that it auto-ranges almost instantly, which overcomes one of the biggest arguments against auto-ranging meters (which, let’s face it, are pretty much standard now).

However, there is one major drawback apart from the modest 4-digit resolution and that is that you need an external accessory to do current measurements – either a shunt or a hall-effect sensor (clamp meter). These are available as accessories; however Micsig does not currently list them or have a price. So that probably means you need a multimeter on hand, in addition to the Micsig MS510S. But that’s not to say the multimeter functions are useless – far from it.

It offers DC and AC voltage in ranges such as 500mV, 5V, 50V along with a maximum of 1000V DC and 750V AC (20kHz bandwidth). The multimeter inputs are fully isolated from the scope inputs. It also does statistics (minimum/average/maximum) and has a bar graph in addition to the numerical read-out.

Other modes include resistance (0-50MΩ), continuity (50Ω threshold), diode test (up to 3.5V), capacitance 100pF-50ΩF), temperature and humidity (requiring an external sensor accessory) and pressure (also requiring an external sensor accessory).

One nice feature of the Micsig MS510S oscilloscope is that the multimeter inputs can also double as calibration outputs for the probes. Small adaptors are supplied to make the connections.

Data Logging

The Micsig MS510S also has a “Recorder” mode where it can log readings from either the meter or oscilloscope input(s). When logging from the meter, you can choose from DC volts, AC volts or DC+AC volts. You can also log DC amps, AC amps, temperature, humidity and pressure but all these extra modes require the appropriate accessory.

The readings are displayed in an automatically-scaled horizontally scrolling chart format and the data can then be saved to a USB flash drive (in an “.MMR” file format) or in a screen grab of the chart. It can be set to either stop storing data when full, or set to a circular buffer mode where it overwrites the earliest data with later data once storage space is exhausted.

For data logging from the oscilloscope input(s), it can either log a low-frequency view of the two input channels or alternatively, it can log one or two of the scope measurements. In the latter case, you need to first enable the measurements you require on the appropriate channels, then about five hours to reach full charge.

Conclusion

As portable oscilloscopes go, the Micsig MS510S is a pretty attractive proposition. Even for bench-top use, the dual isolated channels and ability to easily move it around are quite useful features. While we would like to see a couple of software tweaks and an anti-glare coating on the screen, it’s a very flexible instrument with good overall performance and a responsive user interface.

While the Micsig MS510S is not light, it can be operated hand-held and with the protective rubber surround, appears to be robust enough for field use.

For applications where performance is not so critical, the Micsig MS-310IT oscilloscope is a more economical option. The main difference is the waveform update rate – the Micsig MS510S has 190K samples/second and the Micsig MS310IT only has 50Ksamples/second. Micsig also has the MS-200T series oscilloscopes are even more economical, but as with the MS310IT oscilloscope, this series does not feature isolated inputs.

Established in 2004, NorthTree Associates (Cologne, MN) is a North American distributor that provides unique Electronic Test & Measurement tools for design engineers, test engineers and production engineers.

NorthTree Associates Introduces Micsig tBook Tablet Oscilloscopes With Touch Screen Technology

Micsig Touch Screen Oscilloscopes

Micsig Touch Screen Oscilloscopes

NorthTree Associates introduces the Micsig range of high performance tBook Tablet Oscilloscopes and Handheld Oscilloscopes both with touch screen technology.

As the tBook Tablet Oscilloscope innovator, Micsig has achieved various worldwide patent rights, software copyright for their touch screen tBook Tablet Oscilloscope. Features include: a multi-touch screen, 100MHz to 200MHz bandwidth, 2 or 4 channels, real time sampling rates of 1GS/s to 2GS/s, compact design, high memory depths, and excellent function features.

The affordably priced Micsig handheld oscilloscopes offer bandwidths ranging from 70MHz up to 200MHz, two channels and 1GS/s sampling rate, making them deal for both laboratory testing and field service applications across a wide range of industry sectors.

High performance features offered by Micsig oscilloscopes include isolated inputs for safely carrying out floating measurements, up to 190,000 wfms/s refresh rate, support for serial bus protocol trigger and decode (1553B/429/UART/232/485/LIN/CAN/SPI/12C) in both graphic and text modes, and multi-function operation including digital oscilloscope, digital multimeter and recorder.

In oscilloscope mode, the units offer a wide range of trigger types, 31 automatic measurements, and maths functions including FFT. Isolated input versions offer up to 1000V CAT II 600V CAT III maximum channel floating voltage.

Designed for user-friendly operation with Micsig’s touch screen technology, the oscilloscope offers three operation modes – moving the waveform, zooming in and out, and menu option selection – with the large 5.7 inch TFT LCD screen providing users with a sharp 640 x 480 high resolution display. A user selectable indoor (black background) or outdoor (white background) display mode makes the models particularly useful in field service applications.

The Li-ion batteries provide users with up to 6 hours of continuous operation, while the USB host and slave interface allows users to easily download captured waveforms as well as connect the oscilloscopes to a PC.

NorthTree Associates based in Waconia, MN provides unique Electronic Test & Measurement tools for increasing productivity. You can reach NorthTree Associates at sales@northtreeassociates.com

Posted with permission from our valued partner Micsig.