Wednesday, July 13, 2016

Looking for a bargain 100MHz oscilloscope?

Finding a bargain in 100MHz oscilloscopes is always a challenge.  Specs are confusing and new models are coming out frequently!  What to look for?

All sorts of questions arise when choosing a new digital oscilloscope (DSO) – it can be somewhat daunting!  Where will you use the scope (on the bench, at a customer's site, under the hood of a car)? How many signals do you need to measure at once? What are the maximum and minimum amplitudes of signals that you need to measure?  What is the highest frequency of signal you need to measure?  Are your signals repetitive or single shot? Do you need to view signals in the frequency domain (spectrum analysis) as well as the time domain? Cost is always a factor too. 

Consider capturing good-ol’ USB1.1 data: a frame of data lasts 1ms and has serial data transmitted at 12Mbps (or a 12MHz square wave for 1ms). Bandwidth - to measure the 12MHz signal, scope needs at least 50MHz bandwidth. Sampling rate - to reconstruct the 12MHz signal, a minimum sampling rate of 60MS/s is required for 5 points per waveform. Memory depth - capturing data at 60MS/s for 1ms requires a minimum memory of 60,000 samples. 

So look at these criteria:

1)  Form Factor  traditional bench-top, hand-held, or PC-based.   Need portability?  Battery-powered?
2) Sample Rate/Memory Depth For digital scopes, sampling rate and memory depth are equally important. The Nyquist Criterion states that the sampling rate must be at least twice the maximum frequency that you want to measure: for a spectrum analyzer this may be true, but for a scope you require at least 5 samples to accurately reconstruct a waveform.  A large memory will let you zoom in on small, fast, infrequent glitches.
3) Waveform Capture Rate refers to how quickly an oscilloscope acquires waveforms. If finding and debugging random and infrequent problems is important to you, then waveform update rates are an important consideration in choosing the oscilloscope for your measurements. 
4) Triggering Capabilities A scope's trigger function synchronizes the horizontal sweep at the correct point of its signal: this is essential for clear signal characterization and a steady display. Trigger controls allow you to stabilize repetitive waveforms and capture single-shot waveforms.
5)  Input Ranges (& Probes) Typical scopes offer selectable full-scale input ranges from +/-50mV to +/-50V. Higher voltages can be measured using 10:1 and 100:1 attenuating or isolation probes. An important factor is to check that the scope has a small enough voltage range for the anticipated signals.
6)  Built-in Capabilities   Automatic measurements, built-in pass/fail analysis with relay output, and math functions can save time and make your life easier. Measurement statistics, reference waveform storage, and FFT (Fast Fourier transform) capabilities are available on many oscilloscopes, allowing you to display modified signals or frequency spectra. 
MSO Ready?  If you need to do digital debug too, a mixed-signal scope may be very handy.  Some scopes now come with an MSO socket on the front panel with 8 or 16 digital channels so you can upgrade at a later date.
Built-in AWG?  This is useful if you need a signal source for testing, or to do sweep tests for frequency response.

Maybe this chart will help!

(Missing from this list is the DS1102E at $399.00 with 1Mpt 1GSa/s and 5.6" LCD.)

No comments: