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PicoScope, 유용한 기술정보(Tech Tip)

2011.6.10 How to measure anything

We've updated our "How to measure..." web page to give details of the latest Pico data loggers and other devices. If you're wondering what equipment you need to measure...acceleration, audio signals, automotive signals, battery discharge, current, the beating of a bird's wing, flow, food temperature, frequency, humidity, liquid level, light level, the swing of a pendulum, pH, oxygen in air, pressure, strain, force and load, rainfall, resistance, sound level, temperature, video signals, voltage, WBGT (wet bulb globe temperature), 4-20 mA signals, speed of sound, speed of light, output of a dynamo, or the speed of a car...

...read the new, up-to-date How to measure... page.

Here are some of the questions and answers that have appeared recently on our discussion forum:

Q. How to overlap waveforms. It would be nice if we could overlap two saved waveforms in PicoScope.

A. This is easier than you think. Every saved, or 'reference', waveform has its own draggable axis. Locate the waveform's vertical axis labels, which are color-matched to the waveform, and notice that the cursor changes to a double-headed arrow. Click and drag the labels up and down to move the waveform. This also works for live inputs and math channels. For more accurate control, click the colored button at the bottom of the axis and type in the exact vertical offset that you require.

Q. RS232/UART decoding in ASCII. RS232/UART decoding in PicoScope is an awesome feature. I can't see a way to change the data from hex to ASCII. Am I correct in assuming it is a feature yet to be implemented?

A. It is possible in the current version of PicoScope. Click on View > Display Format in the Serial Decoding window and take your pick from Hex, Binary, Decimal or ASCII.

2010.11.10 Find Glitches Faster with PicoScope

In recent releases of PicoScope, we have added a number of improvements to make it easier to find rare and intermittent events such as glitches and bursts of interference. There are other new features to help search for events in the deep memory of scopes such as the PicoScope 6000 Series, which have up to 1 billion samples of waveform storage.

Find Glitches Faster with PicoScope, a new article added to our Application Notes collection this month, explains various techniques such as mask limit testing, rapid triggering, persistence displays and the buffer navigator, which can help to find transient events hidden in large amounts of data.

Read Find Glitches Faster with PicoScope (412 kB PDF)

Video: Mask Limit Testing with PicoScope

The mask limit testing feature recently added to PicoScope allows you to compare waveforms with a stored reference pattern. If the waveform fails the test then PicoScope can activate an alarm, save a file or execute a command. You can also store thousands of waveforms in the buffer and then search for those that failed the test.

A new video published on picoscope.tv, Mask Limit Testing, shows how this feature can save you time when searching for intermittent glitches.

Watch the Mask Limit Testing video

Tech Tip: Lowpass Filtering revisited

The lowpass filtering feature in PicoScope was introduced way back in release 6.2.0. It is most often used to clean up live waveforms, but did you know that you can use it on saved, unfiltered waveforms?

You will need an oscilloscope that supports lowpass filtering: that's most USB PicoScopes from the 3000 Series upwards. Load a previously saved waveform or retrieve one from the waveform buffer, then go to the Channel Options dialog (click the channel name in the toolbar) and switch on Lowpass Filtering. PicoScope will then apply the selected filter to the waveform on the screen.

2010.10.11. Finding glitches with PicoScope

Recently, in PicoScope 6.4.10, we added the ability to show in the waveform buffer overview only the waveforms that failed a Mask Limit Test. If you're not normally interested in Mask Limit Testing, you may have overlooked this feature, but it can be very useful when you are looking for an infrequent glitch.

Imagine that you have a square wave with an occasional spike that you want to capture. You could switch PicoScope to Persistence mode. In time this will catch the spike, but the display will show an overlay of a large number of waveforms with noise, making it difficult to see the exact shape of the spike. The new Mask Limit Test feature allows you to capture the spike without adding the clutter of the Persistence display.

To use this feature:

Set up PicoScope to trigger on individual pulses in the square wave. For best results, use "Rapid" trigger mode, which captures successive waveforms with minimal trigger re-arm time.
Go to Tools > Masks > Add Masks, select the channel of interest, and click Generate. This generates a testing mask, which appears as a colored area surrounding the waveform.
If necessary, edit the mask to include the normal waveform and exclude the spike. (Right-click, Mask, Edit.)
Start PicoScope capturing, and wait until the waveform buffer is full.
Inspect the waveform buffer using the Buffer Overview button. This will initially show all the waveforms captured, but if you open the drop-down menu and select "Show only Mask Limit Test failures", only the captured waveforms with a spike will be displayed. You can select any of these waveforms to display in the main view.

2010.9.11. Fitting multiple traces on one PicoScope view

If you are used to analog oscilloscopes, you might have got into the habit of fitting multiple waveforms on the screen by increasing the voltage range for each input. This also works with PicoScope 6, but it is not the best method. With digital scopes, it is always best to make the signal use as much of the input range as possible to avoid wasting the scope's resolution. For example, if your signal occupies only half of the input range of your 8-bit scope, you will obtain an effective resolution of only 7 bits.

PicoScope 6 makes it easy to scale multiple waveforms to fit on the screen without losing resolution:

In most cases, you can just right-click on the display and select Auto-arrange axes. This scales all waveforms, including Reference Waveforms and Maths Channels, to fit correctly on the screen.
If you want manual control over the size of each waveform, then you can use the scaling buttons instead. These are the colored buttons at the bottom left and right corners of the display that match the colors of the waveforms. Each button opens a dialog that allows you to set the scale and offset of one waveform.

2010.8.11. Waveform overlays

Did you know that PicoScope can display a saved waveform in the background for comparison? This feature is built into PicoScope, but you might not have discovered it yet. It's called Reference Waveforms.

You will find the Reference Waveforms feature in the Tools menu. Selecting the command opens a dialog that shows all available and saved waveforms. To save a waveform and display it in the background, select the source channel under the "Available" list and click Duplicate. The new reference waveform will then appear in the "Library" list. Next, click OK and the reference waveform will appear in the PicoScope window. You can drag it up and down, or scale and offset it, in the same way as a live waveform. You can also drag a live waveform over it for comparison.

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