PicoScope 7 Automotive Scope School Part 3 – Advanced features
by S Smith

Following on from Scope School Part 2, you will have successfully looked at Signal and Time rulers, Zooming, custom start-up settings, saving and sharing, but where to now? In Scope School Part 3, we will focus on additional capture and analysis features that I hope you find invaluable during your diagnosis.

Coupling

You may have seen the AC/DC coupling option located within each Channel Options button/lozenge, the DC coupling feature informs the scope to display all aspects of the input signal, regardless of the content (both AC and DC).

DC coupling is the default setting, allowing you to see the complete picture of the initial diagnosis. However, if we select the AC coupling feature, we block the DC component of the input signal and only allow the AC (or ripple) to be displayed on the screen.

The value of this coupling feature can be seen in the following example:

With Channels A and B connected across a 12 V battery, start the engine to enable the alternator to commence charging. Leave the coupling feature of Channel A set to DC (+-20 V) and select AC coupling for Channel B (+-500 mV). Channel A will display the DC voltage across the battery (approx. 14 V) whilst Channel B displays the AC content riding on the DC voltage to reveal the alternator AC ripple.

Note: We are measuring at identical points across the battery, but gaining additional information about the system during testing, thanks to the AC & DC properties of the acquired voltage.  

 

Applying this AC coupling feature to fuel rail pressure sensors, and active wheel speed sensors will reveal so much more.

Waveform Navigator

When using a PicoScope to capture intermittent events (whilst focusing on the task at hand), you will inevitably miss the event you were trying to capture. This could be a momentary misfire, or a drop in signal, whilst wiggle testing a wiring harness. Stopping the capture and using the Waveform Navigator feature will enable you to scroll back through each waveform one screen at a time. A PicoScope can store 100’s of screen captures (depending on scope settings), allowing you to find the misfire or signal dropout and ultimately, provide the proof required for you and your customer.

Reference waveforms

Here is a feature that will help you compare a known ‘good’ waveform, against your captured suspect waveform on the same screen. With your known ‘good’ waveform displayed, select Reference waveforms from the left-hand tool panel, followed by if you wish to add a reference of your captured signal on Channel A.

A duplicate of your known ‘good’ waveform will now appear and remain on screen, whilst you capture a suspect waveform for comparison.

Scale and Offset

When reviewing waveforms, the valuable detail may be hidden until we zoom, measure and filter accordingly. Zooming is an invaluable tool (see Scope School part 2), but can add confusion when trying to keep track of the general perspective of the whole waveform (The Zoom overview can help here). However, using the Scale and Offset feature of a PicoScope, you can adjust the individual scale and vertical position of each waveform, revealing additional detail of the captured signals whilst maintaining a view of the overall capture.

The image below has a secondary ignition signal captured on Channel A, with the ignition control signal on Channel B. Please note the compressed appearance of the secondary ignition signal which may hinder analysis.

Using the Scale and Offset feature, found under the Channel Options button/lozenge, we can increase the scale for our secondary ignition signal up to a maximum of 50 times (x50) The image below shows the same secondary ignition waveform after the scale has been increased 5 times (x5.0), and the offset adjusted to 38%, yet the overall waveform view (screen size) remains unchanged.

Scale and Offset adjustments can also be actioned by hovering the mouse pointer over the Y axis. Use the mouse wheel to adjust the scale, or the left mouse button to click, hold and drag to adjust the offset. These shortcut features apply equally to touch-screen users, where ‘pinch zoom’ on the Y axis will adjust the scale, whilst touch, hold and drag will amend the offset.

Events and Actions.

The Events and Actions feature of PicoScope 7 software can be used to instruct the Scope to carry out several Actions automatically, once the specified Event has occurred.

These Actions include Stop, Save, Restart, Capture and Play a sound (Beep), when your waveform Event meets a pre-set criteria.

The Event and Actions menu is accessed by clicking on the Actions button in the left-hand tool panel, whereby all the relevant options can be applied.

A typical application for Events and Actions would involve a vehicle with an intermittent fault, that annoyingly, runs fine with the test equipment attached. However, with a PicoScope connected, you can set a trigger to acquire such faults. Whereby, once triggered, the capture could be stopped, saved and the user notified with a chosen sound, all actioned automatically and unattended!

Below, we have an example where a repeat trigger (see Scope School part 1), has been set to capture the event Every Capture when our 2.5 V level increases beyond 3 V. Once the voltage crosses the trigger threshold, the PicoScope will carry out the Actions configured by the user which include Stop capture and Play a sound (Beep). 

Measurements, Notes and Channel Labels

Within every captured waveform, there are countless pieces of information you may wish to convey, highlight or simply represent using text or numerical values.

Below, we have 3 options available, allowing you to add to any waveform and express any areas of interest.

Measurements

Clicking on the Measurement button in the left-hand tool panel will reveal the measurement options. Choose the desired measurement and select the size of the displayed measurement button/lozenge using the Size control. Below, we have opted for the maximum and minimum voltage of the waveform captured on Channel A in a large format. 

Notes

Clicking on the Notes button in the left-hand tool panel will open a Notes viewport, allowing you to type all the relevant information to accompany the captured waveform (Perfect for technical/warranty reports and training).

Channel Labels

Clicking on the Channel Labels button in the left-hand tool panel will open a Channel Labels viewport. This allows each channel to be identified with a pre-loaded label (simply start typing the name of the component under test), or by adding a custom Channel Label as below. Channel Labels also include a Notes section, providing text boxes for connection information, along with a status selector to indicate if the waveform is ‘good’, ‘bad’ or ‘unknown’.

Be aware that in the above image, any viewport can be reordered or dragged to a new location by clicking on the relevant viewport tab.

Phase rulers 

The Phase rulers allow you to partition between the start and end point of a captured cycle and display any position within the cycle in terms of degrees, percentage or custom values.  

Clicking on the Rulers button in the left-hand tool panel will reveal the Ruler’s menu. Turn on the Phase rulers and choose the applicable Preset boundaries and the number of partitions.

Below, we have captured an in-cylinder pressure waveform and opted to apply the Phase ruler to denote 0-720° of crankshaft rotation between peak compression events. Note, that the 4 chosen partitions denote the 4-stroke cycle, whilst the time ruler can now display degrees of rotation as well as Time. 

Waveform Library

With a PicoScope connected to a PC/Laptop, an internet connection, and a username and password for the Pico Automotive Forum, PicoScope 7 Automotive software will permit access to the Pico Reference Waveform Library (RWL).  

The RWL enables a free and convenient way to store, save and share your waveforms, whilst also providing a means to search and download a waveform of interest (uploaded by other PicoScope users) from our global database.

Click on the Waveform Library button located in the header of PicoScope 7 and enter the username and password for the Pico Automotive Forum.

Once logged into the RWL, you will find several Search Options allowing you to locate a relevant waveform for a specific manufacturer or model. With your search criteria completed, click on the Search button, where you are presented with a selection of waveforms that match your search criteria. In the image below, we have searched for Alfa Romeo’s utilizing a Hall Effect crankshaft sensor, where we currently have 11 waveforms to choose from in the RWL.

Once you have found the waveform of interest, click on the relevant thumbnail and click the Load button to download a reference waveform of the desired channel. Alternatively, you can click the Open Waveform button to download the waveform complete with PicoScope settings.

When logged into the RWL, not only can you download waveforms, but you can also contribute by uploading and sharing your own captures. Assisting other PicoScope 7 software users around the world. To upload and share a waveform, you must first complete the Save dialog box by clicking on the Save button in the header of PicoScope 7 software. Once all fields highlighted with an asterisk are completed, click on Save & Upload to save a copy to your local machine and simultaneously upload a copy to the RWL.

Final note

Many thanks for taking the time to read and digest all of the Scope School episodes, which I hope will help get you started. There will naturally be more questions than answers as you get going, but please stick with it, as we cannot afford to ignore the power of this essential tool and once you have it mastered, “knowledge is power”

Please remember, the PicoScope 7 software is frequently updated with new features along with software enhancements and improved support that not only assists you with scope use, but will improve your theoretical knowledge of complex vehicle systems; and here comes the knockout punch... it’s all free of charge!

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