PicoScope Deep Measure

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PicoScope Deep Measure

Postby Steve Smith » Thu Aug 17, 2017 7:22 pm

Thanks once again to the development team here at Pico, I want to highlight a new feature with huge potential called Deep Measure

An Automotive beta build is due out shortly with this feature included and so I want to give you a brief overview of what to expect.

The waveform below captures the crank and start event of a 4 cylinder diesel engine utilising Piezo injectors.
Channel D captures the control signal at the diesel pump SCV (Suction control valve) or IMI (Inlet Metering Valve) or VCV (Volume Control Valve) depending on where you are in the world and which systems you are accustom too.

IMAGE 1.jpg
Scope Waveform Overview

I want to focus on Channel D which highlights the typical activity evident within the engine bay during the harsh conditions of crank and start.

Given the disruption to the SCV signal (Channel D) during cranking it never ceases to amaze me how these fundamental signals either deliver their message, or carry out their control function as it does here. (NB. This engine starts and runs as normal)

It is for this reason that PWM signals are chosen for such control duties as they are near immune to voltage fluctuations

IMAGE 2.jpg
Scope view added

In order to analyse the PWM signal of Channel D we already have a number of options such as Zooming, Scaling, “Add Measurement”, Add View, physical measurements (Signal and Time Rulers) and Math Channels

All of the above work perfectly well but imagine trying to manually zoom and measure each individual pulse/cycle in order to spot a single glitch within the control signal?

Deep Measure is designed to assist with such a process without the need for the manual technique mentioned above.

So how do we activate Deep Measure?
You will recognise the following procedure if you have used CAN Decoding

Click on Measurements > Deep Measure > Create
Select the channel of interest for Deep Measure (Channel D)
I have left the Threshold and Hysteresis settings at their default values
“Between the Rulers” has been ticked so as to focus Deep Measure on a specific are of interest.
Finally click on OK and OK again at the Deep Measure selection screen

IMAGE 3.jpg
Deep Measure set up

IMAGE 4.jpg
Deep Measure set up 2
IMAGE 4.jpg (21.16 KiB) Viewed 370 times

The waveform below reveals the Deep Measure Table highlighting multiple measurements for every cycle between the Time Rulers for Channel D

IMAGE 5.jpg
Deep Measure Table

Clicking on any of the column headings will allow you to display the data in the relevant order to suit your diagnosis
For Example.
Clicking on Cycle No. indicates the number of cycles between the rulers (175)
Clicking on any row will Pan and Zoom to relevant cycle of interest within your waveform

IMAGE 6.jpg
Pan and Zoom

Clicking on Max Voltage reveals cycle 67 as being subjected to additional noise/spike at 15.159 V which can be confirmed using a Signal Ruler

IMAGE 7.jpg
Peak Voltage

Scrolling through the Deep Measure Table I find it incredible how during the mayhem of “crank and start”, the Cycle Time and Frequency at the SCV remain virtually fixed at 4.9980-4.9970 ms and 200.12-200.08 Hz respectively. This is certainly not the impression the overall waveform gives you on initial capture.

Couple all this data to Excel using the Export feature and we can further analyse the values allowing for the implementation of graphs to reveal trends or additional formulas that may assist deeper analysis of such challenging signals.

Below we have graphed the Max and Min voltages at the SCV between the rulers.
The black vertical line indicates how the instability in the voltage becomes stable once the engine has started (around data points 105-113 on the X Axis)

IMAGE 8.jpg
Excel Graph

I have no doubt when this beta build becomes available you will find further applications for Deep Measure and it would be great to see them shared here as “We live and learn together”

There is more on Deep Measure from our Test and Measurement colleagues here at: https://www.picotech.com/library/oscill ... asure?hpc3

Take care…….Steve
Steve Smith
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Re: PicoScope Deep Measure

Postby STC » Thu Aug 17, 2017 9:58 pm

Hi Steve

Prior to this new concept I have always added frequency and duty math channels to components actuated by PWM. Duty/Frequency sensor outputs too for that matter. For example the newer Bosch MAF where the Frequency represents Air Mass & the Duty within that Frequency is the IAT - cunningly all on one wire.

In fact, after taking the measurement we realise that it is rarely the PWM Command Signal that has value other than confirming command has been issued. More so the Current that is the X Ray into the Actuator.

Clicking on Max Voltage reveals cycle 67 as being subjected to additional noise/spike at 15.159 V which can be confirmed using a Signal Ruler

I want to know if that spike coincides with an injector, coil or similar collapsing field, fan cutting in or out ....... AC Compressor, Workshop compressor causing that noise ??? ........

Some time back I saw a few Audi 3.0 V6 Diesels with electronic, Lin Controlled Turbo Actuators where it was the Non Switched + wire that had high resistance in a splice in the loom. Deep Measure would have nailed that If understand it correctly. I those days a 21w bulb or load pro leads were the weapon of choice.

I have yet to find fault with that measurement technique with an old 3000 series Pico using cheap BNC to 4mm ebay leads. I find the 3m or 5m Pico leads a hindrance and messy when taking measurements in an engine bay so I have 1.2m leads with 3 ground leads cut off. The remaining ground lead is sufficient to ground all 4 channels on the 3000 as you know.

Back to the topic.

Looks like a great feature and I look forward to putting it to use and getting value from it so right now trying to imagine a scenario where it would shine over and above what we already have. Which gap it will fill ??

With no wish to p on any fires and having only had a short time to absorb your post and perhaps it has not quite sunk in yet. Single Point Diesel pressure control variants are more a walk in the park than dual point with a regulator on the rail. Perhaps some additional value can be achieved albeit that Pico could achieve perfection there accurately and brilliantly years ago.

I would love to see a study where it can help us go the extra mile.

Has the Automotive scope now become a datalogger ?

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