PicoScope Superpowers

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PicoScope Superpowers

Postby Autonerdz » Fri Jun 08, 2007 6:41 pm

The Digital Storage Oscilloscope (DSO) is an essential tool in automotive diagnostics and will continue to be for the foreseeable future. There are many choices out there. They all have different features and capabilities. Each also has its own set of limitations too. Some have more limitations than others. :?

If you are reading this, you have heard of PicoScope. The rumors are true, PicoScope has unprecedented superpowers.

So, why would you ever want a scope with this much raw power? Wouldn't most any offering out there be capable enough to capture signals on the modern automobile?

The answer is no.

Modern automotive controls are getting more complex and challenging for scopes to capture. Signal frequencies are increasing and sometimes we need to be able to capture low and high frequency inputs/outputs simultaneously. This presents a unique challenge to the DSO. To capture a low frequency signal, we need quite a long capture time. To capture a higher frequency signal along with that, we need a scope that can maintain robust sample rates at the longer time bases in order to render enough detail to examine the high frequency components in the capture.

To accomplish this, the DSO must collect a lot of samples during the capture time. Here is the problem with most of the available automotive DSO choices. They don't have the ability to do this. The ones that do have this capability can be counted on one hand.

The PicoScope stands alone as far and away the best performance automotive scope in this group. To illustrate, let me share some captures from a 2006 Chevrolet Cobalt drive by wire system. The following captures cannot be duplicated with any other automotive DSO.

This is because of the long time base required combined with the 10KHz TAC motor control signal frequency.

The original post these images are from, and more, can be found on The Autonerdz Community Forums here:

http://www.autonerdz.com/cgi/yabb2/YaBB ... 1180471365

For those of you who are not familiar with Autonerdz, feel free to browse around in the other areas. We are THE PicoScope Automotive Authority in North America. Accept no substitutes :shock:

Victim: 2006 Chevy Cobalt 2.2 Vin F.

Hey, this thing has drive by wire. Let's look at that first.

Brief system description:

The gas pedal is an Accelerator Pedal Position Sensor (APP) which serves as a throttle request from the driver to the ECM. The ECM then controls the throttle plate position with a reversing electric motor in the Throttle Body Assembly. The throttle plate is spring loaded and has a neutral 'rest position'. The motor must pull against the spring to close or open the throttle plate from this position. Feedback about throttle plate position is provided to the ECM by two Throttle Position Sensors (TPS) which work with opposing voltage outputs.

We are going to focus on the TB assembly signals.

In the following captures the channels are:

A: TPS1 (voltage falls when throttle plate opens)
B: TPS2 (voltage rises when throttle plate opens)
C: TAC Close (voltage on close side of TAC motor)
D: TAC current (probe is oriented so that positive current is a close effort and negative current is an open effort)

The captures in this post were done with a PicoScope 3423 running 6.0.6 software. We are collecting samples at 1MHz per channel on each of four channels with two second screens. It would be impossible to duplicate these captures with any other automotive scope. The TAC control is modulated at 10KHz! So, we are looking at signals with widely different frequencies with all of the detail available.

The first image is on key up. Note how the ECM closed the throttle plate to check the min TPS value then finds it's 'happy place'.

The second image is a snap throttle capture with the engine running.

Note that the motor modulation is reflected in the TPS signals as the TPS picks up the RFI from the motor action. Also note the digital pulses on TPS2.

Image


In the following images, we have exchanged the Channel A TPS1 for the TAC Open side of the motor to show more of the motor control strategy. Again, the first one is a key up sequence and the second is a snap throttle with engine running. Note how the voltage is applied to one side of the motor and modulated on the other side to achieve the desired position.

Image

And here is a two stage zoom on the upper capture from the previous image:

Image

We can see that the TAC motor control is Pulse Width Modulated.

And now we zoom way in on the PWM change at just after 1142ms into the capture:

Image

Would you always need a scope with these superpowers? Of course not. But for the times you might like this kind of performance, PicoScope is THE ONE.
Tom Roberts
(The Picotologist)
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PicoScope Superpowers

Postby Carl Grotti » Sat Jun 09, 2007 6:27 pm

Nice post, Tom.

I would just like to add a few things here:

The reason we were able to capture the slow analog Throttle Position Sensor (TPS) signal and the high frequency Throttle Actuated Control (TAC) digital commands and results with great detail was because the 3423 is in a fast streaming mode. This mode goes in to effect when the time base selected is 200mS/div or greater.

As you can see, we had incredible detail with a 10,000Hz signal with a sweep speed at 2 seconds.

Additionally, the captures shown are just one frame of the possible 127 frames (Elements) available during data acquisition.

Superpowers? Absolutely!

Thank you, Pico Technology.

Carl
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Postby Guest » Fri Jul 06, 2007 8:03 am

Streaming long captures allows users to analyse the automotive heartbeat.

As we start to move into the realms of automotive medicine, more and more expertise is developed. For one person to become a Dr in this medicine is a staggering feat. To share this knowledge with everyone is as important as the tools themselves.

There are many PicoScope users out there who barely scratch the surface of the tools capabilities. And there is nothing wrong with this. People are using these tools to undertake their everyday jobs. They have become reliant on these tools for their business. Not finding a fault can be damaging to one's business. Sharing expert knowledge with others helps those who cannot solve their problem, it gives us pleasure in success, it gets the job done and it please our customers.

Embrace this art form and realise that it makes modern day doctors of us all.

Michael
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