Lab scopes

[joecon]

A scope is just an other useful tool if you know how to use it it works, if
you don't want to use it no one will be able to convince you it is worth it.
I have 4 that I have colected over the years one is over 45 years old.
The same debate was going on then.

 

[Danglerb]

You don't get it. It's not how fast you move your foot, it's how fast the system samples the signal. I have no idea what you are talking about with that story on static and dynamic behavior. That is a real head scratcher. When you press on the gas and go to full throttle the computer is acquiring that signal in digital form very fast, eg. many times per second. Importantly, to catch a glitch that causes an error condition in the throttle control software you need to oversample the signal with your test equipment or you will never find the transient. I tried to catch it on peak detect on a good Snap-on multimeter and I could not despite the computer putting the car into limp during a full throttle snap. The multimeter could not catch the transient.

You autoenginuity while "dandy" for your Ford would not be so dandy for my car and would not be fast enough for this.

I'm glad you learned everything you need to 30 years ago, but I don't work that way as I am constantly learning, and I don't just throw parts like that.

What was the point of finding out "how" the throttle sensor was bad? Its bad, move on.

I don't need to see the glitch, only that the brain is seeing a glitch, time for a new sensor after checking the connection is good etc.

BTW you don't ever need to oversample, its a technique for using a different type of input filtering with a lower order cutoff.

Fast signals to me are a fair amount beyond many times per millisecond, but not how I would sample a sensor like a pot.

Static, measuring the sensor output without moving the throttle.
Dynamic, measuring the sensor output while moving the throttle. Measure it with a PowerProbe III and if it glitches you should hear a tick on the speaker.

 

[signcrafter]

Static, measuring the sensor output without moving the throttle.
Dynamic, measuring the sensor output while moving the throttle. Measure it with a PowerProbe III and if it glitches you should hear a tick on the speaker.

Can you explain to me(the less informed) how to use the PPIII for checking things like the throttle sensor? I've never the speaker feature on my PPIII except for as a "test light". Thanks

 

[mvptrukin]

Signcrafter, thanks for bringing this topic up, have lurked on the Autonerdz website forum ( the North American distributor for Picoscope) for years but never pulled the trigger on a scope. Has anyone seen or used the OTC Tech-Scope 3857? It seems to be a PC based lab scope like the Picoscope, only available with 2 channels but is a lot cheaper ! I no longer work on cars for a living--just my own fleet--but have always tried to keep up with some of the auto advancements because they end up in commercial vehicles I work on sooner or later. Picoscope now markets a system aimed towards commercial vehicles.

 

[Danglerb]

Can you explain to me(the less informed) how to use the PPIII for checking things like the throttle sensor? I've never the speaker feature on my PPIII except for as a "test light". Thanks

 

[MrMark]

What was the point of finding out "how" the throttle sensor was bad? Its bad, move on.

I don't need to see the glitch, only that the brain is seeing a glitch, time for a new sensor after checking the connection is good etc.

BTW you don't ever need to oversample, its a technique for using a different type of input filtering with a lower order cutoff.

Fast signals to me are a fair amount beyond many times per millisecond, but not how I would sample a sensor like a pot.

Static, measuring the sensor output without moving the throttle.
Dynamic, measuring the sensor output while moving the throttle. Measure it with a PowerProbe III and if it glitches you should hear a tick on the speaker.

Ok, apparently you didn't read the original post I made. There are two sensors and a total of four circuits between the two sensors. The code does not differentiate as to which of the two sensors (one on the accel pedal and one on the throttle body) had the problem. I didn't know which was bad and I didn't want to throw parts. I imagine scenarios like this come up a lot. Sometimes it pays to read.

As for the speed, let's think about your slow signal pot, there is a hall effect there too for comparison and rationality checking by the way. An engineer would think about and figure out from human testing how fast a human would mash his foot into the pedal to go from nothing to full throttle. How fast do you think that would be? I'm going to guess .1 sec. Let's assume a voltage output range on your slow pot from .5 to 4.5 volts. How many times do you think you should sample that signal within the .1 sec to maintain adequate command and granularity of the throttle? What would that sample rate be?

It doesn't really matter how or what you consider to be a fast signal. What matters is whether the buss communication rate of the OBDII system is fast enough to catch such a glitch. Why don't you tell me the data acquisition rate on that autoenginuity of yours? And then compare that to the sample rate above.

I've never heard those terms used that way. Sounds like Mechanical talk. I was never interested in a "static" measurement as that wouldn't tell me anything other than the baseline throttle position value. Not interesting to me but apparently to you. So be it.

 

[devan7815]

While I value the fact that I am familiar with Lab Scope use it does trouble me that direct guidance from very experienced scope users will be few and far between for most of us. You can get a lot of basics down by watching youtube, reading articles, and some practice at home and in the shop, but one may need to accept that even this can only carry you so far. There is no substitute for the student/teacher relationship and this is what is lacking with the selection and use of this piece of test equipment IMHO. But even with this in mind the level of detail that lab scopes can provide is more than eye-opening. Finally, part of the learning curve involves getting familiar with a lot of known good examples from all types of circuits and applications. This is yet another obstacle. We work in shops trying to make a living NOT research labs that will allow us ample time for this kind of cataloging. So I've had to content myself with what ever a scope might reveal under less than ideal circumstances.