Thinking about an Oscilloscope

[gggGary]

So I was looking at these. Anyone have some advice for a guy who hasn't used a scope since high school science lab? No real hard goals in mind, want to be able to look at MC and auto ignition functions, any other electronic look sees that might happen. This one has a plug wire clamp on probe which seems like a good idea??
This unit is $115 I am willing to use a laptop to help keep cost down.

Hantek PC USB 8CH Auto Diagnostic Oscilloscope/DAQ/Programmable Generator C

​

261130098556

 

[pamcopete]

You should get a scalable probe to be able to look at the primary of the coil. The voltage spikes to 400+ Volts with an electronic ignition and 200+ with points.

 

[xjwmx]

If you can get a storage scope, that makes it much, much more useful. You can set it to trigger on the first pulse of some adjustable voltage level, then it stores events that occur briefly after that and you can take your time and expand it time-wise and look at it very carefully. Without that feature you're limited to looking at repetitive waveforms in real time. Although the input to an ignition coil for example is a repetitive waveform.

I'm guessing most pc-based scopes would have a storage feature. Also, you won't need a very fast scope. The slower the scope the less expensive it is. I've mainly used money is no object scopes at work, so I can't really recommend one. I did buy an old Heathkit scope for $20 once that would have been fine for ignition type stuff. A scope is like a microscope; it opens up a new world.

P.S. Also, you only need one channel, which would really lower the cost, if you can even buy a single channel scope. Number of channels is how many probes you can attach and how many traces you can capture at the same time, usually to compare events in time.

 

[gggGary]

So 10x and 100x probes aren't bad but they want a bit O cash for 1000X probes I guess that's why they include an "inductive type" probe that clamps on the plug wire. Thanks for the hints so far!

 

[xjwmx]

The x value is the factor the input voltage is attenuated by. I always used 1x. You can adjust volts per division so that any will work. The question is how well the inputs to the scope are protected against high voltages, something built into the scope in my experience. If you have a huge spike it just may be mostly off the screen if you have a low volts per division selected in order to see what you're really interested in seeing. If you want to squash a brief spike you should be able to wrap a wire around a ferrite donut and clip one end to your probe and use the other end as your probe...

 

[xjwmx]

I might use a 1000x probe if I was working with 1000v and I wanted it to appear as a tidy 1 volt per division on the scope. There probably aren't a lot of scopes you could just turn down to make it work. It would have to have a 1000v per division setting using a 1x probe.

 

[pamcopete]

So 10x and 100x probes aren't bad but they want a bit O cash for 1000X probes I guess that's why they include an "inductive type" probe that clamps on the plug wire. Thanks for the hints so far!

The 100X probe is all you need to look at the primary of the coil. Looking at the secondary with the clamp type probe is fine, but you won't see the same detail as the primary view and the secondary wave form is not just a mirror image of the primary. I would not rely on the built in Voltage limiter as it will probably work by clamping the voltage to some predetermined value thus distorting what you are trying to see.

 

[xjwmx]

Ha. ha. I was googling Heathkit scopes to see if I could find the one I said I bought for $20 back when --- here it is at the bottom of the page:

http://digitaloscilloscopes.net/oscilliscope-probes/

I never used it for anything except one time I used it to set the bias of an old Fender tube amp. I got it in the early 90s from a TV/radio repair shop and had it in storage until just a couple years ago when Mom had her big yard sale.

The article happens to be about probes, and there might be enough there to let you make your own special probe. What probe depends on what you want to see - if you wanted to measure the 400v spike then you'd need an attenuating probe. If you were interested in the time scale instead then you could ignore the spike, just be aware it's there and that you might see it clipped. Nothing else is going to look like a spike that's flat on top, so you know what it is and can ignore it.

I haven't needed a scope in a long time - my current work up here in the wilderness is with breakers, 480v, induction motors, "starters", "heaters", aux contacts, and the occasional VFD strung together using electrical schematics, rather than electronic ones. Whole different realm and new to me and sort of fun. Not as fun as being in a cubicle with scopes and emulators and a human factors models though. Maybe as fun, but a lot dirtier

 

[xjwmx]

From the article it looks like inside the attenuating probes is basically just a voltage divider. Google voltage divider to see how to select the two resistors, and there you go. Some of the expensive probes you're looking at might be intended basically for scientific use or high frequency use, with a lot of compensation for this or that built in which you don't need.