Attenuators!

Can someone explain to me how you choose which attenuator to use? If you're not sure what the voltage spike is going to be on an ignition system do you just go with a 20:1? instead of buying both can I just get away with always using a 20:1? What's the drawback...less detail?

X20 is pretty much the standard for automotive work, the loss of resolution compared to an X10 isn't a major issue. I have even tried X100 and still got useful captures.

Exploring this topic with a few test demos might be an idea next time I look at injector I will do some captures

It, really, depends on your scope. An Ignition coil control can spike up to 400 volts. Snap-on Scopes can handle a voltage spike of 400 volts, so no attenuator is needed. The Picoscope 4425 has a 200 volt limit, so a 10:1 attenuator is plenty.

Some times a result can be a surprise --- the simplest test was alternator ripple I used the cheap and cheerful Owon VDS1022I
I offer no explanation but they are identical --- might be different with a fast 12 bit Pico

Channel 1 Red with x20 Attenuator
Channel 2 Yellow plain jane 1:1 test lead

This forum never ceases to amaze me. Thank you guys for the information and support. I never heard of owon before. I bought a u-scope to start out with and I've been looking at the hantek, but this owon looks like it might be a good starter scope as well. I noticed the max voltage on the owon is 400 volts. How exactly does the ratio work for an attenuator? A 20:1 will protect your device at 20 times the amount of rated voltage? So max input voltage is 400...with a 20:1 attenuator you're protected up to 8,000 volts (400×20)?

400v is the isolation voltage that is the voltage the scope can experience without zapping your PC. With a a 1x probe you can have a 50v dc screen I checked this by measuring the peak voltage put out by 24v booster battery charger which puts out a whacking 42v peak !!!! I am pretty sure the scope would survive direct to a normal gasoline fuel.injector but I would want an attenuator for a coil primary or diesel. Injector or piezo injector.