Mains Powered Oscilloscope for Automotive testing

[Ted123]

Hi

I have a mains powered 240 vac benchtop oscilloscope.

Its this model.

In the manual it says it can take up to 300 volts DC

I known Dave had the video about earth ground loop and safety.

Would a benchtop oscilloscope like this be suitable for automotive testing such as MAF sensor testing, ignition coils , oxygen sensor , fuel pump voltage etc ?

I'm new to oscilloscopes so didn't want to do anything unsafe.

What about putting the ground on the 12 volt battery terminal and test probe to positive and testing charging voltage on car battery ?

https://www.jaycar.com.au/100mhz-digital-oscilloscope-with-40k-memory-depth/p/QC1936

[slavoy]

The car is a floating voltage source, so there is no problem here.

In the manual it says it can take up to 300 volts DC

The 300 V rating applies to the input itself directly. When you use a 10x probe (which you should practically always use), you divide the input signal by 10.

Of course, you don't want to measure coil voltages directly with a standard probe. Use COP (Coil On Plug) adapters, for example.

Would a benchtop oscilloscope like this be suitable for automotive testing such as MAF sensor testing, ignition coils , oxygen sensor , fuel pump voltage etc ?

It will get the job done, but generally, portable oscilloscopes and scopemeters are more convenient for such work.

[Ian.M]

One big issue is if you use a car lift.  Normally a car will be fairly well insulated from ground by its tires so there is little risk of scope damage provided you respect its input ratings and don't try to put the ground clips on electrically 'hot' terminals.  However when its on a lift, the chassis rails or unibody jacking points may be in electrical contact with the lift, which has its frame electrically grounded for safety.  You therefore have a ground loop through the lift and the scope probe ground leads, and if the point you have clipped probe ground to is at a different voltage to chassis, you risk a high current through the probe grounds that can damage your scope.  e.g. if you try cranking the engine with probe tip and ground across the battery, voltage drop in the battery ground strap is likely to force a large current through the probe ground.

[tatel]

You don't need a 400 bucks device; and even if you want to spend that amount, you could probably get a battery powered device. I think you'll find this thread interesting:

https://www.eevblog.com/forum/beginners/oscilloscope-recommendation-426883/

[Phil1977]

To say it clearly, using a scope on a vehicle grid is much more a risk for the scope than for the operator - it´s not fair to say nothing can happen with 12V, but you don't need to care so much about getting shocked - of course avoiding high-voltage parts like ignition or HID-lights.

The risks for the scope are mainly driven by back-EMF. Cars often have inductive loads like relays coils, solenoids, pumps etc... If these are switched off you can have voltage spikes of 200V nominally or much more if something is defect. This can easily kill an input stage of a scope in a sensitive range.

I think playing with a mains powered scope on the car is fine as long as you

- keep scope GND on the car chassis level - just don't connect the crocodile clip of the scope probe anywhere else than on the car chassis level.
- keep safe distance to ignition or headlamp high voltage
- do not use very sensitive input settings (like AC 10mV/div or probes with 1x) on the power lines

I´m very ambivalent regarding the small battery powered toy scopes. If you really know what you want to measure they can be quite fine, but if you are "probing around" the acquisition rate and display quality of the serious devices can not be replaced.

[CaptDon]

The comment about the 10X probe was a bit misleading, Your scope input was rated for 300V. The posters statement said with a 10X probe you divide by 10, what, and think the input is now only 30V rated....Bogus. The probe will reduce the voltage going into the scope by 10X (and make sure the probe compensation is adjusted correctly!!) but you will still be limited by the probes maximum ratings which may also be 300V OR LESS!! The maximum voltage allowed to be applied to the probe also gets reduced as the frequency or high frequency equivalent transitions go up. The 10X probe may have very severe limits as you approach 60 to 100 MHz!!

[G-son]

The 10X probe may have very severe limits as you approach 60 to 100 MHz!!

Indeed. But for automotive work you probably won't be in the MHz range at all for most work, so not much to worry about. Good to be aware of and keep in mind for high voltage, high frequency signals though.