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.

[Ted123]

Thanks all for the input, sounds like that cheap Hanntek setup is the best or a dedicated scope for automotive with the ignition paddle etc.

[Phil1977]

The Hantek can be okay if you exactly know what you want to measure and it´s in the scope (pun intended) of the instruments resolution - which is really bad compared to lab-grade instruments.

A bench scope is literally showing thousands of waveforms where most cheap USB scopes just show one. Bench scopes have lots of algorithms to visualize a bunch of peaks overlayed to each other to simulate the display of an old-style analogue CRT scope. This is not necessary to work on CAN or automotive sensor lines. But it makes a huge difference in

- finding disturbances
- having fun by "seeing" electrical signals

I´d recommend:
- take the Hantek if you want to proof that some signal is present or not present
- get a real scope (tm) if you feel some curiosity about the electronics in the car

[joeqsmith]

...
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.
...

I wonder how often it would ever get used.   I can think of two times where I used a scope to troubleshoot a vehicle problem.   Most electrical problems I've solved with a basic DMM. 

[Ted123]

What sort of simple things did you fix with the Multimeter , are you talking about stuff like standing battery voltage and alternator output or more complicated stuff ?

[rich t]

FWIW I use my $18 Flea-Scope and a laptop for automotive testing...  You can see a bunch of examples here:

https://www.zx6r.com/threads/running-with-the-tank-off-ignition-injector-adventure.120654/?post_id=1915926#post-1915926

You can even use a phone to control the Flea-Scope if you don't mind the small screen.

With a 10x probe, even if you exceed the maximum input voltage (+/- 60 volts), you won't be damaging the scope circuits (unless possibly you measure the spark directly?) -- I measure the input to the stick coils rather than the output.

Having both the laptop and vehicle floating makes everything pretty safe and convenient.

[slavoy]

Thanks all for the input, sounds like that cheap Hanntek setup is the best or a dedicated scope for automotive with the ignition paddle etc.

The simplest OWON HDS272 is imho the best low cost option for car repairs. Lacking only protocols decoding. Other than that it is a proper scopemeter built to that task.

[tatel]

Are you still thinking about  that benchtop scope?. If so, think about getting some cart. Otherwise, BNCs, etc, could be easily damaged. An automotive workshop is different from an electronics lab.

People that works in it usually prefers Picoscopes. You need also a laptop to work with any USB scope like a Picoscope, but often you need a laptop because any non-vintage car will have an OBDII connector anyway.

You don't need anything fancy to do automotive work, 10 MHz would be plenty. You can do useful things with even the cheapest toyscope in the world, DSO138.  People uses FNIRSI scopes, Zeeweii, Owon like slavoy mentioned in the previous post. You would want to have two channels to look at crank and ignition simultaneously. You have videos linked and some pretty good info about automotive oscilloscope work in the thread I linked previously.

If you are stuck with that benchtop scope, put in over a cart.

[Ted123]

What does "put in over a cart" mean ?

[joeqsmith]

What sort of simple things did you fix with the Multimeter , are you talking about stuff like standing battery voltage and alternator output or more complicated stuff ?

Most components can be checked with a DMM.  Same for the wiring and connectors.  More complex problems, I have some way to connect with the ECM. 

Not being a mechanic by trade,  I only really work on my own engines.  Most friends who are use the MODUS (sp?).   There have been three times I have used a scope to sort out a problem. 

One time my car would change to traction control randomly and apply the breaks.  All these electronics and crap firmware are dangerous.  Problem didn't seem like a wheel bearing, and at a quick glance the sensors appeared fine.  I ended up tapping into the wheel speed sensors harness with my old analog scope in the front seat with a DC/AC inverter.  Saw how the pulses had an odd shape.  The software would filter all this to a degree.  Above a certain speed, they must change their algorithms to enable the traction control.   A closer look at all the tone rings, one had split.   New replacement rings were about double the thickness.  That split created just enough gap that the firmware would see it as a problem, only above a certain speed, then they would slam on the breaks.

I also drive motorcycles.   The last repair I worked on was an instrument cluster.  Here you can see my homemade simulation tool that I use to test the clusters and ECMs.   


Fluke allowed me to convert one of their automotive oscilloscope VHS training tapes and put it into the public domain.  Things were much simpler then...

[Ted123]

Interesting information, are you able to repost those video links as they didn't come through in your post

[tatel]

What does "put in over a cart" mean ?

Something like that?

https://www.fetra.de/en/products/special-trolleys/workshop-cart

[G-son]

I wonder how often it would ever get used.   I can think of two times where I used a scope to troubleshoot a vehicle problem.   Most electrical problems I've solved with a basic DMM.

Scopes can be very useful for a lot of automotive diagnosis work, it's absolutely not limited to electrical.

We've been looking at ignition waveforms since probably the 1950s, it can find a bunch of issues in the ignition system (obviously), but less obvious it can point towards leaking valves (the flow inside the combustion chamber towards the leak upsets the spark), a cylinder running lean (partially clogged or non working fuel injector), cylinder running rich (injector stuck open), low compression issues (lower voltage spark required, with increased spark duration as a result compared to other cylinders) and so on - and that's just some information we can get from hooking the scope to the ignition system.

If we look at battery voltage during cranking (or current if we have a suitable probe) with fuel/ignition disabled so the engine can't start we can see the fluctuations in voltage/current due to the varying load on the starter as each cylinder is on the compression stroke, if the compression is not the same in all cylinder we instantly see one cylinder pulling less current - we have detected a low compression issue in about a minute, just removing the spark plugs for a conventional compression test takes far more time, and if it's one of those horrible modern cars that requires a lot of disassembly to access all spark plugs this may save hours - we still need to perform more tests to figure out why the compression is down, but we have gone a long way in a short time narrowing down where we need to look for problems. Add a sync signal to (for example) cylinder number one and you can figure out exactly which one has the problem.

The battery voltage/current while cranking can also detect a starter about to fail due to worn brushes, as the brushes loose contact intermittently the current will pulsate horribly. A worn fuel pump behaves similarly, but there you really need a suitable current probe to see it.

A bad diode in the alternator will cause a lot of ripple that may interfere with sensor signals, causing strange issues hard to diagnose with other tools - the alternator may still charge to the correct voltage, so hard to detect with a multimeter.

A simple, cheap pressure pulse sensor made out of a piezo speaker (pulled from basically any electronic device that beeps) lets you look at pressure pulses. Connect to intake and you may see if one cylinder doesn't draw in air (failed lifter not opening valve for example), one cylinder pushes air back into intake (leaking valve for example), similar possibilities with the sensor in the exhaust, put it where the dipstick goes and you see pressure due to leakage past a piston, connect to the cooling system and you see pressure pulses in the cooling system from a bad head gasket...

Just a handful of examples, the possibilities are really endless.

[rich t]

Quote

If we look at battery voltage during cranking (or current if we have a suitable probe) with fuel/ignition disabled so the engine can't start we can see the fluctuations in voltage/current due to the varying load on the starter as each cylinder is on the compression stroke, if the compression is not the same in all cylinder we instantly see one cylinder pulling less current - we have detected a low compression issue in about a minute, just removing the spark plugs for a conventional compression test takes far more time, and if it's one of those horrible modern cars that requires a lot of disassembly to access all spark plugs this may save hours - we still need to perform more tests to figure out why the compression is down, but we have gone a long way in a short time narrowing down where we need to look for problems. Add a sync signal to (for example) cylinder number one and you can figure out exactly which one has the problem.

This is awesome!!!

[SteveThackery]

My Rover 75 has the compression test @G-son describes actually built in to its ECU. You activate it via the OBD2 port and the appropriate software on the PC.  As @G-son says, it operates the starter for a few seconds, but without injecting any fuel. Obviously it won't detect the situation where all cylinders are equally low.

[joeqsmith]

We did something similar, running an FFT on the tone wheel to measure the differences in each power stroke between the cylinders.  We could then tune each cylinder for better balance.  It could also be used as an early warning that something was beginning to fail.    No scope needed as it was built into the fuel system.

Normally, for my home engines if compression is an issue, I pick it up in the exhaust temps, using my finger as a sensor.      I also use the licked finger detector for other problems as well. 

One thing I have thought about making over the years and never got around to it was an electronic degree wheel to set the cam timing.

[G-son]

We did something similar, running an FFT on the tone wheel to measure the differences in each power stroke between the cylinders.  We could then tune each cylinder for better balance.  It could also be used as an early warning that something was beginning to fail.    No scope needed as it was built into the fuel system.

I think many modern engine manage ment systems use the crank sensor signal (from a tone wheel somewhere at the crank) to detect misfires, and any oscilloscope that can show frequency as a graph can do the same if you don't have the equipment to access such functions through the OBD-system (non-automotive picoscope oscilloscopes can use a math channel for it, the automotive versions have a dedicated function with a few more bells & whistles). You can clearly see the crank slow down as each cylinder is under compression, and then speed up when the cylinder fires. If one cylinder misfires completely the speed will just keep dropping until the next cylinder fires, smaller problems will be less obvious but still there when you know what to look for.

Funny thing is these engine management built in misfire detection systems can be fooled. Imagine how much head scratching you get when something like a bad universal joint provides a lot of resistance once per rotation, making the engine (and everything else) suddenly slow down and the engine management interprets it as a misfire. No matter how many spark plugs, ignition coils, fuel injectors, compression tests, fuel pumps and whatever else you throw at that engine it will keep complaining about random cylinder misfires when driving. Possibly until the u-joint fails completely so you really have to replace it, and like magic your misfire issues are gone.

[joeqsmith]

That wouldn't surprise me.   My motorcycle simulator supports individual cylinder control but the ECM is pretty basic. 

https://youtu.be/786ELUSXLP8?t=160