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Brymen Crest and Min/Max Function VDC Capability

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Fungus:

--- Quote from: joeqsmith on September 19, 2022, 04:36:28 pm ---If my cars go "click",  I know the battery is dead.   No need for anything too fancy.  If it dies often, I would be looking for the current draw.  I seem to get about six years out of them. 

--- End quote ---

Yep, it's a car FFS.

You don't need to know the exact dip to two decimal places, you just need to know if it dips badly during starting.

7V or 6V? It doesn't matter. You just need to know if it happens or not.

Plus: No matter how accurate a meter's min/max function is it's not going to tell you how long the voltage dipped for or the shape of the dip. That's far more important than knowing the dip voltage to several decimal places.

What's needed is a graph of voltage over time. Only an oscilloscope can do that.

Get the right tool for the job.


--- Quote from: joeqsmith on September 19, 2022, 04:36:28 pm ---bdunham7's scope shot is nice.

--- End quote ---

Yep. Way more useful than a single number on a multimeter.

bdunham7:

--- Quote from: joeqsmith on September 19, 2022, 04:36:28 pm ---If my cars go "click",  I know the battery is dead.   No need for anything too fancy.  If it dies often, I would be looking for the current draw.  I seem to get about six years out of them. 

--- End quote ---

And when that happens in an airport parking lot after 14 hours of security, customs, gate changes and mediocre premium seating in an airplane not of your choice, you may wish you'd been more proactive.


--- Quote ---bdunham7's scope shot is nice.  With a better scope, you should be able to see the compression stroke of each cylinder.   We would expect them to be balanced.    Maybe some monkey math applied to determine a weak cylinder.   Certainly we could see if one was totally gone with a hole in it.   :-DD

--- End quote ---

Better scope?  It's ancient but in some ways still unmatched, IMO.  The Fluke 98 has that compression function as well, implemented in voltage or current configuration with a nice trace or 'relative compression' bars displayed.  Voltage mode seems to not work very well with modern cars and I don't currently have an appropriate amp clamp.  It's good enough to spot single burned exhaust valves on V8 engines that don't have very obvious running problems.

bdunham7:

--- Quote from: armandine2 on September 19, 2022, 04:28:03 pm ---Fluke 98 was re-badged as the Bosch PMS 100

Looking through my copy of Bosch's Engine Test: Fault detection with the oscilloscope they don't mention the crank test - which might indicate that there is some difficulty in the interpretation of trace?

--- End quote ---

I've used the feature many, many times and if it gets a good signal  it gives you your choice trace or bars and both are typically quite easy to interpret.  Obviously since you aren't directly measuring compression, there can be things which will interfere with the process.  b/t/w I don't know if the Bosch PMS100 used the same firmware as the Fluke 98, I think the Bosch was an OEM-specified tool for some makes/models and it may have had different specs as a result.

armandine2:
"easy to interpret" because the car starts or doesn't?"

bdunham7:

--- Quote from: armandine2 on September 19, 2022, 07:14:10 pm ---"easy to interpret" because the car starts or doesn't?"

--- End quote ---

No, easy to interpret as in "oh look, cylinder number 3 is down 40%, that explains the rough idle".  Provided, of course, that you can do a synced test, otherwise it is "oh look, one of the cylinders is down 40%, I wonder which one?"

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