GreigM
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| posted on 18/8/09 at 03:52 PM |
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Using multimeter to measure rpm
I think (hope) my tacho is reading wrong, so would like to get a true reading from the engine (fireblade engine) as to what the rpm are - so if anyone
has done this and can give me tips, I'd very much appreciate it....i.e. where to stick the probes, what kind of reading I'll get and how
to convert that to rpm.....
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MikeRJ
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| posted on 18/8/09 at 03:56 PM |
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Unless you have an automotive multimeter with RPM facility then this isn't really possible.
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MakeEverything
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| posted on 18/8/09 at 04:02 PM |
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Depends how its wired.
If its connected to the positive on the coil, then the voltage should be relative and directly proportionate to the RPM.
If its inductive, then the pulses will need to be calculated using the pre-programmed algorithm inside the rev counter, whatever it might be.
Hope this makes sense.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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BenB
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| posted on 18/8/09 at 04:34 PM |
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You can get cheap optical tachos off Ebay for 20 quid or borrow someone else's. Little reflective sticker on the front pulley (or some other
rotating thing) and jobs a good'un.
With a plain vanilla multimeter there's no way of checking without fabricating a frequency to voltage converter or other bit of electrickity.
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Dangle_kt
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| posted on 18/8/09 at 04:36 PM |
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http://cgi.ebay.co.uk/MICRONTA-HAND-HELD-DWELL-TACHOMETER_W0QQitemZ160355504559QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item2555eed1a
f&_trksid=p3286.c0.m14
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MikeRJ
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| posted on 18/8/09 at 05:15 PM |
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quote:
Originally posted by MakeEverything
If its connected to the positive on the coil, then the voltage should be relative and directly proportionate to the RPM.
Connected across the coil the average voltage will vary with RPM if it's a constant energy electronic system (won't work with points or
transistor assisted) but the meter may not like the 200-300 volt spikes!
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GreigM
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| posted on 11/9/09 at 10:14 PM |
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So I got hold of an automotive multimeter and can get a reading, but at idle it seems to indicate around the 500-600rpm range, which for a bike engine
would seem to be low...this is with the multimeter set on 4cyl - should I simply double this number for a bike engine? Is there a reason the number
would read low (I'm assuming my car doesn't actually idle at 500-600 rpm)?
I suppose at worst case I could warm up the engine and see what reading it hits the limiter at - just a bit of a noisy exercise....
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matt_gsxr
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| posted on 11/9/09 at 11:55 PM |
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hey there,
I have a UT105 multimeter. This is a basic multimeter that you can get from Maplin. It is well made, and also has some automotive functions that
include RPM. It is good value (£25) in my opinion.
On my bike engine (gsxr1100 running wasted spark) if I connect between the earth and one of the coils and set the multimeter at 4cyl then I get an RPM
reading that is half of the true RPM.
I think it expecting a single coil that would pulse for every spark event (i.e. 2 sparks per rpm of the crank for a four stroke engine).
To get it to read properly you can connect it between the two coils, switched side (one side is always at 12V on mine and the earth is switched, this
might vary on different models). This gives the correct number of triggers per crank rotation.
This seems to do the job for me.
Alternatively just double the value on the display in your head.
Matt
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GreigM
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| posted on 12/9/09 at 06:10 AM |
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matt - many thanks for this, its the same model I've got from maplin and this sounds exactly what my problem is...nice to have my suspicions
confirmed.
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