Old diesel engine - best way to obtain revs

[hab1966]

A project at work requires us to obtain the revs of an old diesel engine located in Turkey! From what i am told, there are no electronics and sensors on the vehicle that will allow me to easily obtain the revs.

Im wondering whether anybody would be kind enough to suggest a method to obtain the revs. We are currently looking at monitoring the alternator signal on the power lines to calculate the revs from the waveforms.

Thanks.

[Steve_D]

Quick search finds
Optical. You put a reflective mark on the pulley or flywheel. Probably nothing more than tippex.

http://www.sensors-uk-transducers-instruments.com/...

http://www.foundrometers.co.uk/products/redpoint.h...

I’m sure there is a hand held sonic device as well but I can’t find anything. You may have been able to do that just by getting someone to hold a mobile phone next to the engine.

Steve

[Snake the Sniper]

If there's a new-ish alternator on it, there should be a w pin on it. That should be usable to feed a rev counter. Otherwise, injector pulses, if measurable should give a good idea.

[BB-Q]

I remember using an adaptor 20 years ago which you clamped around the injector pipe which allowed you to use a traditional timing light.

[stevieturbo]

BB-Q said:

I remember using an adaptor 20 years ago which you clamped around the injector pipe which allowed you to use a traditional timing light.

No doubt still available....but pretty sure these are mega expensive.

Alternator is how OE diesels get the signal for their rev counter on the old engines anyway.

[hab1966]

Thanks for the replies. I think i might have been a little too vague in my initial post.

We have a box of electronics that needs to monitor the engine revs. So i need a connection to some point on the vehicle/engine where i can monitor/calculate the revs. Initially we have been looking at monitoring the +ve battery connection.

However, the 'Snake the Sniper' post got me thinking. Are there more than just the battery connections on an alternator? If so, i guess i should be looking at those, instead of using the battery connectors?

Is there a 'standard' for alternators outputs/connections?

[v8ian]

I would think an easy way would be mark the crank pulley, Tippex or similar and use an indipendent, adjustable strobe, we use them at work, plug in, and the strobe runs you can adjust the frequency infinatly with a calibrated knob, Aim at mark on pulley, tune in the strobe, and this should give you what you want,
Or use one of those little hand held, mechanical tachs that you pun on the end of a shaft,
another way is mount a flying magent on a rotational part of the engine, and use a modern aftermarket speedo, you will need to work out the calibration by running the speedo at a known speed on something else that speed can be varified, and then its just simple maths,
Ian

[Fume Troll]

hab1966 said:

Thanks for the replies. I think i might have been a little too vague in my initial post.

We have a box of electronics that needs to monitor the engine revs. So i need a connection to some point on the vehicle/engine where i can monitor/calculate the revs. Initially we have been looking at monitoring the +ve battery connection.

However, the 'Snake the Sniper' post got me thinking. Are there more than just the battery connections on an alternator? If so, i guess i should be looking at those, instead of using the battery connectors?

Is there a 'standard' for alternators outputs/connections?

I'm confused, what's the positive battery terminal going to be doing? Also most vehicle diesel engines I've seen run the alternator off a belt, so the alternator rpm may well not match the engine rpm...


Cheers,

FT.

[SplatSpeed]

hall effect sensor

[hab1966]

What we have seen when we monitor the +ve battery connection is ac ripple generated by the alternator, on top of the DC generated voltage. We can measure the frequency of the ac ripple and doing a bit of maths allows us to arrive at a rpm figure. However, to do this accurately we need information on the alternator. I would prefer not to have to enter too many variables into our software to give us the RPM figure.

As i dont have the engine here, its hard for me to do any investigation work. We were also considering the addition of sensors to monitor a pulley rotating and use this to calculate the revs.

I just wondered whether there was a simpler method? Further investigation into alternators shows that there are other outputs (not just the battery connection) that i can possibly use.

[Snake the Sniper]

I'd still go with the Q pole on an alternator and (usually) double the frequency to obtain RPM. Easiest, cleanest option that I know of. 1 wire and no faffing about having to adjust a strobe. You could even data log it of required, so no/little user interface required. Heck, attach it to a PDA and have it e-mail you the results!

[Steve_D]

The signal from the alternator would be best for a permanent electronic 'black box' type application.
If the alternator does not have the required connection (W terminal) you need to modify it by making a connection to one of the three windings before the diode pack.
This will give you a signal for every revolution of the alternator then you will need to calculate the pulley ratio to get engine revs.

Steve

Edited by Steve_D on Tuesday 18th March 23:10

[Pigeon]

hab1966 said:

What we have seen when we monitor the +ve battery connection is ac ripple generated by the alternator, on top of the DC generated voltage. We can measure the frequency of the ac ripple and doing a bit of maths allows us to arrive at a rpm figure. However, to do this accurately we need information on the alternator. I would prefer not to have to enter too many variables into our software to give us the RPM figure.

All you need is the pulley ratio. If they're v-pulleys you can get figures you can use for this by wrapping a belt round them and measuring across the outside of the belt. Other kinds of pulley are easier The ripple frequency will be 6 x alternator revs unless it's really weird.

[cabs]

Hi, I have bought an Optical rev counter from www.jaycar.com.au CAT. NO QM 1448, it is listed in the test equipment under digital meters. It is quite cheap and the postage was very reasonable even from OZ!! I just mounted a black disc with a single reflective stripe across its diameter onto the cam wheel and it all worked great!