Engine RPM To PLC ????

We are doing some R & D and I was wondering how some of you experts might get an engine rpm measurement to a high speed counter card on a plc. The pulse can be from 5 -24 vdc into the hsc.

I was thinking about maybe a CT with a signal conditioner on a single plug wire or maybe something on the coil wire.

This would have to fit most vehicles (electronic and point distributors) so I don't know how I could interface directly to the distributor electronics.

Does anybody know of a manufacture that makes a CT specifically to fit around plug wires?

Thanks.

Put a prox on a notch in the crankshaft. I don't think you could use a CT on a sparkplug wire, lotta juice in there. On large electric motors (500-5000HP) I've done this with good results.

http://www.bently.com/prod/products/transducers/proxprobes.htm

Hi Zman,

Some alternators on engines have a "W" terminal that should be able to give you a pulse at 12V/24V (depending on your engine battery setup.) This terminal is commonly used to drive a rev counter on the dashboard, I would have thought you could adapt this relatively easily to provide an input into your high speed counter input.

Cheers,

Lee

Thanks guys. Access to the crankshaft would not be feasable.

I will check out the W terminal on the alternator, but I would run into trouble if an alternator did not have this feature.

I was thinking along the lines of the same thing that a timing light uses to clamp around a spark plug wire and run that into a signal conditioner to provide the 5 ~ 24 vdc to the hsc.

I would use a prox on any rotating part with a projection. For example, the bolts on a vibration damper would work. If you had a good enough prox and a fast enough input you could use the teeth on the ring gear.

Red Lion has some great proxes for this kind of thing, and I've had good luck with them in the past.

Another option that I have used on rotating equipment is a reflective photo switch. Most suppliers can sell reflective tape that you can put around any shaft or on the face of any sheave. I used Turk successfully this way on one applicatoin.

I have actually fed the primary coil signal on a single cylinder honda 13hp engine into a plc input. The voltage was 18 volts. It was from the prox sensor at the crank.

I have used Red Lion prox sensors in a variety of applications and some of them work right nice on the shaft keys.

You should be able to mount a prox somewhere.

I was looking for a more generic solution that could me used on a variety of makes and models.

One thing that most cars have (besides diesels) is a spark plug wire.

I don't want to have to figure out how to mount a prox to detect rpm on several models of vehicle.

From what I can tell I need an EM sensor. I am assuming EM stands for Electromagnetic.

I wonder how many manufactures supply a pulse out of their alternator??

Still searching....

You really shouldn't need a sensor at all. What you really want is the same signal that is going to the tachometer in the instrument panel. You should be able to find the appropriate signal at the distributor or the Engine Control Unit for most vehicles. Maybe communicating with the ECU is an even better choice? A diagnostic interface to a PC is pretty common tool these days.

If you use the signal from the distributor (traditional points), I'd expect a 4 cylinder engine at 6000 rpm would be putting out pulses at 200 hertz. (Each cylinder gets a spark on every other revolution). Not all that high a frequency. Watch out for an inductive kickback in the 300 volt range.

If you use an inductive probe on a spark plug wire, it's only 50 Hertz. Since you are only measuring pulses from one cylnder, the same setup works fine for 4, 6 or 8 cylinder engines.

The bottom line here is look at automotive testing equipment rather than industrial sensors. You should be able to get what you want there.

Good luck,

Outrage said:

Hi Zman,

Some alternators on engines have a "W" terminal that should be able to give you a pulse at 12V/24V (depending on your engine battery setup.) This terminal is commonly used to drive a rev counter on the dashboard, I would have thought you could adapt this relatively easily to provide an input into your high speed counter input.

Cheers,

Lee

Click to expand...

---- NEWS FLASH ---- NEWS FLASH ----

Done some further reading and came up with this - sorry if i've led you off in the wrong direction!!

""You may be in luck and able to use the alternator in the Caddy. See if it does have the "W" terminal. It has, well, a "W" right next to it on the back of the alternator, if its present. The "W" terminal provides an alternating current proportional to engine speed. It is also one of the inputs to the upshift light, if the car has one of those.""

Cheers, (Humbled!)

Lee

you can use colour sensors by sticking a specific colour on the rotor shaft, connect this input to the high speed input card

before selecting Input card please make sure it is capable to read high speed Input, otherwise use Input Immediate Instuction to read the same

If the intention is to make something which can be used on most cars I would try to avoid using the ignition system for this. Aside from the obvious case of diesel engines many modern petrol (gas) engines have neither a distributor or plug leads. The ignition coils are fitted directly to the plugs and are fired by an engine management system. Most industrial engines use a magnetic pickup to sense flywheel ring gear teeth so this approach is well tried and tested.

Andybr

In terms of portability the reflective tape and optical switch should be good. Every engine has a sheave on one end for running alternators and water pumps and such. This also relives you of the need to have the switch mounted within fractions of an inch of the pickup point as is required with a prox.

Just about all engines have a magnetic pickup option, the hard part of this will be finding one specific component that will work with all engines, as mentioned some have distributors and some do not.

I agree rsdoran. At the moment I have an old timing light that I have torn apart. I am trying to figure out where I can get a 5~24vdc pulse off the circuitry.

It looks like I may be able to get it at the primary side of a high voltage transformer that powers the gas timing bulb.

I will experiment and try to reply Monday.

Thanks for the ideas guys.