Diesel engine speed (rpm) sensor and display instrument 3

[Paulista]

I looked up ISSPRO´s web site and noted that there is a non-alternator-derived rpm sensor and display instrument.

This device seems to be built around an array of sensors that is glued (?) on the flywheel and a pickup located somewhere on the flywheel housing.

It can be fitted to Ford 6.9/7.3, GM 6.2/6.5 and Cummins 6BTA diesel engines, or at least, the online catalogue says so.

ISSPRO´s site has no detailed data on this setup.

Can someone who has actually installed this device offer some input ? Is it more accurate than alternator-derived rpm indicators ?

Has someone also tried ISSPRO´s hand-held rpm indicator that gets its input from a reflective tape that is stuck on the main crankshaft pulley ?

 

[Aquaduct]

Don't know how these small guys do it, but we use a hall-effect sensor that reads teeth on the crankshaft. I'd wager this is the same setup. Much more accurate than the alternator. Literally reading the position of the crankshaft and not the accesory drive belts.

 

[Aquaduct]

It was late when I wrote that. It should have said a hall effect sensor (in the flywheel housing) that reads teeth on the flywheel. Duh. Sorry.

 

[Comcokid]

The common ways for RPM to be measured on a diesel engine is:
#1 - off an ECU tach output.
#2 - off a rotary magnetic pickup device that is tied to the injector pump shaft (sometimes referred to as a 'Tach-Gen'. This couples directly to a shaft or gear via a small flexible shaft or small coupler shaft. Rotary motion inside the pickup moves magnets past coils to produce pulses. The engine must have provisions for this type of pickup for it to be used. Accurate as RPM is measured directly from the engine (Number pulses/rev and possibly pickup point gear ration must be taken into account).
#3 - off a magnetic pickup (coil/magnet or hall-effect) that senses the teeth on the flywheel. This usually is a cylindrical-shaped threaded sensor that is screwed-into a threaded opening in the bell housing to achieve close proximity to the teeth without actually touching them. Good accuracy as RPM is measured directly. Number of teeth on the flywheel must be taken into account to get pulses per rev. Good accuracy as RPM is measured directly.
#4 - by taping onto the AC side of the alternator to count alternator pulses. Least preferred of the methods as belt slippage, and belt wear result in approximate RPM measurement that will vary over time. Pully ratio and pole-pairs on alternator must be taken into account to get pulses per rev.

Not exactly what you were asking for. Isspro being one of the smallest instrument makers may not have tooled for all applications.

Other threads dealing with similar questions.
thread67-80211
thread67-110687

 

[Paulista]

Many thanks to both of you. My alternator-derived RPM indicators suffer from the limitations you have pointed out.

I am interested in item #4 above - would be the simplest to implement, given that a hole would need to be drilled and tapped in the flywheel´s circumferential housing

How close (inches or mm) to the teethed-flywheel is the Hall effect sensor placed ? It probably comes with an adjustable lock-nut, once you have managed to get it to respond.

Are after-market DIY RPM Hall-sensor /display instrument kits available on the market ? Who manufactures them ?

Don´t know if ISSPRO´s is a Hall-effect type, because it seems to pick up info from half-a-dozen or so strips that are cimented to the flywheel disc. Could it be a laser-type device, with the strips made of reflecting-tape ? Dunno !

For a diesel engine in a boat engine-room, Hall-effect would win over the laser-type, just on resilience alone - right or wrong ?

 

[Comcokid]

Most of the #3 types of sensors are of a magnetic-type. These consist of a coil biased by a magnet. As the flywheel teeth pass by, they induce a voltage. The output of the pickup looks like a sine-wave with the frequency and amplitude varying with RPM. It's the frequency that is measured by the tach. At low RPM, the output amplitude is too low for easy use. Hall-effect types are used for RPM measurement where near-zero RPM is measured. However, since engines have idle-speed, and RPM below this is unimportant, the magnetic-type are used for engine RPM.

The tach you use with the pickup will need to have a frequency adjustment range that covers the large number of pulses/RPM of your application (# of flywheel teeth). These tach have a range-selector switch and access to a fine-adjust trimmer. With a shop tach you can dial them in exactly.

A quick visit to the Datcon web site (

http://www.Datcon.com)

and selecting the 'Heavy Duty Sender' link gives a list of possible magnetic-type selections(and also the tach-gen types as discussed in #2). A picture of the magnetic-type is shown as the rightmost picture.

If you fillow the previous-thread link of my earlier post, you will find a list of other manufacturers. I'm not exactly sure what the Isspro device you describe is as I've been out of this industry for a few years now. I don't recall exactly what the air gap requirement is, but you can probably get technical advice from the manufacturer.