Tachometer for Inertia Dynamometer.

[Eng1001]

Hi,
I'm currently involved in a project designing an inertia dynamometer. Were looking for a suitable tachometer that we can use to measure the rpm with, it should give a voltage output in the form of an analogue sinusidal signal. This is so we can interphase it with a p.c.
Does anyone have any ideas where i can get one from, is it possible to stip down a scrap car to get one? Initaly it doesn't have to be to accurate because we need one to set up our programing with, later a more suitable one could be brought.
Any advice would be appreciated.
Regards...

 

[FredGarvin]

What you are looking for is any kind of tach generator. Aircraft engines use them quite a bit. Do a search for tach generators and see what pops up.

 

[Carvinos]

there are tachometers available in the market with usb port. you can attach usb to serial port to get the output via serial port so that your coding becomes compatable with the hardware.

 

[mender]

A distributor generates a tach signal; you could get one and hook it up with a belt drive for now and calculate the % compensation needed. Imbedding magnets in a rotating part would also work and be more accurate for the later stage.

 

[DickL]

There are magnetic tach probes that read gear teeth and generate an ac wave with the frequency proportional to the speed. These are often used with both driving gears and with 'dummy gears' installed just for tach purposes. Fairly inexpensive and quite accurate.

 

[Ranger Mike]

i recommend you see

http://www.mcmaster.com/#digital-tachometers/=cm2jd4

 

[HowlerMonkey]

Do you have exposed gear teeth to sample from?

If so, some cars sample the ring gear of the starter for misfire date in OBDII compliant powertrains.

The nissan V6 single cam engine first found in the 1984 300zx (vg30e) was later run to OBDII standards by fitting a sensor that read the "tone" of the teeth of the starter ring gear passing in front of a sensor that is located near the bellhousing flange behind the driver's cylinder head.

It is found on VG30 and VG33e engines on 1996-until discontinued to go with double overhead cam engines...in such applications as nissan quest, nissan frontier, and possibly some infiniti suv and nissan pathfinders.

Just because I mentioned these cars doesn't mean this is where you must look but this is one application where they do sample a steel gear with a sensor rather than a custom shutter wheel.

If your rotating parts have any gears or sprockets, then a variety of sensors will work.

From there it is a function of cleaning up the signal.

I would use the general motors HEI module which will clean up a variety of waveforms into a sweet square wave.

Of course...you could use an entire GM hei distributor that has a tach output wire to do your mechanical to electrical conversion if you don't have a toothed cog or gear to sample from.

If you can access to end of the "axle" that is spinning, a car distributor can be mounted or even something smaller like the modular cam angle sensors used on the fronts of many different engines but are fairly simple in the (again nissan) or infiniti double overhead cam v-6 engines, some 4s, and some v8s.

Many have two signals from them so you can pick which one better suits your sampling rate.

Also...be really careful because there is a lot of energy involved when working with a dyno.

Our roller surfaces speed to over 200mph and tolerate 2200hp and the fury displayed is pretty humbling so try to keep any connections as close to the center of the rotating parts as possible.