Do you mean the vibration measured nt the component (eg the engine, or the wheel), or do you mean the vibration measured on the body, as a result of those excitations?

Cheers

Greg Locock

Thanks for quick reply.  

In answer to your question - the body.  

OK, I was afraid you were going to say that! The only exact figures I know by heart are commercially sensitive, but if you can hang fire for 6 days I'll get some averaged stuff from other cars. Which area of the body are you interested in? IP, steering column, seat track are all we routinely measure. What engine configuration are you interested in? What sort of car (roughly)?

A quick answer in the meantime is that the vibration in the car is around the 24 hour comfort limit for human body exposure.

Cheers

Greg Locock

Explaining my application will no doubt help.  I have a piece of lab equipment that that I plan to take in a car to do some work.  It can not be operated in measurment mode when the car is moving because of vibrations.  There are times when the operator forgets to set instrument in standby mode and this creates an adverse instrument condition. I was investigating the specs in order to program a circuit using an on-board 2 axis acceleromter chip/microcontroller to sense car motion and aotmatically put the instrument in standby mode.

Thanks for your help in this matter.

OK, that is a lot clearer. Where's the lab gear carried? If it is strapped to the seat (say) then it gets additional isolation, at most frequencies, whereas if it is bolted to the floor then it's another thing entirely.

I can't help feeling that in this case there is a simpler solution - picking up the speedo drive, so when the car starts to move the instrument shuts down.

Oh, do you want the thing to work when the engine is running but the car is in neutral?

Cheers

Greg Locock

Greg,

The instrument will be sitting on the floor, not bolted to it.  Since any number of vehicles can be used, integrating it into each car directly adds complexity.  All I am looking for is rough order of magnitude numbers (ROM).  I plan to go out and make some measurements with prototype board, but the ROM numbers would be helpful in programming the firmware and preliminary circuit design.  

Bill

Fine. Roughly 1 mm/s, rms, 5 hz-250 hz. I'll get you a better number on Friday. Do you need to differentiate between engine  running in neutral, and when the vehicle is travelling? It can be quite difficult to tell the difference.

Cheers

Greg Locock

What about this solution--
a fore-aft accelerometer (or a set of accelerometers) which actuates the standby mode. A single fore-aft acceleration beyond, say 100 mm/sec^2 (0.01 g) would cause this to shutoff.  My logic for this is the following--in order to drive the car, there must initially be some non-trivial fore-aft acceleration.  When the instrument feels that the car is starting to move, then it will shutoff the device.  Don't worry about average 'drive' accelerations, just worry about the initial acceleration that the undergoes when it starts to drive.

Three potential issues which I already see, but which may not be a big deal for you:
1) Is the damage already done once that initial acceleration occurs?
2) This presumes that the fore-aft driving acceleration is sufficiently higher than your machine's general in-use acceleration environment.  I presume this to be true based on your discussion, but that is yours to confirm.
3) Your initial statement was that you wanted to detect the fact that the engine is running.  You have since stated that the concern is actually the car in motion.  This proposed solution focuses on the car in motion.  This would not turn off the car for the non-moving engine running situation.

And Greg, throw in your input on my solution.  I think it holds water, but if I've overlooked something, I'm quite sure that you'll pick up on it (and I mean that as a sincere compliment).

Brad

Gentlemen,

Thank you for the inputs.  To answer Brad's questions,

1.  No, instrument will not be damaged.
2.  I am fairly certain the in-use acceleraton environment is lower than acceleration when driving.  I was planning to measure at rest, engine running no movement and car moving since the firmware can be used to look at a relative change in either frequency, amplitude or both instead of a absolute value.  This typically provides a lower false alarm rate in other measurement methods I have used in the past.
3.  I am interested in a moving vehicle.  In reviewing my original request for input, I was looking for any available data either moving OR engine idle without moving just to get started on my feasibility path.  I thought someone could point to a site with a tabulation of data on either situation.  

I want to thank you both (Greg and Brad) for the inputs you have provided to my questions.

Greg, (or Brad )if you have any other ROM type data and are willing to share it, I would appreciate it.


Cheers

Bill