Accel/Force transducer combination to measure driving point

[bjpil]

Hello,
I am trying to set up modal test using a shaker with a rated output force of 7lb pk. I am in the process of finding a force transducer to mate up to the stinger and test part. Does anyone have a recommendation for a force transducer? Most of the equipment that we use are from PCB. Should I be using an integrated force/accelerometer transducer to measure the drive point or is this really necessary (cost being higher vs. simple force transducer)? If so, why?

Thanks in advance,
BJP

 

[IRstuff]

But don't you need to measure the acceleration anyway?

Don't you take the accelerations from the remainder of the unit under test and divide out the driving point acceleration?

TTFN

 

[bjpil]

IRstuff,

I will have other accels mounted to the part. The question I was woundering about is what does the integrated accel at the driving point (force transducer) do for me that the other accels would not?

Do I need to divide out the acceleration to get proper results? I just assumed it was like impact testing where all you need is an input force and an output (accel, velocity, disp).

BJP

 

[IRstuff]

I guess it depends on what type of testing you do.

Most of the stuff I've seen required adherence to a test standard that was usually expressed as an acceleration/frequency curve.

On top of that, if there are resonances, we would divide out the base acceleration to determine the transmissibility curve.


TTFN

 

[GregLocock]

B&K sell (or at least sold) a nice little impedance head. I'm not sure if it is good for 7 lb peak force, but that sounds fine.

The reason you might need one is that the driving point FRF can be sensitive to the errors in orientation and position (especially) associated with using a normal accelerometer alongside the force transducer. This is particularly the case for driving sheet metal and so on.

The way to decide whether you need one is to do a survey local to the force transducer, if your repeatbility is good then you will probably get away without one. Another clue is if your DP FRF does not obey the phase rule, ie phase from 0 to 180 only

I've never need one.



Cheers

Greg Locock

 

[bjpil]

IRstuff and Greg,

Thanks for the help.

BJP