hi friends :

when i used seismec probe to measure absolute bearing vibration ,how long i must put the magnetic probe temporary ?
is it 2or 3 or 4 ... sec or min?

i am appressiate for any one help me
best regards

Hi..
What's your problem?
Do you face the skislope too high?
For skislope problem, the time required depends on your sensor settling time.
If it is about how to set time required for acuiring vibration data, it depends on your Fmax, number of lines set, windowing type and overlap set.

Regards,


rahardi
rahardi@gmail.com

Settling time for my general purpose accelerometers in room temperature environment takes something like 10 20 seconds. Then I start the actual measurement. My favorite general purpose measurement takes about 1/2 minute, but I have to select my filters and paratmeter sets carefully

I find it very usefull to view the live spectrum display during the measurement. It you are taking 4 to 8 spectra average, then you will know if the measurement needs to be repeated. Generally most problems occur when the accelerometer magnetic base is mounted quickly or with impact, when the actual vibrations are low, and when measuring low frequecies (low Fmax).

Walt

Hi..
Assumed, the problem is skislope :
CSI gudence (from Application paper):
"Allow 3-5 seconds settling time for accelerometers that have been snapped down into position or impacted in any way".
And also you can live dispaly your measurment into time waveform & spectrum together in one screen, and monitor the timewaveform stability. If signal has too much fluctuation, do not capture it...replay acquiring data.


Regards,


Rahardi
rahardi@gmail.com

I watch the overall "live time" when collecting data. If it is stable, I punch the button.
If I'm on a normal route, collecting all the GOOD data I can in as short a time as possible, I set my box for 3 sec. settling, and then watch overall as stated above. Usually about 5 sec. per reading before punching button. Shame on you if you're putting the transd. on so hard it takes longer
Ski slope can come from things other than punching button too quickly. Very low filter (< 20) with a high res. transducer (LLLOOONNNGGG settling time), Cable problem (usually with ground)which is not uncommon, or a cracked crystal in transducer. I'm sure there are more, these are just the ones I've dealt with.

Edit: A saturated transducer will also give a big ski slope.

Dave

This message has been edited. Last edited by: RRS_Dave,

Dan, what type of accel do you use? Was that Ten to twenty seconds to settle? What type of environment?
That just seems like a very long time for settling.
I use Commtest equipment and they have an internal settling time that does not allow the machine to take the data until it "sees" that the sensor has settled. Most of the time it is probably less than 3 seconds. Only on very high vibrations asy approaching ONE INCH PER SECOND does it take longer somtimes up to 10 seconds.

the skislope problem could be due to the way the transducer was mounted or a faullt in the transducer or cable:
transducer faults :
1- electraical fault : trasducer settling time , when power is applied to the transducer the signal will become un stable while the circuit settles - spectrum will have ski slope.

2- thermal effects: when the sensor movies from a cold surface to a very hot surface or vise versa it will go a thermal transient - cause ski slope.


3- mechanical effect : when the transducer magnetic base is mounted quickly with impact.

also dirty surface causes loss highe frequency content

thank you all
if i found or remember new things i will write

thank you