Hi guys,

I dropped my accelerometer again!! Now it is around five times i dropped it. Thank God, itz still working fine!! But i think these types of impacts will normally change the natural frequency of the sensors to some extends. ryt? I read somewhere that if you drop your sensor then itz better to change!!

How can i check what my accelerometer giving is a reliable reading or not? Don't say i have to purchase a shaker table for that!!

i like to know how you are handling these issues and how each impact will affect on the reading!!

Have a nice day!!

Put a new one beside it: they should read the same. Compare it to a recent spectrum of a stable machine. Compare it to data collected from a permanent transducer - collect data from the panel.

A drop shouldn't change resonance; if it does consider a real problem does exist interanlly.

Check the bias voltage - if it is very low, you may have damaged the amplifier - check if your getting a dynamic signal. If the bias voltage is normal 10-14 Vdc a damaged amplifier will show low frequency ski slope in the FFT and a choppy waveform.

What may happen when an accelerometer is dropped is that the crystal may crack. This probably won't show up with a hand-held shaker calibration at 100 Hz. The clear indication is a shift in resonance frequency or multiple resonance peaks.

What can happen in this case is anti-nodes in the measurement range. Low frequency harmonics may be fine, but sometimes higher order frequencies may be amplified or just disappear! The gear mesh frequency you're monitoring may have increased without your noticing, or it may just look like a huge increase. Either way, the results of a bad call could be very costly.

If the crystal is cracked, a side-by-side comparison with a known-good accelerometer may not really tell you much. Since an anti-node or resonance can be very sharp, if there's not an exciting force at a given frequency, you won't notice a problem!

Accelerometers dropped from any distance should be re-calibrated to be certain of taking reliable data. The costs otherwise can just be too great. CTC accelerometers come with a free yearly calibration, which is a pretty good calibration interval considering the abuse accelerometers used with portable data collectors are subject to. You might consider a pool of accelerometers, "retiring" any that are dropped until the calibration is verified.

Jon
Spintelligent Labs

I have a couple of accels that have been dropped and now rattle when you shake them. I assume that the crystal is cracked in them. The thing that tipped me off (before I shook them) was truncated waveforms.

Hi guys,

These are new information for me!! We are calibrating our Analyzer yearly, but never thought about calibrating our accelerometers. Did anybody here are sending their accelerometers for calibration? We have accelerometers from CSI!!

Jon,

So you mean that if the crystal is cracked it may possibly affect the HF range. Then if we compare acceleration readings from a known sensor and the suspected one may reveal the problem. ryt?

quote:

What can happen in this case is anti-nodes in the measurement range.

What do u mean by these anti-nodes?

Have a nice day!!

Does Wilcoxn still make the accels for CSI? Jon gave excellent advise. Normally on a walkabout or field checks; I just make the comparsion check. Maybe quick and dirty but you should know something. Also if your using two particular one's for balancing you may want to set them side-by-side to ensure they read the same phase - a good field check. But, Jon's advise is solid and may be a compliance demand depending on your Company's ISO-9000/1 certification rules?

Just buy them from CTC at < $100 each and if you drop it, send it to them and they'll check it for free and replace it for free if it's broken.... doesn't get much simpler than that.

The best way to think of an anti-node is sort of as the opposite of a resonance. Where a resonance amplifies a signal, an anti-node attentuates a signal. Usually these are very sharp, so only tones of a very narrow range are affected.

Wilcoxon, PCB/IMI, Endevco and independant labs all offer calibration services. But Rusty makes an excellent point. You can pay around $90 to calibrate your accelerometer once.....or you can buy a new CTC accelerometer for the same price and have it calibrated yearly at no charge. And if it doesn't meet specs, it will be replaced!

Spintelligent Labs does represent CTC.

Danny, the crystal may be cracked or the tiny circuit board with the integral electonics may be broekn loose. Bad news in any case! The best thing to do with these accelerometers is to cut the case off with a Dremel tool to have a look at what's inside. With the exception of replacing a defective intergral cable, accelerometers are pretty much non-repairable.

Jon
Spintelligent Labs

Jon,

I plan to do just that. I am curious and I think it will be good experience for my trainee.

Danny

I havn't had time to cut into these, but I did find that the one that gave me the waveform identical to the one Jenish posted has a rattle like the others, but not as severe and directional-i.e. it rattles when shaken in some directions and not in others.

I think before I cut into them, I would like to do some research so that maybe we can eliminate the uncertainty about this.

Anny suggestions on what data should be recorded prior to disassembly?

If you drop it once again, you are fired !

just kidding

Hi guys,
I think itz better to buy a new one than send my old one for calibration to CSI. If it is free calibration for CTC accelerometers, i have to think about that!! Ok. I will first inquire about some local agents supplying this.

Ha ha ha... Eugene,
I was using that accelerometer for 4years now. Anyway it should be dropped.

Have a nice day!!

CTC does have distributors in Saudia Arabia.

You could contact them for assistance:

Khalid Al-Dossary
Engineering Equipments, EST (3E)
Al-Khobar, Saudi Arabia
[966] 3-899 -5079

ksd3e@sahara.com.sa

Regards,

Jon
Spintelligent Labs

quote:

Originally posted by Jenish:
Anyway it should be dropped.

Old method to justify the purchase of a new one.

Thanks Jon,

Itz really interesting!!We are purchasing our CSI accelerometers from them.

Eugene,
I don't have a reply..It may be partially true.Ha ha ha ...

Have a nice day!!

Perhaps if you paid for the accelerometers out of your own pocket, you might just not drop it as often?

Yvan,
If itz from my pocket,i will definitely go for CTC Accelerometers. Atleast they have free calibration...

Yesterday i received a Slow Speed Accelerometer Kit. Sensor,Cable and Magnet...Around 7000SR. How can i drop a 7000SR so easily!!

Have a nice day!!

One way you can drop it is harder, because it is bigger and heavier. A drop should kill it easier.

If you follow the Manual:

A Slow Speed Accelerometer Kit should only be dropped SLOWLY (very slowly if it is very sensitive)!!!

Walt