Tektronix Technical Forums are maintained by community involvement. Feel free to post questions or respond to questions by other members. Should you require a time-sensitive answer, please contact your local Tektronix support center here.

measuring very low frequency vibrations

KUSB and KPCI DAQ Data Acquisition Products
Post Reply
cavibs
Posts: 2
Joined: July 6th, 2015, 6:12 pm
Country: United States

measuring very low frequency vibrations

Post by cavibs » July 7th, 2015, 5:55 pm

I wish to measure vibrations that come from sound. The sound is likely well under 100 hz since it can never be heard. It is only felt as a mild pressure sensation. I may refer to it as "sound", perhaps it is better to call it something else.

My goal is not necessarily to get an extremely accurate level of whatever unit, rather to get a somewhat accurate - AND consistent reading - if the 'sound' remains the same each time it is measured.

I had used a Vibrometer app on my smart phone (a Samsung Galaxy S4). I was clearly able to see that 'ordinary' events within a building where it was used resulted in a relatively low reading, then the 'sound' - which I knew was present due to the feeling it produces, produced a much higher reading.
So, I saw it work. Over time the characteristics of the 'sound' changed, and
although I could still feel it, the reading on the phone app was noticeably lower. I suspect that the frequency was lowered rather then its power or amplitude.

So, I am looking for a better way to measure the sound. I've been told that it is best not to view this as measuring 'sound', since to most that implies 'audio' frequencies over 200 hz, and also that the equipment available for that purpose is not suited to very low frequencies.

Ideally, I'd like to be able to measure the sound, and get that in the form of a digital output that I can record with my computer - my strong preference is RS232. I would rather not play with any sort of analog output as that would be of little use to me. I'd need to convert that, and I do not want to go through the hassle.

I looked at devices like this on eBay

http://www.ebay.com/itm/VM-6360-Digital ... 4abc715370

("VM-6360 Digital Vibration Tester Meter Vibrometer")

but had some questions I didn't know how to answer. First, I wanted to get an idea of how well my phone app could perform at the lower frequencies compared to devices like this. For example, if my phone app handle frequencies down to 5 hz, then perhaps a gadget like this would not be useful. If my phone app only handled frequencies down to 80 hz, then perhaps a device like this would be useful to me.

Secondly, I am not at all sure if this sort of device would be able to measure vibrations in the air. I suspect these devices were meant to be bolted to some machinery that is being evaluated. I know the phone app does NOT use the microphone - but rather other sensors within the phone. So, I guess that is essentially what these devices do.

I'd appreciate any insight.

Andrea C
Keithley Applications
Keithley Applications
Posts: 1263
Joined: October 15th, 2010, 10:35 am
Country: United States
Contact:

Re: measuring very low frequency vibrations

Post by Andrea C » July 8th, 2015, 5:25 am

With the smartphone, it sounds like the app is accessing the accelerometer in the phone.

You may find this link to be helpful:
https://www.sparkfun.com/pages/accel_gyro_guide

cavibs
Posts: 2
Joined: July 6th, 2015, 6:12 pm
Country: United States

Re: measuring very low frequency vibrations

Post by cavibs » July 8th, 2015, 6:12 pm

Interesting, but after reading data sheet twice, it still is not clear to me what the output signal is or how to interpret it. Maybe in the morning.

Post Reply

Return to “Keithley DAQ Data Aquisition Products”

Who is online

Users browsing this forum: No registered users and 7 guests