Hi

Thanks for your comments - I am finding out that Vibration sensing is pretty specialised - seem to be mainly designed for rotating machines and various vehicle applications where the sensor produces an RMS output over time.

I will need to get much more info on the types of Vibration we will be trying to identify (Frequency and Amplitude).

Chris

On 11/01/2012 21:06, Jerry Scharf wrote:
Sorry, I had to jump in.

Accelerometers are not good at measuring vibration. Accelerations are measured instantaneously and are designed to operate above the noise floor of the sensor. The accelerometers have filters to remove the noise to give less erratic readings. The filters are a best guess by the designer of the maximum meaningful rate of acceleration change (jerk) vs the amount of noise to allow through. Most tend to lean toward heavily smoothed readings.

Vibration sets the noise floor of acceleration in rough terms. You need something that internally integrates the various frequencies of noise into RMS and peak vibrational energy measurements. Depending on what you want, it is often better to measure the vibration in multiple frequency bands.

My guess the specific reading regimens are driven by the military and space applications areas, they are the most demanding/knowledgeable about the area. Things shake quite a bit on rockets and ships, and the equipment needs to be able to survive that. I have never needed to deal with this, but can get more information from a friend if others want it. At higher frequencies, it becomes audio noise and then it's a whole different set of techniques and constraints (microphones, SPL meters.)

jerry

On 01/11/2012 02:14 AM, Mick Sulley wrote:
I have not actually tried it, but the Wii remote has accelerometers inside, that may be a cheaper source than buying the components.

Mick


On 11/01/12 06:35, Chris Lautre wrote:
Hi

Thanks for all your suggestions. Yes will use the DS2438.

I am looking at some accelerometers that give out 4-20mA.
Seem to be very expensive.
Will continue looking for a cheaper sensor.

Chris

On 10/01/2012 20:57, Mark Richards wrote:
On 1/10/2012 13:07, Chris Lautre wrote:
I am thinking along the lines of finding a sensor that produces 4-20mA and
using a DS2450 to convert to 1 Wire.
You might consider a DS2438 and using the current sense pins... As others have stated, the 2450 is done for.

How would you implement the sensor portion? Accelerometer? Intriguing..

/m





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