Tag Archive: accelerometer


Measuring vibration without a touch

Like I said last post, I found a paper about a new type of non contact sensor for ground vibration tests.

The sensor replaces the accelerometers that need to be placed on the airplane. It’s called a NIRV (noncontact inertia reference velocity) sensor, internally it is the combination of a laser displacement sensor and an accelerometer.

airplane

The sensors are mounted on large stands that surround the airplane, the laser displacement sensors in the NIRV sensors determine the distance between the sensor and the airplane. Because the stands are very big, they will wobble a bit themselves. To compensate this wobble of the sensor, he uses the accelerometer and makes the distance measurement more accurate.

During the GVT’s, the displacement of the airplane is registered and is expressed in terms of velocity per unit force, just like the data that the normal accelerometers produce. Because the data is expressed in the same unit, the NIRV measurements can then be compared to the results of normal accelerometers, they concluded that the 2 types give an equally good result.

The NIRV sensors have a big advantage, because the sensors are mounted on the stands, these can be used on most airplanes, so this will make you save time in the setup of a measurement. This because there is no tear down or build up needed between 2 measurements, like with the normal accelerometers.

 

So guys, see you later and hope you understood everything.

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Sensing vibration

There is already a post about ground vibration tests (GVT).

In these tests they normally use accelerometers, so I think this is a good thing to blog about.

There are 2 types of accelerometers, first you have the AC – and secondly the DC – coupled devices. The AC – coupled device can’t measure static acceleration, so it doesn’t register the gravity. While a DC device can measure starting from zero Hertz.

An AC device isn’t suited to follow slow motions, because of the limitations by its RC time constant which defines its high-pass characteristics. The DC on the other hand has no problem tracking a slow motion.

A typical AC sensor is a piezoelectric accelerometer. While a typical DC-accelerometer is the capacitive (used in air-bags and mobile devices) or a piezoresistive one.

I have found a good paper about this, it gives a lot of info and a good comparison.

In GVT they use AC and DC sensors, also force and temperature sensors. The fact they also use temperature sensors is because DC piezoresistive sensors are very temperature dependent.

 

But of course the technology isn’t standing still so there is a new kind of sensor they are testing for the GVT. So stay tuned for my next post if you want to know more about it.

 

See you next time followers.