Archive for February, 2014


The internet of things

Due to the increasing connectedness of all the sensors mainly through the internet they increasingly influence our social life and behaviour. In the near future the number of devices equipped with sensors connected to the internet will explode. The amount of data that is collected will be enormous. .

The internet of things (IoT) has stated benefits like higher business productivity, increased energy and transport efficiency and many more. Due to the data collected through the internet of things it’s possible to improve upon many facets. A commonly given example is a smart grid and a smart public transport. All kind of devices connected to the smart grid can determine when energy is available from local solar installations or when the price is low. A single device can’t deliver enough information to smooth out energy usage but if all devices are connected through the IoT they can easily adapt to each other.

However the advantages have to be balanced against privacy and security risks. All devices connected to the internet provide information for less noble usages. A simple example is how easy it becomes for any criminal to determine if you’re at home or not. The fabricant of your coffee machine knows how much and when you make coffee. While at first sight this information is worthless it can become valuable if combined with other information. This paper provides more details about the social impact of the internet of things.

Another example is the decision to obligate an e-call system in any vehicle sold after October 2015 in the European union. With such a system in each car the government knows at any given time the exact position of your car. They say privacy is guaranteed because continuous logging isn’t permitted, however it’s difficult to check it. They will log the type of vehicle, the fuel type, time, exact location, driving direction and the nr of safety belts in use.  This information is indeed useful for the counsellors in case of an accident.

eCall

What do you think about connecting every device to the internet. Are the advantages worth the privacy risks or not?

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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.

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.

connectedness

Using a single sensor delivers a limited amount of information. Sensors almost always appears in networks. If you look back at previous blogposts most applications use a network of sensors to achieve their goal. For example, a single Tile node would be of limited use. You only gain full advantage of the functions when there is a large number of nodes connected through a network. Thus a large part of the development process of a sensor application is the network connecting the sensors and their driving electronics.

datalogger_CAN

(image by Vector)

 

A very important and widely adopted interface is the CAN (controller area network) messaging protocol. Originally developed by Robert Bosch GmbH for use in the automotive industry the CAN bus has huge economic importance. Over 100 million of nodes are connected each year using the CAN protocol. Nowadays the CAN bus is widespread across different industries and continues to gain  importance in aerospace industry. Air-conditioning, door management, fire detection, cabin management and the aircraft galley electronics are typically connected using a CAN bus under the ARINC standards. This makes the CAN bus suitable as the network to connect our sensors.

You can read more about the economically  importance of the CAN protocol on this site. The CAN bus is even used in livestock facilities. If you are interested in the CAN implementation you can read this introduction guide (for beginners).

Ground vibration testing

As stated in my last post this one is providing some details about ground vibration testing (GVT). These tests are performed at the end of the development process. The main goal is to collect vibration data. This data is used to validate the aircraft structure and is helpful to predict the flutter behavior of the plane. Due to their huge importance in safety-critical flight tests multiple configurations must be tested. This causes an extreme time pressure for the engineers. The GVT is economically important for aircraft manufacturers. The video below is displaying some of the GVT tests of the solar impulse airplane. Shakers excite the airplane and accelerometers placed all over the airplane collect the responses. It’s important the exact position of all the accelerometers is known accurately. An entire GVT cycles can be done in just under a month which is rather fast for placing 700 accelerometers and over 25km of wiring. (EADS-CASA completes large-scale Airbus A400M ground vibration test in less than a month’s time

You can find more information about GVT on the LMS site

You can also check out these interesting papers about GVT:

Advanced systems and services for Ground Vibration Testing –  Application for a research test on an Airbus A340-600 aircraft

Ground Vibration Testing of Large Aircraft – State-of-the-Art and Future Perspectives