Impact Sensor

What sort of impact and does it have to resist this impact? Can it just register it from a distance. Some more info will narrow down the options.

Thank you ,the impact is to be registerd from an automobile crash.The device should be able to send an electrical signal that will activate a system after a crash.

Do you know the direction or plane in which the impact will occur? If that plane is horizontal, a simple weight hanging on a flexible wire that barely makes contact with a point or surface would be knocked away by the impact.

To get a correct answer you should put a precise question:

1- movement before and after impact, which accelerations do you expect from the impact, what kind of materials and body geometries are involved

2- is the sensor in series with the 2 bodies at the impact point

3- how many impacts the sensor should resist

4- what kind of signal do you need to activate the other device

5- can you supply your sensor with an electricity

6- how big can be the sensor mass does it change the behavior of you impact system

7- is the impact destructive for one of the bodies

8- do you want to buy or to make the sensor

If you can give those informations it is possible to give you a correct answer.

If you cannot then look at piezoquarz accelerometers with charge amplifiers. There are many suppliers you can find via google global spec or other search engines.

Thanks,the sensor is meant to register an automobile crash ,and spontaneously send an electrical signal to activate another device.

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Provided that the impact to be detected lies in a single plane, you could hardly get a simpler system than a ball bearing held into a dimple or hole in a steel surface by a magnet.

The strength of the magnet and shape and depth of the hole set the level of accelleration detected. A movement of the ball breaks, (or makes), a circuit and activates your device.

'Rock and a Stick` simple.

<VERY SIMPLE IMPACT SENSOR>

Take a cheap Gas- lighter lying in your kitchen.

Position its spring -return "press-to-spark" mechanism to receive the IMPACT.

The high voltage spark/s you will get needs to be limited before SIGNAL enters circuit.

As priciple you are right there is only a small problem if the "energy" of the spark is not sufficient the system will not work since the following components will have a damping effect on the amplitude.

Piezo Electric sensors can work up to medium impact level. Type of application or the impact level is not mentioned in your application. Passive band pass filters and zener diodes are necessary to achieve a clean pulse at the time of impact.

You can get more knowledge about these sensors at http://en.wikipedia.org/wiki/Piezoelectric_sensor

At higher impact levels you need some sort of mechanical arrangement.

For an off the shelf sensor, Try a search for Bruel & Kjaer.

Look under accelerometers.

In your case to be used as a decelerometer, I used them before to measure quite extreme deceleration.

On a budget, then otherwise as already suggested, a piezo sensor may be home made and generate the signal you require, even a modified old loud speaker with a weight on the coil may give the results you need. Without knowing the application, only general idea's may be suggested.

Hope this helps.

i believe all late model Ford's (possibly all cars with electric fuel pumps) have an inertia type impact switch that will drop power to the pump so that fuel does not continue to flow after a crash. As compared to a mechanical fuel pump that only pumps when the motor is turning.

If you actually want a signel to be sent, as compared to merely opening a switch, you'd have to have add another circuit.

I suggest you read, Robert Metz, "Impact and Drop

Testing with ICP Force Sensors," Sound & Vibration

Magazine, February 2007, Pages 18 -20 (www.SandV.com)

Then, Google some of the Piezoelectric force sensor manufacturers,

Dytran, Endevco, PCB, Kistler. You may be able to buy some

used sensors on eBay.

After some measurements, you will have data on force versus

time allowing you to properly design a system.

Go buy an Air Bag sensor. That's exactly what they do.