Impact hammer
An impact hammer is a hammer equipped with a force sensor for exciting an object with an impulse .
The transmission of this impulse in the object can be examined using additional sensors attached to the same object. Such investigations allow conclusions to be drawn about the acoustic properties of the object. If necessary, this method is suitable for well-studied objects, material defects inside the respective construction or material determine and assess their extent.
Acoustics
In the acoustic metrology impact hammers are used to stimulate the body sound. In order to determine the transfer behavior of certain components - especially in the transfer path analysis - the building structure is excited with a force curve known (by the force sensor) with the impact hammer. The vibration of the component can be determined with structure-borne sound sensors and the radiated air-borne sound with microphones. The transmission behavior of the component can be calculated from these measured signals.
Use with timber
A decrease in the speed of sound can cause internal defects such as B. Show cracks and voids in different stages. There are a number of devices for measuring the speed of sound in trees or construction timber .
The impact hammer measures the time it takes for an impulse to travel from an impact screw to the sensor screw across the tree. Since every tree species has more or less characteristic sound velocities, the measured value can be used to make statements about the inner workings of the tree or construction timber in the event of strong deviations. A statement about the type, shape and location of the defect is only possible with a detailed series of measurements .
For the measurement process, a hammer screw is screwed in on one side of the object to be tested, which guides the sound pulse through the wooden body. A sensor on the opposite side, also fastened with a screw, receives the pulse. The time between the impulse wave entry and the finish is measured at the sensor .
The characteristic values of the speed of sound for wood allow conclusions to be drawn about the tree (wood part) to be examined. If the throughput speed does not correspond to the characteristic value and is below that, one can assume that the sound wave hit a barrier (e.g. a crack, rot, etc.) and had to take a detour, which accordingly cost time.
With the impact hammer you can examine the entire space between the impact screw and the sensor. By moving the screws, the location of the defect can also be identified more precisely. In order to then localize the exact geometry and dimensions of the defect, more precise measuring methods such as sonic or electrical resistance tomography or drilling resistance measuring devices are necessary.
For some years now, further developed devices have been available that allow statements to be made about the entire cross-section in the event of significantly less damage to the tree (sonic or pulse tomograph).
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