Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-11-09
2004-11-09
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S600000, C073S602000
Reexamination Certificate
active
06813948
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for examining materials, in particular trees, other kinds of wood, and concrete, with a pulse generator for generating a pulse that can be introduced into the material, with at least one sensor adapted for being associated to the material for detecting the pulse, and with an electronic evaluation device for discriminating the pulse from interfering pulses.
Devices for examining materials of the initially described kind are known from practice, and they exist in a large variety of types. They are, for example, devices, wherein the pulse time delay of shock waves is measured. From this pulse time delay, conclusions are drawn with respect to the quality of the material being examined. In the case of wood, for example, utility poles, the time delay of the shock waves correlates in the direction of growth or grain with the modulus of elasticity in the bending of wood, which enables an assessment of the load capacity, and the therefrom dependent categorization into quality classes. This influences the purchase price in the case of new poles.
In most cases, it is common to introduce into the material the shock wave or the pulse with a hammer serving as a pulse generator, either in a direct manner or via a screw or a bouncing pin. In the case of an axial irradiation of a pole by sound waves, the pulse is typically introduced at the front end. A sensor arranged at the other end of the material or pole detects the pulse that has been introduced into the material. A current pulse corresponding to this pulse is then guided from the sensor to a central electronic evaluation device, where the current pulse is analyzed by discriminating interfering pulses.
More specifically, an acceleration sensor in the pulse-generating hammer transmits in the instant of applying the stroke, the resultant current pulse via a line to a central electronic unit or electronic evaluation device, which analyzes the pulse, and starts a clock, depending on the result, namely a successful discrimination from, for example, interference vibrations. As soon as the sensor at the other end of the material or the other end of the measured length registers the arrival of the shock wave, it will likewise transmit a corresponding current pulse to the central electronic unit, which stops the clock, if the pulse meets the requirements with respect to intensity and length. Both the pulse from the hammer and the pulse from the sensor must each be electronically discriminated, i.e., be distinguished from other vibrations. This occurs each time in the central electronic evaluation device. For purposes of being able to distinguish between real pulses and spurious pulses, a user may normally adjust “gain” and “offset” in the central electronic evaluation device. From the time delay of the pulse and the distance between shock application and detector, it is possible to determine the pulse or shock velocity. Same allows to make statements as to the internal condition and the quality of the material being examined or the test piece, not only in the case of wood, but also in the case of concrete and other materials.
In the known device, the electronic signals of the acceleration sensors, the pulse generator, and the detectors, are transmitted via cables to a central electronic detection and evaluation device. This device also accommodates an accurate electronic clock. The discrimination and evaluation of the pulses, which were converted into electronic current pulses, previously introduced, and subsequently detected, thus occurs in a central location by means of corresponding electronic circuits. In this connection, the pulse shape is decisive for differentiating between real pulses and interference pulses. Thus, the pulse shape should not be altered or falsified on its way from the sensor through the cable to the electronic evaluation device, for example, by electromagnetic interferences or technical cable properties. To accomplish this, the transmission cables must be shielded and be of an extremely high quality, which leads to high prices, limited length of few meters, and restricted handling. Cables of this kind with a corresponding shielding react very sensitively to low temperatures and other external effects, so that they can be used only with limitations, and are very prone to interference. For example, for purposes of avoiding interferences, such cables should not extend in a loop. In particular, in the case of very long or large test pieces of the material being examined, it is not possible to use the known device, since there exist no adequately long cables, which enable an interference-free transmission of current pulses from the sensor or sensors to the central electronic evaluation device.
Consequently, the use of the known device for examining materials, in particular with respect to large test pieces, is very restricted on the materials being tested. A universal application of the known device is therefore not possible.
It is therefore an object of the present invention to describe a device for examining materials of the initially described kind, which enables a universal application with constructionally simple means, in particular also in the case of large test pieces of the material being examined.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by a device of the type which is designed and constructed such that an electronic evaluation device is associated to each sensor.
According to the invention, it has first been recognized that the foregoing object is accomplished in a surprisingly simple manner alone because of a suitable arrangement of the electronic evaluation device. Furthermore, in accordance with the invention, a separate electronic evaluation device is associated for this purpose to each sensor. This association of respectively one electronic evaluation device to each sensor permits avoiding great cable lengths between the sensors and the electronic evaluation device, in particular with the use of a plurality of sensors. In comparison therewith, it is not possible to avoid in the case of most sensors, great cable lengths with the use of a central electronic evaluation device for all sensors in use, which are often arranged at great distances between one another.
The device of the present invention makes it now possible to perform the discrimination of pulses quasi directly on the sensors with minimal communication lengths. Since an electronic evaluation device is associated to each sensor, the spacings between the sensors are no longer important. Therefore, it would also be possible to arrange the sensors at a great distance between one another, while yet enabling a reliable discrimination of pulses.
Consequently, the device for examining materials according to the invention realizes a device, which permits a universal application with constructionally simple means, in particular also in the case of large test pieces of the material being examined.
As regards the kind of pulse, two alternatives present themselves. In this connection, the pulse could be a mechanical and/or an electrical pulse. A mechanical pulse is, for example, a shock wave, which is triggered, for example, by means of a hammer. However, it is also possible to introduce electrical pulses into the material being examined. In this instance, it is also possible to measure the time delay of the current pulse and/or its attenuation. The pulse may be a direct current or an alternating current pulse. In the case of the alternating current pulse, it is also possible to examine. its frequency response while passing through the material.
As regards a very short and reliable communication length between the sensor and the electronic evaluation device, the latter could be arranged directly adjacent to the sensor or be integrated in the sensor. In particular, the integrated arrangement of the electronic evaluation device in the sensor ensures a particularly compact and evaluation-reliable configuration of the device.
As regards a pa
Alston & Bird LLP
Saint-Surin Jacques M.
Williams Hezron
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