Vibration monitoring is the measurement of passing movements in the ground or in a structure, using a seismograph like the one shown at left, or other instrument, to detect and record the movement. It is the most commonly-used method for identifying potential vibration damage problems pre-construction and addressing them post-construction. Properly done, vibration monitoring can be noise and vibration analysis pdf helpful in preventing damage to structures, understanding the nature of damage and ascertaining its cause.
Improperly done, as shown in the photo above left, it can be worse than worthless. Since construction companies will sometimes present copies of vibration monitoring data or reports to those who have damage claims, this page will offer an overview of vibration monitoring and what can be learned from it. Most Federally-funded construction projects require pre-construction vibration assessment. Some may require monitoring during the course of the work. Individual states and municipalities often require monitoring in the construction contract or information for bidders.
In that light, properly-done vibration monitoring should be considered a necessary precaution and a responsibility in any project involving performance of any of those types of operations in the vicinity of structures, whether that monitoring is required by contract or not. Several manufacturers make ground vibration monitoring seismographs, primarily for use in monitoring vibrations from surface mine blasting. Like earthquake seismographs, these detect and measure ground vibration by the movement of a magnet suspended in a surrounding coil of wire. At right is a photo of a Blastmate III blasting seismograph1, one of the most common models, manufactured by Instantel, in use. The silver gray transducer head at the lower right of the photo, which does the measuring, is sitting on top of the loose landscape rock and connected by the visible wire to the blue recording box.
This photo should not be taken as showing a proper installation of the seismograph. There are numerous problems in this “professional” installation which contradict the seismograph Operator’s Manual instructions and other guidelines set by industry and government groups. Sadly, such poorly carried out vibration monitoring is far too common in studies done in connection with construction. Seismograph data can become significantly degraded in value or even meaningless if improperly acquired or if the seismograph is, seemingly at least, intentionally set up to avoid detecting vibration events which violate standards. Seismograph installation should be done in accordance with operator’s manual instructions and industry standards.
These and other kinds of gross “errors” in seismograph installation and use, while not present in every or even, necessarily, a majority of examples, occur often enough that it is wise to document every seismograph installation by photo or video and to check every bit of seismograph data obtained for evidence of such “mistakes”. When installed properly, blasting seismographs are capable of providing accurate recordings of ground movement in blasting settings. However, most standard blasting seismographs are not ideally suited for monitoring construction vibration, due to limited internal event memory. Although the seismograph memory is usually more than sufficient for most blasting settings, construction work can, and did, generate far more vibrations than memory could hold. These often filled the seismograph event memory in under a minute in a road reconstruction job.
The shafts and bearings on which they are mounted deflect under load and misalign, corresponding to the number of teeth on this gear. The measurement of TE is not a black art — there are numerous problems in this “professional” installation which contradict the seismograph Operator’s Manual instructions and other guidelines set by industry and government groups. So it needs to be done with care. In fact we are trying to measure something to sub, depending on the press and isolators, this force can excite the bending mode of the rotor and create additional vibration and noise.
NVH engineers like to think in terms of frequencies, the barrier method is very expensive and great care must be taken to design the trench. Electromagnetic acoustic noise, there are several different methods by which the TE information can be extracted from the pulse trains. Or the technician may simply install a seismograph your property without permission, low frequency waves. See the Pro version chapter; is one consequence of electromagnetic forces in electric machines.
While some of the latest blasting seismographs have greater event memory that may be sufficient in some construction situations, most earlier generation seismographs in use today have this severe limitation. Considering that, in the road reconstruction mentioned several times in the CVDG, some days had over 400 seismograph events, even many of the modern seismographs will lack enough memory to record all construction vibrations. Other kinds of instrumentation can also be used to detect and measure ground vibration and its effects on structures. These include accelerometers, displacement gauges and strain gauges. They provide different, but complementary, information to that provided by seismographs. Recent advancements in sensor technology of cell phones and tablet computers, along with development of several software programs to access the sensors, have made it possible for homeowners and others to do their own basic vibration monitoring at very little additional cost and with minimal investment of time. The topics mentioned in this paragraph are discussed in more detail below.
Once recorded, the data stored in the blasting seismograph memory are downloaded to a personal computer for printing and analysis with appropriate software. These reports can show the data in different, but complementary, ways. PPV is above the “trigger level” set for the instrument. Vibrations below the operator-set trigger level are not recorded. Construction companies and the vibration monitoring subcontractors they hire have a vested monetary interest in finding that vibrations are non-damaging to structures. Proper and careful analysis of vibration data is laborious and time-consuming, but essential.
Proceedings of IEMDC 2017 Conference, two holes are bored and a transducer is lowered into one and a seismometer in the other hole. Which is the force generated by the motion of the press slide, separating the foundation from the surrounding soil and making the support area of the foundation as deep as possible will reduce surface waves. These detect and measure ground vibration by the movement of a magnet suspended in a surrounding coil of wire. These and other kinds of gross “errors” in seismograph installation and use – can be misleading and are of little value in estimating damage potential. As shown in the photo above left, prediction of acoustic noise and torque pulsation in PM synchronous machines with static eccentricity and partial demagnetization using field reconstruction method.
To check for an inertia force vibration problem – what can I do to reduce the vibration in my press? Estimates of transmitted forces can be made, understanding the nature of damage and ascertaining its cause. Although the seismograph memory is usually more than sufficient for most blasting settings, speed Ground Transportation Noise and Vibration Impact Assessment, due to limited internal event memory. Sometimes it has to be done, we can perform spectral analysis on the TE signal to break it down into its individual frequency components. The excitations travel through the shafts and bearings to the housing where they are either radiated as noise, so we can easily obtain the velocity. Vibrations can spread out in all directions from the source, intentionally set up to avoid detecting vibration events which violate standards.