# Measurements of Human Perception of Train Vibration
## 3 Measurement Methodology
### Using a Special Measuring Disk  
For measuring the human perception of vibrations in passive scenarios, the use of a measuring disk is recommended. This disk should be positioned at the designated measuring point, with sensors for capturing vibration parameters affixed in three perpendicular directions. Support for the disk should be provided at three points, and it should possess a diameter of 30 cm and a minimum weight of 30 kg. To meet this weight requirement, additional weight may be added if necessary. Similar disks were previously utilized in the Laboratory of Deformation and Vibration of Structures at the Institute of Structural Mechanics, predating the development of a new disk version [17] (refer to Figure 4). Following the analysis of vibration measurement results, it was evident that in certain instances, the mass of the disk alone, amounting to several kilograms, was inadequate. Consequently, issues related to the vibrations of the disk itself surfaced. Based on experience, it was determined that loading the disk with 10 kg weights was necessary. Initially, two weights were employed, but it became apparent that this was insufficient. Consequently, each measuring disk was equipped with three weights (refer to Figure 5). The measurement disk offered an advantage over other methods due to its capacity for non-invasive and non-destructive vibration measurement, a critical consideration in residential structures. The optimal placement of weights became a subject of debate, and challenges arose with vibrations induced by additional weights. This led to a recognition of the necessity for stable mass distributions. The literature suggests a solution in [18], presenting a steel disk with a diameter of 300 mm and a thickness of 4 mm. The disk features three support points (legs) positioned at 120\({}^{\circ}\) angles to each other (see Figure 6). Figure 4: The old version of the measuring disc. Based on experiences and archival versions of discs in [16], a new disc was proposed (Figure 7). The proposed solution is free from the disadvantages of other previously used devices. The disk is an integral system with a sensor mounting and a load ensuring good contact of the disk with the floor surface regardless of its structure and surface layer. The disc enables non-invasive measurements and repeatability of results. The disc consists of a plate equipped with three ball supports and is characterized by the fact that inside the plate (1), there is ballast material (2), and in its central part, there is a spacer element (3) with a height similar to the height of the plate side surface (1), where a cube with holes (4) is attached to the spacer element (3) (comp. Figure 8). Using a disc does not require drilling holes in the floor, cutting the carpet, cutting holes in the carpet, or the constant presence of third parties in the room conducting research. Thanks to the use of the disk, the time needed to prepare the test stand is significantly shortened, as it is only necessary to place the disk on the tested surface and properly orient it about the selected coordinate system. In vibration tests, sensors are often attached to the tested surface with glue or screws or pins. In such cases, however, the measurement may not be accurate enough because the upper layer of the floor, without any weight, may vibrate differently than the entire ceiling. In turn, mounting with screws or glueing is highly invasive and often requires damage to the tested surface (e.g., drilling holes in the floor, cutting out fragments of the carpet, etc.). Figure 5: The old version of the measuring disc with three additional weights. Figure 6: Plan and cross-section of the disc used in the USSR. The disk used in this research allows for our testing of the impact of building vibrations on humans with the least possible invasion of the tested facility and the least disruption to the functioning of the people staying there while ensuring high measurement accuracy. Moreover, the disk is easy to transport and to install at the place of research.