معلومة اسوقها للجميع ولأنهاء اللبس عن الاجهزة الإستشعارية او البواحث طويلة او متوسطة المدى وهنا لسنا نتكلم عن الأسياخ والأجهزة التي تحاكيها وتوجيهية فهذه الأجهزة بناءها علميا ثابتة. فمن فهم نطم الاتصالات VLF- LF -TF وفق بإذن الله لبناء هذه الأجهزة بدقة عالية واليكم المبدأ وباللغة الانجليزية خصوصا لمتابعينا من المناطق التي لا تتكلم العربية Locators for the LF / VLF and TF range enable the detection of electromagnetic field anomalies in the ground.
Secondary field secondary field
In contrast to normal metal detectors, the devices described are mainly passive receiving systems. Depending on the sensor system used, the signals they receive are direct emissions or emissions from a secondary field of strong long and long-wave transmitters (radio signals) as well as TF signals, such as mains harmonics. In particular, the targeted pipe and pipe tracking can also be carried out with the aid of the active signals of special generators. For non-conductive piping systems, their use is essential.
Radio signals cause a high-frequency current flow through the ground and in particular are placed on metal pipes and pipes. But also particularly conductive layers in the soil act as wave guides. The effect is the more pronounced, the longer the conductors are and the more clearly their alignment coincides with the direction towards the transmitter. The current flow causes the formation of a secondary field in the wave guide. Underground gas and water pipelines as well as power and signal cables often form very strong secondary fields due to their good conductivity and their usually considerable length, making them one of the most striking objects that can be located with the devices.
The secondary fields generate in the usually vertically oriented sensor coil of the locating device when crossing the object a distinctive voltage level profile.
Sensor coil sensor coil
Voltage level curve Voltage level profile
Also particularly conductive soil structures, which form in a heaped occurrence of certain minerals, ores, etc., sometimes lead to quite significant signal level differences. Iron-reinforced foundations, bunkers or similar belong with appropriate size also to the relatively easily detectable objects. Also underground cavities, e.g. Extensive tunnels and corridors can be detected, provided, however, that there is a suitably conductive ground environment.
The location is difficult to impossible in spatially very narrow structures, smaller object dimensions and subterranean cavities, resulting in an unfavorable, i. non-conductive soil environment.
The location of power cables, conductive pipelines and iron-reinforced underground structures may also be based on TF signal reception.
The selective tracking of cables and conductive piping is possible by coupling a generator signal. There are different methods for this. The return from the end of the object to the generator can take place via an auxiliary line or over the ground. The coupling is done with ground spikes. If only the beginning of the cable can be reached, the generator must be connected to the ground via a ground spike. The signal feedback from the fed cable takes place via capacities coupling to ground. The inductive coupling can be done with the aid of generator-fed loops.
Auxiliary line auxiliary line
Soil soil 90 ° 90 °
Non-metallic pipe systems, for example made of clay or plastic can be located using a plug-in detection cable or a plug-in coil. The power is supplied by a special generator. The combination of generator module and localization module can also be used for metal detection. For this purpose, the coils of the systems must be arranged at an angle of 90 ° and adjusted by fine adjustment so that no voltage is induced in the receiving coil without object interference. When influenced by a metal object then field changes occur, which lead to a voltage generation in the receiving coil
