Coal mining generates significant adverse environmental impacts. Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. Underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions.
The term 'OVD' (Optically Variable Device) is used to describe both laser generated hologram images and electron beam generated images. These optically variable devices are created in highly-secure facilities and are at the forefront of overt asset and brand protection programmes.
Linear Variable Differential Transformer. How LVDTs Work. The LVDT or Linear Variable Differential Transformer is a well established transducer design which has been used throughout many decades for the accurate measurement of displacement and within closed loops for the control of positioning.