A class of borehole imaging devices that work on the principal of acoustic signal return sourced from a rotating sonde; in effect, a down hole and spinning mechanical bat. A rotating transducer, within a centralised assembly, emits and records a chirped high frequency acoustic signal, and as the tool is drawn up the borehole collects a spiral of data from around the entire borehole wall. The tool gathers measurements of travel time and return signal amplitude. Travel time is the period from the emission to collection at the sonde of the signal and is a function of drilling mud properties and hole size. Amplitude is the reflected signal amplitude and is a function of drilling mud, hole size, wall microrugosity and wellbore acoustic impedance contrasts. These data can be converted to images and oriented, allowing interpretation. Amplitude data usually provides better quality images over the travel time data. The major advantage of televiewers is that they function in resistive (oil-based) drilling muds, unlike many dipmeters and resistivity imaging tools, and through sections that would often be resistivity saturated e.g. evaporites.
See also density and photoelectric effect imaging devices, resistivity imaging devices, curve saturation.
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