AGC for Crosshole Test
AGC - Automatic Gain Control is a unique capability of our CHUM - CrossHole Ultrasonic Monitor. Another feature that helps you get better results with less effort making testing with CHUM more efficient and enabling up to 4Km profile measurements a day! Yes, 4000 meters per day!AGC was introduced in 1999 in the very first CHUM version. Instead of manually setting the gain for each profile distance, the CHUM automatically sets the ideal gain for you and ensures the best signal reception. The signal will be strong enough to properly detect the coming FAT (First Arrival) but not too strong to saturate the signal and amplify the noise, resulting in a poor SNR (signal-to-noise ratio) for good FAT detection.
What do others do when they do not have an AGC with their CSL system?
They keep the gain level to the maximum hence destroying the RE (Relative Energy) measurements and increasing the noise, making proper FAT detection less reliable and generating many unsafe false-negative measurements.
Some major manufacturer even makes it worse by always dividing the RE level by two, ignoring the ASTM D6760 standard guidelines.
All in more detail in this paper about the Importance of Automatic Gain Control in Crosshole sonic logging
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