casing collar locator (CCL)

1. n. [Perforating, Well Completions]
A downhole tool used to confirm or correlate treatment depth using known reference points on the casing string. The casing collar locator is an electric logging tool that detects the magnetic anomaly caused by the relatively high mass of the casing collar. A signal is transmitted to surface equipment that provides a screen display and printed log enabling the output to be correlated with previous logs and known casing features such as pup joints installed for correlation purposes.