A technician uses which device to troubleshoot existing loops that are already installed in the field?

A loop analyzer is specifically designed to troubleshoot and diagnose problems in induction loops already installed in the field. It can measure various attributes of the loop, such as its inductance, resistance, and the presence of faults. This device is equipped to detect issues like broken loops, short circuits, or poor connections, which are essential for ensuring the loop's proper functionality in traffic management systems.

In contrast, a circuit tester is generally used for basic electrical testing and is not specialized for the specific needs of loop diagnostics. A signal simulator primarily creates test signals to evaluate the performance of signal controllers rather than diagnosing existing loop conditions. Lastly, a controller emulator is utilized for testing and simulating controller functions but does not provide the specific loop diagnostics needed for troubleshooting existing loops. This specialization makes the loop analyzer the most appropriate choice for this task.