Which device converts a visible light signal into an analog signal for instruments?

The device that converts a visible light signal into an analog signal for instruments is indeed a photoelectric transducer. Photoelectric transducers work by detecting light and converting the intensity of that light into an equivalent electrical signal, usually in the form of voltage or current. This process allows monitoring and control systems to interpret the information carried by the light signal and translate it into a format that instruments can use for further analysis or action.

In applications where light signals are used to convey information—such as in optical communication systems or certain types of sensor technologies—photoelectric transducers play a critical role. They effectively allow the integration of light-based sensing with traditional electrical measurement and control systems, enabling a seamless connection between different signal types.

The other options listed do not perform this specific function: controllers manage system operations but do not convert light signals; PE switches are used for electrical control but not for light signal processing; current-to-pneumatic transducers convert electrical current signals into pneumatic signals, rather than performing any conversion related to light. Therefore, the choice of a photoelectric transducer is the most accurate in this context.