What type of sensor is installed directly in the process stream?

The correct answer is immersion sensor. Immersion sensors are specifically designed to be placed directly into the process stream of liquids or gases to measure parameters such as temperature or pressure. The installation style allows for real-time monitoring of process conditions and enhances accuracy since the sensor is affected directly by the properties of the fluid it’s in contact with.

In the context of the other options, insertion sensors are also used in fluid measurement, but they do not always imply direct placement in the stream; they are often partially immersed or inserted through a fitting. Averaging sensors are designed for measuring averages over a range, typically in applications where multiple points are sampled to get an overall reading, rather than being installed directly in the stream. Remote bulb sensors are designed to be located away from the process stream, with a sensing bulb that is connected by a capillary tube, which again does not involve direct contact with the stream.

Thus, immersion sensors are the most fitting choice for those requiring direct contact with the process fluids for accurate data collection and monitoring.