What is not a part of a closed control loop?

In a closed control loop, the system requires specific components to function effectively. The sensor or transmitter serves to measure the variable being controlled, such as temperature, pressure, or flow. The controller processes the measurement from the sensor and compares it to the desired setpoint to determine the necessary adjustments. The final control element then acts on the system to bring the variable back to the setpoint, whether that's through valves, motors, or other means.

The pipe coil, while it may be essential in certain systems, is not a required component of a closed control loop in itself. Its presence depends on the specific application and system design rather than being a fundamental part of the control loop mechanism. Therefore, identifying the pipe coil as not a part of the closed control loop is accurate, as it does not inherently contribute to the core function of controlling and regulating the system according to feedback.