 Piping and instrumentation diagrams provide information that include component identification, how instruments are connected, where instruments are located, and their function within a process. Comprehension of P&ID diagrams assists technicians when troubleshooting and monitoring specific processes. Comparing a heat exchanger to the piping and instrumentation diagram illustrates the symbol's function within a process. Steam is conveyed through a pipe into a sealed enclosure that acts as a heat exchanger. As the water passes through the heat exchanger, the temperature of the water is elevated. To read the control loop, a series of steps are performed. Identification of the control loop is notated by the tag number 401 within the balloons. The valve that allows steam to flow through the pipe is the symbol with two triangles. In the top portion of the symbols is the functional identifier and the first letter denotes the measured variable. The first letter of each functional identifier is the letter T, which defines the process of temperature control. The instrument connected to the heat exchanger contains two other types of information. The second letter in the functional identifier indicates it is a transmitter and the balloon with no line inside its symbol indicates the device is field mounted. A capillary tube that sends a signal from the heat exchanger to the transmitter is represented in the diagram by the line with X's. A dashed line between components indicates an electrical signal. The controller and indicator is the instrument where the transmitter sends an electrical signal and is shown in the functional identifier at the second and third letters I and C. Balloons with a solid dividing line indicates that the instrument is board mounted. An electronic signal from the controller is indicated by the dashed line. The controller output is connected to the transducer that controls the steam flow indicated by the second letter Y of the functional identifier. The transducer converts an electronic signal to a pressure signal and is indicated by the square containing the letters I and P. The line with diagonal marks designates a pneumatic connection. The pneumatic controlled diaphragm actuator that opens and closes the globe valve regulates steam in the process. The actuator is represented by the half circle in the P and ID. The arrow pointing downwards from the actuator indicates a fail closed valve type.