# How to read simple control loops on a PFD (Process flow diagram)

**URL:** <https://forumautomation.com/t/how-to-read-simple-control-loops-on-a-pfd-process-flow-diagram/713>\
**Category:** Field Instrumentation\
**Created:** [January 10, 2016, 5:53am UTC](https://forumautomation.com/t/how-to-read-simple-control-loops-on-a-pfd-process-flow-diagram/713 "2016-01-10T05:53:05Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![denizen](https://forumautomation.com/letter_avatar_proxy/v4/letter/d/848f3c/32.png) [@denizen](https://forumautomation.com/u/denizen)\
**Post date:** [January 10, 2016, 5:53am UTC](https://forumautomation.com/t/how-to-read-simple-control-loops-on-a-pfd-process-flow-diagram/713/1 "2016-01-10T05:53:05Z")

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Control loops on a PFD identify areas where variable must be properly maintained.

Main variables controlled in a process.

T - Temperature P - Pressure L - Level F - Flow rate

Example of s simple control loop

What will be indicated 1.What kind of controller is being used (temperature,pressure,level,flowrate)

2.Where the controller is receiving its signals

3.How the controller is controlling the variable ([valve](https://forumautomation.com/t/basics-of-control-valves-and-parts-of-control-valve/392),variable power supply)

![How to read a control loop from PFD](https://cdn.forumautomation.com/original/1X/aedb42bc58daeff3dee8a5afdcb7a2f77f5f7b0a.jpg)

Here Temperature controller is used. Pneumatic signal is used to give the controller output to [final control element.](https://forumautomation.com/t/basics-of-control-loop/209)