# What are the important symbols used in P&ID diagram

**URL:** <https://forumautomation.com/t/what-are-the-important-symbols-used-in-p-id-diagram/2479>\
**Category:** Instrumentation\
**Tags:** calibration\
**Created:** [October 19, 2017, 9:45pm UTC](https://forumautomation.com/t/what-are-the-important-symbols-used-in-p-id-diagram/2479 "2017-10-19T21:45:35Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![sivaranjith](https://forumautomation.com/letter_avatar_proxy/v4/letter/s/ba9def/32.png) [@sivaranjith](https://forumautomation.com/u/sivaranjith)\
**Post date:** [October 19, 2017, 9:45pm UTC](https://forumautomation.com/t/what-are-the-important-symbols-used-in-p-id-diagram/2479/1 "2017-10-19T21:45:36Z")

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All the devices like transmitters, gauges, and other equipment etc., in a control loop, cannot be picturised to understand the logic. So in a P& id diagram, all the devices are symbolised.

Letters and numbers are written inside the circle to show the function of the instrument and it’s identification, circles used are of different types:

![](https://cdn.forumautomation.com/original/1X/b4b7de5b2dbaec42418b0fd15b305fa156faeafd.png)

The instrument described in the blank circle is mounted in the field

![](https://cdn.forumautomation.com/original/1X/972ff1e61437799acdcfaa76fd9476037360511a.png)

The instrument is located on the front of a control room panel. ![](https://cdn.forumautomation.com/original/1X/bda60648c1d0813f62718d7b6e8db37ce43003f6.png)

Circle with the single broken line. The instrument is located behind a control panel. ![](https://cdn.forumautomation.com/original/1X/0fe8f89268e0de1d3d4afde393a2403720a917f8.png)The instrument is mounted in the field control panel. ![](https://cdn.forumautomation.com/original/1X/633d8b95a6c07b2821aecef09d0c84cb9d9e0a01.png)Circle with double dotted line. The instrument is mounted behind the field control panel. ![](https://cdn.forumautomation.com/original/1X/7ccdf410e3af75708117090898b1ddcbbc3d2f52.png)The above symbol tells about 1. where the instrument is located 2. what the instruments is, here it’s a level indicating controller. 3, what part of a control loop it is.

There are different types of abbreviations used to know the type of instruments here. Such abbreviations are listed inthe table below

 ![](https://cdn.forumautomation.com/original/1X/237c055cd7dc0fe8fcdf541f2f4736f55d30ba64.png) .