Cause and consequence in instrumention

 Cause and consequence in instrumention

Some projects categorize cause and effect as part of a process document, and some other projects consider cause and effect as part of tool outputs. Literally, "cause" means something that causes something else to happen, and "effect" is what happens as a result of the cause.

The interaction between cause and effect can be simple or complex. For a simple example in process control: the cause can be a high liquid level alarm in the tank and the consequence can be the opening of the outlet valve of the tank. A complex example could look like this: If at least two flame detectors detect a fire in area 1 and coincide with one flame detector detecting a fire in area 2, then it should close valve A, close valve B, open valve C, disconnect power. outlet etc.

Cause and effect are presented as a matrix form. Causes are listed on the left while effects are listed on the top, both described in the form of a tag number with their description (other supplementary information such as P&ID may be added). A marked intersection between the two means they are cause-and-effect related. Markers can be "X" which means the effect will be activated, "T" which means the effect will be activated with a time delay, "P" which means the cause will enable the effect.

There are two categories of cause and effect diagram:

ESD C&E diagram

C&E Fire and Gas Scheme

Reference Document: SAFE Chart, ESD Logic Diagram, Philosophy

The SAFE Chart presents the required safety devices for each process device. The SAFE table must ensure that all safety requirements are met and what powerful actions the safety devices perform.

The philosophy provides the narrative and the engineer translates it into cause and effect interaction so that the plant works as the intended philosophy.

The ESD logic diagram shows the plant shutdown hierarchy and describes the input that initiates the shutdown and the output as the results after the shutdown.

Purpose of the document Cause and effect

The cause and effect document will be translated into a programming language by the control system engineer and implemented into the control system as logic. This logic will always monitor the device during operation and operates if predetermined conditions are met.