FAQ ON PROCESS OPERATOR INTERFACE DESIGN

 

  1. How to arrange the operator displays?

 

The basic method can be to provide an overview of the facility and then make the operator to drill down for details.

For Control System displays, the following hierarchy levels can be considered:

Overall Facility overview

Various process area overviews

Common facility overview

Process cell details

 

Unit details

Unit details

Equipment details

Equipment details

For Safety System displays, the overview can provide the various safety-groups or hierarchies as designed. The detailed displays can be Safety Instrument Function based.

 

  1. Is it necessary to separate SIS and Process Control displays in case of common operator interface?

 

Yes.

 

  1. Points to look in display page design?

 

-        Mechanism should be in place to avoid operator from performing conflicting operations. For example, on a motor faceplate if the motor is running, the operator should not be able to operate START push button.

-        The only monitoring points should be differentiated with operator action points.

-        All important operator actions should be confirmed before execution.

-        Operator data entry should be validated.

-        Avoid displaying alarm condition or status or limit detected condition when alarm condition or status is not active.

-        Provide clear indication of modes and states.

-        Clear color conventions should be established. Define meaning of each color and avoid a long list. Say, Red reserved for safety, Orange for failures, Cyan for warning and Green for normal operation. These colors should not be mixed with other display colors.

-        Different area displays can be differentiated with different background colors.

-        Controls and operator action items which look similar should operate similar.

-        No more than 5-7 operator action items is advisable in a display.

-        As a thumb rule provide a minimum of 30-40 percent blank space.

-        All control displays can follow a typical template and safety displays can follow another typical template.

Standard display elements can include display title, process identification, standard links and menu items.

 

  1. What is most important point in display design?

 

Consistency!   Consistency! Consistency!!

 

  1. What contents should there be in a display?

 

Each display must have a well defined objective that is developed by considering:

-        what will be done with the display i.e. tasks that needs to be executed.

-        Who will do it, and

-        When the display will be used. 

 

  1. What are the types of coding techniques are necessary for the display?

 

-        Color coding: Redundant indicators such as shape change or label should be considered along with color coding.

-        Size coding: Large pumps can be shown bigger and small ones smaller. Do not use too many sizes.

-        Shape coding: Establish shapes library and use them consistently.

-        Attention coding: reverse video effect, increased brightness, flashing.

-        Use of abbreviations

 

  1. Is it recommended to have separate displays for sequence control functions?

 

Yes.

 

  1. Points on alarm displaying:

 

-        Call operator attention on alarms irrespective of whichever display the operator is in.

-        Distinguish new alarms from acknowledged alarms.

 

  1. Is operator involvement necessary in display design?

 

Yes its highly recommended. A questionnaire can be designed to collect the inputs. The focus can be on overview display, preferred format for the display, trend & alarm requirements, control station components and any other special display requirements.

Operator reviews can be carried out using walk-through techniques.  

 

 

© Palaniappan R Kannan