IC-DCS Flashcards
State the purpose of DCS
Provides a means of: Receiving data from the field Interpreting that data Applying algorithms to that data Provides digital outputs to display and/or control plant parameters
DCS Definitions
Algorithm:
:
A set of rules, procedures, and mathematical formulas that define a desired control strat
DCS Definitions Analog
Conditions/values that vary across some range
A point that is associated with I/O hardware that converts a field signal (voltage) to a signal that can be used by the processor.
DCS Definitions Arbitrator
An alternate signal used to determine which is the valid input signal for an algorithm with one input failed
Drawing that represents the control scheme (DCS)
Control builder sheet
A drop used to control a process (DCS)
Controller
Distributed Control System (Ovation)
DCS
A range of values that an input signal can vary without initiation of an action that changes the output signal
Deadband
Signals or conditions that are either on or off
Digital
A term for a network end point (controller, workstation, server) in the ovation network
Drop
EWS
Engineering work station
A drop that collects and stores process data and other information
Also called Historical Storage and Retrieval drop (HSR)
Historian
Individual hard-wired circuits connecting field devices with the processor
I/O
Manual/Automatic station
Can be a hard controller on the MCB or a diagram in Ovation (‘soft’)
M/A Station
A drop that is used to control and monitor plant operation
Operator Work Station (OWS)
Processes diagrams
Graphical images that represent actual plant processes control equipment
Indicates point condition to the operator station and to the algorithms
Quality
The desired value of a variable
Setpoint
Small Loop Interface Module
Wired to a control loop
Can be used along with soft controls and will continue to function in the even that the soft controls fail
SLIMs
Used to connect multiple Ovation stations together
Switch
Display that plots process variables over time
Trend
DCS Hardware
Know that the SLIMs connect directly to the I/O devices downstream of the controllers. If the controllers fail, the SLIMs will still be able to directly control the process variables. Soft controls will no longer work
DCS Component function
Controller
Redundant controllers in each control cabinet execute the control functions to operate the system.
One controller operates in control while the other is in standby mode. Both controllers maintain constant communication so if one fails, the other will seamlessly take control of the system.
I/O
Interface field signals from plant processes to the controller.
Interface directly to the SLIMs
Electronics Modules
Contains the two circuit boards (logic and field) that facilitate communication
Personality Modules
Part of I/O that configures the Electronics Modules
Ovation Network Switches
Hardware that connects network drops
DCS HMI
Human interface stations (control room computers)
OWS/EWS
OWS is the operator work station and contains all the DCS graphics, trends, etc
EWS provides the tools for making engineering changes to the system such as adding or deleting database points, modifying graphics or controls
SLIMs
Provide the operator with a control panel mounted panel
In each SLIM are redundant controllers should one fail
SLIMs still function even with the loss of its associated controller
When a component is in Auto or Manual on the Soft control or the SLIM a change is mirrored on both component’s (ie in Manual opening a valve is shown on the SLIM as well as soft control)
Placing a SLIM in ‘L’ Manual locks out the soft controls so that only the SLIM can control the parameter
Graphic Display
Provide all the functionality of a SLIM on the computer (no Local button)
DCS Signal Processing
Median Signal Selector
Uses 3 inputs and selects the middle output
If one of the three inputs fail, the average of the remaining two inputs is used as the output
Median Select 2nd highest selector
4 inputs going into 4 Median Selectors (3 inputs each) which each spit out the four median or average (if one value has failed) outputs. These outputs are fed into a High
select box which provides the highest of the 4 inputs. This output is the 2nd highest of the 4 original inputs
Two Channels with Arbitrator
Takes the average of two inputs while comparing the inputs to another variable (arbitrator).
If one of the inputs fails, it is kicked out after being compared to the arbitrator.
