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What is a "Displacement Step Diagram"?
What is a "Displacement Step Diagram"?
A Displacement Step Diagram (DSD) - a type of Timing Diagram - is a graphical representation of the timing and order of events in a control system.
They are is used to design and document control systems in industrial automation, and it is a specialized tool for PLC programming.
A DSD typically consists of a series of steps or actions represented by individual blocks, each block representing a specific function or a set of related functions.
The blocks are connected by transition arrows that indicate the flow of control between the functions.
The DSD starts with an initial step, and ends with a final step. The DSD also shows the timing of each step, such as time delays or clock pulses.
DSDs are important because they provide a clear representation of the timing and order of events in a control system, making it easy to understand, analyze and improve.
It also facilitates the design and implementation of automation systems by specifying the steps of the process and the timing of each step in a logical and sequential manner.
DSD is particularly useful in PLC programming, as it allows the programmer to clearly visualize the process control logic and the timing of events in the control system.
It also facilitates the debugging and troubleshooting of the PLC program by providing a clear representation of the order and timing of the PLC instructions.
Graphical representations of Systems next to their respective DSD's
Troubleshooting with a DSD
Troubleshooting with a DSD
An operator can use a Displacement Step Diagram (DSD) to troubleshoot a mechatronics system in several ways:
Identify the problem: By reviewing the DSD, the operator can identify where in the control system the problem is occurring. For example, if there is a problem with a specific output, the operator can look for the corresponding block on the DSD.
Isolate the problem: Once the operator has identified where the problem is occurring, they can use the DSD to isolate the problem to a specific function or set of functions. This can help the operator to focus their troubleshooting efforts on the specific function or set of functions that are causing the problem.
Identify the cause of the problem: By reviewing the DSD, the operator can identify the cause of the problem. For example, if there is a problem with a specific output, the operator can check the inputs and conditions that lead to that output and see if there is an issue with the input or the conditions. This can help the operator to understand why the problem is occurring and what steps need to be taken to fix it.
Check the timing of the events: By looking at the DSD, the operator can check the timing of the events and see if there is a problem with the timing of the control system. This can help the operator to identify if the problem is caused by a malfunctioning sensor, actuator, or controller, or if it is caused by a timing issue.
Identify potential solutions: By reviewing the DSD, the operator can identify potential solutions to the problem. For example, if there is a problem with a specific output, the operator can look for ways to improve the output, such as adjusting the input conditions or adjusting the timing of the events.
Making a DSD
Making a DSD
When making a Displacement Step Diagram, there are some general rules of thumb to follow to make the job easy:
Identify the sequence of events: Start by identifying the sequence of events that need to occur in the process, and use them as the basis for the DSD.
Order actuators by sequence: Once you've identified the sequence of events, order the actuators from first to last in the regular sequence of function.
Use resting state as low and actuated state as high: Regardless of whether an actuator is fully extended or retracted when in its resting/nonfunctioning state, always have the resting condition be the low point, with the activated/functioning position as the high point.
Trace inputs and outputs: Draw lines connecting where actuators activate input(s) to where the corresponding output(s) trigger other actuators to activate
Review and test: Review the DSD with stakeholders and test it with a small group of users to identify any issues or areas for improvement.
Use software: There are many software programs available that can help to create DSDs, such as Siemens STEP 7, Rockwell Automation Studio 5000, and IEC 61131-3, which can help to make the process easier & more standardized
3.4✔ CHECKPOINT
3.4✔ CHECKPOINT
DSD - Dispenser System
DSD - Dispenser System
For the Dispenser System pictured here & physically available in the IMO Lab (Room 114 in Building 24):
Operate the system in both Auto & Manual mode
Hint: Make use of the lights on the PLC & various sensors to help provide further context
Create a Displacement Step Diagram (DSD) for the "Dispenser" system
Note: Look to the example EMI/PWC Chart of the "Pick 'N Place" System (pictured below & physically next to the Dispenser System)
Once done, upload documentation of your progress (text/pictures/gifs/videos) to your previously-created "Systems Approach Tools" project page on your portfolio website, including:
Your DSD, compared side-by-side to the system throughout a complete operating cycle
Descriptions/summaries of what you did/learned
"Pick 'N Place" System (Example Only, DO NOT Analyze)
Sample DSD of "Pick 'N Place" System (Example Only) - *Requires instructor action*
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