Sequence control from SCADA in SCADA systems - Step-by-Step Execution

Process Flow - Sequence control from SCADA

Start SCADA Sequence

↓

Check Initial Conditions

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Send Command to Device 1

↓

Wait for Device 1 Confirmation

↓

Send Command to Device 2

↓

Wait for Device 2 Confirmation

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Continue Sequence or Stop

Yes No↓

Next Step

The SCADA system starts a sequence by checking conditions, sending commands step-by-step to devices, waiting for confirmations, and deciding to continue or stop.

Execution Sample

SCADA systems

1. Start sequence
2. Check if pump is ready
3. Turn on pump
4. Wait for pump ON confirmation
5. Open valve
6. Wait for valve open confirmation

This sequence controls a pump and valve step-by-step, ensuring each step completes before moving on.

Process Table

Step	Action	Condition/Check	Result	Next Step
1	Start sequence	None	Sequence started	Check pump readiness
2	Check pump readiness	Pump status == READY	True	Send command: Turn on pump
3	Send command: Turn on pump	Command sent	Pump turning ON	Wait for pump ON confirmation
4	Wait for pump ON confirmation	Pump status == ON	True	Open valve
5	Send command: Open valve	Command sent	Valve opening	Wait for valve open confirmation
6	Wait for valve open confirmation	Valve status == OPEN	True	Sequence complete
7	Sequence complete	All steps done	Sequence ended successfully	End

💡 Sequence ends after all devices confirm successful operation.

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
pump_status	UNKNOWN	READY	ON	ON	ON
valve_status	UNKNOWN	UNKNOWN	UNKNOWN	OPEN	OPEN
sequence_state	NOT_STARTED	IN_PROGRESS	IN_PROGRESS	IN_PROGRESS	COMPLETED

Key Moments - 2 Insights

Why does the sequence wait after sending a command before continuing?

The sequence waits for confirmation (see steps 4 and 6 in execution_table) to ensure the device completed the action before moving on, preventing errors.

What happens if the pump is not ready at step 2?

If the pump is not ready, the condition at step 2 fails and the sequence would not proceed to turn on the pump, preventing unsafe operations.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pump_status after step 4?

A READY

B ON

C OFF

D UNKNOWN

💡 Hint

Check the 'pump_status' variable in variable_tracker after step 4.

At which step does the sequence confirm the valve is open?

A Step 6

B Step 5

C Step 3

D Step 7

💡 Hint

Look at the 'Wait for valve open confirmation' action in execution_table.

If the pump was not ready at step 2, what would happen to the sequence_state?

A It would become COMPLETED

B It would stay IN_PROGRESS

C It would stop before IN_PROGRESS

D It would remain NOT_STARTED

💡 Hint

Refer to the condition check at step 2 and sequence_state changes in variable_tracker.

Concept Snapshot

Sequence control in SCADA:
- Start sequence and check device readiness
- Send command to device
- Wait for device confirmation
- Proceed step-by-step
- Stop when all steps complete
- Ensures safe, ordered operations

Full Transcript

Sequence control from SCADA means the system runs steps one after another. It starts by checking if devices like pumps or valves are ready. Then it sends commands to turn them on or open them. After each command, it waits for confirmation that the device did the action. This way, the system avoids mistakes by making sure each step finishes before the next starts. The sequence ends when all devices confirm success.