Data quality flags in SCADA systems - Step-by-Step Execution

Process Flow - Data quality flags

Data Input

↓

Check Sensor Status

↓

Apply Quality Flags

↓

Store Flagged Data

↓

Use Flags for Decisions

↓

Alert or Correct if Needed

Data flows from sensors, quality flags are applied based on checks, then stored and used for decisions or alerts.

Execution Sample

SCADA systems

sensor_value = 75
if sensor_value < 0 or sensor_value > 100:
    quality_flag = 'BAD'
else:
    quality_flag = 'GOOD'
print(quality_flag)

This code checks if a sensor value is within a valid range and assigns a quality flag accordingly.

Process Table

Step	Action	Condition	Result	Quality Flag
1	Read sensor_value	N/A	sensor_value = 75	N/A
2	Check if sensor_value < 0	75 < 0	False	N/A
3	Check if sensor_value > 100	75 > 100	False	N/A
4	Assign quality_flag	Both conditions False	quality_flag = 'GOOD'	GOOD
5	Print quality_flag	N/A	Output: GOOD	GOOD

💡 sensor_value is within valid range, so quality_flag is set to GOOD

Status Tracker

Variable	Start	After Step 1	After Step 4	Final
sensor_value	undefined	75	75	75
quality_flag	undefined	undefined	GOOD	GOOD

Key Moments - 2 Insights

Why do we check both sensor_value < 0 and sensor_value > 100?

Because valid sensor values must be between 0 and 100. The execution_table rows 2 and 3 show these checks to decide if the data is good or bad.

What happens if sensor_value is exactly 0 or 100?

The conditions sensor_value < 0 and sensor_value > 100 would both be false, so the quality_flag will be 'GOOD' as shown in the logic at step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the quality_flag after step 4?

A GOOD

B BAD

C undefined

D ERROR

💡 Hint

Check the 'Quality Flag' column in row for step 4 in the execution_table.

At which step do we determine the sensor_value is valid?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Result' column where quality_flag is assigned in the execution_table.

If sensor_value was 150, how would the quality_flag change in the execution_table?

A It would be GOOD

B It would be BAD

C It would be undefined

D It would cause an error

💡 Hint

Check the condition sensor_value > 100 in step 3 and its effect on quality_flag in step 4.

Concept Snapshot

Data quality flags mark sensor data as GOOD or BAD based on checks.
Check sensor values against valid ranges.
Assign flags accordingly.
Use flags to decide if data is reliable.
Helps detect sensor errors or bad readings.

Full Transcript

In SCADA systems, data quality flags help identify if sensor data is good or bad. The process starts by reading the sensor value. Then, the system checks if the value is within a valid range, for example between 0 and 100. If the value is outside this range, the data is flagged as BAD; otherwise, it is flagged as GOOD. This flag is stored with the data and used later to make decisions or trigger alerts. The example code reads a sensor value of 75, checks the conditions, and assigns a GOOD flag because 75 is within the valid range. This step-by-step check ensures only reliable data is used for control or monitoring.

Practice

1. What does a GOOD data quality flag indicate in a SCADA system?

easy

A. The sensor is offline and not sending data.

B. The sensor data is missing or unavailable.

C. The sensor data is suspected to be incorrect.

D. The sensor data is reliable and accurate.

Solution

1. Step 1: Understand the meaning of data quality flags

   Data quality flags classify sensor data status to help users trust or ignore readings.

2. Step 2: Identify the meaning of the GOOD flag

   The GOOD flag means the data is reliable and accurate, suitable for use in decisions.

3. Final Answer:

   The sensor data is reliable and accurate. -> Option D

4. Quick Check:

   GOOD flag = reliable data [OK]

Hint: GOOD means data is trustworthy and accurate [OK]

Common Mistakes:

• Confusing GOOD with MISSING or BAD flags
• Assuming GOOD means sensor is offline
• Mixing SUSPECT with GOOD data

2. Which of the following is the correct way to represent a BAD data quality flag in a SCADA system configuration file?

easy

A. flag = "BAD"

B. flag = BAD

C. flag = 'bad'

D. flag = bad

Solution

1. Step 1: Review syntax for string assignment in configuration

   Flags are usually strings and must be enclosed in quotes to be valid.

2. Step 2: Identify correct string syntax for BAD flag

   Using double quotes around "BAD" is correct; unquoted or lowercase without quotes is invalid.

3. Final Answer:

   flag = "BAD" -> Option A

4. Quick Check:

   String flags need quotes [OK]

Hint: Use quotes around string flags in configs [OK]

Common Mistakes:

• Omitting quotes around string values
• Using lowercase without quotes
• Confusing variable names with string literals

3. Given the following SCADA data quality flag array: flags = ["GOOD", "SUSPECT", "BAD", "GOOD", "MISSING"], which flags indicate data that should be excluded from analysis?

medium

A. ["BAD", "MISSING"]

B. ["SUSPECT", "GOOD"]

C. ["GOOD", "SUSPECT"]

D. ["GOOD", "MISSING"]

Solution

1. Step 1: Identify flags that mark unreliable data

   BAD and MISSING flags indicate data that is incorrect or unavailable and should be excluded.

2. Step 2: Match these flags to the options

   ["BAD", "MISSING"] correctly lists BAD and MISSING as flags to exclude from analysis.

3. Final Answer:

   ["BAD", "MISSING"] -> Option A

4. Quick Check:

   Exclude BAD and MISSING data [OK]

Hint: Exclude BAD and MISSING flags from analysis [OK]

Common Mistakes:

• Including GOOD or SUSPECT data for exclusion
• Confusing SUSPECT as always bad
• Ignoring MISSING data in filtering

4. You have a SCADA script that filters out BAD data using:

filtered = [d for d in data if d.flag != "BAD"]

but it still includes some BAD data. What is the likely cause?

medium

A. The data list is empty, so filtering does nothing.

B. The list comprehension syntax is incorrect and causes errors.

C. The flag comparison is case-sensitive and some flags are lowercase "bad".

D. The filter should use == instead of != to exclude BAD data.

Solution

1. Step 1: Analyze the filtering condition

   The condition excludes items where flag equals "BAD" exactly, case-sensitive.

2. Step 2: Identify case sensitivity issue

   If some flags are lowercase "bad", they won't match "BAD" and won't be excluded.

3. Final Answer:

   The flag comparison is case-sensitive and some flags are lowercase "bad". -> Option C

4. Quick Check:

   Case sensitivity causes filtering errors [OK]

Hint: Check case sensitivity in string comparisons [OK]

Common Mistakes:

• Assuming != excludes all BAD flags regardless of case
• Thinking list comprehension syntax is wrong
• Using wrong comparison operator

5. You want to create a SCADA alert that triggers only when sensor data is either BAD or MISSING. Which logical condition correctly implements this?

hard

A. if flag == "BAD" and flag == "MISSING":

B. if flag == "BAD" or flag == "MISSING":

C. if flag != "BAD" or flag != "MISSING":

D. if flag == "GOOD" or flag == "SUSPECT":

Solution

1. Step 1: Understand alert condition requirements

   The alert should trigger if the flag is BAD or MISSING, meaning either condition is true.

2. Step 2: Choose correct logical operator

   Using 'or' checks if flag equals BAD or equals MISSING, which matches the requirement.

3. Final Answer:

   if flag == "BAD" or flag == "MISSING": -> Option B

4. Quick Check:

   Use 'or' to combine conditions for alert [OK]

Hint: Use 'or' to check multiple flag conditions [OK]

Common Mistakes:

• Using 'and' which requires both flags simultaneously
• Using negation incorrectly
• Checking for GOOD or SUSPECT instead