Trend charts and historical data in SCADA systems - Step-by-Step Execution

Process Flow - Trend charts and historical data

Data Collection

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Store Data in Database

↓

Query Historical Data

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Generate Trend Chart

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Display Chart to User

↓

User Analyzes Trends

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Optional: Export or Alert

Data is collected from sensors, stored, queried, then shown as trend charts for user analysis.

Execution Sample

SCADA systems

1. Collect sensor data every minute
2. Save data with timestamp in database
3. Query data for last 24 hours
4. Plot data points on trend chart
5. Show chart on SCADA screen

This process collects sensor data, stores it, retrieves recent data, and displays it as a trend chart.

Process Table

Step	Action	Data State	Result
1	Collect sensor reading	Raw sensor value with timestamp	Data point ready
2	Store data point	Database updated with new entry	Data saved
3	Query last 24 hours data	Database returns list of data points	Data retrieved
4	Generate trend chart	Data points processed	Chart image created
5	Display chart	Chart rendered on screen	User sees trend
6	User analyzes chart	Visual trend available	User gains insight
7	Optional export or alert	Data/chart exported or alert triggered	Action completed

💡 Process ends after chart display and optional user actions

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
sensor_data	empty	value + timestamp	stored in DB	queried list	processed for chart	chart rendered	user views chart
database	empty	empty	updated with data point	returns data list	unchanged	unchanged	unchanged
trend_chart	none	none	none	none	created image	displayed	visible to user

Key Moments - 3 Insights

Why do we store data with timestamps?

Timestamps let us know when each data point was recorded, so the trend chart shows changes over time (see execution_table step 1 and 2).

What happens if the query returns no data?

The chart will be empty or show no trend, because no data points exist for that time range (see execution_table step 3).

How does the system update the trend chart?

It queries fresh data and regenerates the chart image each time before display (see execution_table steps 3 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the data state after step 3?

A Database updated with new entry

B Database returns list of data points

C Data points processed

D Chart rendered on screen

💡 Hint

Check the 'Data State' column for step 3 in the execution_table.

At which step does the trend chart become visible to the user?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look for 'Display chart' and 'User sees trend' in the execution_table.

If sensor data is not collected every minute but every 5 minutes, how does the execution table change?

A Fewer data points collected and stored

B Trend chart generation step is skipped

C More data points stored in database

D User cannot analyze trends

💡 Hint

Think about how data collection frequency affects the number of data points in variable_tracker.

Concept Snapshot

Trend charts show how sensor data changes over time.
Data is collected regularly and stored with timestamps.
Historical data is queried from the database.
Charts are generated from queried data and displayed.
Users analyze trends to understand system behavior.

Full Transcript

In SCADA systems, trend charts help visualize how sensor data changes over time. The process starts by collecting sensor readings regularly, usually every minute, and storing them in a database with timestamps. When a user wants to see trends, the system queries the historical data for a specific time range, like the last 24 hours. This data is then processed to generate a visual chart, which is displayed on the SCADA screen. Users can analyze these charts to detect patterns or issues. Optionally, users can export the data or set alerts based on trends. This step-by-step flow ensures continuous monitoring and easy understanding of system performance.

Practice

1. What is the main purpose of a trend chart in SCADA systems?

easy

A. To show how data changes over time

B. To control devices remotely

C. To store user login information

D. To display static images

Solution

1. Step 1: Understand the function of trend charts

   Trend charts are designed to visualize data points collected over time, showing how values change.

2. Step 2: Compare options to the purpose

   Only To show how data changes over time describes showing data changes over time, which matches the purpose of trend charts.

3. Final Answer:

   To show how data changes over time -> Option A

4. Quick Check:

   Trend charts = show data changes over time [OK]

Hint: Trend charts always show data over time [OK]

Common Mistakes:

• Confusing trend charts with control functions
• Thinking trend charts store data instead of displaying it
• Assuming trend charts show static information

2. Which of the following is the correct way to set a time range for a trend chart in a SCADA system configuration?

easy

A. timeRange = '24hrs ago to now'

B. timerange = 24hours

C. time-range = last24hours

D. time_range = 'last 24 hours'

Solution

1. Step 1: Identify correct syntax for setting time range

   In SCADA configurations, parameters are usually set with clear variable names and string values in quotes.

2. Step 2: Evaluate each option's syntax

   time_range = 'last 24 hours' uses a clear variable name with an equals sign and a quoted string, which is standard syntax. Others have missing quotes or invalid variable names.

3. Final Answer:

   time_range = 'last 24 hours' -> Option D

4. Quick Check:

   Correct syntax uses variable = 'string' [OK]

Hint: Use clear variable names and quotes for strings [OK]

Common Mistakes:

• Omitting quotes around string values
• Using invalid variable names or hyphens
• Combining words without spaces or quotes

3. Given this snippet of SCADA trend chart setup code:

data_source = 'sensor1'
time_range = 'last 1 hour'
refresh_rate = 60  # seconds
chart.display()

What will happen when this code runs?

medium

A. The chart shows sensor1 data for the last hour and updates every 60 seconds

B. The chart shows sensor1 data for the last hour but does not update

C. The chart shows all data from sensor1 without time limit

D. The code will cause an error due to missing parameters

Solution

1. Step 1: Analyze the parameters set

   data_source is set to 'sensor1', time_range limits data to last 1 hour, refresh_rate is 60 seconds meaning the chart updates every minute.

2. Step 2: Understand chart.display() behavior

   Calling chart.display() will show the chart with the given data and refresh settings.

3. Final Answer:

   The chart shows sensor1 data for the last hour and updates every 60 seconds -> Option A

4. Quick Check:

   Data source + time range + refresh rate = live updating chart [OK]

Hint: Refresh rate controls how often chart updates [OK]

Common Mistakes:

• Assuming chart does not update without explicit refresh call
• Ignoring time_range limits
• Thinking missing parameters cause errors here

4. You wrote this configuration for a trend chart:

data_source = sensor1
time_range = last 24 hours
refresh_rate = '60'

Why does the chart fail to display data?

medium

A. Data source name must be uppercase

B. Refresh rate should be a string, not a number

C. Missing quotes around sensor1 and last 24 hours cause syntax errors

D. Time range cannot be more than 12 hours

Solution

1. Step 1: Check syntax for string values

   In configuration, string values like sensor names and time ranges must be in quotes to be valid.

2. Step 2: Identify errors in given code

   data_source = sensor1 and time_range = last 24 hours lack quotes, causing syntax errors. refresh_rate as string is acceptable.

3. Final Answer:

   Missing quotes around sensor1 and last 24 hours cause syntax errors -> Option C

4. Quick Check:

   Strings need quotes in config [OK]

Hint: Always quote string values in configs [OK]

Common Mistakes:

• Using unquoted strings causing syntax errors
• Confusing data types for refresh rate
• Assuming data source case matters

5. You want to create a trend chart that shows historical data from two sensors over the last 12 hours, updating every 5 minutes. Which configuration is correct?

hard

A. data_source = 'sensor1, sensor2'
time_range = '12h'
refresh_rate = '5min'

B. data_sources = ['sensor1', 'sensor2']
time_range = 'last 12 hours'
refresh_rate = 300

C. data_sources = 'sensor1; sensor2'
time_range = last 12 hours
refresh_rate = 5

D. data_source = ['sensor1', 'sensor2']
time_range = 'last 12 hours'
refresh_rate = 300

Solution

1. Step 1: Identify correct variable for multiple sensors

   Using data_sources as a list with sensor names in quotes is correct for multiple inputs.

2. Step 2: Check time range and refresh rate formats

   time_range as 'last 12 hours' is clear and refresh_rate as 300 seconds (5 minutes) is correct numeric value.

3. Step 3: Evaluate other options for errors

   data_source = 'sensor1, sensor2' time_range = '12h' refresh_rate = '5min' uses a single string with comma, which may not parse correctly. data_sources = 'sensor1; sensor2' time_range = last 12 hours refresh_rate = 5 lacks quotes and uses wrong separators. data_source = ['sensor1', 'sensor2'] time_range = 'last 12 hours' refresh_rate = 300 uses singular data_source with list, which is inconsistent.

4. Final Answer:

   data_sources = ['sensor1', 'sensor2'] time_range = 'last 12 hours' refresh_rate = 300 -> Option B

5. Quick Check:

   List for multiple sources + correct time + numeric refresh [OK]

Hint: Use list for multiple sensors and numeric seconds for refresh [OK]

Common Mistakes:

• Using single string for multiple sensors
• Omitting quotes around strings
• Using wrong units for refresh rate