Alarm management on HMI in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to acknowledge an alarm when the button is pressed.

PLC Programming

IF Button_Pressed THEN Alarm_[1] := TRUE; END_IF;

Drag options to blanks, or click blank then click option'

AAcknowledge

BReset

CTrigger

DClear

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Reset' instead of 'Acknowledge' clears the alarm instead of confirming it.

Using 'Trigger' or 'Clear' does not match the action of acknowledging.

The 'Acknowledge' flag is set to TRUE to confirm the alarm has been noticed.

2fill in blank

medium

Complete the code to display the alarm message on the HMI screen.

PLC Programming

IF Alarm_Active THEN HMI_Display := [1]; END_IF;

Drag options to blanks, or click blank then click option'

AAlarm_Message

BAlarm_Code

CAlarm_Status

DAlarm_Time

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Alarm_Code' shows a number, not a message.

Using 'Alarm_Status' or 'Alarm_Time' does not display the message.

The 'Alarm_Message' contains the text to show on the HMI when the alarm is active.

3fill in blank

hard

Fix the error in the alarm reset logic.

PLC Programming

IF Reset_Button AND Alarm_[1] THEN Alarm_Active := FALSE; END_IF;

Drag options to blanks, or click blank then click option'

ATriggered

BActive

CReset

DAcknowledge

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'Acknowledge' instead of 'Active' causes reset to fail.

Using 'Reset' or 'Triggered' is incorrect for this condition.

The condition should check if the alarm is active before resetting it.

4fill in blank

hard

Fill both blanks to filter and display only active alarms with high priority.

PLC Programming

FOR i := 1 TO Alarm_Count DO
  IF Alarms[i].[1] AND Alarms[i].Priority [2] 5 THEN
    Display_Alarm(Alarms[i]);
  END_IF;
END_FOR;

Drag options to blanks, or click blank then click option'

AActive

B>

C<=

DAcknowledged

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Acknowledged' instead of 'Active' shows alarms already handled.

Using '<=' instead of '>' shows low priority alarms.

We check if the alarm is active and if its priority is greater than 5 to display it.

5fill in blank

hard

Fill all three blanks to create a dictionary of alarm messages for active alarms only.

PLC Programming

Alarm_Dict := {Alarms[[1]].ID: Alarms[[2]].[3] FOR [1] IN 1..Alarm_Count IF Alarms[[2]].Active};

Drag options to blanks, or click blank then click option'

Ai

Bj

CMessage

DStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for keys and values causes errors.

Using 'Status' instead of 'Message' stores wrong data.

We use the same index 'i' to get the alarm ID and message for active alarms only.

Practice

1. What is the main purpose of alarm management on an HMI?

easy

A. To alert operators about abnormal conditions quickly

B. To slow down the machine operation

C. To display decorative graphics on the screen

D. To store historical data only

Solution

1. Step 1: Understand the role of alarms on HMI

   Alarms notify operators when something unusual or wrong happens in the system.

2. Step 2: Identify the main goal of alarm management

   The goal is to alert operators quickly so they can fix problems fast and keep the system safe.

3. Final Answer:

   To alert operators about abnormal conditions quickly -> Option A

4. Quick Check:

   Alarm management = alert operators fast [OK]

Hint: Alarms warn operators about problems fast [OK]

Common Mistakes:

• Thinking alarms slow down machines
• Confusing alarms with decorative features
• Assuming alarms only store data

2. Which of the following is the correct way to define an alarm condition in a PLC program for HMI?

easy

A. alarm = ON IF temperature == 100

B. alarm = temperature + 100

C. SET alarm WHEN temperature < 100

D. IF temperature > 100 THEN alarm ON

Solution

1. Step 1: Identify correct alarm condition syntax

   Alarm conditions usually use IF statements to check if a value crosses a limit.

2. Step 2: Check each option for proper condition

   IF temperature > 100 THEN alarm ON correctly uses IF temperature > 100 THEN alarm ON, which means alarm triggers when temperature is too high.

3. Final Answer:

   IF temperature > 100 THEN alarm ON -> Option D

4. Quick Check:

   Alarm condition uses IF and comparison [OK]

Hint: Alarm conditions use IF with comparison operators [OK]

Common Mistakes:

• Using assignment instead of condition
• Confusing < and > operators
• Writing incomplete or invalid syntax

3. Given this alarm logic snippet:

IF pressure < 50 THEN alarm = TRUE ELSE alarm = FALSE

What will be the value of alarm if pressure is 45?

medium

A. TRUE

B. 50

C. FALSE

D. Error

Solution

1. Step 1: Analyze the condition with given pressure

   The condition checks if pressure is less than 50. Since 45 < 50, the condition is true.

2. Step 2: Determine alarm value based on condition

   Because the condition is true, alarm is set to TRUE.

3. Final Answer:

   TRUE -> Option A

4. Quick Check:

   45 < 50 means alarm TRUE [OK]

Hint: Check condition result to set alarm TRUE or FALSE [OK]

Common Mistakes:

• Confusing TRUE and FALSE values
• Ignoring ELSE branch
• Assuming alarm equals pressure value

4. You wrote this alarm condition:

IF level > 80 THEN alarm = TRUE ELSE alarm = FALSE

But the alarm never triggers even when level is 90. What is the most likely error?

medium

A. The condition should use < instead of >

B. The alarm variable is not linked to the HMI alarm tag

C. The ELSE part should be removed

D. The level variable is misspelled

Solution

1. Step 1: Check the condition logic

   The condition level > 80 is correct for triggering alarm when level is 90.

2. Step 2: Consider why alarm does not trigger

   If alarm variable is not linked to the HMI alarm tag, the HMI won't show the alarm even if alarm = TRUE.

3. Final Answer:

   The alarm variable is not linked to the HMI alarm tag -> Option B

4. Quick Check:

   Alarm variable must connect to HMI tag [OK]

Hint: Check variable linkage to HMI alarm tag [OK]

Common Mistakes:

• Changing correct condition operator
• Removing ELSE causing undefined alarm state
• Assuming variable spelling error without proof

5. You want to create an alarm on the HMI that triggers only if temperature is above 100°C and pressure is below 30 PSI. Which of these alarm conditions is correct?

hard

A. IF temperature > 100 AND pressure > 30 THEN alarm = TRUE ELSE alarm = FALSE

B. IF temperature > 100 OR pressure < 30 THEN alarm = TRUE ELSE alarm = FALSE

C. IF temperature > 100 AND pressure < 30 THEN alarm = TRUE ELSE alarm = FALSE

D. IF temperature < 100 AND pressure > 30 THEN alarm = TRUE ELSE alarm = FALSE

Solution

1. Step 1: Understand the alarm trigger conditions

   The alarm should trigger only when temperature is above 100 AND pressure is below 30 simultaneously.

2. Step 2: Check each option's logic

   IF temperature > 100 AND pressure < 30 THEN alarm = TRUE ELSE alarm = FALSE uses AND with correct comparisons: temperature > 100 AND pressure < 30, matching the requirement exactly.

3. Final Answer:

   IF temperature > 100 AND pressure < 30 THEN alarm = TRUE ELSE alarm = FALSE -> Option C

4. Quick Check:

   Use AND for both conditions true [OK]

Hint: Use AND to combine multiple alarm conditions [OK]

Common Mistakes:

• Using OR instead of AND
• Reversing comparison operators
• Mixing up greater than and less than