In WinCC Explorer, alarms are configured in the Alarm Logging editor. Message blocks define what each message shows, message classes define acknowledgement behaviour and state colours, and message types refine them within a class. Analog alarms use limit monitoring with a delay time and hysteresis, and the WinCC Alarm Control displays the result in runtime.
- Message blocks are configured once for the whole project; get them right before creating hundreds of messages.
- Acknowledgement philosophy is a design decision made per message class, not per message.
- Delay time and hysteresis on analog limits are what stop a signal sitting on its limit from flooding the list.
How the WinCC Message System Is Built
Open Alarm Logging from WinCC Explorer. The message system is built from three layers, and the order you configure them in matters.
- Message blocks: the columns every message can carry. System blocks such as date, time, number and state are fixed; user text blocks hold your message text, location and instructions; process value blocks embed live values in the message.
- Message classes and types: the behaviour and colour scheme applied to whole groups of messages.
- Individual messages: the actual entries, each linked to a trigger tag and bit.
Configure message blocks first. Adding a user text block after five hundred messages exist means revisiting every one of them, so decide early whether you want separate blocks for equipment tag number, location and operator instruction.
Messages are triggered from PLC tags. A message word or double word in the controller carries one bit per condition, and the message number in Alarm Logging maps to the bit number. Keeping the numbering identical on both sides is what lets a maintenance engineer jump from an alarm on screen to the exact rung in the PLC. The controller side of this is covered in TIA Portal to WinCC alarm configuration.
Message Classes, Types and Acknowledgement
A message class defines the acknowledgement philosophy and the display colours for came in, went out and acknowledged states. A message type sits inside a class and refines the colours, so one class can serve several priorities.
| Class | Acknowledgement | Use for |
|---|---|---|
| Error | Single acknowledgement required | Trips and faults that stop production |
| Critical error | Dual acknowledgement, came in and went out | Safety-related and high-consequence events |
| Warning | Without acknowledgement | Conditions needing attention but not a stop |
| System | Without acknowledgement | Communication and server diagnostics |
| Operating message | Without acknowledgement | Mode changes, batch start and end |
Dual acknowledgement means the message stays in the list until the condition has cleared and the operator has acknowledged it. Use it sparingly; applying it to every message guarantees the list is never clean and operators start acknowledging in bulk without reading.
Writing message text that works
Use the user text blocks properly. One block for the equipment tag number, one for the plain-language condition and one for the first action. "P-102 discharge pressure low, check suction strainer" is worth more than fifty perfectly configured colours.
Acknowledgement can be written back to the PLC through an acknowledgement tag, so the control program can require an operator action before a fault reset is accepted.
Analog Limit Monitoring, Delay and Hysteresis
Discrete messages come from bits. Numeric values are handled by the limit monitoring add-in inside Alarm Logging, where you attach limits to a tag and assign each limit its own message.
- Upper and lower limits: configure several per tag, typically low low, low, high and high high, each in a different message class.
- Delay time: the value must stay beyond the limit for this duration before the message is generated.
- Hysteresis: a percentage or absolute band the value must return through before the message clears.
- Hysteresis effect: choose whether it applies when the alarm comes in, goes out or both.
Without delay and hysteresis, a pressure hovering on its high limit produces hundreds of come-and-go pairs in a shift. The archive fills, the list scrolls, and the operator learns to ignore it. These two settings do more for alarm quality than any amount of colour tuning.
| Signal | Suggested delay | Suggested hysteresis |
|---|---|---|
| Tank level | 5 to 10 s | 2 to 5 percent |
| Line pressure | 2 to 5 s | 2 percent |
| Furnace temperature | 30 to 60 s | 1 to 2 degrees |
| Motor current | 3 to 5 s | 5 percent |
| Flow during start-up | 10 to 20 s | 5 percent |
Configure a full WinCC alarm system in class
Practical WinCC Explorer sessions covering Alarm Logging, Tag Logging, archives and reporting on live projects.
Alarm Control, Archiving and Flood Control
Add the WinCC Alarm Control to a screen in Graphics Designer and select which message blocks appear as columns. Configure two views rather than one.
- Message list: currently active and unacknowledged messages, sorted with the newest first.
- Short-term archive list: recent history, so a supervisor can see what happened an hour ago.
- Long-term archive list: the full archive for investigations, opened from a history screen.
Enable the operator filter and hit list so staff can narrow to one area or one message class. A message window is also worth placing on the screen template, showing the highest priority active message everywhere in the project.
Archive configuration
The message archive is sized in the Alarm Logging settings. Set the archive period and the number of archives to hold, and configure a backup path so closed segments are copied before they are overwritten. Sites with regulatory requirements normally back up to a network share and keep several years.
Controlling floods
- Group related messages so one plant trip does not produce sixty simultaneous entries.
- Use message suppression by a controlling tag when a unit is deliberately shut down or in maintenance.
- Rationalise: if nobody can name the action for a message, it is not an alarm, it is an operating message.
- Review the hit list monthly and fix the top ten repeating messages.
The same discipline applied at panel level is covered in HMI alarm configuration in TIA Portal.
Hands-On Lab: Configure a WinCC Alarm Class and Analog Limit
Hands-on- WinCC Explorer with a project connected to an S7 PLC or a simulated tag set
- A message word tag and one analog process value tag
- Simulation only, no live plant equipment
- Estimated time: 40 minutes
Configure message blocks
Open Alarm Logging and add user text blocks for equipment tag, condition and first action.
Create message classes
Create an Error class with single acknowledgement and a Warning class without acknowledgement, each with its own state colours.
Add four discrete messages
Link messages to bits 0 to 3 of the message word, with full text in the user blocks.
Add an analog limit
Attach a high limit to the process value with a delay of five seconds and two percent hysteresis.
Add the alarm control
Place an alarm control on a screen with message list and short-term archive views, enable filtering, and acknowledge a message.
Message blocks carry useful text, acknowledgement behaviour is set by class, the analog limit uses delay and hysteresis, and both live and archived views are available to the operator.
Frequently asked questions
What is the difference between a message class and a message type in WinCC?
The class defines acknowledgement behaviour and the basic state handling. The type sits inside a class and refines the display colours, so one class can serve several priority levels.
When should I use dual acknowledgement?
Only for high-consequence or safety-related messages. Dual acknowledgement keeps the message listed until the condition has cleared and the operator has acknowledged, which is intrusive by design.
How do delay time and hysteresis reduce alarm floods?
Delay requires the value to stay past the limit before a message is generated, and hysteresis requires it to return through a band before the message clears. Together they stop a signal sitting on its limit from repeatedly triggering.
Can WinCC send an acknowledgement back to the PLC?
Yes. Assign an acknowledgement tag to the message so the control program can require an operator acknowledgement before it accepts a fault reset.