The industrial fire suppression system is an important guarantee for production safety. The intelligent control solution based on Siemens PLC can achieve rapid response and precise fire extinguishing, effectively reducing fire risks.
1. Hardware Configuration
1.1. PLC and Expansion Module Selection
The core control of the industrial fire suppression system adopts the Siemens S7-1200 series PLC, which has high reliability and anti-interference capability. Depending on the project scale, the CPU 1214C DC/DC/DC main unit is selected, along with SM 1231 AI and SM 1232 AO analog modules, and SM 1222 DO digital output module for expansion.
1.2. I/O Point Allocation Table
| Address | Function Description | Signal Type |
|---|---|---|
| I0.0 | Smoke Sensor 1 | Digital Input |
| I0.1 | Smoke Sensor 2 | Digital Input |
| I0.2 | Temperature Alarm | Digital Input |
| I0.3 | Manual Start Button | Digital Input |
| I0.4 | System Emergency Stop Button | Digital Input |
| I0.5 | Gas Cylinder Pressure Switch | Digital Input |
| IW64 | Zone 1 Temperature Value | Analog Input |
| IW66 | Zone 2 Temperature Value | Analog Input |
| Q0.0 | Alarm Light | Digital Output |
| Q0.1 | Alarm Horn | Digital Output |
| Q0.2 | Fire Extinguishing Agent Release Valve 1 | Digital Output |
| Q0.3 | Fire Extinguishing Agent Release Valve 2 | Digital Output |
| Q0.4 | Exhaust Fan Control | Digital Output |
| QW64 | System Status Indicator | Analog Output |
1.3. System Wiring Points
All signal wires use shielded twisted pair, and proper grounding is ensured.
The temperature sensors use PT100 connected to the analog module, with a 3-wire connection method.
Digital inputs use leakage-type wiring for easier fault diagnosis.
The fire extinguishing agent release valve control circuit must be equipped with relay isolation to enhance safety.
2. Control Program Design
2.1. Program Architecture Design
The program adopts a three-layer architecture design:
OB1: Main loop, responsible for calling various function blocks.
FB: Function modules, including sensor data processing, alarm logic, fire control, etc.
DB: Data blocks, storing system parameters, operating status, and alarm information.
pascal
ORGANIZATION_BLOCK "Main"
BEGIN
// System Initialization
CALL "SYS_INIT", "SYS_INIT_DB"
// Sensor Data Collection and Processing
CALL "SENSOR_PROCESS", "SENSOR_DATA_DB"
// Fire Detection Logic
CALL "FIRE_DETECT", "FIRE_STATUS_DB"
// Fire Control Logic
CALL "FIRE_CONTROL", "FIRE_CONTROL_DB"
// Fault Diagnosis
CALL "FAULT_DIAG", "FAULT_DB"
// HMI Data Interaction
CALL "HMI_COMM", "HMI_DATA_DB"
END_ORGANIZATION_BLOCK2.2. Function Block Design
Taking the fire detection function block as an example:
pascal
FUNCTION_BLOCK "FIRE_DETECT"
VAR_INPUT
Smoke_Sensor1: Bool; // Smoke Sensor 1
Smoke_Sensor2: Bool; // Smoke Sensor 2
Temp_Alarm: Bool; // Temperature Alarm
Manual_Start: Bool; // Manual Start
Zone1_Temp: Int; // Zone 1 Temperature
Zone2_Temp: Int; // Zone 2 Temperature
END_VAR
VAR_OUTPUT
Fire_Alarm: Bool; // Fire Alarm
Fire_Level: Int; // Fire Level (1-3)
Alarm_Zone: Int; // Alarm Zone
END_VAR
VAR
Temp_Threshold: Int := 65; // Temperature Threshold (°C)
Timer_Delay: TON; // Confirmation Delay Timer
Alarm_Confirmed: Bool; // Alarm Confirmation Flag
END_VAR
BEGIN
// Smoke + Temperature Composite Logic to Determine Fire
IF (Smoke_Sensor1 AND Zone1_Temp > Temp_Threshold) THEN
Alarm_Zone := 1;
Fire_Level := 2;
Alarm_Confirmed := TRUE;
ELSIF (Smoke_Sensor2 AND Zone2_Temp > Temp_Threshold) THEN
Alarm_Zone := 2;
Fire_Level := 2;
Alarm_Confirmed := TRUE;
ELSIF (Smoke_Sensor1 AND Smoke_Sensor2) THEN
Alarm_Zone := 3; // Multi-zone
Fire_Level := 3;
Alarm_Confirmed := TRUE;
ELSIF Manual_Start THEN
Alarm_Zone := 0; // Manually Triggered
Fire_Level := 1;
Alarm_Confirmed := TRUE;
ELSE
Alarm_Confirmed := FALSE;
END_IF;
// Add Delay Confirmation to Prevent False Alarms
Timer_Delay(IN := Alarm_Confirmed,
PT := T#3S); // 3 seconds confirmation delay
Fire_Alarm := Timer_Delay.Q;
// Emergency Trigger if Temperature Exceeds 80°C
IF (Zone1_Temp > 80) OR (Zone2_Temp > 80) THEN
Fire_Alarm := TRUE;
Fire_Level := 3;
END_IF;
END_FUNCTION_BLOCK2.3. State Control Design
The system adopts a state machine design pattern, defining the following main states:
STANDBY: Standby state, system monitors normally.
PRE_ALARM: Pre-alarm state, detects potential fire.
ALARM: Alarm state, confirms fire, activates audible and visual alarms.
EXTINGUISHING: Fire extinguishing state, releases extinguishing agent.
VENTILATION: Smoke exhaust state, activates exhaust system.
FAULT: Fault state, system detects a fault.
System behavior is controlled through a state transition matrix to ensure the fire extinguishing process is safe and reliable.
3. Safety and Redundancy Design
3.1. Safety Circuit Design
The fire suppression system is related to personal safety and must achieve high reliability control:
Dual-channel Confirmation: Important sensors use dual-channel design, requiring both channels to trigger simultaneously for fire extinguishing.
Hardware Interlock: The extinguishing agent release circuit adds hardware interlock relays to prevent false actions.
Watchdog Timer: A watchdog is set in the PLC program to monitor program running status.
Fail-safe Design: Key components adopt the “fail-safe” principle, automatically switching to a safe state when power is disconnected.
3.2. Redundant Control Strategy
To improve system reliability, the following redundancy measures are adopted:
Sensor Redundancy: Multiple sensors are configured in key areas for cross-detection.
Processor Redundancy: In important situations, a dual-CPU hot backup scheme can be used.
Communication Redundancy: A dual-network architecture is used to ensure communication reliability.
Power Redundancy: The control system is equipped with UPS and automatic switching between dual power supplies.
3.3. Fault Safety Mechanism
pascal
FUNCTION_BLOCK "SAFETY_HANDLER"
VAR_INPUT
System_State: Int; // System State
PLC_Heartbeat: Bool; // PLC Heartbeat Signal
Sensor_Fault: Bool; // Sensor Fault
Valve_Feedback: Bool; // Valve Feedback Signal
Command_Valve: Bool; // Valve Control Command
END_VAR
VAR_OUTPUT
System_Healthy: Bool; // System Health Status
Emergency_Stop: Bool; // Emergency Stop
Manual_Mode: Bool; // Switch to Manual Mode
END_VAR
VAR
Watchdog_Timer: TON; // Watchdog Timer
Valve_Monitor_Timer: TON; // Valve Action Monitoring Timer
Fault_Count: Int; // Fault Counter
END_VAR
BEGIN
// Watchdog Monitoring
Watchdog_Timer(IN := NOT PLC_Heartbeat,
PT := T#2S); // Trigger after 2 seconds without heartbeat
// Valve Action Monitoring
Valve_Monitor_Timer(IN := Command_Valve <> Valve_Feedback,
PT := T#5S); // Valve state must respond within 5 seconds
// Fault Condition Judgment
IF Watchdog_Timer.Q OR
Valve_Monitor_Timer.Q OR
Sensor_Fault THEN
Fault_Count := Fault_Count + 1;
System_Healthy := FALSE;
// Continuous faults switch to manual mode
IF Fault_Count > 3 THEN
Manual_Mode := TRUE;
END_IF;
// Dangerous fault triggers emergency stop
IF Watchdog_Timer.Q THEN
Emergency_Stop := TRUE;
END_IF;
ELSE
System_Healthy := TRUE;
Fault_Count := 0;
END_IF;
END_FUNCTION_BLOCK4. Human-Machine Interface Design
4.1. Interface Layout Description
The HMI interface of the industrial fire suppression system adopts intuitive area division:
System Overview Area: Displays overall status, key parameters, and alarm information.
Zone Monitoring Area: Graphically displays the status of each protection zone.
Operation Control Area: Contains manual control buttons, mode switching, etc.
Alarm Display Area: Real-time display of current and historical alarm information.
The interface design principle focuses on intuitive information and easy operation, using color coding to represent different states: green for normal, yellow for pre-alarm, red for alarm, and gray for offline.
4.2. Parameter Setting Description
Through a dedicated parameter setting page, the following content can be configured:
Alarm Thresholds: Temperature alarm points, smoke sensitivity.
Delay Parameters: Alarm confirmation delay, extinguishing release delay.
Control Strategies: Single-zone/multi-zone linkage, manual/automatic mode.
Communication Settings: Communication address, timeout, etc.
All parameter modifications require permission verification, and modification history is recorded to ensure system security.
5. Fault Diagnosis and Troubleshooting
5.1. Common Fault Analysis
| Fault Phenomenon | Possible Causes | Exclusion Methods |
|---|---|---|
| System Fails to Start | Power Failure, PLC Failure | Check Power Supply, Check PLC Running Light |
| Sensor False Alarm | Sensor Dirt, Interference Signal | Clean Sensor, Check Shielding Grounding |
| Extinguishing Agent Fails to Release | Valve Failure, Insufficient Cylinder Pressure | Check Valve Feedback, Check Pressure Gauge |
| Communication Interruption | Network Failure, Address Error | Check Network Connection, Verify Communication Parameters |
| System Frequently Resets | Unstable Power Supply, Program Logic Error | Check Power Supply, Review Program Loop |
5.2. Diagnostic Tool Usage
Siemens PLC provides various diagnostic tools to assist in fault troubleshooting:
Status Forcing Table: Monitors and forces I/O states.
Variable Monitoring Table: Real-time tracking of key variable changes.
Program Debugging: Breakpoint setting, single-step execution.
Diagnostic Buffer: View system events and error history.
Through the TIA Portal online diagnostic function, faults can be quickly located, improving maintenance efficiency.
6. Conclusion
The industrial fire suppression system solution based on Siemens PLC has high flexibility and reliability, and through reasonable hardware configuration, program design, and safety strategies, it can achieve precise and reliable fire protection. Feel free to share your implementation experiences in the comments!
