Detailed Safety Control Solutions for Hazardous Materials Production Using Siemens PLC

Detailed Safety Control Solutions for Hazardous Materials Production Using Siemens PLC

In hazardous materials production workshops, the reliability of the safety control system directly relates to personnel and property safety. This article will introduce a safety control solution based on the Siemens S7-1200 PLC, focusing on how to construct a stable and reliable safety control system through multiple protective measures such as hardware redundancy, software interlocking, and emergency shutdown.

1

Overall System Architecture

The safety control system adopts a dual PLC redundancy architecture, with the main station using S7-1214C and the backup station using S7-1212C. The two PLCs achieve data synchronization and switching control through a PROFINET network. The system is configured with 16 digital input points for collecting various sensor signals and 12 digital output points for controlling actuators.

Key hardware list:

• Main control PLC: Siemens S7-1214C

• Backup PLC: Siemens S7-1212C

• Safety relay: PILZ PNOZ X3

• Emergency stop button: Siemens 3SB3

• Safety light curtain: Keyence SF4B

• Gas detector: Dräger Polytron 8000

2

Safety Interlocking Design

Safety interlocking is the core of the entire control system. Multiple interlocking protections are achieved through ladder diagram programming:

1. Hardware interlocking layer

• The emergency stop circuit directly cuts off the total power supply of the system

• The safety relay monitors the status of each protective door

• Gas concentration exceeding standard immediately cuts off the power supply of related equipment

1. Software interlocking layer

• Process parameter limit protection

• Equipment startup sequence control

• Interlocking of linked mechanisms

Key Note: Although software interlocking is important, it cannot fully rely on software interlocking. Hardware interlocking is the last safety barrier.

3

Key Program Implementation

The main safety control programs include:

// Emergency stop handling program
NETWORK 1
LD     "Emergency Stop Button"
AND    "System Run Allowed"
OUT    "System Total Start"
// Gas concentration monitoring
NETWORK 2
LD     "Gas Concentration Value"
GT     "Alarm Threshold"
R      "Production Equipment Start"
S      "Sound and Light Alarm"
// Equipment startup sequence control
NETWORK 3
LD     "Ventilation System Running"
TON    "Start Delay", 10s
LD     "Delay Completed"
AND    "Safety Conditions Met"
OUT    "Production Equipment Allowed to Start"

4

Redundant Switching Control

The two PLCs monitor and switch through a watchdog program:

1. The main station sends a heartbeat signal to the backup station every 500ms

2. If the backup station does not receive the heartbeat signal for three consecutive times, it determines that the main station has failed

3. The backup station takes over system control and issues a fault alarm

Key points for the switching process:

• Ensure no data loss during the switching process

• Avoid both PLCs controlling simultaneously

• Record switching events and reasons

5

Alarms and Interlocks

The system sets up three levels of alarms:

1. Prompt Alarm

• Process parameters deviate from normal range

• Equipment running time is too long

1. Warning Alarm

• Safety door is opened

• Gas concentration is approaching alarm value

• Equipment failure warning

1. Emergency Alarm

• Gas concentration exceeds standard

• Emergency stop is triggered

• Important equipment failure

Alarm response measures:

• Prompt Alarm: Sound and light prompts on-site and in the control room

• Warning Alarm: Key equipment runs at reduced speed

• Emergency Alarm: The system shuts down urgently, cutting off the source of danger

6

Common Issues Handling

1. False Alarm Handling

• Check if the sensors are normal

• Investigate interference sources

• Appropriately adjust alarm thresholds

1. Equipment Cannot Start

• Check interlocking conditions

• Confirm the status of the emergency stop circuit

• Check fault records

1. System Response Delay

• Optimize program scanning cycle

• Check network communication load

• Reasonably set data acquisition cycle

7

Safety Management Requirements

1. Daily Maintenance

• Conduct safety interlock tests for each shift

• Regularly calibrate gas detectors

• Check the function of the emergency stop button

1. Operating Permissions

• Set operator and administrator permissions

• Key parameter modifications require a password

• Record important operation logs

1. Emergency Plans

• Develop a complete emergency response process

• Regularly conduct emergency drills

• Backup important programs and parameters

8

Practical Suggestions

Debugging and operational maintenance of the safety control system:

1. System Debugging

• Conduct interlock tests step by step

• Simulate various fault conditions

• Record debugging data and processes

1. Operational Maintenance

• Establish a regular maintenance system

• Maintain complete technical files

• Train operating and maintenance personnel

1. Optimization and Improvement

• Collect operational data for analysis

• Continuously improve control strategies

• Timely update safety measures

This safety control solution fully utilizes the reliability and flexibility of PLCs, providing comprehensive safety assurance for hazardous materials production processes. In practical applications, targeted optimization and adjustments need to be made in conjunction with specific process requirements and site conditions.

Key points:

• Safety control must ensure redundancy

• Hardware interlocking takes precedence over software interlocking

• Regular maintenance and testing are crucial

• Continuous optimization and improvement of control solutions

1. On-site Wiring Key Points

• Use dual independent circuit design for emergency stop circuits

• Use shielded special control cables

• Connect the emergency stop button in series to the safety relay

• Reserve more than 20% spare wires

1. Sensor Wiring

• Gas detectors use shielded cables

• Signal lines and power lines are wired separately

• Ground wires are laid separately

• Explosion-proof areas use explosion-proof sealed joints

1. Communication Network Wiring

• Use industrial Ethernet cables between the main and backup PLCs

• Avoid strong electrical interference sources in network layout

• Set up a repeater every 50 meters

• Waterproof treatment for cable joints

Wiring Precautions:

• All cables must have clear identification

• Terminal blocks must be numbered according to regulations

• Explosion-proof areas must strictly follow explosion-proof requirements

• Keep complete wiring diagrams

9

Debugging Experience Sharing

I remember once debugging a similar system at a chemical plant, I encountered a problem: the system frequently alarmed and shut down inexplicably. After checking for a long time, I found out that the gas detector was incorrectly installed, being blown by the cooling air from nearby equipment, leading to inaccurate readings.

This lesson taught me:

1. Sensor location selection should consider environmental factors

2. System debugging should be conducted under actual working conditions

3. Fault causes may be in unexpected places

10

System Upgrade Recommendations

1. Hardware Upgrade Directions

• Add redundant sensors

• Configure industrial tablets for on-site operation stations

• Switch to explosion-proof touch screens

• Add UPS uninterruptible power supply

1. Software Upgrade Directions

• Develop a fault diagnosis expert system

• Add predictive maintenance functions for equipment

• Add mobile remote monitoring

• Integrate video surveillance systems

11

Program Optimization Example

// Optimized gas monitoring program
NETWORK 1
// Gas concentration sampling and filtering
LD     "Sampling Enabled"
MOVD   "Gas Concentration Value", "Sampling Buffer[0]"
L      10                           // Sampling times
L      0
FOR
   L     "Sampling Buffer[#]"
   L     "Sampling Sum"
   +I
   T     "Sampling Sum"
   L     #Loop Count
   +     1
NEXT
// Calculate average value
L      "Sampling Sum"
L      10
/I
T      "Gas Concentration Average Value"
// Level alarm judgment
LD     "Gas Concentration Average Value"
GT     "Warning Threshold"
S      "Warning Output"
GTD    "Alarm Threshold"
S      "Alarm Output"
R      "Production Equipment Running"
GTD    "Emergency Threshold"
CALL   "Emergency Shutdown"

12

Safety Operation Data Analysis

1. Key Data Collection

• Gas concentration trends

• Equipment running time

• Alarm frequency statistics

• System switching records

1. Data Application

• Generate operational reports

• Analyze equipment status

• Optimize control parameters

• Predictive maintenance

Data management key points:

• Important data should be backed up regularly

• Establish a data analysis mechanism

• Keep historical records for at least one year

• Analyze and handle abnormal data in a timely manner

13

Personnel Training Requirements

1. Operator Training

• Basic operation process of the system

• Common fault handling methods

• Emergency situation handling procedures

• Safety precautions

1. Maintenance Personnel Training

• System hardware structure

• Basic logic of the program

• Daily maintenance requirements

• Fault diagnosis methods

14

Emergency Plan Details

1. Emergency Shutdown Process

• Press the nearest emergency stop button

• Cut off the power supply to the relevant area

• Start the emergency ventilation system

• Evacuate personnel on site

1. System Fault Response

• Switch to the backup system

• Record fault information

• Handle according to the emergency plan

• Timely report to relevant personnel

1. Accident Investigation and Analysis

• Protect site data

• Analyze fault causes

• Develop rectification measures

• Improve control solutions

15

Cost Control Suggestions

1. Equipment Selection

• Choose well-known brands for key components

• Regular components can choose domestic products

• Reasonably store spare parts

• Consider maintenance costs

1. Construction Plan

• Reasonably plan construction steps

• Optimize wiring plans

• Standardize installation processes

• Ensure on-site protection

Investment Focus:

• Safety interlocking devices

• Gas detection systems

• Communication network devices

• Control system redundancy

After several years of project practice, it has been found that investment in safety systems must strike a balance, ensuring safety and reliability while controlling costs. This can be achieved by optimizing design solutions and selecting cost-effective equipment.

Safety is always the top priority, but how to achieve the most reliable protection with the most economical investment requires a deep understanding of process characteristics and accurately identifying hazards, only then can the best control solutions be developed.

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