Allen-Bradley Sequential Function Charts (SFC) for Pump Control

Implementing Pump Control with Sequential Function Charts (SFC)

Pump Control systems in Water & Wastewater require careful consideration of intermediate control requirements, real-time responsiveness, and robust error handling. This walkthrough demonstrates practical implementation using Allen-Bradley Studio 5000 (formerly RSLogix 5000) and Sequential Function Charts (SFC) programming.

System Requirements:

A typical Pump Control implementation includes:

Input Devices (5 types):
1. Pressure transmitters: Critical for monitoring system state
2. Flow meters: Critical for monitoring system state
3. Level sensors: Critical for monitoring system state
4. Temperature sensors: Critical for monitoring system state
5. Vibration sensors: Critical for monitoring system state

Output Devices (5 types):
1. Centrifugal pumps: Controls the physical process
2. Variable frequency drives: Controls the physical process
3. Control valves: Controls the physical process
4. Dosing pumps: Controls the physical process
5. Isolation valves: Controls the physical process

Control Logic Requirements:

1. Primary Control: Automated pump systems using PLCs for water distribution, chemical dosing, and pressure management.
2. Safety Interlocks: Preventing Pressure regulation
3. Error Recovery: Handling Pump sequencing
4. Performance: Meeting intermediate timing requirements
5. Advanced Features: Managing Energy optimization

Implementation Steps:

Step 1: Program Structure Setup

In Studio 5000 (formerly RSLogix 5000), organize your Sequential Function Charts (SFC) program with clear separation of concerns:

• Input Processing: Scale and filter 5 sensor signals


• Main Control Logic: Implement Pump Control control strategy


• Output Control: Safe actuation of 5 outputs


• Error Handling: Robust fault detection and recovery

Step 2: Input Signal Conditioning

Pressure transmitters requires proper scaling and filtering. Sequential Function Charts (SFC) handles this through perfect for sequential processes. Key considerations include:

• Signal range validation


• Noise filtering


• Fault detection (sensor open/short)


• Engineering unit conversion

Step 3: Main Control Implementation

The core Pump Control control logic addresses:

• Sequencing: Managing water distribution


• Timing: Using timers for 2-4 weeks operation cycles


• Coordination: Synchronizing 5 actuators


• Interlocks: Preventing Pressure regulation

Step 4: Output Control and Safety

Safe actuator control in Sequential Function Charts (SFC) requires:

• Pre-condition Verification: Checking all safety interlocks before activation


• Gradual Transitions: Ramping Centrifugal pumps to prevent shock loads


• Failure Detection: Monitoring actuator feedback for failures


• Emergency Shutdown: Rapid safe-state transitions

Step 5: Error Handling and Diagnostics

Robust Pump Control systems include:

• Fault Detection: Identifying Pump sequencing early


• Alarm Generation: Alerting operators to intermediate conditions


• Graceful Degradation: Maintaining partial functionality during faults


• Diagnostic Logging: Recording events for troubleshooting

Municipal water systems implementations face practical challenges:

1. Pressure regulation
Solution: Sequential Function Charts (SFC) addresses this through Perfect for sequential processes. In Studio 5000 (formerly RSLogix 5000), implement using Ladder Logic features combined with proper program organization.

2. Pump sequencing
Solution: Sequential Function Charts (SFC) addresses this through Clear visualization of process flow. In Studio 5000 (formerly RSLogix 5000), implement using Ladder Logic features combined with proper program organization.

3. Energy optimization
Solution: Sequential Function Charts (SFC) addresses this through Easy to understand process steps. In Studio 5000 (formerly RSLogix 5000), implement using Ladder Logic features combined with proper program organization.

4. Cavitation prevention
Solution: Sequential Function Charts (SFC) addresses this through Good for batch operations. In Studio 5000 (formerly RSLogix 5000), implement using Ladder Logic features combined with proper program organization.

Performance Optimization:

For intermediate Pump Control applications:

• Scan Time: Optimize for 5 inputs and 5 outputs


• Memory Usage: Efficient data structures for ControlLogix capabilities


• Response Time: Meeting Water & Wastewater requirements for Pump Control