Unitronics Sequential Function Charts (SFC) for Pump Control: Complete Programming Guide

Implementing Sequential Function Charts (SFC) for Pump Control using Unitronics VisiLogic / UniLogic requires a documented design, applicable standards, and project-specific acceptance criteria. This guide organizes practical checks for code structure, diagnostics, testing, and maintenance.

The example references Jazz 2-family terminology, but model capabilities vary. Verify the controller manual, the installed VisiLogic / UniLogic version, and any applicable machinery, process, electrical, or functional-safety requirements for the actual project.

Best practices for Pump Control encompass multiple dimensions: proper handling of 5 sensor types, safe control of 5 different actuators, managing pressure regulation, and ensuring compliance with relevant industry standards. The Sequential Function Charts (SFC) approach, when properly implemented, provides perfect for sequential processes and clear visualization of process flow, both critical for intermediate projects.

This guide presents a reviewable approach to Unitronics Sequential Function Charts (SFC) programming for Pump Control, covering code organization, documentation, test procedures, and maintenance handoff. The sample logic is educational and must be compiled, simulated, peer-reviewed, and tested against the project's acceptance criteria before use on equipment.

Unitronics VisiLogic / UniLogic for Pump Control

VisiLogic / UniLogic is a programming environment associated with Unitronics controller families such as Jazz 2, Samba 7", Vision V350. This guide uses Sequential Function Charts (SFC) terminology from the supplied guide dataset, but controller capabilities and language support can change by model, firmware, software edition, and license.

Verify Before You Start:

The selected controller supports the required Sequential Function Charts (SFC) constructs

The project version matches the installed VisiLogic / UniLogic release

Required communications, motion, safety, and simulation options are licensed

Firmware and device-description files are compatible with the project

The vendor manuals used for the design match the exact hardware revision

Application Planning:

For a Pump Control exercise, map the required inputs and outputs before writing logic. The example considers 5 sensor types, including Pressure transmitters, Flow meters, Level sensors, and 5 actuator types.

Control Equipment for Pump Control:

Centrifugal pumps for high flow applications

Positive displacement pumps for metering

Submersible pumps for wet well applications

Booster pump systems for pressure maintenance

Controller-family references used in this guide include:

Jazz 2: Confirm CPU, I/O, memory, communications, and Sequential Function Charts (SFC) support in the current selection guide

Samba 7": Confirm CPU, I/O, memory, communications, and Sequential Function Charts (SFC) support in the current selection guide

Vision V350: Confirm CPU, I/O, memory, communications, and Sequential Function Charts (SFC) support in the current selection guide

Vision V570: Confirm CPU, I/O, memory, communications, and Sequential Function Charts (SFC) support in the current selection guide

Hardware Selection Checklist:

Count local and remote I/O, including planned expansion

Measure the required task and communications update rates

Identify memory, data-retention, diagnostics, and cybersecurity requirements

Treat safety functions as a separate, standards-led design activity

Confirm lifecycle status, regional availability, licensing, and support

Source and Validation Note:

This page does not represent a vendor certification or a hardware acceptance test. Use current Unitronics manuals, release notes, and safety documentation as the authority for product-specific behavior. Validate adapted logic in a simulator or isolated test setup before connecting it to equipment.

Investment Considerations:

For Pump Control projects, compare hardware, software licensing, training, engineering, test equipment, commissioning, spares, and ongoing support. Obtain current pricing and lifecycle information directly from the vendor or an authorized regional supplier.

Understanding Sequential Function Charts (SFC) for Pump Control

Sequential Function Chart (SFC) is a graphical language for programming sequential processes. It models systems as a series of steps connected by transitions, ideal for batch processes and machine sequences.

Execution Model:

Only active steps execute their actions. Transitions define conditions for moving between steps. Multiple steps can be active simultaneously in parallel branches.

Core Advantages for Pump Control:

Perfect for sequential processes: Critical for Pump Control when handling intermediate control logic

Clear visualization of process flow: Critical for Pump Control when handling intermediate control logic

Easy to understand process steps: Critical for Pump Control when handling intermediate control logic

Good for batch operations: Critical for Pump Control when handling intermediate control logic

Simplifies complex sequences: Critical for Pump Control when handling intermediate control logic

Why Sequential Function Charts (SFC) Fits Pump Control:

Pump Control systems in Water & Wastewater typically involve:

Sensors: Pressure transmitters for discharge and suction pressure, Flow meters (magnetic, ultrasonic, or vortex), Level transmitters for tank or wet well level

Actuators: Variable frequency drives (VFDs) for speed control, Motor starters (DOL or soft start), Control valves for flow regulation

Complexity: Intermediate with challenges including Preventing cavitation at low suction pressure

Control Strategies for Pump Control:

constant: Maintain fixed speed or output

pressure: PID control to maintain discharge pressure setpoint

flow: PID control to maintain flow rate setpoint

Programming Fundamentals in Sequential Function Charts (SFC):

Steps:
- initialStep: Double-bordered box - starting point of sequence, active on program start
- normalStep: Single-bordered box - becomes active when preceding transition fires
- actions: Associated code that executes while step is active

Transitions:
- condition: Boolean expression that must be TRUE to advance
- firing: Transition fires when preceding step is active AND condition is TRUE
- priority: In selective branches, transitions are evaluated in defined order

ActionQualifiers:
- N: Non-stored - executes while step is active
- S: Set - sets output TRUE on step entry, remains TRUE
- R: Reset - sets output FALSE on step entry

Best Practices for Sequential Function Charts (SFC):

Start with a clear process flow diagram before implementing SFC

Use descriptive step names indicating what happens (e.g., Filling, Heating)

Keep transition conditions simple - complex logic goes in action code

Implement timeout transitions to prevent stuck sequences

Always provide a path back to initial step for reset/restart

Common Mistakes to Avoid:

Forgetting to include stop/abort transitions for emergency handling

Creating deadlocks where no transition can fire

Not handling the case where transition conditions never become TRUE

Using S (Set) actions without corresponding R (Reset) actions

Typical Applications:

1. Bottle filling: Directly applicable to Pump Control
2. Assembly sequences: Related control patterns
3. Material handling: Related control patterns
4. Batch mixing: Related control patterns

Understanding these fundamentals prepares you to implement effective Sequential Function Charts (SFC) solutions for Pump Control using Unitronics VisiLogic / UniLogic.

Implementing Pump Control with Sequential Function Charts (SFC)

Pump control systems use PLCs to regulate liquid flow in industrial processes, water treatment, and building services. These systems manage pump operation, protect equipment, optimize energy use, and maintain process parameters.

This walkthrough demonstrates practical implementation using Unitronics VisiLogic / UniLogic and Sequential Function Charts (SFC) programming.

System Requirements:

A typical Pump Control implementation includes:

Input Devices (Sensors):
1. Pressure transmitters for discharge and suction pressure: Critical for monitoring system state
2. Flow meters (magnetic, ultrasonic, or vortex): Critical for monitoring system state
3. Level transmitters for tank or wet well level: Critical for monitoring system state
4. Temperature sensors for bearing and motor monitoring: Critical for monitoring system state
5. Vibration sensors for predictive maintenance: Critical for monitoring system state

Output Devices (Actuators):
1. Variable frequency drives (VFDs) for speed control: Primary control output
2. Motor starters (DOL or soft start): Supporting control function
3. Control valves for flow regulation: Supporting control function
4. Isolation valves (actuated for remote operation): Supporting control function
5. Check valves to prevent backflow: Supporting control function

Control Equipment:

Centrifugal pumps for high flow applications

Positive displacement pumps for metering

Submersible pumps for wet well applications

Booster pump systems for pressure maintenance

Control Strategies for Pump Control:

constant: Maintain fixed speed or output

pressure: PID control to maintain discharge pressure setpoint

flow: PID control to maintain flow rate setpoint

level: Control tank/wet well level within band

Implementation Steps:

Step 1: Characterize pump curve and system curve

In VisiLogic / UniLogic, characterize pump curve and system curve.

Step 2: Size VFD for application (constant torque vs. variable torque)

In VisiLogic / UniLogic, size vfd for application (constant torque vs. variable torque).

Step 3: Implement primary control loop (pressure, flow, or level)

In VisiLogic / UniLogic, implement primary control loop (pressure, flow, or level).

Step 4: Add pump protection logic (minimum flow, temperature, seal)

In VisiLogic / UniLogic, add pump protection logic (minimum flow, temperature, seal).

Step 5: Program lead/lag sequencing with alternation

In VisiLogic / UniLogic, program lead/lag sequencing with alternation.

Step 6: Implement soft start/stop ramps for smooth operation

In VisiLogic / UniLogic, implement soft start/stop ramps for smooth operation.

Unitronics Function Design:

Function block design in Unitronics uses user-defined FBs in UniLogic (more limited in VisiLogic). Extensive vendor-provided helper FBs cover common tasks (PID, motion, communication, HMI utilities). OEM machine builders typically maintain private FB libraries for their common machine patterns, though code reuse is less mature than in mainstream PLC ecosystems.

Common Challenges and Solutions:

1. Preventing cavitation at low suction pressure

Solution: Sequential Function Charts (SFC) addresses this through Perfect for sequential processes.

2. Managing minimum flow requirements

Solution: Sequential Function Charts (SFC) addresses this through Clear visualization of process flow.

3. Coordinating VFD speed with system pressure

Solution: Sequential Function Charts (SFC) addresses this through Easy to understand process steps.

4. Handling pump cycling with varying demand

Solution: Sequential Function Charts (SFC) addresses this through Good for batch operations.

Safety Considerations:

Dry run protection using flow or level monitoring

Overtemperature protection for motor and bearings

Overload protection through current monitoring

Vibration trips for mechanical failure detection

Emergency stop with proper system depressurization

Performance Metrics:

Task and I/O timing: Record minimum, average, and maximum values under a defined test load

Accuracy: Define an acceptable tolerance and compare it with calibrated reference measurements

Throughput: Count completed cycles over a fixed interval and record rejected or incomplete cycles

Fault response: Measure detection, safe-state, alarm, and recovery behavior for each test case

Resource use: Record memory, communications load, and diagnostic-buffer behavior

Unitronics Diagnostic Tools:

UniLogic (current) and VisiLogic (legacy) integrated debuggers with breakpoints,Built-in simulator covering PLC logic, HMI screens, alarms, recipes, and data tables,Web visualisation for UniStream — remote HMI viewing without additional software,SD card logging with PC-side export tools for offline trend analysis,Modbus RTU/TCP transaction logging built into the IDE,Controller status monitor — CPU load, scan time, memory usage,HMI event logger capturing operator actions for audit purposes,CAN bus diagnostic tools for CANopen-equipped models,Remote support tool — Unitronics' own screen-sharing for technical support,User community forum with active troubleshooting discussions

Use the monitoring and diagnostic functions available in your VisiLogic / UniLogic version, and record the software, firmware, hardware, workload, and test procedure with every result.

Unitronics Sequential Function Charts (SFC) Example for Pump Control

Illustrative Sequential Function Charts (SFC) example for Pump Control using Unitronics terminology. Adapt the syntax to your VisiLogic / UniLogic release, compile it, and verify it in an isolated test environment before use on equipment.

// Unitronics VisiLogic / UniLogic - Pump Control Control
// Sequential Function Charts (SFC) Implementation for Water & Wastewater
// Unitronics projects use IDE-managed tag names rather than ra

// ============================================
// Variable Declarations
// ============================================
VAR
    bEnable : BOOL := FALSE;
    bEmergencyStop : BOOL := FALSE;
    rPressuretransmitters : REAL;
    rCentrifugalpumps : REAL;
END_VAR

// ============================================
// Input Conditioning - Pressure transmitters for discharge and suction pressure
// ============================================
// Standard input processing
IF rPressuretransmitters > 0.0 THEN
    bEnable := TRUE;
END_IF;

// ============================================
// Safety Interlock - Dry run protection using flow or level monitoring
// ============================================
IF bEmergencyStop THEN
    rCentrifugalpumps := 0.0;
    bEnable := FALSE;
END_IF;

// ============================================
// Main Pump Control Control Logic
// ============================================
IF bEnable AND NOT bEmergencyStop THEN
    // Pump control systems use PLCs to regulate liquid flow in ind
    rCentrifugalpumps := rPressuretransmitters * 1.0; (* Illustrative scaling only *)

    // Process monitoring
    // Add specific control logic here
ELSE
    rCentrifugalpumps := 0.0;
END_IF;

Code Explanation:

1.Sequential Function Charts (SFC) structure organized for a Pump Control training example
2.Input conditioning handles Pressure transmitters for discharge and suction pressure signals
3.Safety interlock ensures Dry run protection using flow or level monitoring always takes priority
4.Main control implements Pump control systems use PLCs to regulat
5.Adapt the scan-cycle assumptions to the selected Jazz 2 task configuration and verify them by measurement

Best Practices

✓Follow Unitronics naming conventions: Unitronics projects use IDE-managed tag names rather than raw memory addressing.
✓Unitronics function design: Function block design in Unitronics uses user-defined FBs in UniLogic (more limi
✓Data organization: Unitronics uses its own tag database concept rather than IEC-standard data block
✓Sequential Function Charts (SFC): Start with a clear process flow diagram before implementing SFC
✓Sequential Function Charts (SFC): Use descriptive step names indicating what happens (e.g., Filling, Heating)
✓Sequential Function Charts (SFC): Keep transition conditions simple - complex logic goes in action code
✓Pump Control: Use PID with derivative on PV for pressure control
✓Pump Control: Implement soft start ramps even with VFD (200-500ms)
✓Pump Control: Add flow proving before considering pump operational
✓Debug with VisiLogic / UniLogic: Use the built-in simulator to reproduce issues before hardware visit
✓Safety: Dry run protection using flow or level monitoring
✓Use a compatible simulator or isolated test rig to test Pump Control logic before deployment

Common Pitfalls to Avoid

⚠Sequential Function Charts (SFC): Forgetting to include stop/abort transitions for emergency handling
⚠Sequential Function Charts (SFC): Creating deadlocks where no transition can fire
⚠Sequential Function Charts (SFC): Not handling the case where transition conditions never become TRUE
⚠Unitronics common error: VisiLogic-to-UniLogic migration issues — not all projects convert cleanly
⚠Pump Control: Preventing cavitation at low suction pressure
⚠Pump Control: Managing minimum flow requirements
⚠Neglecting to validate Pressure transmitters for discharge and suction pressure leads to control errors
⚠Insufficient comments make Sequential Function Charts (SFC) programs unmaintainable over time

Related Certifications

🏆Unitronics Certified Integrator

🏆UniLogic Developer Training

Applying Sequential Function Charts (SFC) to Pump Control using Unitronics VisiLogic / UniLogic requires understanding the platform, the process, and the project's acceptance criteria. This guide has covered implementation structure, an illustrative code example, verification practices, and common pitfalls for a intermediate Pump Control exercise.

Use the practices outlined here to create a design that can be reviewed and tested. Define performance targets in the project requirements and confirm them with repeatable measurements.

Next Steps:

1. Check Sources: Read the current VisiLogic / UniLogic help, controller manual, release notes, and relevant standards
2. Practice Safely: Adapt the example in a simulator or isolated training setup
3. Review: Have the I/O map, state behavior, faults, and recovery steps reviewed
4. Test: Record normal, boundary, fault, restart, and communications test results

Sequential Function Charts (SFC) Foundation:

Sequential Function Chart (SFC) is a graphical language for programming sequential processes. It models systems as a series of steps connected by tran...

Project duration depends on scope, reviews, hardware availability, software and firmware versions, testing, commissioning, and site constraints. Remember: Use PID with derivative on PV for pressure control

For further learning, explore related topics including Assembly sequences, Wastewater treatment, and Unitronics platform-specific features for Pump Control optimization.