The flavor mixing system is the core equipment for food flavor production, achieving precise formula control and efficient production. This article introduces the key points of the application of Siemens PLC in flavor mixing systems.
1. Hardware Configuration
1.1. PLC and Expansion Module Selection
For the specific needs of the flavor mixing system, it is recommended to use the Siemens S7-1500 series PLC as the core controller. This series has fast processing speed and high precision in analog control, making it particularly suitable for precise measurement and multi-recipe management. The specific configuration is as follows:
CPU Unit: S7-1516-3 PN/DP, with powerful data processing capabilities and rich communication interfaces
Analog Input Module: SM 531, 16 points, used to connect various tank level sensors and flow meters
Analog Output Module: SM 532, 8 points, used to control proportional valves and variable frequency pumps
Digital Input Module: SM 521, 32 points, used to receive various switch signals
Digital Output Module: SM 522, 16 points, used to control solenoid valves, indicator lights, etc.
1.2. I/O Point Allocation Table
| Address | Description | Type |
|---|---|---|
| %I0.0-%I0.7 | Tank level switches | Digital Input |
| %I1.0-%I1.3 | Emergency stop buttons | Digital Input |
| %I1.4-%I1.7 | System operation status feedback | Digital Input |
| %Q0.0-%Q0.7 | Solenoid valve control | Digital Output |
| %Q1.0-%Q1.3 | Alarm indicator lights | Digital Output |
| %IW64-%IW78 | Tank level analog values | Analog Input |
| %IW80-%IW94 | Flow meter readings | Analog Input |
| %QW64-%QW70 | Proportional valve control | Analog Output |
| %QW72-%QW76 | Variable frequency pump control | Analog Output |
1.3. System Wiring Key Points
All analog signals use shielded twisted pair cables, and should be wired away from high voltage equipment
The variable frequency drive control lines should be wired separately, avoiding parallel runs with other signal lines
The sensor grounding points should be unified, to prevent ground loops
Key valves should use 24V DC power supply, equipped with UPS for safety
2. Control Program Design
2.1. Program Architecture Design
The flavor mixing system adopts a hierarchical program structure, which is convenient for maintenance and upgrades:
plaintext
- OB1: Main loop program, calls various function blocks
|- FB1: System initialization (Init_System)
|- FB2: Recipe management (Recipe_Manager)
|- FB3: Mixing control (Mixing_Control)
|- FB4: Valve control (Valve_Control)
|- FB5: Flow control (Flow_Control)
|- FB6: Alarm handling (Alarm_Handler)
|- FB7: HMI communication (HMI_Comm)2.2. Function Block Design
Taking the flow control function block as an example, it achieves precise flow control:
pascal
FUNCTION_BLOCK "Flow_Control"
VAR_INPUT
Target_Flow: REAL; // Target flow value L/min
Flow_Feedback: REAL; // Flow meter feedback value
Enable: BOOL; // Enable control
END_VAR
VAR_OUTPUT
Valve_Position: REAL; // Valve opening output 0-100%
Flow_Error: BOOL; // Flow error flag
END_VAR
VAR
PID_Ctrl: FB41; // PID controller instance
PID_DB: DB41; // PID data block
Error_Calc: REAL; // Error calculation
END_VAR
// PID controller call
"PID_Ctrl"(
Setpoint:=#Target_Flow,
Input:=#Flow_Feedback,
Output=>#Valve_Position,
DB:=#PID_DB
);
// Error monitoring
#Error_Calc:=ABS(#Target_Flow-#Flow_Feedback);
IF #Error_Calc>0.5 AND #Enable THEN
#Flow_Error:=TRUE;
ELSE
#Flow_Error:=FALSE;
END_IF;2.3. State Control Design
The flavor mixing system uses a state machine approach for control, ensuring orderly execution of each process:
pascal
CASE #System_State OF
0: // Standby state
IF #Start_Command AND #All_Conditions_OK THEN
#System_State := 10; // Transition to initialization
END_IF;
10: // Initialization state
// Initialization code
IF #Init_Complete THEN
#System_State := 20; // Transition to recipe loading
END_IF;
20: // Recipe loading
// Recipe loading code
IF #Recipe_Loaded THEN
#System_State := 30; // Transition to mixing preparation
END_IF;
30: // Mixing preparation
// Preparation code
IF #Ready_For_Mixing THEN
#System_State := 40; // Transition to mixing execution
END_IF;
40: // Mixing execution
// Mixing execution code
IF #Mixing_Complete THEN
#System_State := 50; // Transition to completion state
END_IF;
50: // Completion state
// Completion state code
IF #Reset_Command THEN
#System_State := 0; // Return to standby state
END_IF;
ELSE // Exception state
// Exception handling code
#System_State := 0; // Return to standby state
END_CASE;3. Data Management and Storage
3.1. Parameter Configuration Table
The flavor recipe parameters are stored in a data block for easy access and modification by the HMI:
pascal
DATA_BLOCK "Recipe_DB"
STRUCT
Recipe_ID: INT; // Recipe ID
Recipe_Name: STRING[30]; // Recipe name
Recipe_Date: DATE; // Creation date
Component_Count: INT; // Number of components
Components: ARRAY[1..20] OF STRUCT
Material_ID: INT; // Material ID
Material_Name: STRING[20]; // Material name
Percentage: REAL; // Percentage (0-100%)
Target_Weight: REAL; // Target weight (kg)
Tolerance: REAL; // Allowable error (%)
END_STRUCT;
Total_Weight: REAL; // Total weight (kg)
Mixing_Time: TIME; // Mixing time
Mixing_Speed: INT; // Mixing speed (0-100%)
Temperature: REAL; // Mixing temperature (°C)
END_STRUCT3.2. Operating Data Recording
The system operating data is recorded in a circular buffer data block, supporting data traceability and analysis:
pascal
DATA_BLOCK "Process_Data_DB"
STRUCT
Current_Index: INT := 0; // Current record index
Max_Records: INT := 1000; // Maximum number of records
Records: ARRAY[0..999] OF STRUCT
Timestamp: DTL; // Timestamp
Recipe_ID: INT; // Recipe ID
Batch_ID: DINT; // Batch number
Component_ID: INT; // Component ID
Target_Value: REAL; // Target value
Actual_Value: REAL; // Actual value
Deviation: REAL; // Deviation
Valve_Position: REAL; // Valve position
Flow_Rate: REAL; // Flow rate
Status: WORD; // Status word
END_STRUCT;
END_STRUCT4. HMI Design
4.1. Interface Layout Description
The HMI interface of the flavor mixing system adopts a multi-level structure, with the main interface layout as follows:
Top Area: System title, date and time, login status, alarm indication
Left Area: Navigation menu (recipe management, production control, system monitoring, alarm history, parameter settings)
Central Area: Process flow diagram, dynamically displaying tank levels, valve statuses, and flow data
Right Area: Current production information (batch number, recipe name, progress bar, countdown)
Bottom Area: System status bar, information prompts
4.2. Parameter Setting Description
The recipe parameter setting interface provides the following functions:
Recipe creation, editing, copying, deletion
Component ratio graphical display (pie chart)
Batch import/export of parameters (CSV format)
Parameter validity verification (sum check, boundary check)
Permission control (operator/engineer/admin)
5. Fault Diagnosis and Troubleshooting
5.1. Common Fault Analysis
| Fault Phenomenon | Possible Causes | Troubleshooting Methods |
|---|---|---|
| Unstable flow | 1. PID parameters are inappropriate2. Flow meter failure3. Valve response is slow | 1. Retune PID parameters2. Check flow meter signal3. Check valve actuator |
| Recipe loading failure | 1. Recipe data error2. DB access permission issues3. Communication interruption | 1. Check recipe data integrity2. Check DB attribute configuration3. Check HMI communication status |
| Mixing accuracy deviation | 1. Sensor drift2. Flow meter not calibrated3. Calculation precision issues | 1. Calibrate the sensor2. Recalibrate the flow meter3. Check data type conversion |
5.2. Use of Diagnostic Tools
During fault diagnosis, the following tools can be used to improve efficiency:
TIA Portal Online Diagnostics: Real-time monitoring of variable values, using tracking functions to analyze flow fluctuations
ProDiag Function: Configure monitoring points, automatically capture abnormal conditions
HMI Trend Graphs: Analyze historical curves of key parameters to identify abnormal patterns
Alarm Statistical Analysis: Statistics on alarm frequency, identifying frequent fault points
6. Conclusion
The Siemens PLC in the flavor mixing system can achieve high-precision formula control and intelligent production management. For any special application needs, feel free to communicate and discuss!
