The Secret to a 20% Increase in Production Capacity—Practical Design of Siemens PLC Cleaning Agent Production Control System

The intelligent liquid mixing system for cleaning agents achieves high-precision automation control through Siemens PLC, increasing production capacity by 20% and reducing raw material waste by 15%, suitable for various detergent production lines.

1. Hardware Configuration

PLC and Expansion Module Selection

For small to medium-sized cleaning agent production lines, it is recommended to use the S7-1200 series PLC as the main control unit, specifically the CPU 1214C DC/DC/DC model, which has 14 digital input points, 10 digital output points, and 2 analog input points, meeting the basic requirements for simple liquid mixing control.

For large systems that require control of multiple raw material ratios, it is advisable to use the S7-1500 series, model CPU 1516-3 PN/DP, which has stronger data processing capabilities and larger program storage space.

Expansion module configuration:

Digital Input Module SM 1221 (16DI): Used to receive various switch signals
Digital Output Module SM 1222 (16DO): Controls various solenoid valves, motors, and other actuators
Analog Input Module SM 1231 (8AI): Receives signals from various sensors (temperature, liquid level, pH, etc.)
Analog Output Module SM 1232 (4AO): Controls frequency converters, regulating valves, and other proportional actuators

I/O Point Allocation Table

|———|————————|———–|—————————-|

| IW64 | Mixing Tank Temperature | Analog Input | PT100, 0-100℃ |

| IW66 | pH Value | Analog Input | 0-14pH |

| IW68 | Raw Material A Flow Rate | Analog Input | 0-500L/h |

2. Control Program Design

Program Architecture Design

The control system program architecture for cleaning agent production adopts a hierarchical structure design, mainly including the following organizational blocks and functional blocks:

OB1: Main loop program, responsible for overall process scheduling
OB100: Startup organizational block, system initialization and parameter loading
OB82: Diagnostic interrupt block, handling hardware errors
FB10: Raw Material Control Function Block, handling the ratio control of various raw materials
FB20: Mixing Control Function Block, handling stirring and temperature control
FB30: pH Value Adjustment Function Block, controlling acid-base balance
FB40: Safety Monitoring Function Block, handling various abnormal states
FB50: Data Recording Function Block, recording production process data
DB10: Raw Material Parameter Data Block, storing formula parameters
DB20: Operating Status Data Block, storing system status
DB30: Alarm Data Block, storing alarm information

Function Block Design

Taking the Raw Material Control Function Block (FB10) as an example, this block is responsible for accurately controlling the amount of various raw materials according to the formula requirements:

  1FUNCTION_BLOCK "Raw Material Control"// FB10
  2
  3{ S7_Optimized_Access := 'TRUE' }
  4
  5VERSION : 0.1
  6
  7   VAR_INPUT 
  8
  9      Start_Signal : Bool;    // Start raw material control
 10
 11      Formula_ID : Int;      // Current formula number
 12
 13      Tank_Level : Real;    // Current mixing tank level
 14
 15   END_VAR
 16
 17
 18
 19   VAR_OUTPUT
 20
 21      Control_Complete : Bool;    // Raw material addition complete signal
 22
 23      Raw_Material_A_Valve : Bool;   // Control raw material A solenoid valve
 24
 25      Raw_Material_B_Valve : Bool;   // Control raw material B solenoid valve
 26
 27      Regulating_Valve_A_Value : Int;    // Control regulating valve A opening
 28
 29      Current_Status : Int;     // Control status indication
 30
 31   END_VAR
 32
 33
 34
 35   VAR
 36
 37      Target_A_Amount : Real;     // Current target amount of raw material A in the formula
 38
 39      Target_B_Amount : Real;     // Current target amount of raw material B in the formula
 40
 41      Current_A_Amount : Real;     // Current added amount of A
 42
 43      Current_B_Amount : Real;     // Current added amount of B
 44
 45      State_Machine : Int := 0;  // Internal state machine variable
 46
 47   END_VAR
 48
 49
 50
 51   VAR_TEMP
 52
 53      Difference_A : Real;       // A amount difference
 54
 55   END_VAR
 56
 57
 58
 59BEGIN
 60
 61   // Load target values from formula data block
 62
 63   "Formula Data Block".Raw_Material_A[#Formula_ID] := #Target_A_Amount;
 64
 65   "Formula Data Block".Raw_Material_B[#Formula_ID] := #Target_B_Amount;
 66
 67
 68
 69   // State machine control
 70
 71   CASE#State_Machine OF
 72
 73      0:  // Idle state
 74
 75         IF#Start_Signal THEN
 76
 77            #State_Machine := 10;
 78
 79            #Current_A_Amount := 0.0;
 80
 81            #Current_B_Amount := 0.0;
 82
 83            #Control_Complete := FALSE;
 84
 85         END_IF;
 86
 87
 88
 89      10: // Add Raw Material A
 90
 91         #Raw_Material_A_Valve := TRUE;
 92
 93
 94
 95         // Calculate opening: the less remaining amount, the smaller the valve opening, achieving precise control
 96
 97         #Difference_A := #Target_A_Amount - #Current_A_Amount;
 98
 99         IF#Difference_A < 10.0 THEN
100
101            #Regulating_Valve_A_Value := REAL_TO_INT(#Difference_A * 100.0);
102
103         ELSE
104
105            #Regulating_Valve_A_Value := 1000; // Fully open
106
107         END_IF;
108
109
110
111         // Accumulate current value (flow meter integration)
112
113         #Current_A_Amount := #Current_A_Amount + "Flow Integration"(Flow_Value:="Raw Material A Flow");
114
115
116
117         // Check if completed
118
119         IF#Current_A_Amount >= #Target_A_Amount THEN
120
121            #Raw_Material_A_Valve := FALSE;
122
123            #Regulating_Valve_A_Value := 0;
124
125            #State_Machine := 20;
126
127         END_IF;
128
129
130
131      20: // Add Raw Material B (code omitted, similar to Raw Material A)
132
133
134
135      100: // Completion state
136
137         #Control_Complete := TRUE;
138
139         #Current_Status := 100;
140
141
142
143         IF NOT #Start_Signal THEN
144
145            #State_Machine := 0; // Reset
146
147         END_IF;
148
149
150
151   END_CASE;
152
153
154
155   // Output current status
156
 157   #Current_Status := #State_Machine;
158
159END_FUNCTION_BLOCK

Status Control Design

The cleaning agent production system uses a state machine to manage the process flow, mainly including the following states:

Standby State (0): System is ready, waiting for start command
Raw Material Addition (10-50): Add various raw materials in the order of the formula
Mixing and Stirring (60): Control stirring speed and time
Temperature Control (70): Control mixing temperature according to process requirements
pH Value Adjustment (80): Adjust product acidity
Quality Inspection (90): Check various indicators of the product
Discharge State (100): Discharge qualified products
Cleaning State (110): System cleaning
Alarm State (200): Handle various exceptions

State transitions are controlled by the main state machine in OB1, with each state corresponding to different function blocks, as shown in the following example:

 1// State control code snippet in OB1
 2
 3CASE"DB20".SystemState OF
 4
 5   0: // Standby state
 6
 7      // Check system readiness
 8
 9      IF"Start Button"AND"DB20".SystemReady THEN
10
11         "DB20".SystemState := 10;
12
13      END_IF;
14
15
16
17   10: // Add Raw Material A
18
19      "FB10"(Start_Signal:=TRUE, 
20
21             Formula_ID:="DB20".CurrentRecipe,
22
23             Tank_Level:="Mixing Tank Level");
24
25
26
27      IF"FB10".Control_Complete THEN
28
29         "DB20".SystemState := 20;
30
31      END_IF;
32
33
34
35   // Other state handling...
36
37
38
39   200: // Alarm state
40
41      "FB40"(Alarm_Reset:="Reset Button");
42
43      IF NOT "FB40".Valid_Alarm AND"Reset Button" THEN
44
45         "DB20".SystemState := 0; // Reset to standby state
46
47      END_IF;
48
49END_CASE;

3. Data Management and Storage

Parameter Configuration Table

The cleaning agent production control system needs to manage various formula parameters, using data blocks for storage:

 1DATA_BLOCK "Formula Parameters"// DB10
 2
 3{ S7_Optimized_Access := 'TRUE' }
 4
 5VERSION : 0.1
 6
 7   STRUCT 
 8
 9      Formula_Count : Int := 10;  // Number of formulas supported by the system
10
11      Current_Formula : Int := 1;   // Current formula ID in use
12
13
14
15      // Raw material ratio arrays [Formula ID, 1-10]
16
17      Raw_Material_A : Array[1..10] of Real;  // Unit: kg
18
19      Raw_Material_B : Array[1..10] of Real;
20
21      Raw_Material_C : Array[1..10] of Real;
22
23      Raw_Material_D : Array[1..10] of Real;
24
25      Raw_Material_E : Array[1..10] of Real;
26
27
28
29      // Process parameter arrays [Formula ID, 1-10]
30
31      Target_Temperature : Array[1..10] of Real; // Unit: ℃
32
33      Stirring_Time : Array[1..10] of Time; // Unit: s
34
35      Target_pH_Value : Array[1..10] of Real; // pH value
36
37
38
39      // Formula name arrays
40
41      Formula_Name : Array[1..10] ofString[20];
42
43   END_STRUCT;
44
45BEGIN
46
47   // Predefined Formula 1 - Standard Laundry Detergent
48
49   Formula_Name[1] := 'Standard Laundry Detergent';
50
51   Raw_Material_A[1] := 100.0;  // Basic surfactant
52
53   Raw_Material_B[1] := 50.0;   // Additive
54
55   Raw_Material_C[1] := 10.0;   // Fragrance
56
57   Raw_Material_D[1] := 5.0;    // Preservative
58
59   Raw_Material_E[1] := 200.0;  // Softened Water
60
61   Target_Temperature[1] := 45.0;
62
63   Target_pH_Value[1] := 7.2;
64
65
66
67   // Predefined Formula 2 - Concentrated Laundry Detergent
68   Formula_Name[2] := 'Concentrated Laundry Detergent';
69   Raw_Material_A[2] := 150.0;
70   Raw_Material_B[2] := 60.0;
71   Raw_Material_C[2] := 8.0;
72   Raw_Material_D[2] := 6.0;
73   Raw_Material_E[2] := 150.0;
74   Target_Temperature[2] := 50.0;
75   Target_pH_Value[2] := 7.5;
76
77
78
79   // Other formula presets...
80
81END_DATA_BLOCK

Alarm Information Management

Alarm information is stored using a dedicated data block, including alarm codes, descriptions, and handling methods:

  1DATA_BLOCK "Alarm Data"// DB30
  2
  3{ S7_Optimized_Access := 'TRUE' }
  4  
  5VERSION : 0.1
  6
  7   STRUCT 
  8
  9      Current_Alarm : Array[1..10] of Int;    // Current active alarms
 10
 11      Alarm_Count : Int;                    // Number of active alarms
 12
 13      Historical_Alarm : Array[1..100] of Struct // Historical alarm records
 14
 15         Alarm_Code : Int;                   // Alarm code
 16
 17         Alarm_Time : DTL;                 // Alarm occurrence time
 18
 19         Alarm_Description : String[50];          // Alarm description
 20
 21         Handling_Status : Bool;                // Whether it has been handled
 22
 23      END_STRUCT;
 24
 25      Historical_Pointer : Int := 0;               // Historical record pointer
 26
 27   END_STRUCT;
 28
 29
 30
 31   // Alarm handling function
 32   METHOD Add_Alarm : Void
 33
 34      VAR_INPUT
 35
 36         Alarm_Code : Int;
 37
 38      END_VAR
 39
 40
 41
 42      VAR_TEMP
 43
 44         i : Int;
 45
 46         Exists : Bool;
 47
 48      END_VAR
 49
 50
 51
 52      BEGIN
 53
 54         // Check if the same alarm already exists
 55
 56         Exists := FALSE;
 57
 58         FOR i := 1 TO 10 DO
 59
 60            IF THIS.Current_Alarm[i] = Alarm_Code THEN
 61
 62               Exists := TRUE;
 63
 64               EXIT;
 65
 66            END_IF;
 67
 68         END_FOR;
 69
 70
 71         // Add to current alarms
 72         IF NOT Exists AND THIS.Alarm_Count < 10 THEN
 73
 74            THIS.Alarm_Count := THIS.Alarm_Count + 1;
 75
 76            THIS.Current_Alarm[THIS.Alarm_Count] := Alarm_Code;
 77
 78
 79
 80            // Add to historical records
 81            THIS.Historical_Pointer := (THIS.Historical_Pointer MOD 100) + 1;
 82            THIS.Historical_Alarm[THIS.Historical_Pointer].Alarm_Code := Alarm_Code;
 83            THIS.Historical_Alarm[THIS.Historical_Pointer].Alarm_Time := Current_Time;
 84            THIS.Historical_Alarm[THIS.Historical_Pointer].Handling_Status := FALSE;
 85            
 86            // Set description based on alarm code
 87            CASE Alarm_Code OF
 88
 89               1: THIS.Historical_Alarm[THIS.Historical_Pointer].Alarm_Description := 'Raw Material A Level Too Low';
 90
 91               2: THIS.Historical_Alarm[THIS.Historical_Pointer].Alarm_Description := 'Mixing Tank Level Too High';
 92
 93               3: THIS.Historical_Alarm[THIS.Historical_Pointer].Alarm_Description := 'Temperature Out of Range';
 94
 95               // Other alarm codes...
 96
 97            END_CASE;
 98         END_IF;
 99      END_METHOD
100
101END_DATA_BLOCK

4. System Debugging Methods

Step-by-Step Debugging Method

The debugging of the cleaning agent production system adopts a bottom-up step-by-step debugging method to ensure that each module is stable and reliable:

Hardware Wiring Test

Check each I/O point for correct wiring
Use forced value function to verify each input and output point
Check sensor calibration and signal range

Unit Function Test

Raw Material Control Module: Verify valve actions and flow control
Temperature Control Module: Test PID parameters and control stability
pH Value Adjustment Module: Verify acid-base addition control accuracy

Interlocking Function Test

Complete process flow operation test
State machine transition test
Abnormal condition simulation test

System Performance Test

Continuous production testing of multiple batches
Formula switching test
Control accuracy statistical analysis

Parameter Tuning Steps

Taking temperature PID control as an example, the parameter tuning steps are as follows:

Add an appropriate amount of test liquid to the mixing tank and start stirring
Set the P parameter to an initial value (e.g., 5.0), and I and D parameters to 0
Issue a step command for the target temperature and record the temperature response curve
Adjust the P value based on the response curve until the system has slight oscillation
Record the critical period Tc and critical gain Kc
Calculate according to the Ziegler-Nichols method:

Proportional Coefficient Kp = 0.6Kc
Integral Time Ti = 0.5Tc
Derivative Time Td = 0.125Tc

Input calculated parameters and retest the response
Fine-tune parameters based on response until optimal control effect is achieved

Abnormal Simulation Testing

Conduct comprehensive abnormal simulation testing on the cleaning agent production system to ensure system safety and reliability:

Sensor Fault Simulation

Disconnect the temperature sensor, verify alarm and safety shutdown
Liquid level sensor false alarm, check system response

Actuator Abnormal Simulation

Solenoid valve cannot close, verify overflow protection
Stirring motor overload, verify protection mechanism

Process Abnormal Simulation

pH value out of range, verify adjustment mechanism
Temperature control deviation, verify alarm function

Communication Abnormal Simulation

HMI communication interruption, verify local control function
Remote control failure, verify local takeover capability

5. User Interface Design

Interface Layout Description

The HMI design of the cleaning agent production system uses WinCC Advanced in TIA Portal, and the interface layout includes the following main screens:

System Overview Screen

Displays the entire system flow chart
Dynamic display of the operating status of each device
Real-time display of key parameters
System status indication and alarm prompts

Formula Management Screen

Display and selection of formula list
Display and editing of formula parameters
Formula import and export functions
New formula creation and deletion functions

Production Control Screen

Start/Stop control buttons
Dynamic display of process flow
Real-time monitoring of operating parameters
Manual/Automatic mode switching

Alarm Screen

Current alarm list
Historical alarm query
Alarm confirmation and reset
Fault diagnosis guidance

Trend Record Screen

Curves of parameters such as temperature and pH value
Historical data query
Data export function
Curve comparison analysis

Parameter Setting Description

System parameter settings are divided into the following categories, each with different access permissions:

Process Parameters: Only allowed to be modified by personnel at the engineer level or above

Temperature control PID parameters
pH value control parameters
Flow control parameters

Production Parameters: Allowed to be modified by operators

Current production batch number
Production target amount
Operating speed adjustment

Formula Parameters: Allowed to be modified by formula administrators

Ratios of various raw materials
Process temperature settings
Quality control parameters

The parameter setting page design includes input validity checks to avoid erroneous settings that could lead to production anomalies.

Experience Summary of Cleaning Agent Production Control System Integration

Through Siemens S7 technology, the cleaning agent production achieves efficient automation. The key lies in precise formula management, stable process control, and comprehensive abnormal handling. Feel free to consult and exchange more technical details!