Lamtec FA1 User manual

www.lamtec.de
Sensors and Systems for Combustion Engineering
Manual
Burner Control FA1

2
Table of Contents
Table of Contents
1 General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Validity of these Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 For Your Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Brief Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 Display and Operational Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 Use of the Operating Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 Connecting the Burner Control FA1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Operating Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1 Starting without Pilot Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2 Starting with Pilot Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Starting without Control Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Basic Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2 Password Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3 Select Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4 Start with or without Pilot Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.5 Pre-purge Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.6 Deactivate Firing Rate Control Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.7 Running Time of the Regular Firing Rate Input with TPS-Input . . . . . . . . . . . . . . . . . . . 16
6.8 Minimum Running Time of the Fuel/Air Ratio Control . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.9 Post-purge Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.10 Delaytime of the Air Dampers During Pre-purge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.11 Parameters of the Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.12 Deactivating Valve Leakage Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.13 Set Pilot Burner (Maintenance Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.14 Automatic Restart after Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.15 Burner Firing Rate Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.15.1 Enter Set Point Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.15.2 Control Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.15.3 Setting the Control Thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.15.4 Controller Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.15.5 Outside Temperature Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.15.6 Display of the Units of the Burner Firing Rate Controller Values . . . . . . . . . . . . 23
6.15.7 Display Range in Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.16 Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.16.1 Setting the Limit Switches of the Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.16.2 Adjusting Control Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.16.2.1 Enter the Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.16.2.2 Clear Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.16.3 Programming the Ignition Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.16.4 Programming the Base Firing Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.16.5 Programming the 3rd up the 10th Point. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.16.6 Saving Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.16.7 Changing Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

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Table of Contents
6.16.8 Saving Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.17 Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.17.1 Reading Faults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.17.2 Resetting Faults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.17.3 Recalling Fault History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7 System Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1 Release Settings by Customer Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.2 Displaying the Running Time Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.3 Displaying Checksums and Safety Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.4 Re-enter Range Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8 Internal Burner Firing Rate Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.2 Brief Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.3 Range Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.4 Moving Screen "Actual Temperature is too high". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.5 How to Change the Burner-Firing-Rate Controller with the Customer Interface . . . . . . 31
8.6 Changing Setpoint of Burner-Firing-Rate Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.7 Input Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.8 Operating Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.9 Steam Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.10 Control by Atmospheric Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.11 Setpoint Changeover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.12 Start-up Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.13 Thermostat and Control Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8.14 Manual Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.15 How to Adjust the Burner Firing Rate Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.16 Control Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.17 Checking the Safety Limiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.18 Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
8.19 Aides for Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9 Valve Leakage Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.1 Valve Leakage Test Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
9.2 Calculation Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
10 Standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
10.1 Standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
10.2 Specification of the burner sequencer function "Standby Mode" . . . . . . . . . . . . . . . . . . 45
10.3 Switching into Standby Mode via LSB module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
11 Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
11.1 Mode Abbreviations Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
11.2 Flame Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.2.1 Integral Flame Monitoring (Option) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.2.1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.2.1.2 Characteristics flame sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.2.1.3 Self Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.2.2 General Information of the Optical Flame Monitoring . . . . . . . . . . . . . . . . . . . . 50
11.2.3 Optical Flame Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

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Table of Contents
11.2.3.1 Switching to Display the Flame Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
11.3 Avoiding EMC Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
11.4 Fault Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
11.5 Calling Up the Condition of the Digital Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
11.6 Tips and Tricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
11.6.1 Set Pilot Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
11.6.2 Checking the Safety Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
11.7 Process Sequence Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
11.8 Connection Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
11.9 Connection Examples of Firing Rate Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
11.10 Flame Scanner and Sensor Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
11.10.1 Flame Scanner Connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
11.10.2 Flame Sensor Connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
11.10.2.1 FFS07 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
11.10.2.2 FFS08 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.11 LAMTEC SYSTEM BUS (LSB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
11.11.1 LSB Connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
11.11.2 LSB Cable Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
11.12 Inernal Connecting Diagram of the Control Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
11.13 Valve Leakage Test Venting Over the Roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
11.14 Switch- and Key Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
11.14.1 Programming Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
11.14.2 Customer Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
11.15 Feedback at Three-Point-Step Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
11.15.1 Connect with Positive Locking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
11.15.2 Fail-Safe Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
11.15.3 Examples of Potentiometers and Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
11.16 Replacing the Device and Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
11.16.1 Replacing a Burner Control FA1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
11.16.2 How to Replace a Servo Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
11.16.3 How to Replace a Potentiometer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
11.17 Changing EPROMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
11.18 Wiring Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
11.18.1 Shields Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
11.18.2 PE Busbar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
11.18.3 Control Cabinet Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
11.19 Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
11.19.1 FA1 BurnerControl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
11.19.2 Customer Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
11.19.3 Programming Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
11.20 Burner Control FA1 without integral flame detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
11.21 Flame Scanner FFS07/FFS08 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
11.22 Declaration of Conformity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

5
1 General Information
1 General Information
1.1 Validity of these Instructions
These instructions apply to the FA1 and in any configuration.
These devices conform to the following standards and regulations:
• DIN EN 298: 2012-11
• DIN EN 1643: 2014-09
• DIN EN 13611:2011-12
• DIN EN 60730-2-5: 2015-10
• DIN EN 60730-1:2012-10
• 2014/35/EU Low Voltage Directive
• 2014/30/EU EMC-Directive
• 2014/68/EU Pressure Equipment Directive
• (EU) 2016/426 Gas Appliance Directive
• 2011/65/EU RoHS
Test symbols: CE-0085 AU 0207
The FA1 is a control unit for combustion systems.
NOTICE
Respect the national safety regulations and standards.

6
2 Safety
2 Safety
2.1 For Your Safety
The following symbols are used in this document to draw the user's attention to important safe-
ty information. They are located at points where the information is required. It is essential that
the safety information is observed and followed, and that applies particularly to the warnings.
DANGER!
This draws the user's attention to imminent danger. If it is not avoided, it will result in death or
very serious injury. The plant including its surroundings could be damaged.
WARNING!
This draws the user's attention to the possibility of imminent danger. If it is not avoided, it may
result in death or very serious injury. The plant including its surroundings could be damaged.
CAUTION!
This draws the user's attention to the possibility of imminent danger. If it is not avoided, it may
result in minor injuries. The plant including its surroundings could be damaged.
NOTICE
This draws the user's attention to important additional information about the system or system
components and offers further tips.
The safety information described above is incorporated into the instructions.
Thus, the operator is requested to:
1 Comply with the accident prevention regulations whenever work is being carried out.
2 Do everything possible within his control to prevent personal injury and damage to prop-
erty.

7
3 Brief Description
3 Brief Description
The Burner Control FA1 is suitable for control of burners and combustion systems for gase-
ous, liquid and solid fuels, with permanent operation, also in hot air generators.
Connections for Interbus-S, PROFIBUS DP, CANopen, TCP/IP (Modbus TCP) and Modbus
RTU are available as optional equipment. The connection of other plant components e.g. O2
trim is by the LAMTEC SYSTEM BUS interface to a 9-pole Sub-D connector.
The operation is via optional PC software or programming unit. As display for end user, a cus-
tomer interface is connectable by LAMTEC SYSTEM BUS. The operation by PC software is
described in a separate manual
The FA1 continuously monitors its own functions and those of the connected control elements.
230 V outputs:
– actuation of the gas valves
– actuation of the oil valves
– actuation of the oil pump/rotary atomiser
– actuation of the ignition valve and the ignition transformer
– fan release
– fault message
– OPEN/CLOSE control signals (three-point-step or 4 ... 20 mA) for the mechanical fuel/air
ratio control
External signals to the FA1 are transmitted via floating contacts or chains of contacts.
The following signals can be pre-set:
– 3 separate safety interlock chains
– gas < max
– air pressure monitor
– pre-purge suppression
– minimum gas pressure monitor (for valve leakage test) gas >min
– flame signal
– burner on
– fuel selection
– oil pressure min / atomiser air pressure
– oil pressure max
– ignition position acknowledgement
– internal burner firing rate controller in combination with the control output

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4 Display and Operational Controls
4 Display and Operational Controls
Fig. 4-1 Customer interface
Intent of the keys:
 Reset
 Burner firing rate/fault history up
 Burner firing rate/fault history down
 MANUAL mode ON/OFF
 Changing display
Display: Status burner firing rate – Setpoint value/actual value of
firing rate controller (1)
4 = External firing rate – Setpoint external/internal firing rate
23 = Internal firing rate – Flame intensity (1)
– Operating hours
(1) available if activated only
Changing display
– Status
– Firing rate controller
–O
21)
– Flame intensity
Fig. 4-2 Operating Unit

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4 Display and Operational Controls
4.1 Use of the Operating Unit
With the operating unit you may operate and the program the burner control system.
4.2 Connecting the Burner Control FA1
1. Connect the operating unit to the FA1 by using a 9-pin Cannon connector. To do so, use
the supplied connecting cable, type 663R0430.
Data transmission takes place by the LAMTEC SYSTEM BUS.
2. Alternatively:
Connect the operating unit with the cable of the customer interface. An adapter cable,
type 663R0426, is supplied for this purpose.
Disconnect the 6-pin connector from the customer interface and connect the adapter cable
to the 6-pin connector.
Fig. 4-3 Connection of the operating unit