[Abstract] This paper introduces the composition of the control system for the drying oven in a tobacco production line, describes the processing method of analog signals by AB series PLC, controls the frequency converter and adjusts the motor speed through DeviceNet network, and uses iFIX database technology to write alarm information into an EXCEL spreadsheet to create a daily report of alarm information.
[Keywords] AB PLC DeviceNet network iFIX alarm report
Abstract: This article describes the composition of the oven control system in the tobacco leaf production line. The paper tells the analog approach about AB Series PLC. The system regulates the motor speed by controlling invert through the DeviceNet. iFIX alarm information will be written to EXCEL table to create daily report for alarm.
Key words: AB PLC DeviceNet iFIX daily report for alarm
1 Introduction
Paper-based reconstituted tobacco technology can easily improve the formulation, effectively reducing tar and energy consumption without affecting tobacco quality, making it a green and environmentally friendly high-tech solution. In the post-processing stage of paper-based sheet production, the wet reconstituted tobacco from the pre-processing stage needs to be dried to a suitable moisture content. Appropriate oven temperature is crucial for maintaining the flavor and quality of the tobacco. Stable production lines and timely fault detection and troubleshooting are essential in highly automated production processes; convenient and quick fault location tracking and accurate understanding of the cause are indispensable for the continuous and efficient operation of the production line. The original production line had excessively high moisture content in the wet tobacco leaves, failing to meet process requirements, and lacked a timely and accurate alarm system, necessitating modification.
2. Overall System Composition
The newly added drying oven production line system consists of three parts: on-site monitoring and control equipment, PLC substations, and a host computer. The entire tobacco production line uses a ControlLogix AB series PLC control system from Rockwell Automation. To fully utilize the existing Logix5000 system and maintain the original control system's functionality and scalability, this upgrade uses the AB PLC's 1734ADN POINT I/O module to build a new subnet for the on-site monitoring and control equipment. A new DeviceNet substation was built based on the existing DeviceNet module 1756-DNB in the main network.
A PT100 platinum resistance thermometer detects the oven temperature, which is converted into a 4-20mA standard current signal by a current transmitter and input to the PLC. After processing by the PLC, the signal is displayed in real time on the host computer, and the speed is simultaneously output to the frequency converter to control the speed of the exhaust fan and the blower fan. The exhaust fan and blower fan motors are controlled by Schneider's Altivar 71 frequency converter. The blower fan blows hot air heated by radiators into the oven to heat it; the exhaust fan extracts the warm air from the oven to cool it down. During normal operation, both the exhaust fan and the blower fan operate at low speed. When the temperature is higher than the set value, the exhaust fan runs at high speed and the blower fan runs at low speed; when the temperature is lower than the set value, the exhaust fan switches to low speed and the blower fan runs at high speed. The hardware structure of the oven control system is shown in Figure 1.
Figure 1 Hardware structure diagram of the oven control system
The supervisory control system is built using GE FANUC's iFIX configuration software. iFIX is a leading global HMI/SCADA automation monitoring configuration software, a truly file-based configuration software. Its convenient, flexible, reliable, and easily expandable alarm system can report system activity and potential problems, ensuring safe system operation. iFIX distributed alarm management provides a variety of alarm management functions and has embedded VBA scripting capabilities. This system utilizes iFIX's powerful VBA scripting to access the iFIX alarm database via ODBC, enabling the querying and confirmation of real-time and historical data.
3 System Software Implementation
When the temperature changes, the resistance of the PT100 changes accordingly. This resistance is then converted into a standard 4-20mA current signal by a current transmitter. This signal is then input to the 1734 IE2C analog input module and converted into a digital signal by an A/D converter within the PLC. Commonly, the upper and lower limits of the converted digital signal are specified by the PLC manufacturer, and different PLCs have different upper and lower limits. This means that when users use analog input modules from different manufacturers' PLCs, they need to remember the different upper and lower limits, which is very inconvenient. To simplify the user experience and reduce the burden of memorization, the analog input modules of the AB series PLCs allow users to easily adjust the upper and lower limits of the digital signal corresponding to the input signal. In Rockwell's accompanying programming software RSNetWorx, the upper and lower limits of the digital signal corresponding to the current signal can be changed in the property settings of the 1734IE2C.
Figure 2 1734 IE2C Network Configuration
As shown in Figure 2, parameter 7 (Input Range #0) indicates that the signal input to analog channel 0 is a standard current of 4-20mA (which the user can change according to their needs). Specifically, parameter 11 (Low Scaling #0) corresponds to a 4mA current signal, and parameter 13 (High Scaling #0) corresponds to a 20mA current signal. To change the upper and lower limits of the digital signal corresponding to analog channel 0, the user can change the current values of parameters 11 and 13. In this way, the actual value can be obtained by performing a simple linear transformation on the input signal.
The Altivar 71 frequency converter is designed to be compatible with all communication networks, meeting all configuration requirements that may be encountered in industrial communication environments. The DeviceNet network communication card can perform protocol conversion, converting the converter's internal MODBUS protocol to the AB PLC's DeviceNet protocol. This makes the converter transparent to the DeviceNet network and allows for configuration within it. Therefore, the frequency converter can be controlled via the network from the host computer to change the motor speed according to process requirements. To write control parameters, the converter's address in the CPU must first be mapped in RSNetWorx.
Figure 3 Inverter address mapping
After mapping the address, control parameters need to be written to the frequency converter to achieve network control. To ensure interchangeability with frequency converters from other brands, this system uses the ODVA AC frequency converter profile, selecting component 21 (extended speed control output) and component 71 (extended speed control input). The frequency converter must be configured with a Drivecom profile in standalone mode. The DeviceNet card translates commands, behaviors, and monitoring information from the ODVA profile (on the network) to the Drivecom profile (in the frequency converter).
Figure 4. Inverter control parameters of component 21
In DeviceNet for each inverter, 32-bit input addresses and 32-bit output addresses are mapped. In the input address, byte 0 is used to write control parameters, byte 1 stores unused data, and bytes 2 and 3 are used to write the set speed. In the output address, byte 0 outputs control parameters, byte 1 outputs inverter fault information, and bytes 2 and 3 output the actual speed. The figure shows the meaning of each bit in the inverter control parameter byte when output component 21 is selected. Because network control is used, the reference is provided by the terminals. In the Logix5000 programming software, bit 5 needs to be set to 1 and bit 6 written to 0. The Bit Field Assignment (BTD) instruction is used in the program to write the control parameters and write the speed setpoint to the inverter.
Figure 5 Inverter control parameters and speed value settings
iFix is an advanced industrial automation software provided by GE FANUC, offering functions such as production process visualization, data monitoring, and historical data querying. iFix's alarm system can easily identify system problems and the causes of malfunctions, ensuring the safe operation of the production line. It can record operator operation information, and when an accident occurs, user information related to the erroneous operation can be retrieved from the historical alarm database.
iFix's alarm control only displays currently unacknowledged alarms in real time. To query historical alarms, you need to use iFix's alarm database. iFix's alarm service requires the user to create an alarm database beforehand and then associate this database with the iFix alarm service. When an alarm occurs, the alarm information is stored in the alarm database. To create the database, you need to open ODBC Data Sources in the Administrative Tools of the Control Panel and configure the ODBC Data Source Manager. Here, add a database named ALARM in the System DNS of the ODBC Data Source Manager to record alarm information that occurs during system operation.
Figure 6. Creation of the alarm database
After the database is created, the ODBC alarm database alarm service configuration needs to be configured in the iFIX system configuration. This establishes a connection between the created alarm database ALARM and iFIX. In the iFIX system configuration SCU, enable the alarm ODBC service, modify the ODBC alarm service configuration, and open the window shown in Figure 7.
Figure 7 iFIX ODBC alarm service configuration
In this way, when an alarm occurs, the alarm information is automatically written to the FIXALARMS table in the ALARM database. Using the VisiconX data control and VisiconX grid control provided in the iFIX toolbox, historical alarm information in the ALARM database can be read. However, the alarm information in the iFIX database does not automatically generate daily alarm reports; instead, all data is written to a single table in the alarm database, and this data can only be stored for a maximum of 365 days. Therefore, it is necessary to utilize iFIX's powerful VBA scripting capabilities to programmatically write the daily alarm data into an Excel spreadsheet for permanent storage, generating a daily alarm report. An event-based scheduling mechanism is established in iFIX. When an alarm occurs, the alarm database is opened, an Excel object is referenced, and the system automatically checks if the report for that day exists. If it does not exist, the report for that day is created; otherwise, the report is opened directly, and the new alarm information is appended to the end of the report, completing the creation and data update of the alarm report. The code for opening the alarm database is shown below.
Dim cnADO As New ADODB.Connection
Dim rsADO As New ADODB.Recordset
Dim Sql As String
Dim startTime As String
startTime = Format(Now(), "yyyy-MM-dd")
Sql = "Select * FROM FIXALARMS " & _
"Where (FIXALARMS.ALM_NATIVETIMELAST >= {ts '" & startTime & "00:00:00'}"
cnADO.ConnectionString = "Provider = Microsoft OLE DB Provider for ODBC Drivers;DSN=ALARM;UID=;PWD="
cnADO.Open
rsADO.Open Sql, cnADO, 1, 1
4. Conclusion
This oven modification can bake the moisture content of tobacco leaves to the appropriate level according to process requirements. The frequency converter can flexibly control the motor speed. When an alarm occurs, it can quickly and accurately locate the alarm point, providing operators with a reliable basis for timely and effective troubleshooting and understanding the historical operation of the equipment.
5 References
[1] Altivar71 DeviceNet Card User Manual VW3 A3 309, 2005/5
[2] POINT I/O DeviceNet Adapter, Catalog Numbers 1734-ADN, 1734-ADNX,2005/4
