Explosion-protected mobile computers with barcode scanners and wireless connection to the process control system ensure the real-time availability of all relevant data for the control of the production processes or for the management of formulas.
In the manufacturing of chemical products, a variety of raw materials are mixed together in facilities specially designed for the purpose according to predefined formulas and a reaction is initiated. It is necessary here to stick very precisely to the formula in order to obtain the desired product. The real-time availability of the relevant data directly in production is thus absolutely required. In particular, this means that during production initially a lot of stock movement is necessary, stock must be taken from the warehouse and transported to the production facility. The raw materials may be liquid or powder and can be stored in packaging such as cartons, barrels, cans, or sacks. These materials are combined in special reactors and warmed, cooled, subjected to pressure or vacuum to initiate a reaction.
In the individual production steps, wireless technology supports warehouse retrieval, starting a transport order, ending a transport order, and the later filling of the finished product. The work steps taken at various times in the manufacturing are documented with mobile computers. This also allows batch traceability. The containers with the materials are provided with individual barcodes which are read using the mobile devices. The user is able to enter the stock movement from the SAP ERP system with software templates available on the device’s screen. SAP makes regular assessments of demand and automatically orders the stock from the suppliers. On delivery, the material receiving control and warehousing are also carried out with the mobile devices.
In the present application, the MC 95xxex-NI mobile computers from BARTEC were used as end-devices for use in zone 2 of the potentially explosive area. They are certified in accordance with ATEX and UL. The devices in the MC 95xxex-NI series offer data input, using both stylus and keyboard, with a variety of keyboard configurations. The large, backlit 3.7” VGA color display (TFT) is very readable. The touchscreen technology offers additional ease of use. The integrated miniature scan engine provides efficient recording of barcodes, even in strong sunlight. Thanks to their robust construction, the devices in this series can withstand drops to hard ground from a height of 1.20 meters. Replaceable lithium-ion batteries provide maximum operation time. They can be used in a temperature range from -20 to +50°C.
Wireless LAN in the ex area
With the AP 5131 access points, which can be installed in the ex zone 1, flat antennas are built into metal housings certified for ignition protection type ex d. The cover of the pressure-resistant, encapsulated enclosure has a glass pane. Functionality is ensured, despite loss through the pane and the metal housing. External rod antennas certified for the ex area are used in very long passages or warehouse spaces filled with shelves, where the wireless coverage is insufficient.
In the production halls and open spaces, a wireless measurement first had to be conducted to determine where access points would be installed. The criteria here were the wireless coverage, the local conditions, and the possibility of cabling. Because the area is classified as ex zone 1, further points had to be taken into consideration. Explosion-protected measurement devices had to be used for the measurement. However, there was a pilot light available which indicated that there is no explosive atmosphere at the given time. In addition, this was assured with a gas monitor. In addition, the wireless measurement staff had to wear safety shoes, safety glasses, safety helmet, and flame-retardant clothing while they were in the ex area.
Security in the wireless network
The AP 5131 offers application-oriented, production-line safety for the IEEE 802.11b, 802.11a, 802.11g standards. In addition, it offers an intelligent solution for adaptation to the 802.11b and 802.11a standards. With the option of rules-based networks, the system can assign the bandwidth of the wireless data transmission, the security parameters, and the network services for devices, users, applications, and locations. The IEEE 802.11 standard describes encryption in accordance with the RC4 algorithm. A 64-bit key is used for data encryption, divided into a secret 40-bit key and a 24-bit initialization vector (IV). In addition, Motorola offers their customers a 128-bit encryption which is divided into a secret 104-bit key and a 24-bit IV.
In order to increase data security, the IEEE 802.11(b) standard offers the user the option of defining four secret keys. The mobile end device must adapt to the provided key of the new access point when roaming (changing from one access point to the next).