Detailed explanation of the hottest industrial app

Detailed industrial application of Bluetooth

Abstract

there are many devices interconnected in different ways in the factory, some are non intelligent simple data connection units (i/o), and more are intelligent devices (such as intelligent sensors, single loop controllers and PLC) and monitoring systems (used as HMI for data recording and monitoring). These devices are interconnected by various communication protocols and media, some of which can be replaced by Bluetooth wireless technology. This paper will discuss how to use Bluetooth to connect these devices, as well as some special requirements for Bluetooth technology in this field

this paper divides the industrial application of Bluetooth into four aspects:

1 Replace serial cable. Wireless Bluetooth connection can replace the current serial cable

2. Combine Bluetooth and Internet technology. Use the CPU processing power brought by Bluetooth to add more functions to the device, such as the built-in web user interface

3. Industrial access point. Several Bluetooth devices are connected to traditional wired networks through access points, such as IP networks (such as Ethernet) or industrial fieldbus networks (such as ControlNet and PROFIBUS)

4. Wireless sensors and starters. Bluetooth is used to connect the devices most closely related to the physical process (sensors, starters and simple analog/digital IO devices) to the monitoring system

instead of serial cables

at present, many industrial devices use traditional serial interfaces (such as RS232, RS422 or RS485) to connect configuration tools or programming tools These tools are specially connected to the device when it needs to be reconfigured or programmed. They are usually operated on a standard computer, and generally use some independent method or device specific communication protocol to connect with the device. These factors make this field a good place for Bluetooth. Figure 1 shows a PC programming tool that uses serial cable to connect PLC

there are two ways to replace the serial cable with Bluetooth: one is to use the external Bluetooth adapter connected to the external serial port of industrial equipment, and the other is to use the internal Bluetooth adapter connected to the electronic part of the equipment. Bluetooth adapter can simulate serial port and use rfcomm protocol to transmit data over the air (support serial port profile). The computer can use PC card or other additional devices to support Bluetooth. The application of Bluetooth in computers enables the serial port profile of Bluetooth to play a role similar to that of a communication, so that the original computer configuration and programming tools can continue to be used

Bluetooth can also replace serial cables in the field of more advanced industrial devices that support built-in tcp/ip devices and web servers. At this time, the support of Bluetooth adapter for lap (LAN access profile) can reach the level of rfcomm, while other software stacks are included in industrial devices (PPP, IP and web servers). This enables external HMI devices (such as laptops or PDAs) that support lap (LAN access profile) to access the built-in web user interface of the device without installing special application software

Figure 2 shows the basic structure of Bluetooth adapter instead of serial cable

combination of Bluetooth and interconnection technology

suppose there is a valve with a built-in control system, which continuously transmits the dynamic state and control variable information to the computer through the standard Modbus Protocol (as shown in Figure 3)

add a Bluetooth adapter to the device (external or internal). The Bluetooth adapter communicates with the valve through Modbus protocol. The web/wap page is provided by the built-in web/wap server and written with the help of Modbus protocol to display and modify dynamic data. Bluetooth can use lap (LAN access profile) to obtain web/wap pages, so as to configure, repair and monitor devices

the structure diagram of this concept is shown in Figure 4:

it can be seen from the figure that in addition to modbus, Bluetooth adapter can also use other industrial protocols to communicate with device control system. WAP over Bluetooth can be used to access the built-in WAP user interface. WAP over Bluetooth specification fixes the "routing" function as part of the function. This allows local WAP pages to have a hyperlink to another page in the wide area (WAN). Wan can be accessed through GMS, GPRS or future UMTS technology. A typical example of this application is to alarm with the help of local WAP pages. This page can be connected to the WAN page, which contains information on how to deal with the problems reflected by the alarm, and can constantly update the information related to the alarm

industrial access point

using wireless communication in industrial environment will be a step-by-step process. This requires that industrial equipment must be able to use Bluetooth function and connect with existing wired networks, such as IP networks (such as Ethernet) or industrial fieldbus networks (such as ControlNet and PROFIBUS)

we take the connection between Ethernet based wired network and Bluetooth industrial equipment as an example (as shown in Figure 5). As mentioned above, the industrial equipment here (still taking valves as an example) also adopts embedded web servers

the built-in web interface of the device is accessed through the access point (AP, as shown in 1 in Figure 5). AP is like a "exchanger", connected to each valve. Web users access the AP. All connected Bluetooth devices can be displayed through the built-in web interface in the AP. The user selects one of the devices and establishes a lap (LAN access profile) connection with the device, and then the AP starts to perform the function of a router. At the same time, users can directly access the web-based HMI of all devices through Bluetooth (as shown in 2 in Figure 5)

the second example is a variant of the previous example. At this time, the access point (AP) uses modem, GSM, GPRS or future UMTS technology to perform the function of a dial-up AP (as shown in Figure 6)

at present, there are many kinds of industrial fieldbuses, including standard ones and proprietary ones of some manufacturers. The following example shows a device with Bluetooth function (still taking the valve as an example) if it uses fieldbus access point to connect to the original wired network (as shown in Figure 7)

here, the Bluetooth device transmits data to the access point through a Bluetooth dedicated transmission protocol (as shown in 1 in Figure 7). The data is converted into the format supported by the fieldbus and transmitted to a device in the fieldbus network that sends out request instructions

as can be seen from the figure (as shown in 2 in Figure 7), the Bluetooth device can also be used as an interconnection device with a built-in web HMI (refer to the previous content) and a data acquisition device that sends and receives data with the access point (and further with the fieldbus network)

another application isplast is another TPU, which enables the access point to support Bluetooth LAN access profile and built-in web server. This is used to access data from Bluetooth devices and devices connected to the fieldbus through the web HMI

figure 8 shows the basic structure of Fieldbus access point

the data transmission protocol here is an industry-specific protocol running at the top of the Bluetooth protocol stack. It can call the Bluetooth stack on the L2CAP layer or rfcomm. Industrial devices using Bluetooth must support this protocol. In this field, realizing the interoperability between different manufacturers' equipment is the expectation of everyone, and it is also a main task of the future sig industrial application working group and expert group (please refer to the content of "sig industrial application working group and expert group" later in this document)

wireless sensors and starters

sensors and starters have different types. Some are highly intelligent, while others are simple devices, which are only used as the low-end interface of process equipment. Therefore, the requirements for wireless Bluetooth schemes are also different. If it is an intelligent device, it may have good enough local operation function to enable the manufacturing process to run in a limited mode when the Bluetooth connection is disconnected. To achieve this, the control algorithm can be divided into two parts. One part is used for monitoring, which is executed on the main system, and the other part is used for task critical control, which is executed on the sensor or starter. This method can also be used when the performance requirements cannot be met with the help of Bluetooth. The fast control loop and fast data acquisition are performed locally, while the slow control loop is performed through Bluetooth, and the buffer data is also transmitted through Bluetooth. This puts forward some requirements for Bluetooth (for example, for time synchronization between Bluetooth nodes, please refer to the content of 4-ball friction and wear tester in the "requirements of industrial applications for Bluetooth" section for details)

different processes have different requirements for Bluetooth solutions. Some processes do not require high performance, and may now be very suitable for real-time control using Bluetooth

wireless sensors and starters are very suitable for mobile industrial equipment applications. The vibration sensor installed on the moving shaft is a good example. This application requires an alternative power supply scheme (such as using batteries or other power supplies) to support a complete wireless scheme. Bluetooth supporting low-power mode is very suitable for this application, but special attention must be paid to the application requirements when developing the scheme

the control system (PLC) in the first example (Figure 9) includes some simple i/o devices and two intelligent sensors/starters (here is a single loop controller), in which the i/o devices are connected through a standard wired i/o bus. Even if the Bluetooth connection is temporarily interrupted, the single loop controller can still operate

the simple i/o device of the control system in the second example (Figure 10) is connected through Bluetooth. This scheme requires extra care to ensure the stability of communication. For example, this scheme can be used in processes with low real-time requirements, that is, if temporary interference interrupts the connection, the process is allowed to have a relay, or the process is running in a controlled environment with known interface mode

the above example mentioned low speed and fast control. Connectblue has conducted a closed control loop test through Bluetooth connection, and the results show that the cycle time (from controller to i/o and return) can be controlled within 15ms

requirements of industrial applications for Bluetooth

the current Bluetooth technology has been able to be used in many industrial application fields, but industrial applications have some other requirements for Bluetooth. If these requirements are met, the possibility of Bluetooth application in industry is greater

Bluetooth was originally designed for communication between computers and peripheral devices, and can also be used in data/voice access points, ad hoc networks, cable replacement and other fields. This technology is most suitable for voice applications, file transmission, and the transmission of information such as business cards and numbers. The information it transmits is usually very short, but the safety and speed of information transmission are very important. This requires Bluetooth technology to have higher quality of service (QoS) and be able to resist various external interference (such as the "adaptive frequency hopping" scheme proposed in radio 2 WG). Timestamp is also a very important factor. Bluetooth currently has an ARQ scheme (not suitable for voice packets), which is not conducive to the security of data transmission. In the future Bluetooth specification, transparent packets will appear. In this way, no matter whether there is an error message in the packet, it can be received within the specified time. The system can decide whether to resend the data packet, or