Digital hospital is a new trend of modern medical development in China. The digital hospital system is a three-in-one integrated information system composed of hospital business software, digital medical equipment, and network platform. The digital hospital project helps hospitals achieve resource integration, process optimization, and reduced operation. Cost, improve service quality, work efficiency and management level. According to the requirements of the hospital, the system is designed with high standards and high quality to improve the performance and price ratio of the product, fully reflect the intention of the builder in the design, and take into account the convenience of the user's use, maintenance and maintenance in the future. The overall plan. The program is divided into two parts: the ward call system and the ward monitoring system. The hospital monitoring system is an underlying distributed monitoring local area network in the hospitalization management system. These so-called bus-based monitoring systems, because they use traditional serial communication protocols, can only achieve point-to-point communication. The nodes that constitute the system are limited by the load of the master device, and the scalability is very poor. Fieldbus has been used in recent years. First, a new technology developed in the field of industrial control.
As a new technology first developed in the field of industrial control in recent years, fieldbus has not yet been widely used in the field of hospital ward monitoring. CAN (Controller Area Network) bus is recognized as one of the most promising field buses, and its application in a fully open distributed system for ward monitoring will have very important practical innovation significance. This article mainly realizes the point-to-point communication between the central monitoring station and the bed monitors through the CAN bus, and completes the system functions from the hardware design and software implementation. The communication design of the system is simple and easy to implement, and it is easy to be widely promoted in the hospital.
1. Development and current status of distributed monitoring system in hospital wards
Various microcomputer monitors and monitoring systems. At first, such monitoring systems generally used special devices to form an independent system, which did not provide an interface with external systems and could not perform remote monitoring. With the rapid development and application of digital communication technology, serial communication technology adapted to remote information transmission has gradually matured and is widely used. The hospital ward monitoring system has begun to introduce serial communication technology, which is realized by using on-site monitoring instruments and equipment distributed in various wards. Real-time data collection of patient's physiological parameters, long-distance transmission of data information through serial communication interface, analysis and processing of data parameters by medical staff with the help of remote computers to form patient medical order information, and transmission to nurses on duty to perform clinical monitoring of patients At the same time, nurses on duty can also get real-time patient monitoring request information and simple monitoring feedback information in the duty room.
The first serial communication protocol adopted is the RS-232 interface standard. The system structure is shown in Figure 1. The system uses common twisted-pair wires as the transmission medium to achieve point-to-point communication between the central monitoring station and the patient bedside monitor. However, with the increase in the number of monitored patients in the entire system, there are too many networking lines, and due to the earlier appearance of the RS-232 interface standard, there are some deficiencies in communication, mainly including the following four points:
(1) The signal level value of the interface is high, which is easy to damage the chip of the interface circuit, and because it is incompatible with the TTL level, a level conversion circuit is required to connect to the TTL circuit.
(2) The transmission rate is low. In asynchronous transmission, the baud rate is 20Kbps.
(3) The interface uses a signal line and a signal return line to form a common ground transmission form. This common ground transmission is prone to common mode interference, so it is weak against noise interference.
(4) The transmission distance is limited. The standard value of the maximum transmission distance is 50 feet. In fact, it can only be used around 50 meters.
In response to the shortcomings of RS-232, some new interface standards have emerged, RS-485 is one of them, and it is quickly applied in the field of ward monitoring. The system structure is shown in Figure 2.
Smart meters developed with the maturity of single-chip technology in the early 1980s, and now the world meter market is basically monopolized by smart meters. The reason is the need of enterprise informatization. One of the necessary conditions for enterprises in the selection of meters is to have a network communication interface. Initially, it was a simple process of data analog signal output. Later, the instrument interface was an RS232 interface. This interface can realize point-to-point communication, but this method cannot realize the networking function. The subsequent RS485 solved this problem. It has the following advantages:
(1) The signal level of the RS-485 interface is lower than that of RS-232, and it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level and can be easily connected to the TTL circuit.
(2) The maximum data transmission rate of RS-485 is 10Mbps.
(3) The RS-485 interface is a combination of a balanced driver and a differential receiver, which enhances the ability to resist common mode interference, that is, has good resistance to noise interference.
(4) The standard value of the maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters. In addition, the RS-232 interface allows only one transceiver to be connected to the bus, that is, single station capability. The RS-485 interface allows up to 32 transceivers to be connected on the bus. That is, it has multi-station capability, so that users can easily establish a device network using a single RS-485 interface.
Although there are many advantages, compared with the fully open distributed system composed of fieldbus, there are still some insurmountable defects in itself:
(1) The error detection, correction, and error localization capabilities on the hardware are weak, and the system's own monitoring and maintenance functions are poor;
(2) No bus disconnection function, once the RS-485 transceiver on a node is short-circuited or a serious error occurs, the entire bus will not work properly;
(3) There is no cache function on the hardware;
(4) The data communication mode is command response, which results in poor system flexibility;
(5) RS-485 bus needs to maintain a fixed current on the bus when it is idle, which has an impact on the life and power consumption of the device
(6) The communication between the devices of the RS-485 bus network can only be achieved through the transfer of the "Master" device, and only one master device is allowed in this bus network, and the rest are all slave devices. Therefore, each node does not have interoperability, and cannot form a multi-master redundant system, and the system reliability is poor;
(7) RS-485 bus does not have the characteristics of open Internet, and it cannot constitute a fully open and distributed interconnected communication network system.
2. The characteristics of fieldbus technology and its advantages in the fully open distributed monitoring system of hospital wards
Due to the shortcomings of the traditional bus system, we analyzed the characteristics of the field bus technology developed and applied in the field of automatic control for many years, and introduced it into the hospital ward monitoring, forming a fully open distributed monitoring system in the hospital ward can well overcome the traditional bus The lack of the system.
The field bus refers to the network mainly based on the digital communication between the measurement and control machines in the factory, also known as the field network. It is a network that specializes the communication between sensors, various operation terminals and controllers, and the communication between controllers. It turns out that the main wiring between these machines is ON / OFF, contact signal and analog signal. Through the digitization of communication, time division, multiplexing and multipointing are possible, so as to achieve high performance, high reliability and easy maintenance 2. Save wiring (wiring sharing). The field bus system has the following characteristics in technology:
(1) Openness of the system The open system refers to the open communication protocol, which can be interconnected and exchange information between devices of different manufacturers. Fieldbus developers are committed to building an open system for a unified plant bottom network. Openness here refers to the consistency and openness of relevant standards, emphasizing consensus and compliance with standards. An open system that can be connected to any other device or system that adheres to the same standard. For a fieldbus network with bus functions, the system must be open; the open system gives the user the right to integrate the system.
(2) Interoperability and interoperability Interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and can implement point-to-point and point-to-multipoint digital communication.
(3) Intelligentization and functional autonomy of field equipment It will decentralize the functions of sensory measurement, compensation calculation, engineering quantity processing and control to field equipment. The basic functions of automatic control can be completed by field equipment only, and Diagnose the running status of the equipment at any time.
(4) Highly decentralized system structure Because the field devices themselves can complete the basic functions of automatic control, the field bus has constituted a new fully distributed control system architecture.
(5) The adaptability to the field environment works at the front end of the field equipment. As the field bus at the bottom of the factory network, it is designed specifically for the field environment. It can support twisted pair, coaxial cable, optical cable, radio frequency, infrared, Power lines, etc., have strong anti-interference ability, can use two-wire system to realize power transmission and communication, and can meet the requirements of intrinsic safety explosion-proof.
A complete and efficient hospital operation management information network system plays a very important role in the modernization and informatization of hospital operation management and improving the efficiency of hospital rash monitoring management. The monitoring system of the hospital ward belongs to a subsystem of the hospital management information network. Therefore, the hospital ’s monitoring and nursing of each ward is most suitable for using the field bus to form the underlying local area network, and can also use the intelligent Patient care monitoring is automated. And because of the above characteristics of the field bus, especially the simplification of the field bus system structure, it has shown its superiority in the design, installation, normal operation and maintenance of the hospital ward monitoring system.
(1) Save hardware quantity and investment;
(2) Save installation costs;
(3) Save maintenance costs;
(4) Users have a high degree of system integration initiative;
(5) Improve the accuracy and reliability of the system;
(6) The design is simple and easy to refactor;
3. A CAN bus-based hospital ward fully open distributed monitoring system model and its hardware and software components
CAN is the abbreviation of Controller Area Network (CAN). It was developed by the German BOSCH company, which is famous for the development and production of automotive electronic products, and eventually became an international standard (ISO118? 8). It is one of the most widely used field buses in the world. In North America and Western Europe, the CAN bus protocol has become the standard bus for automotive computer control systems and embedded industrial control local area networks, and has a J1939 protocol designed for large trucks and heavy industrial machinery vehicles with CAN as the underlying protocol. In recent years, its high reliability and good error detection capabilities have been valued, and it is widely used in automotive computer control systems and industrial environments with harsh environmental temperatures, strong electromagnetic radiation, and large vibrations. It has the following basic characteristics:
(1) The CAN protocol follows the ISO / OSI model and uses the three-layer structure of the physical layer, data link layer, and application layer.
(2) The communication rate of CAN is: 5Kbps / 10km, 1Mbps / 40m, the number of nodes can reach 110, and the transmission medium can be twisted pair, optical fiber, etc.
(3) The signal transmission of CAN adopts short frame structure, each frame has 8 effective bytes, so the transmission time is short and the probability of interference is low. And, when a serious error occurs in the CAN node, CAN has the function of automatically shutting down the node, automatically cutting off the connection with the bus, so that other nodes on the bus and their communication are not affected. Therefore, it has strong anti-interference ability.
(4) CAN nodes adopt point-to-point, point-to-multipoint and broadcast several kinds of sending and receiving data, which can realize a fully distributed multi-machine system, and there is no master and slave.
(5) CAN uses non-destructive bus arbitration technology.
(6) CAN can support explosion-proof areas.
The intelligent measurement and control system usually based on CAN bus is shown in Figure 3:
According to the characteristics of ward monitoring: at least one central monitoring station is generally required to be monitored by the doctor in charge of the guardianship. Secondly, the nurses ’duty room is set up on each floor for real-time monitoring and care of the beds in charge, and on-site online monitoring of the beds of each ward Composition, therefore, the entire monitoring system can be divided into three levels: management level-monitoring level-field level. The system structure based on CAN bus is shown in Figure 4:
The following is a brief introduction to the system hardware and software components:
　　
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