Implementation of a fully open and distributed monitoring system for hospital wards based on fieldbus

As a new technology developed in the field of industrial control in recent years, fieldbus has not been widely used in the field of hospital ward monitoring. The CAN (Controller Area Network) bus is recognized as one of the most promising fieldbuses. Its application in ward monitoring and full open distributed systems will have important practical and innovative significance. This paper mainly realizes the point-to-point communication between the central monitoring station and the bed monitor through the CAN bus, and completes the system function from the hardware design and software implementation. The communication design of the system is simple and easy, and it is easy to be widely promoted in the hospital.

Digital hospital is a new trend of modern medical development in China. Digital hospital system is a three-in-one comprehensive information system composed of hospital business software, digital medical equipment and network platform. Digital hospital project helps hospitals realize resource integration, process optimization and reduce operation. Cost, improve service quality, work efficiency and management level. According to the requirements of the hospital, in line with the high standard and high quality, the performance and price ratio of the product are improved, the constructor's intention is fully reflected in the design, and the system is designed in consideration of the convenience of use, maintenance and maintenance of the user 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 area network in the hospital management system. These so-called bus-based monitoring systems, which use traditional serial communication protocols, can only achieve point-to-point communication. The nodes that make up the system are limited by the load of the master device, and the scalability is poor. Fieldbus has been used in recent years. First of all, a new type of technology developed in the field of industrial control.

1. Development and current status of distributed monitoring system in hospital wards

The monitoring and monitoring system of various microcomputers, the initial monitoring system generally uses a dedicated device to form a separate system, does not provide an interface with an external system, and cannot perform remote monitoring. With the rapid development and application of digital communication technology, the serial communication technology adapted to remote information transmission has matured and been widely used. The hospital ward monitoring system has begun to introduce serial communication technology, using on-site monitoring instruments distributed in various wards. Real-time data acquisition of patient physiological parameters, long-distance transmission of data information through serial communication interface, analysis and processing of data parameters by medical staff to form patient medical information, and transmission to nurse attendant to perform clinical monitoring on patients At the same time, the nurse attendant can also get the patient's real-time 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 a common twisted pair as the transmission medium to realize point-to-point communication between the central monitoring station and the patient bedside monitor. However, as the number of guardian patients increases, the number of networked lines is too large, and because RS-232 interface standards appear earlier, there are some shortcomings in communication, mainly the following four points:

(1) The signal level of the interface is high, which is easy to damage the chip of the interface circuit. Because it is not compatible with the TTL level, it needs to use the level conversion circuit to connect with 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 the noise immunity is weak.

(4) The transmission distance is limited. The maximum transmission distance is 50 feet. In fact, it can only be used at 50 meters.

In response to the shortage of RS-232, some new interface standards have emerged. rs-485/'target='_blank'>RS-485 is one of them, and it is quickly applied in the field of ward monitoring. The system structure is as follows. The figure shows.

Smart meters developed with the maturity of single-chip technology in the early 1980s, and now the world instrument market is basically monopolized by smart meters. The reason is the need of enterprise informationization. One of the necessary conditions for enterprises to select instruments is to have a network communication interface. Initially, the data analog signal output is a simple process. Later, the instrument interface is an RS232 interface. This interface can implement a point-to-point communication method, but this method cannot achieve networking functions. The subsequent emergence of RS485 solved this problem. It has the following advantages:

(1) The signal level of the RS-485 interface is lower than that of the RS-232, and the chip of the interface circuit is not easily damaged, and the level is compatible with the TTL level, which is convenient for connection with the TTL circuit.

(2) The maximum transmission rate of RS-485 data is 10Mbps.

(3) RS-485 interface is a combination of balanced driver and differential receiver, which has enhanced anti-common mode dry capability, that is, good anti-noise interference.

(4) The maximum transmission distance of the RS-485 interface is 4000 feet, which is actually up to 3000 meters. In addition, the RS-232 interface allows only one transceiver to be connected to the bus, that is, the 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 users can easily establish a device network with 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:

(1) The hardware detection, error correction, and error location capabilities are weak, and the system's own monitoring and maintenance functions are poor;

(2) No bus disconnect function, once the RS-485 transceiver on a node is short-circuited or a serious error occurs, the entire bus will not work normally;

(3) There is no caching function on the hardware;

(4) The data communication method is command-responsive, resulting in poor system flexibility;

(5) The RS-485 bus needs to maintain a fixed current on the bus when it is idle, which affects the lifetime and power consumption of the device.

(6) The communication between the devices of the RS-485 bus network can only be realized through the transfer of the "master" device, and only one master device is allowed in the bus network, and the rest are slave devices. Therefore, each node does not have mutual operability, and cannot constitute a multi-master redundant system, and the system reliability is poor;

(7) The RS-485 bus does not have the characteristics of an open Internet, and it cannot constitute a fully open and distributed interconnected communication network system.

2. Fieldbus technology features and advantages in the use of fully open distributed monitoring systems in hospital wards

Due to the shortcomings of the traditional bus system, we analyzed the characteristics of the fieldbus technology developed and applied in the field of self-control for many years, and introduced it into the hospital ward monitoring, which constitutes a hospital ward full open distributed monitoring system can overcome the traditional bus. Insufficient system.

Fieldbus refers to a network based on digital communication between measurement and control machines in a factory, also known as a field network. That is, a network that specializes communication between sensors, various operating terminals, and controllers and controllers. Originally, the main wiring between these devices is ON/OFF, contact signal, and analog signal. By digitizing the communication, time division, multiplexing, and multi-pointing are possible, thereby achieving high performance, high reliability, and simple maintenance. Save wiring (sharing sharing). The fieldbus system has the following technical features:

(1) Open open system of the system means that the communication protocol is open, and devices of different manufacturers can be interconnected and exchange information. Fieldbus developers are committed to building a unified open system for the underlying network of the factory. 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 standards. For a fieldbus network with bus function, the system must be open; the open system gives the user the right to integrate the system.

(2) Interoperability and interoperability The interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and can implement point-to-point, point-to-multipoint digital communication.

(3) The intelligent and functional autonomy of the field device disperses the functions of sensing measurement, compensation calculation, engineering quantity processing and control into the field equipment, and the basic functions of automatic control can be completed only by the field device. Diagnose the operating status of the device at any time.

(4) Highly dispersive system structure Since the field device itself can complete the basic functions of automatic control, the field bus has formed a new architecture of a fully distributed control system.

(5) Adaptability to the on-site environment At the front end of the field equipment, as the field bus at the bottom of the factory network, it is designed for the field environment work, it can support twisted pair, coaxial cable, optical cable, radio frequency, infrared, Power line, etc., has strong anti-interference ability, can use two-wire system to realize power transmission and communication, and can meet intrinsic safety explosion-proof requirements.

A complete and efficient hospital management and management information network system plays an important role in the modernized informationization and intelligentization of hospital management and the improvement of hospital rash monitoring and management efficiency. The monitoring system of the hospital ward belongs to a subsystem of the hospital management information network. Therefore, the hospital's monitoring and care for each ward is most suitable for using the field bus to form the underlying local area network, and can also utilize the intelligentization of the on-site medical, diagnostic, monitoring and other equipment. The patient's care monitoring is automated. Moreover, due to the above characteristics of the field bus, especially the simplification of the structure of the field bus system, the superiority is reflected in the design, installation, normal operation and maintenance of the hospital ward monitoring system.

(1) Saving hardware quantity and investment;

(2) saving installation costs;

(3) saving maintenance overhead;

(4) The user has a high degree of system integration initiative;

(5) Improve the accuracy and reliability of the system;

(6) Simple design and easy to reconstruct;

3. Fully open distributed monitoring system model of hospital ward based on CAN bus and its software and hardware components

CAN is the abbreviation of Controller Area Network (CAN). It was developed by German BOSCH company, which is famous for developing and producing automotive electronics products, and eventually became an international standard (ISO118?8). It is one of the most widely used fieldbuses 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 LANs, and has the J1939 protocol designed for large trucks and heavy machinery vehicles with CAN as the underlying protocol. In recent years, its high reliability and good error detection capability have been paid attention to. It is widely used in automotive computer control systems and industrial environments with harsh ambient temperature, strong electromagnetic radiation and high vibration. It has the following basic features:

(1) The CAN protocol follows the ISO/OSI model and adopts a three-layer structure of a physical layer, a data link layer, and an application layer.

(2) CAN communication rate is: 5Kbps/10km, 1Mbps/40m, the number of nodes can reach 110, and the transmission medium can be twisted pair, fiber, etc.

(3) The signal transmission of CAN adopts a short frame structure, and the number of valid bytes per frame is 8, so that the transmission time is short and the probability of interference is low. Moreover, when a serious error occurs in the CAN node, the CAN has the function of automatically shutting down the node, automatically disconnecting 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 use point-to-point, point-to-multipoint and broadcast several kinds of sending and receiving data, which can realize fully distributed multi-machine system, and there is no master-slave.

(5) CAN uses non-destructive bus arbitration technology.

(6) CAN can support explosion-proof areas.

Temperature And Humidity Sensor

The temperature and humidity sensors mostly use the temperature and humidity integrated probe as the temperature measuring element to collect the temperature and humidity signals, which are converted into current signals or voltage signals that have a linear relationship with temperature and humidity after being processed by circuits such as voltage stabilizing filter, operation amplification, nonlinear correction, V / I conversion, constant current and reverse protection, It can also output 485 or 232 interfaces directly through the main control chip.

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