Infusion Remote Monitoring System Based on Power Line Carrier Technology

The power grid is a popular physical network with a user base that is unmatched by any other network, and the main purpose of the power grid is to transmit electric energy. How to utilize the potential of power network resources to achieve narrowband or broadband communication without affecting the transmission of electric energy, and make it another communication network after telecommunications, telephones, wireless communications, and satellite communications, has been another goal of technical research by domestic and foreign scientific and technological personnel for many years. Power line carrier communication is a carrier communication that uses power lines as transmission channels and is a communication method unique to power systems. Compared with other communication methods, power line carrier communication has its own unique advantages. It does not require wiring construction, the network is widely extended, and the existing network has stable and reliable guarantees. Therefore, it is very practical and promising to use power line communication to achieve communication and monitoring in medical equipment.

1. Overall design of the infusion remote monitoring system

The functions of the infusion remote monitoring system are mainly in two aspects: on the one hand, the liquid level information of the patient's drip bottle is collected in the ward, and a local alarm is issued when the infusion is finished to attract the attention of the patient and his family; on the other hand, the nurse observes the patient's infusion status in real time at the workstation, and handles the alarm signal in time after receiving it, thus realizing remote monitoring of infusion.

This design divides the infusion remote monitoring system into two parts according to its functions. One part is installed in the ward, called the ward infusion information collector (lower computer), which collects the patient's liquid level information. The other part is placed in the nurse station and monitored by the nurse on duty, receiving the data uploaded by the collector and the infusion end alarm. This part is called the infusion monitoring control center. The specific structure is shown in Figure 1.

Figure 1 Structure diagram of infusion remote monitoring system

2. Hardware design of carrier communication controller

Both the infusion collector and the infusion monitoring and control center require a carrier communication system, except that the infusion information collector has added infusion information collection and control functions.

2.1 Communication system structure

In this system, SC1128 with spread spectrum communication function is used as power line carrier chip, AT89C51 is used as communication control and infusion information collection (in the lower computer) chip, and RS232 port is used for point-to-point communication. Figure 2 is the hardware block diagram of the communication system.

Figure 2 Hardware block diagram of the communication system

As shown in Figure 2, the signal enters the SC1128 chip from the power line through the coupler, bandpass filter and pre-amplifier. After being processed by the microprocessor, the data is sent to the host computer for reception. The signal is sent to the power line through the SC1128 through the power amplifier and coupler for transmission.

2.2 Design of SC1128 peripheral hardware

The SC1128 peripheral circuit consists of a power supply circuit, a coupling circuit, a filter, an automatic gain preamplifier and a power amplifier.

The power supply circuit is composed of an industrial frequency transformer, a filter diode bridge, a filter capacitor, a three-terminal voltage regulator, etc., and mainly provides +12V and +5V power for the system. The coupling circuit is composed of an intermediate frequency transformer, a surge protection diode, and a diode that acts as a limiter. It is a channel for signal transmission, and the carrier signal is coupled to the 220V AC circuit through it. The bandpass filter is composed of a capacitor and an inductor. The signal is input by the coupling circuit, the clutter is filtered out, and then the signal is input to the automatic gain preamplifier circuit. The automatic gain preamplifier amplifies the received signal without distortion and then inputs it into the on-chip amplifier circuit of SC1128. The power amplifier circuit amplifies the pulse processed by the SC1128 chip (this output is an OC gate output, and a pull-up resistor should be connected during use. The pull-up resistor value of this circuit is 2k. The power amplifier is powered by 12V DC). The specific circuit diagram is omitted.

2.3 Interface between SC1128 and MCU

Figure 3 is the interface diagram of SC1128 and AT89C51. Pin 28 of SC1128 is the crystal oscillator output of half of the circuit working main clock. Pin 32 is the voltage monitoring terminal. Pin 33 is the watchdog input terminal, which should produce a high and low potential change within 768ms when working normally. Pin 34 is the watchdog output terminal, which cooperates with pin 33 and outputs a low level when normal, otherwise it outputs a reset pulse with a duty cycle of one-third. Pin 35 cooperates with pin 32. When the power supply signal is lower than the monitoring value, it outputs a low level, and when it is higher than the monitoring value, it outputs a high level. Pin 36 is the transceiver control terminal, 0 is receiving, and 1 is transmitting. Pin 37 generates a synchronous pulse signal after transmitting and receiving synchronization, and the frequency changes with the changes of the working main clock and cycle. Pin 38 is the output of the data sent and received. Pin 39 is the input and output terminal for setting data and status. Pin 40 is the synchronous setting clock input terminal. Pin 41 is the chip select input terminal. When in the transmitting state, the MCU sets the SR terminal (pin 36) high, the SC1128 chip sends a synchronization pulse (pin 37), and the MCU sends data synchronously through the TX terminal (pin 38). When in the receiving state, the MCU sets the SR terminal (pin 36) low, and if the SC1128 chip receives data, it generates a synchronization pulse and sends the data synchronously to the MCU through the TX terminal (pin 38).

Figure 3 Interface diagram of SC1128 and AT89C51

3. Software design of carrier communication system

The programs of the communication module mainly include sending test program, sending interrupt service program, and receiving interrupt service program, which mainly complete the data receiving and sending process. The program list is omitted.

When communicating, you should also pay attention to the coordination of interrupts and communications. You should first set the communication status and then open the corresponding interrupt. In addition, you should pay attention to letting the receiving party work before letting the sending party send data, which can ensure that no data is lost.

When writing a communication program, it is important to ensure that the communication rates of the receiver and transmitter are consistent. The threshold value is only meaningful to the receiver. The threshold value will affect the communication bit error rate, but the higher the threshold value, the better. It should be selected according to the communication conditions and the corresponding rate. When SC1128 is communicating, the timing of the receiver and transmitter should be coordinated.

4. Design of infusion information collector

The infusion information collector adds the infusion information collection and control functions on the basis of the carrier communication controller. As can be seen from Figure 3, only the P1 port and serial communication pin of AT89C51 are used in the communication controller, so the design of the infusion information collector cleverly avoids the P1 port and serial communication pin of AT89C51, and makes full use of the P2 and P3 ports of AT89C51 to realize the detection and control functions. The specific circuit is shown in Figure 4.

Figure 4: Dripping speed control and liquid level detection alarm circuit diagram

As shown in Figure 4, the microcontroller is programmed to send the dripping speed detection signal to the microcontroller for comparison with the dripping speed set in the microcontroller, and then the microcontroller sends a control signal to the driver chip SAA1027 to control the forward and reverse rotation of the motor to achieve height control of the liquid storage bottle. In this way, the dripping speed can be controlled.

Install the photoelectric sensor on the infusion bottle. When the liquid level of the infusion bottle reaches the warning level, the output voltage of the sensor changes due to the change of the medium. Thus, the liquid level warning value detection and limit value detection are realized. The sound and light alarm uses the I/O port of the single-chip microcomputer AT89C51 to control and drive the light-emitting tube and buzzer to work, realizing the sound and light alarm.

5. System debugging

The test of the power carrier terminal was carried out on a single phase within the same transformer. One power carrier terminal was equipped with one receiver for power carrier communication test. The tests were carried out at different time periods and different communication distances. The specific test results are shown in Table 1.

Table 1 Test data of power line carrier terminal

The test results show that during close-range testing, in the presence of load and strong interference, such as when there are more than a dozen running computers and several charging devices between the power carrier terminal and the receiver, the power carrier terminal can still communicate reliably, fully meeting the requirements of communication and measurement and control.

The author's innovation: using the spread spectrum communication power line carrier chip SC1128 and AT89C51 single-chip microcomputer to design an infusion remote monitoring system. The system uses the power line carrier and the low-voltage power line as the communication medium, without the need for rewiring construction to achieve communication networking and remote monitoring of the infusion system in the ward. At the same time, it also proves that the spread spectrum modulation technology has better adaptability and advancement, and further demonstrates the bright development prospects of low-voltage power line communication.

References

[1] Liu Jianwei, Yu Yongquan, Bian Zengyuan. Smart home network based on power line spread spectrum communication. Microcomputer Information (Measurement and Control Automation). 2005, 12-1:160-162

[2] Chen Jing, Zhang Jianping, Liu Yumei. Design and implementation of automatic infusion monitoring system. Control Engineering China. 2006, (6)

[3] Chen Yangui, Chen Zhiwei, Guan Dexin. Wireless spread spectrum communication system based on SC128. Electronic Technology Application. 2005, (12)

[4] Zhou Wenguang. Development of a simple liquid level detection and alarm device for medical infusion equipment. Medical Equipment. 2004, (6)

［5］ Li Hetai, Zhao Xin, Li Xin, Xia Jiakuan. Development of intelligent infusion monitoring system. Journal of Shenyang University of Technology. 2006, 28(3)