Design and implementation of medical intelligent oxygen flowmeter
O Introduction
For a long time, when the patient's oxygen is inhaled in China's medical system, a floating-ball oxygen flowmeter is used to monitor the flow rate of oxygen inhaled by the patient. This flow is only the basis of medical treatment, and cannot be used as the basis of billing. The patient is billed according to the time of oxygen inhalation. This kind of billing method is objectively unreasonable, causing a certain contradiction between hospitals and patients. With the advancement of medical reform, this contradiction is increasingly prominent, and there is an urgent need for a convenient and reliable, low cost A medical oxygen flowmeter that can automatically record the patient's oxygen intake to solve the problem of billing according to the patient's oxygen intake.
It seems that it is not difficult to achieve automatic measurement and recording of oxygen absorption using modern sensor technology. However, the impact of sensor components and packaging materials on patient health is a big problem, which requires a lot of demonstration and experimentation, and requires special Institutional evaluation and certification, which increases the cost of equipment and brings certain difficulties to popularization.
Through the research of the existing oxygen inhalation system in the hospital, it is found that the position (rotation angle) of the valve switch handle of the float type flowmeter that monitors the oxygen flow in the existing oxygen inhalation system determines the amount of oxygen flow. Correspondence. The instantaneous flow of oxygen can be obtained by automatically reading the rotation angle of the switch handle, and the cumulative oxygen absorption during the patient's oxygen inhalation process can be obtained by using the single-chip microcomputer for timing and calculation.
1 System composition and basic principle
This design is a simple, reliable, and practical medical oxygen flow measurement system. It uses the correlation between the rotation angle of the valve switch handle of the metal float type oxygen flow meter and the oxygen flow in the existing oxygen absorption system for measurement.
Install a code disk on the valve handle, divide the code disk into 4 equal parts in the radial direction, and divide it into 16 sectors of equal area in the circumferential direction, and then rotate these 16 sectors in a clockwise direction to the radial 4 Two equal areas are coded according to the rule of binary numbers, and painted black and white respectively (black stands for "O" and white stands for "1"). In this way, 16 different rotation angles of the handles represented by OH ～ 15H are formed on the coding disk. The positions represent different oxygen flows. Install 4 pairs of infrared light emitting and receiving tubes on one side of the encoding disc, and try to align them with the four encoding areas in the radial direction of the encoding disc. When the valve handle rotates, the infrared receiving tube can receive a coding sequence, and Transmit to AT89C55 one-chip computer. The AT89C55 microcontroller analyzes and compares these codes to determine the rotation direction, angle, number of rotations and final stop position of the handle, thereby calculating the corresponding oxygen flow, and recording the start time and end time of oxygen inhalation, and finally calculating the patient ’s Total oxygen uptake. In the process of oxygen inhalation, oxygen inhalation time, flow rate, oxygen inhalation and other information are displayed and the query function is provided. At the end of oxygen inhalation, the oxygen inhalation information is transmitted to the upper computer through RS 232 serial interface.
The system consists of coding disk, infrared light reading device, oxygen flow recording and calculating device, display device, operation panel, RS 232 serial interface and application system software. The block diagram of its system design is shown in Figure 1.
2 Hardware implementation plan
2.1 Encoding disk
As shown in Figure 2, the coding disk is made of a plastic circular plate with a thickness of 2 mm and a diameter of 80 MM. The coding disk is installed on the valve handle of the float oxygen flowmeter. The "0H" position of the coding disk corresponds to the closed state of the valve The remaining 16 positions correspond to different oxygen flow rates.
2.2 Infrared optical code reading device
The infrared light reading device is composed of 4 pairs of reflective infrared switch tubes, and uses the different reflectivity of the black and white areas on the code disk to infrared light to identify different codes. The reflection of infrared light by black is very weak, the receiving tube is in a cut-off state, and the reflection of infrared light by white is strong, and the receiving tube is in a saturated state. The signal is directly connected to the P1 port of AT89C55. Its main circuit is shown in Figure 3.
2.3 Oxygen flow recording and calculation device
This design uses the AT89C55 single-chip microcomputer as the core of oxygen flow recording, calculation, and query, and the DS12887 provides the real-time clock. The MCU reads the encoded information once every minute and calculates the flow rate, and simultaneously stores and displays. The MCU receives the interrupt signal generated by the operation key through the interrupt mode, and calls the corresponding subroutine to complete the time setting, flow setting, query, and clearing.
2.4 Display device
The display device uses the SMG1926 liquid crystal module circuit as the display, and its main circuit is shown in FIG. 4.
2.6 Power supply
The working voltage of the chip connected to the single chip and the peripheral is required to be +5 V. First, the 220 V AC voltage is converted to +9 V by the AC to DC converter, and then the +9 V voltage is stabilized to +5 V through the voltage regulator to power the system. Considering the anti-interference problem of the power supply part, it is necessary to add photoelectric isolation to prevent affecting the normal operation of the entire system. The main circuit is shown in Figure 6.
2. 7 RS232 serial interface
RS 232 serial interface is an indispensable link for the communication between the microcontroller and the host computer. AT89C55 one-chip computer contains a full-duplex programmable serial I / O port, and adopts RS 232 standard in serial communication. The RS 232 standard uses negative logic, which specifies that any level between +3 to +15 V is logic “Oâ€, and any level between -3 to -15 V is logic “1â€. Convert TTL or CMOS level to RS 232 level, this design uses MAX232 chip to complete the level conversion, its circuit is shown in Figure 7.
3 Software design
The software design adopts the single-chip microcomputer C language design. The overall program design includes: time setting module design, flow setting module design, metering module design, query module design, display module design, clearing module design, operation key setting module design, etc. The flow chart is shown in Figure 8.
4 Conclusion
A simple, practical, safe, reliable, and low-cost intelligent medical oxygen flowmeter is designed and implemented. On the basis of not changing the existing oxygen inhalation system and facilities of the hospital, the use of this instrument can easily solve the problem of charging patients according to the amount of oxygen inhaled during oxygen inhalation. It has a high promotion value and will be a medical reform in China. make a contribution.
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