A defibrillator is an effective medical rescue instrument that uses a high-energy pulsed current that is instantaneously released to remove ventricular fibrillation (VF) or atrial fibrillation (AF) from a heart by a brief electric shock and restore it to normal heart rhythm. Obviously, the performance of the defibrillator will directly affect the effectiveness of clinical first aid. The defibrillator test analyzer developed by the author can perform calibration tests on various functional parameters of the defibrillator, including discharge energy, maximum current and voltage, synchronous trigger delay time, and defibrillator discharge time, and can simulate human body output. A variety of heart rate, a variety of lead standard ECG waveforms and specific waveforms to characterize defibrillator performance, and a defibrillation discharge function that detects synchronization with ECG signals.
In the development process of the defibrillator test analyzer, the interference phenomenon was analyzed, the cause of the interference and the characteristics of the interference were analyzed. Some anti-interference measures were adopted, and the EMI (electromagnetic interference) filter was applied. The strong interference generated by the discharge pulse inside the instrument is removed, and the defibrillator test analyzer is stable and reliable, and has good electromagnetic compatibility.
1 Basic principles and interference characteristics of the system
The instrument takes Philips single-chip microcomputer 80C52 as the control core, completes the test and analysis of the functions of the defibrillator, and analyzes the display and transmission of the analysis results through the interface circuit. The principle block diagram is shown in Figure 1. The defibrillator test analyzer mainly performs two functions: (1) complete accurate measurement of the defibrillator discharge energy; (2) accurately and stably output various electrocardiogram waveforms and test waveforms. To verify the defibrillator's automatic defibrillation function and its characteristic parameters, the analyzer can output a variety of waveforms, including ECG (electrocardiogram) waves with multiple lead outputs and adjustable amplitude, while outputting high amplitude ECG signals, DC pulse, square wave, triangle wave, composite wave, sinusoidal filter of multiple frequencies, and standard R wave of various heart rhythms. The output of each waveform is digitally synthesized, and the waveform generated by the program is output through a D/A converter, and then converted into a desired output mode by an analog circuit. The detection of discharge energy is based on the high-voltage discharge pulse of the defibrillator discharged through an analog resistance (typical resistance of 50Ω) simulating the body impedance, and is attenuated and sent to the variable gain amplifier to become the input signal of the A/D converter. Then process and display.
According to the requirements of the instrument, in addition to the completion of various functions, when testing the discharge of the defibrillator, it must be able to withstand the strong interference caused by the discharge pulse, not crash, no reset, without interference avoidance method, When the system intelligent reset method and other measures, the program can still be executed normally. At the same time, since the instrument must have the function of restoring the discharge pulse waveform, the measurement analog channel cannot adopt filtering, surge damping and other measures on the discharge signal. This puts higher requirements on the anti-jamming performance of the instrument.
Part of the system's interference source is the internal digital circuit of the instrument, the interference generated by the power supply and the electromagnetic interference from the external space of the instrument; the other part interferes with the discharge pulse from the defibrillator. Its interference has the following characteristics:
(1) The voltage peak is high and the energy is large, the highest voltage can reach 5000V, and the maximum discharge energy can reach 360J;
(2) The discharge time is short, the defibrillator discharge pulse time is only about 10ms, and the pulse front time is about 2ms;
(3) The discharge waveform is complex. For different types of defibrillators, the shape of the discharge pulse is different, and there are one-way exponential decay type, two-way exponential decay type, one-way cut-off type and two-way cut-off type;
(4) Interference directly enters the inside of the instrument. Since the instrument is a portable instrument, a 50Ω resistor that simulates the human body is placed in the instrument, so interference is generated inside the instrument;
(5) The interference is complicated. Since the power required to simulate the 50Ω resistor of the human body is large (the resistor is generally a wirewound resistor), the resistor has a large distributed inductance and a distributed capacitance, and the discharge pulse inevitably generates a strong complex interference through the resistor.
2 Anti-interference design and selection of EMI filter
The electromagnetic interference signal generated by the interference source is generally transmitted to the interfered object through the electrostatic coupling of the capacitor, the magnetic coupling of the inductor, the ground power coupling of the common disturbance, and the electromagnetic radiation inductive coupling. Since the strong interference source and the measurement control circuit are placed in the same chassis and are close to each other, the electromagnetic interference propagation is near-field induction, that is, capacitive coupling and magnetic coupling. In addition, the common impedance coupling is also an important way to transmit interference. Therefore, in addition to the commonly used software anti-interference measures (such as the use of empty instructions, digital filtering, etc.), the electromagnetic compatibility design of the whole machine is also carried out from the following aspects to solve the interference. problem.
2.1 Suppressing interference sources
In order to effectively reduce the interference of the interference source, the 50Ω high-power resistor for simulating the human body uses non-inductive resistors. Pay attention to reduce the parasitic reactance parameters brought by the leads and properly allocate the spatial position of the discharge sampling resistors during wiring, paying special attention to the large current path. The welding quality is to prevent the spark discharge from causing stronger interference caused by poor contact; the low frequency circuit chip can effectively reduce the noise and improve the anti-interference ability of the system.
2.2 About the design of the shielding layer
The purpose of shielding is to ensure system signal transmission performance under disturbing environmental conditions. This anti-interference measure can interfere with the screen externally, and can also reduce the radiation energy itself. The measure of device transmission performance is the ACR value (attenuation/crosstalk ratio). Unshielded lines can transmit bandwidth and transmission rate much higher than standard bandwidth and standard transmission rate if the ACR value meets the requirements. However, when the signal is transmitted in the line at a very high rate, due to external electromagnetic interference and internal crosstalk, data transmission errors are likely to occur, and the performance of the system is degraded. Therefore, the system transmits data at a lower rate to increase the reliability and security of the system.
In order to effectively reduce external electromagnetic interference, shielding measures can be used. Shielding is divided into electrostatic shielding and magnetic shielding. Electrostatic shielding requires reliable grounding. The actual shielding system has some problems that must be paid attention to, such as the grounding method, the grounding conductor, and the integrity of the shielding. Shielded cables should be used with caution, as shielding not only causes signal transmission imbalance, but also changes the capacitive coupling of the cable, resulting in increased attenuation and reduced signal output balance. At the same time, considering that the interference source and the measurement control circuit are in the same instrument, the distance is very close. If the shielding layer is used internally and the shielding is not well connected, the increased capacitance effect will be very obvious. In view of the above considerations, no shielding measures are used between the internal discharge resistors of the system and the circuit boards and connecting cables. However, the shielding of the plastic casing must be carefully considered. In order to reduce the external electromagnetic interference, the metal shielding layer is sprayed, and the coating is required to reach a certain thickness and the gap and the hole are leaked, and special attention is paid to grounding reliably.
2.3 Coupling channels for suppressing interference and anti-interference measures for sensitive circuits
In order to facilitate the installation of the instrument and simplify the structure, combined with the above analysis of shielding and non-shielding, no shielding measures are adopted inside the instrument. In order to solve the interference problem, in addition to the software and common hardware anti-interference measures, multi-layer circuit boards and EMI filters are also used to increase the anti-interference ability of the instrument.
(1) Based on the circuit principle, the discharge energy detection circuit uses a differential active attenuation circuit to float the discharge pulse sampling resistor and reduce the interference caused by the electrical coupling of the common impedance. The attenuation resistor network uses multiple precision metal film resistors to improve attenuation proportional accuracy and reduce reactance distribution parameters.
(2) The circuit board design uses a multi-layer circuit board to reduce electromagnetic interference. Reasonably arrange the device distribution, and separate the signal acquisition and preprocessing part, the waveform generation part and the like from the digital signal part (such as the MCU control unit, memory, expansion I/O port, etc.). In addition, the power generation part is concentrated in one area, so that the circuit board plane is as close as possible to the instrument backplane (the bottom board is shielded by the instrument casing), which acts as a multi-layer board; reasonable wiring, minimizing the loop area to reduce radio frequency interference; The direction of the trace on the board should be avoided as much as possible. Otherwise, the impedance will be discontinuous and radiation will be generated, causing radio frequency interference. Since the instrument is a portable instrument, a low power CMOS circuit must be used. However, due to the high input impedance of the CMOS circuit, it will cause a very serious signal reflection distortion, thereby increasing the noise of the system, so the wiring is as short as possible, and the number of vias is minimized.
2.4 Application of EMI Filter
There are many types of EMI electronic components, such as inductor tips, capacitors, varistors, LC assemblies, and conventional EMI filters. Various types include many types, such as three-lead wafer capacitors with ferrite beads, laminated chip surge absorbers, ferrite turbulence diagrams, and so on.
Since the interference is near-field interference, the interference is intense and complicated. To do this, the filter must be mounted on the board, not only with EMI filters for the signal lines, but also with EMI filters for the power supply. In order to save space, the welding type is adopted, and at the same time, in order to ensure the filtering performance, special attention is paid to the welding work.
When selected as a filter, it is mainly to determine the cutoff frequency of the filter. The cutoff frequency must be chosen to ensure that the passband of the filter covers the bandwidth of the wanted signal, ensuring proper operation of the device while maximizing the filtering of unwanted interference. In order to prevent digital signal transmission errors caused by electromagnetic radiation, causing crashes and resets, etc., an EMI filter against high frequency interference is connected to the digital signal channel. The equivalent circuit of the three-lead wafer capacitor DSS310 series EMI filter with ferrite beads produced by Murata Co., Ltd. is shown in Fig. 2. The relationship between insertion loss and frequency is shown in Fig. 3.
For the anti-jamming of analog signals, similar EMI filters are also used, but only the bandwidth of the signal is guaranteed when the cutoff frequency is selected. Considering the impact surge interference caused by the near-field to the public line, the three-lead wafer pressure-sensitive one-capacitor type EMI filter DSS710 series with ferrite beads is selected, and FIG. 4 is a suppression special film for power supply interference. And compression features. The varistor voltage is 22V, and the capacitance can reach 22000pF. With the action of ferrite beads, the suppression frequency of electromagnetic interference can be reduced to more than 3MHz, the attenuation is greater than 20dB, and the suppression frequency range is obviously broadened. This type of filter is used in various power channels of the system.
HP's CodeMaster defibrillator was tested several times and compared with the defibrillator analyzer QA-45 from METRON, Sweden. The test data is shown in Table 1 (QA-45 in the given test). Within the range, the accuracy is ±2%). Only the performance index of the defibrillator discharge energy is analyzed. In the low energy test (<50J), the error is much less than 2%; in the high energy test, the error can be controlled within 2%. After several consecutive high-energy discharge tests, the system has proven to have good repeatability and stability, and fully meets the performance requirements of the design.
Table 1 Test data table
KNM5 Series Moulded Case Circuit Breaker
KNM5 series Moulded Case Circuit Breaker is MCCB , How to select good Molded Case Circuit Breaker suppliers? Korlen electric is your first choice. All moulded Case Circuit Breakers pass the CE.CB.SEMKO.SIRIM etc. Certificates.
Moulded Case Circuit Breaker /MCCB can be used to distribute electric power and protect power equipment against overload and short-current, and can change the circuit and start motor infrequently. The application of Moulded Case Circuit Breaker /MCCB is industrial.
Korlen electric also provide Miniature Circuit Breaker /MCB. Residual Current Circuit Breaker /RCCB. RCBO. Led light and so on .
KNM5 series Molded Case Circuit Breaker,Small Size Molded Case Circuit Breaker,Electrical Molded Case Circuit Breaker,Automatic Molded Case Circuit Breaker
Wenzhou Korlen Electric Appliances Co., Ltd. , https://www.korlenelectric.com