Just as there is a real science behind every medical procedure, there is also a science behind the determination of airflow and silicon-based pressure sensors in complex medical devices used to assist in the diagnosis and treatment of diseases. The three medical applications that use airflow and silicon-based pressure sensors are: anesthesia machines, sleep ventilators, and hospital diagnostic equipment.
Anesthesia Machine
The drugs used in anesthesia machines pose unique challenges for the equipment. These chemicals are usually highly viscous and may build up inside the equipment. When manufacturing such equipment, such factors must be taken into consideration and corresponding restorative measures must be taken.
Because medical equipment is very important to patients, choose a sensor that can provide excellent sensitivity and accuracy throughout the life of the equipment. Choosing a sensor that can meet the performance requirements and maintain stable performance for a long time can ensure that the sensor is used normally during the entire service life of the medical device. If you choose the right sensor, you can achieve a 10-year sensor life cycle.
The engineer should consider the patient's breathing frequency. The range of patients may range from adults with poor health and slow breathing rate to adults who are healthy, breathing fast and have a large lung capacity. The sensing part needs to be very sensitive in order to correctly measure the patient's inhalation and exhalation and the anesthetic gas delivered into the airflow. Therefore, two (sometimes three) airflow sensors are used to measure specific pneumatic subsystems. Designers should probably set up a dedicated airflow sensor for all important subsystems in the equipment.
Because the combination of anesthetic agent and high humidity will cause a harsh environment for the sensor, it can be considered that the differential pressure sensor in the expiratory circuit is superior to the airflow sensor. Differential pressure sensors are more adaptable to gaseous medium pollution caused by moisture, anesthetic agents and other materials. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
In cases where a high-pressure delivery source is required, or the sensor requires direct contact with concentrated oxygen or anesthetic agent, a sensor isolated from the medium should be used. At this time, the choice of stainless steel pressure sensor isolated from the medium may be the most ideal, because it is more durable.
If portable equipment is needed, low-power airflow and pressure sensors should be considered, which can reduce the size of the power supply required and help limit the total weight of the unit. Mounting the sensor to the manifold of the airflow channel can help reduce the design size and weight.
Another consideration is output. Digital outputs, such as I2C and SPI protocols, can optimize the resolution of the sensor and integration with the microprocessor. But there is still a demand for analog output. The main reason is that in some safety circuits, software is not allowed due to the need for rectification. The user may wish to use the raw output of the sensor to trigger an alarm or security condition. The ability to provide both digital and analog options is important.
Finally, the response time of the sensor is critical to the effective delivery of anesthetic drugs to the patient. Using current technology, anesthesia machine manufacturers can achieve a response time of 1ms.
Sleep ventilator
As far as sleep ventilator is concerned, when it comes to the total error band, it is usually more concerned about the patient's comfort and convenience, and the performance requirements are not harsh. Because they are usually used in conjunction with humidifiers, they need to operate under conditions of higher humidity and maintain stable performance. They must be durable because they are usually operated and used by various people in the home environment.
The user's requirements for the device are mainly focused on accuracy, stability, portability and unit size / weight. The noise requirement is also important because this device is used during sleep. An airflow sensor with a lower pressure drop needs to be used because if the pressure drop is too high, the working intensity of the motor is greater (the pressure drop is equal to the impedance in the sensor), thereby increasing noise and shortening the life of the motor.
So engineers should choose sensors that can sense differential pressure or airflow at a very low rate. The sensor should be able to measure the peak of the patient's breathing, or the turning point between inspiration and expiration. For more complicated sleep ventilators, air flow sensors are sometimes selected instead of pressure sensors because the ventilator needs to be more sensitive at low air flow levels.
Once the pressure, gas flow and medium requirements are determined, the accuracy and stability requirements should be considered, including the total error band. Home sleep ventilator must be durable, because external factors will affect the performance of the unit.
For price considerations, enhanced digital products are usually selected. It is more expensive to add components to adjust the signal size later than buying a sensor that has already been amplified. At the same time, if this is done, the time for integration will be shorter, which allows designers to implement sensors faster and bring the final device to market faster.
Depending on the type of sleep ventilator, mechanical requirements (such as size, installation, and drilling) may also have a certain impact on the design of the device, because customers want smaller, beautiful, and portable devices. It may also be necessary to consider customer calibration functions, especially for CPAP (Continuous Positive Airway Pressure) applications, to maximize product performance and best match the patient's breathing pattern.
Hospital diagnostic equipment
Hospital diagnostic equipment includes mass spectrometers, chromatographs (for example, for gas, liquid, and high-performance liquid chromatography), laboratory automation systems, and analyzers, such as for blood, hematology, immunoassay, and clinical chemistry instrument.
When selecting sensors for hospital diagnostic equipment, high resolution, high accuracy, and high stability are all key factors to consider. The equipment needs to be able to detect even the smallest mass. Therefore, diagnostic devices generally have the highest resolution requirements, usually 16 bits or higher. The accuracy and stability of the sensor are very important for obtaining accurate data, and accurate data is very important for the laboratory test results, and will directly affect the patient's life and safety.
Determining the full range and increment of pressure and air flow to be detected is the primary factor to consider. The application of sensors in the field of hospital diagnosis may also require compatibility with media other than clean, dry air. In some diagnostic equipment, the gas released from plastic or adhesives, although insignificant, can contaminate the sample and skew the test results. Accuracy, especially for linearity and hysteresis errors, is very important. Because the sensitivity of the entire system is related to the sensitivity of the sensors used, the hysteresis should be minimized. An accuracy error of 0.25% is optimal (non-linearity and hysteresis error), while 0.5% is usually the maximum value allowed.
As mentioned above, high resolution is critical, which is why users of diagnostic and analysis equipment may choose unamplified sensors to obtain as much core / raw sensor output as possible and create their own compensation and amplification algorithms the reason. Some sensor manufacturers provide products with amplification through high-resolution A / D converters. Note that the high-resolution A / D converter is not the resolution of the sensor-you need to consider the resolution of the sensor itself. If the resolution of the sensor is low, the extra digits of the A / D will only provide additional useless data.
Stability is very important, because drift may accidentally affect the sensor reading. If the sensor drifts after the device is made (calibration is done before the device is shipped), the results will be biased. In the process of manufacturing and installation of the sensor, how to prevent the influence of thermal stress and mechanical stress must be considered, because this will affect the stability of the device performance. In hospital diagnostic applications, 0.5% or less is an acceptable maximum for errors related to drift and instability.
Unlike other medical applications, for diagnostic equipment, size is not a particularly critical factor, because most of them are large, inconvenient to move equipment, and fixed in the laboratory. Resolution, accuracy and stability should be considered first, followed by physical factors such as output, size, installation, drilling and power requirements. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
ECU-MEM-CONNECTOR is used to connect the ECU-MEM to the DIAG-LAYER. This part of ODX also links the ECU-MEM-objects with DIAG-COMMS e.g. used to read idents, download or upload the data. It allows an ECU to be flashed using ODX.
ECU Connector Section
ECU Connector Section
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