The innovation of medical and health care equipment requires more attention to safety, and the degree of attention is no less than the electronic equipment used in hospitals. Safety includes many aspects and requires electrical safety. Therefore, when connecting with non-medical communication equipment or other household appliances, high voltage or leakage current will not flow into the human body. Electrical safety is largely ensured by isolation. Isolate and block the electrical path from the main power supply or other medical equipment (such as defibrillators and other equipment generating high voltage) to the equipment power supply.
The main source of unexpected signals in electronic equipment is the power grid. Medical applications must be able to block AC leakage, transients caused by lightning strikes, switch noise, and line fault conditions on 50 Hz to 60 Hz lines. This is not only for medical devices; However, medical equipment has more strict requirements in this regard, and the leakage level depends on the way the equipment is connected to the patient.
The connection between the equipment and the patient must also be isolated, so as to prevent the use of other connections as another circuit when the patient uses multiple medical devices, resulting in unexpected current direction. In addition, if the patient can contact any equipment connected to the safe grounding of the building (such as household appliances or metal bedsteads), the current must not pass through that path. The insulation for patients requires two independent insulation systems, or a single system that has been proved to be equivalent to two systems. This is called double patient protection isolation.
Typical home healthcare electronic devices need to communicate with other medical devices or existing home electronic facilities. It should be able to meet the privacy and security requirements and ensure that information is not intercepted or destroyed. It shall meet the leakage and safety requirements in IEC60601. Generally, the electrical connection needs to provide dual patient protection, with a rated withstand voltage of 4kV and very low capacitive leakage and anti-defibrillation rated performance.
The most reliable way to achieve communication is to use wired isolation interface. It has the stability of wired interface; It can also provide power through the built-in isolated DC-DC converter. It supports high-speed upload and download, and can be used when the device is connected to the patient. The wired interface does not need to encrypt data, reducing the processor overhead. Software maintenance can also be completed while the equipment is working. The interface can also be set to realize real-time remote monitoring at high data rate. For example, doctors can obtain ECG remotely when patients need routine follow-up. The isolation of these interfaces traditionally relies on devices such as optical couplers, which have speed limitations and poor integration capability. In new applications, medical grade digital isolators are replacing optical couplers, without these limitations.
The defibrillator in Figure 1 has several different interfaces and uses a variety of isolation technologies, so it is a good example to check the isolated communication interface. The device must use ECG to monitor the patient's heart activity in order to determine whether to perform defibrillation. The ECG data path must be isolated from the high-voltage part of the defibrillator, so that sensitive ECG electronic devices will not be fused when electric shock is applied to the patient. Internal isolation can be achieved through isolation grid driver and digital isolator. The device can also integrate Ethernet interface to monitor the status when the device is idle on the wall; Ethernet is mechanically interlocked, so it cannot be used when the defibrillator is removed from the wall. Similarly, the battery charging system is also connected to the wall and interlocked. The last function to be isolated is the communication port, which allows downloading ECG and defibrillation data for doctors to view and analyze. This connection generally isolates the USB interface, so data can be obtained without disconnecting the device from the patient.