The electromagnetic compatibility (EMC) of medical equipment is directly related to the accuracy of clinical diagnosis and patient safety. As a core coagulation testing device in operating rooms, ICUs, and clinical laboratories, even minor deviations in the test results of a semi-automated thromboelastography analyzer can lead to incorrect clinical decisions and potentially endanger patient lives. As the hospital electromagnetic environment becomes increasingly complex, electromagnetic interference generated by MRI machines, electrosurgical units, wireless communication devices, as well as issues such as electrostatic discharge during operation and power surges, impose stringent requirements on the EMC performance of semi-automated thromboelastography analyzers.

Shanghai Leiditech, as a leading domestic supplier of EMC protection solutions and components with over 16 years of deep experience in the protection field, has developed a complete ESD and surge protection solution for the specific application scenarios of semi-automated thromboelastography analyzers. Based on the IEC 60601-1-2 international medical equipment EMC standard and the domestic standards GB/T 18268.1 and GB/T 18268.26, this solution helps equipment manufacturers easily pass medical certifications and ensures stable and reliable operation of the equipment in complex hospital environments. In this article, the Leiditech EMC team will comprehensively analyze the EMC protection technology for semi-automated thromboelastography analyzers, covering product functional architecture, standard requirements, protection principles, and specific component selection.

I.Functional Architecture of Semi-Automated Thromboelastography Analyzers

1.1  Core Product Functions and Clinical Value

A semi-automated thromboelastography analyzer is an analytical instrument that simulates the human coagulation process to monitor the dynamic changes of blood clotting in real time. It can comprehensively reflect the entire process from coagulation factor activation and fibrin formation to clot lysis, providing key coagulation parameters such as R value (reaction time), K value (clot formation time), α angle (clot formation rate), and MA value (maximum amplitude). It is widely used in clinical scenarios such as perioperative coagulation management in surgery, trauma resuscitation, diagnosis and treatment of cardiovascular and cerebrovascular diseases, and prevention of obstetric hemorrhage. It serves as an important basis for guiding clinical blood transfusion and anticoagulation therapy.

1.2 Core System Architecture

A typical semi-automated thromboelastography analyzer is mainly composed of the following core modules:

· Power supply system: Includes the AC 220V power input unit and the DC12V/24V internal power supply unit, providing stable electrical power for the entire device.

· Main control system: Centered around a high-performance microprocessor (MCU), responsible for data processing, algorithm computation, and overall device control.

· Detection system: Uses a high-precision mechanical sensor to detect viscoelastic changes during the blood coagulation process. This is the core detection unit of the device.

· Human-machine interface system: Includes an SPI interface display, buttons, indicator lights, etc., to enable operation control and result display.

· Communication system: Includes USB 2.0, RS-232, RS-485, Ethernet, and other interfaces for data transmission, print output, and remote control.

1.3 EMC Protection Challenges in the Hospital Environment

In the complex electromagnetic environment of a hospital, semi-automated thromboelastography analyzers face multiple EMC challenges:

· External RF interference: RF electromagnetic fields generated by MRI machines, electrosurgical units, wireless access points, mobile phones, etc., can couple into the device's signal lines, interfering with the acquisition and processing of weak sensor signals and causing inaccuracies in key parameters such as R value and K value.

· Power conducted interference: Voltage fluctuations, harmonics, electrical fast transients (EFT), and surges present in the hospital power grid can intrude into the device through the power lines, potentially damaging circuit components.

· Electrostatic discharge (ESD) interference: Electrostatic discharge generated by medical staff when inserting or removing test reagent bottles or connecting external devices can cause device crashes, data loss, or even hardware damage.

1.4 Overall EMC Protection Block Diagram

To systematically address the above EMC issues, Leiditech has designed the following overall EMC protection block diagram for a semi-automated thromboelastography analyzer. It follows the principle of "graded protection with defense in depth," with corresponding protection devices placed at the power entry point and each external interface:

Semi-Automated Thromboelastography Analyzer Block Diagram

II.Detailed Explanation of Leiditech's One-Stop EMC Protection Solution

2.1 EMC and Reliability Design for the AC Power Interface

Standard requirements:

According to IEC 60601-1-2:2014 "Medical electrical equipment — Part 1-2: General requirements for basic safety and essential performance — Collateral standard: Electromagnetic compatibility — Requirements and tests" and GB/T 18268.1-2010 "Electromagnetic compatibility requirements for electrical equipment for measurement, control and laboratory use — Part 1: General requirements," the AC power interface of medical equipment must meet the following:

· Electrostatic discharge (ESD): Contact discharge ±6kV, air discharge ±8kV (IEC 61000-4-2)

· Electrical fast transient (EFT): ±2kV (power lines) (IEC 61000-4-4)

· Surge: Differential mode ±1kV, common mode ±2kV (IEC 61000-4-5)

Protection principle: The AC power interface is the main path for electromagnetic interference to intrude into the device. Leiditech adopts a three-stage protection solution consisting of "GDT + MOV + common-mode filter."

DC 12V/24V secondary power protection:
Similar to the AC power interface, the DC power interface also needs to meet corresponding ESD, EFT, and surge requirements. Additionally, since the DC power supply typically powers internal sensitive modules, the requirements for clamping voltage are more stringent.

Leiditech adopts a four-stage protection solution consisting of "GDT + MOV + common-mode filter + TVS." Building upon the AC power protection, a TVS transient voltage suppressor is added to further clamp the voltage and protect the downstream sensitive DC/DC converters and internal circuits. TVS devices offer advantages such as fast response time (nanosecond level), low clamping voltage, and small size, making them very suitable for protecting sensitive semiconductor devices.

For 12V, select the SMBJ15CA; for 24V, the SMBJ28CA is recommended. These meet IEC 61000-4-2 Level 4 (8kV contact discharge, 15kV air discharge). For compliance with high-level IEC 61000-4-5 surge testing, high-power SMC devices are required.

2.2 Protection Solution for Sensor Interfaces

The sensor interface is the most sensitive part of the device and must be protected using ESD devices with ultra-low leakage current and ultra-low capacitance to avoid affecting measurement accuracy.

Advantages of the solution:

• Ultra-low leakage current design does not divert or affect the weak signals from the sensor.

• Low parasitic capacitance does not affect the frequency response of the signal.

• Meets the highest level of ESD protection requirements of IEC 61000-4-2 Level 4

2.3 Protection Solution for USB Interfaces

The USB interface is the main channel for communication between the device and external equipment, and is also a high-risk area for electrostatic discharge. Leiditech provides a dedicated USB ESD protection solution with high integration and strong protection capability.

USB 2.0 interface protection circuit:

Leiditech recommends using a single device for protection, saving space, ensuring signal integrity, and filtering out common-mode interference. The SR05 meets IEC 61000-4-2 Level 4, contact discharge 20kV, air discharge 20kV.

2.4 Protection Solution for Ethernet Interfaces

For semi-automated thromboelastography analyzers that support network connectivity, the Ethernet interface requires protection against ESD, EFT, and surge interference.

Leiditech has designed a surge protection solution for 1000M Ethernet ports using a two-stage protection architecture. It operates stably and reliably, effectively ensuring signal integrity under high-temperature conditions. It complies with IEC 61000-4-2 Level 4, supporting ±30kV for both contact and air discharge. At the same time, it meets the IEC 61000-4-5 standard with a 10/700μs waveform, 40Ω impedance, and 6kV voltage for 5 positive and 5 negative tests. Signal transmission remains stable under high-temperature conditions with no packet loss.

Advantages of the solution:

• Multi-stage coordinated protection meets both ESD and surge protection requirements.

• Ultra-low capacitance design ensures Ethernet signal integrity.

2.5 Protection Solution for RS232/RS485 Serial Ports

RS232/RS485 serial ports are used to connect external devices such as printers and barcode scanners, and require protection against ESD and surge interference.

The RS-232 standard interface, also known as EIA RS-232, is one of the commonly used serial communication interface standards, typically applied to short-distance point-to-point communication. On communication equipment, this interface serves as a debugging interface, an inter-board communication interface, and a monitoring signal interface, with a maximum data rate of 115200 baud.

Leiditech recommends using the integrated devices SMC12/SMC15 for protection. They ensure signal integrity while passing ESD testing, meeting IEC 61000-4-2 and ISO 10605-2 Level 4 with 30kV contact discharge and 30kV air discharge.

RS485 interface protection circuit:

Leiditech's EMC support team recommends using the multi-channel integrated device SM712 for protection. It ensures signal integrity while filtering out noise and passing ESD testing, meeting IEC 61000-4-2 and ISO 10605-2 Level 4 with 30kV contact discharge and 30kV air discharge.

2.6 Protection Solution for the Operator Panel and Touchscreen

The operator panel and touchscreen are the main interfaces for human-machine interaction and are frequently subjected to human body electrostatic discharge.

Button interface:

Leiditech's EMC support team recommends using the standard low-capacitance integrated device SDA05CW for ESD protection, meeting IEC 61000-4-2 Level 4 with 8kV contact discharge and 15kV air discharge.

Touchscreen interface:

Medium-to-low speed interface solution

MIPI provides transmission speeds for medium-to-low-speed interfaces (10M-1Gbps). Leiditech recommends using the integrated device ULC3304P10 for protection. With a parasitic capacitance of <1pF, it ensures signal integrity and complies with IEC 61000-4-2 Level 4 with 8kV contact discharge and 15kV air discharge.

The Leiditech components used in this solution are summarized as follows:

As a critical clinical coagulation testing device, the EMC performance of the semi-automated thromboelastography analyzer is directly related to medical safety and diagnostic accuracy. With 16 years of industry experience in EMC protection, Shanghai Leiditech has conducted in-depth research into the specific application scenarios and standard requirements of medical equipment, providing a complete and reliable ESD and surge protection solution for the semi-automated thromboelastography analyzer.

Leiditech's solution strictly follows the IEC 60601-1-2 international medical equipment EMC standard and the domestic standards GB/T 18268.1 and GB/T 18268.26, adopting the design philosophy of "graded protection with defense in depth." Comprehensive protection design has been implemented from the power entry point to each external interface, effectively suppressing various electromagnetic interferences and ensuring stable and reliable operation of the equipment in complex hospital environments. Leiditech not only provides high-quality protection components but also has a professional technical support team — the Leiditech EMC Team — capable of offering customers one-stop services ranging from solution design and component selection to EMC testing and rectification.