German Helmholz plug, Helmholz model, Helmholz price

Helmholz plug is a common line or path used in computers to connect various functional components and transmit data between them. In computer systems, buses can be classified according to the objects they connect: chip bus, also known as device-level bus, which is the bus inside the central processor chip; internal bus, also known as system bus or board-level bus, which is the transmission path between various functional components of the computer, and the microcomputer bus is usually called the internal bus; external bus, also known as communication bus, which is the transmission path between computer systems, or between the computer host and peripheral devices. In computer systems, the common path for transmitting information between various components is called the bus, and microcomputers use a bus structure to connect various functional components.

Helmholz plug introduction

Any microprocessor must be connected to a certain number of components and peripheral devices. However, if each component and every type of peripheral device were directly connected to the CPU using a separate set of lines, the wiring would become intricate and complex, making implementation difficult. To simplify hardware circuit design and system architecture, a common set of lines, equipped with appropriate interface circuits, is used to connect to various components and peripheral devices. This shared set of connection lines is called a bus. Adopting a bus structure facilitates the expansion of components and devices; especially when unified bus standards are established, interconnection between different devices becomes easier. In microcomputers, buses generally include internal buses, system buses, and external buses. An internal bus is the bus between peripheral chips inside the microcomputer and the processor, used for chip-level interconnection; a system bus is the bus between plug-in boards and the system board in a microcomputer, used for board-level interconnection; an external bus is the bus between the microcomputer and external devices. As a device, the microcomputer exchanges information and data with other devices through this bus, which is used for device-level interconnection. Additionally, broadly speaking, computer communication methods can be divided into parallel communication and serial communication, with the corresponding communication buses referred to as parallel buses and serial buses. Parallel communication offers high speed and good real-time performance, but due to the large number of signal lines occupied, it is not suitable for miniaturized products. Although serial communication has a lower rate, it appears simpler, more convenient, and more flexible in microprocessor circuits where data communication throughput is not very high. Serial communication is generally divided into asynchronous mode and synchronous mode. With the development of microelectronics and computer technology, bus technology continues to develop and improve, resulting in a wide variety of computer bus technologies, each with its own characteristics.

Helmholz plug types

1) 232-C is a serial physical interface standard developed by the EIA Electronic Industry Association. RS is the abbreviation for "Recommended Standard," 232 is the identification number, and C indicates the revision count. The RS-232-C bus standard features 25 signal lines, including one main channel and one auxiliary channel. In most cases, the main channel is primarily used. For general full-duplex communication, only a few signal lines are required, such as one transmit line, one receive line, and one ground line. The RS-232-C standard specifies that the driver allows a capacitive load of 2500pF. The communication distance is limited by this capacitance. For example, when using a communication cable with 150pF/m, the maximum communication distance is 15m; if the capacitance per meter of cable decreases, the communication distance can increase. Another reason for the short transmission distance is that RS-232 uses single-ended signal transmission, which suffers from common ground noise and cannot suppress common-mode interference. Therefore, it is generally used for communication within 20m. 2) RS-485 Bus: When communication distances range from tens of meters to over a kilometer, the RS-485 serial bus standard is widely adopted. RS-485 uses balanced transmission and differential reception, thus possessing the ability to suppress common-mode interference. Additionally, the bus transceiver has high sensitivity and can detect voltages as low as 200mV, allowing the transmission signal to be recovered at distances beyond a kilometer. RS-485 operates in half-duplex mode, meaning only one node can be in the transmit state at any time; therefore, the transmit circuit must be controlled by an enable signal. RS-485 is very convenient for multi-point interconnection, saving many signal lines. Applying RS-485 allows networking to form distributed systems, permitting up to 32 drivers and 32 receivers to be connected in parallel.

Helmholz plug main parameters

1) Rated Voltage: Rated voltage, also known as operating voltage, mainly depends on the insulating materials used in the connector and the spacing between contact pairs. Certain components or devices may fail to perform their intended functions when operated below their rated voltage. The rated voltage of a connector should effectively be understood as the maximum operating voltage recommended by the manufacturer. In principle, connectors can operate normally at voltages below the rated voltage. The author tends to select the rated voltage reasonably based on the connector's withstand voltage (dielectric strength) specifications, according to the usage environment and safety level requirements. This means that with the same withstand voltage specification, different maximum operating voltages can be applied depending on the usage environment and safety requirements. This aligns well with objective usage conditions. 2) Rated Current: Also known as operating current. Like rated voltage, connectors generally operate normally when the current is below the rated current. In the connector design process, thermal design is used to meet rated current requirements because when current flows through contact pairs, heat is generated due to conductor resistance and contact resistance. When the heating exceeds a certain limit, it will damage the connector's insulation and cause softening of the contact pair surface plating, leading to failure. Therefore, limiting the rated current effectively means limiting the temperature rise inside the connector to not exceed the design specified value. An issue to note during selection is that for multi-core connectors, the rated current must be derated. This deserves greater attention in high-current applications. For example, for φ3.5mm contact pairs, the rated current is generally specified as 50A, but for 5 cores, a derating of 33% must be applied, meaning the rated current per core is only 38A. The greater the number of cores, the larger the derating magnitude. 3) Contact Resistance: Contact resistance refers to the resistance generated at the contact interface between two conductive contacts. Two issues should be noted during selection. First, the contact resistance specification of a connector is effectively the contact pair resistance, which includes both the contact resistance and the conductor resistance of the contact pair. Since conductor resistance is usually small, contact pair resistance is often referred to as contact resistance in many technical specifications. Second, in circuits handling small signals, pay attention to the conditions under which the given contact resistance specification was tested, because oxide layers, oil stains, or other contaminants on the contact surfaces can create film resistance. As the film thickness increases, the resistance rises rapidly, turning the film into a poor conductor. However, the film can undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and high current. For some small-volume connectors, the designed contact pressure is quite low, and the application levels are only in the mA and mV range, making it difficult for the film resistance to break down, which may affect signal transmission. One of the contact resistance test methods in GB5095 "Basic Test Procedures and Measurement Methods for Electromechanical Components Used in Electrical Equipment," specifically the "Contact Resistance - Millivolt Method," stipulates that to prevent breakdown of the insulating film on the contacts, the DC or AC peak open-circuit electromotive force of the test circuit shall not exceed 20mV, and the DC or AC test current shall not exceed 100mA. 4) Shielding: In modern electrical and electronic equipment, the increasing density of components and their related functions imposes strict limits on electromagnetic interference. Therefore, connectors are often enclosed in metal housings to prevent internal electromagnetic radiation or interference from external electromagnetic fields. At low frequencies, only magnetic materials provide significant shielding against magnetic fields. In this case, there are specific requirements for the electrical continuity of the metal housing, which relates to the housing contact resistance.

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