Medical PPE HS code verification

List of contents of this article:

• 1,Medical PPE HS code verification Describe the fare system of the urban rail transit system?
• 2, There are three types of systems for the third-generation mobile communication system internationally, which are ().
• 3. What is the most widely used system in China? Why is the most used in China?
• 4, Introduction to LTE system types?
• 5, What is the power supply system of China's traction power supply system

Describe the fare system of the urban rail transit system?

1. The fares of various systems of China's urban rail transit mainly include the one-ticket system of the route (one-ticket system for a single line, and you need to repurchase the ticket for transferring to other routes), mileage segmentation (setting the starting price and starting mileage to increase the price by advancing the mileage) and segmented segmentation (according to the station area There are three forms of ticket prices.

2. Single fare system (referring to the distance of the ride, only one ticket is issued on the whole line) Advantages: the ticketing speed is fast, the ticket inspection system is implemented, and there is no ticket inspection when entering and leaving the station, which can reduce the number of station operators. Disadvantages: It is not conducive to attracting short-distance passenger flow. Segmented fare system (referring to the distance or number of stations to sell tickets of different fares.

3. [Answer]: (1) The fare system of the urban rail transit system mainly includes the single fare system, the metering fare system, the section fare system and the regional fare system. ( 2) The single fare system refers to the implementation of a price regardless of the length of the operating mileage.

4. The first stage: manual ticket sales and inspection stage, single ticket price, paper tickets. For example, at the beginning of the opening of Line 1. ( 2) The second stage: manual ticket sales and inspection methods. For example, during the trial operation of Line 3, the ticket price adopts the multi-level metering ticket system and paper tickets.

There are three types of systems for the third-generation mobile communication system internationally, which are ().

1. The third-generation mobile communication system mainly has three systems: WCDMA, CDMA2000 and TD-SCDMA, among which EuropeZhou's WCDMA and U.S. CDMA2000 were developed on the basis of GSM system and CDMA system respectively, and TD-SCDMA is China's standard.

2. At present, there are four third-generation mobile communication standards: CDMA2000 in the United States, WCDMA in Europe, and TD-SCDMA and LAS-CDMA in China. From the perspective of technological development trend and business function, the three standards based on the CDMA system: TDSCDMA, WCDMA and CDMA2000 are regarded as the three mainstream application technology standards of 3G.

3. The three mainstream standards of G system are WCDMA (broadband CDMA), cdma2000 and TD-SCDMA (time-diplex synchronous synchronous CDMA).The comparison of the basic technical parameters of these three standards is shown in Table 1.

The system of the environmental control system is the most widely used in China. What is the reason?

The system of the subway station environmental control system is divided into the following three types: Bus system: This system uses a unified bus to Connect all sensors and actuators for data transmission and control operations through the bus.

Open system: The open system is to apply mechanical or "piston effect" to exchange air between the inside of the subway and the outside world, and use the outside air to cool stations and tunnels. This system is mostly used in subway systems with an average monthly temperature of less than 25℃ and less transportation in the hottest local months.

According to the cooling capacity: large-scale airAdjustment system: Generally, the working area is very large, ranging from thousands of square meters to tens of thousands or even hundreds of thousands of square meters, and some can be up to hundreds of thousands of square meters. The system load capacity is usually hundreds to tens of thousands of cold tons.

The environmental control system of the subway has two main parts: the station ventilation and air conditioning system and the tunnel ventilation system. 1 Station ventilation and air conditioning system The ventilation and air conditioning system of the subway should be given priority to the ventilation system. When the ambient temperature reaches a certain condition, the station will adopt an air conditioning system.

The world's TV format is divided into PAL, NTSC and SECAM. The TV format adopted in China is PAL.

China adopts the PAL-D system, so the LCD TVs used in China should at least be compatible with the PAL-D system. LightningThe video signal of the video program is an analog signal composed of video analog data and video synchronization data, which is used to display images correctly at the receiving end. The details of the signal depend on the video standard or "system" applied.

Introduction to LTE system types?

According to different duplex modes, the LTE system is divided into FDD-LTE (Frequency Division Duplexing) and TDD-LTE (Time Division Duplexing). Both technologies The main difference lies in the physical layer of the empty port (such as frame structure, time design, synchronization, etc.).

LTE is actually a network system. What is well known isGSM, CDMA, GPRS, EDGE, etc. In fact, LTE is just a network system. TD-LTE is a wireless communication technology, and it is one of the 4G network wireless communication technologies that is faster than 3G networks.

LTE mainly includes two versions: TDDLTE and FDDLTE. The two systems are selectively applied according to the previous different 3G networks. For example, China Mobile adopts TDDLTE, because TDDLTE is very compatible with the 3G network independently developed by China Mobile.

What is the power supply system of China's traction power supply system

1. The traction power supply system willThe AC medium-voltage voltage is converted into a voltage of DC 1,500 V or DC 750 V through voltage reduction and rectification, which provides traction power for electric trains. It includes a traction substation and a traction network. The traction network includes contact network and return network. The contact network has two suspension methods: overhead contact network and contact rail.

2. The traction network implements single-phase power supply, which is composed of feeder wire (referred to as feeder wire), contact network, (electric locomotive), track circuit and return flow line, etc. In order to supply electricity to electric locomotives effectively and reliably, phase-split insulators, segment insulators and other equipment are also installed on the traction network, and there are also sub-sections, opening and closing stations, etc. in the power supply system.

3. Power supply system Urban rail transit power supply system composition; substation, contact network, return network. The power supply system of the traction network mainly refers to the current system, voltage level and feeding mode.China's national standard subway DC traction power supply system stipulates two power supply systems: DC1500V and DC750V.

4. The "AC-DC-AC) variable frequency speed regulation method is usually adopted. Although the AC asynchronous motor is used on electric vehicles, its contact grid line power supply voltage is still DC. From the perspective of power supply, it can still be regarded as an expanded application of the DC power supply system.