Ⅰ Types of wireless sensor

1.Vibration sensor

The maximum sampling rate of each node can be set to 4KHz, and each channel is equipped with an anti-aliasing low-pass filter. The collected data can be wirelessly transmitted to the computer in real-time, or stored in the built-in 2M data memory of the node, ensuring the accuracy of the collected data. The effective outdoor communication distance can reach 300m, the node power consumption is only 30mA, and the built-in rechargeable battery can be used for continuous measurement for 18 hours. If you choose a node with a USB interface, you can either charge the node through the USB interface or download the data in the memory to the computer quickly.

2.Strain sensor

The node has a compact structure and a small size. It consists of a power module, a collection and processing module, and a wireless transceiver module, and is encapsulated in a PPS plastic casing. Each channel of the node has an independent high-precision 120-1000Ω bridge resistance and amplifying and conditioning circuit, which can be easily switched automatically by software to select 1/4 bridge, half-bridge, and full-bridge measurement methods. It is compatible with various types of bridge sensors, such as strain, load, torque, displacement, acceleration, pressure, temperature, etc. The node supports both 2-wire and 3-wire input modes, and the bridge circuit is automatically trimmed, and it can also be stored in the node's built-in 2M data memory. Effective outdoor communication distance can reach 300m. It can measure continuously for more than ten hours.

3.Torque sensor

The node structure is compact, small in size, and encapsulated in a resin shell. Each channel of the node has a built-in high-precision 120-1000Ω bridge and amplifying circuits. The bridge circuit is automatically trimmed. The air transmission rate of the node can reach 250K BPS. The effective real-time data transmission rate can reach 4K SPS, and the effective indoor communication distance can reach 100 meters. The node is designed with special power management software and hardware. In the case of real-time uninterrupted transmission, the node power consumption is only 25mA. Using an ordinary 9V battery, it can be continuously measured for dozens of hours. For long-term monitoring applications, the torque value is sent every 5 minutes, and the battery does not need to be replaced for several years, which greatly improves the maintenance-free performance of the system.

Ⅱ Application Technology of wireless sensor

1.Low power design

All modules are designed with ultra-low power consumption, and the entire sensor node has very low current consumption. It can work for several years with two ordinary dry batteries, which greatly extends the maintenance cycle. Therefore, a miniature vibration generator can also be used to collect the weak vibration energy generated by the structure using the piezoelectric principle. The weak vibration energy is converted into electricity to provide power for the sensor. To reduce power consumption, the sensor uses ultra-low power consumption products.

2.Time synchronization

BEETECH wireless sensor, based on time synchronization and fixed routing table TDMA transmission protocol, can achieve "simultaneous" sleep and "simultaneous" wake up, which is suitable for wireless sensor industrial automation online monitoring and detection.

Ⅲ Wake up mode of wireless sensor

In wireless sensor networks, there are several ways to wake up nodes:

1.Full wake-up mode: In this mode, all nodes in the wireless sensor network wake up at the same time to detect and track the targets appearing in the network. Although higher tracking accuracy can be obtained in this mode, it is at the cost of huge network energy consumption.

2.Random wake-up mode: In this mode, the nodes in the wireless sensor network are awakened randomly by a given wake-up probability p.

3.The wake-up mode is selected by the prediction mechanism: In this mode, the nodes in the wireless sensor network can selectively wake up the nodes that have a greater gain in tracking accuracy according to the needs of the tracking task, and predict the next moment of the target based on the information of the shot and wake up the node.

4.Task cycle wake-up mode: In this mode, nodes in the wireless sensor network are periodically awakened. Nodes in this working mode can coexist with nodes in other working modes and assist nodes in other working modes to work.

Ⅳ Network structure of wireless sensor

sensor network system

The sensor network system usually includes sensor nodes, sink nodes, and management nodes. A large number of sensor nodes are randomly deployed in or near the monitoring area and can form a network through self-organization. The data monitored by the sensor node is transmitted hop by hop along with other sensor nodes. During the transmission, the monitoring data may be processed by multiple nodes, routed to the sink node after multiple hops, and finally reach the management node through the Internet or satellite. The user configures and manages the sensor network through the management node, releases monitoring tasks, and collects monitoring data.

Ⅴ Applications of wireless sensor

1.Bridge health detection and monitoring

Bridge Structural Health Monitoring (SHM) is a sensor-based active defense method that can make up for structures where safety performance is very important. It is reliable and inexpensive to place sensor networks in bridges, buildings, and aircraft. The formation of defects can be detected for the first time. This kind of network can report defects in key structures to maintenance personnel early, thereby avoiding catastrophic accidents.

2.Granary temperature and humidity monitoring

Wireless sensor network technology is the most common application in the field of temperature and humidity monitoring of granaries. This is because the temperature and humidity of the granaries have many measuring points and are widely distributed. The use of criss-cross signal lines will reduce the fire safety factor. The application of wireless sensor network technology has low power consumption, low cost, simple wiring, easy installation, easy networking, easy management, and maintenance.

3.Concrete pouring temperature monitoring

In the concrete construction process, the digital temperature sensor is installed in a metal casing with good heat conduction, which can ensure that the sensor responds quickly to changes in concrete temperature. Each temperature monitoring metal pipe is connected to a wireless temperature node, and the wireless temperature nodes of the entire site are transmitted to the construction monitoring center through the wireless network. There is no need to lay long cables on the construction site. The installation and deployment are convenient, which can effectively solve the low survival rate of the temperature measurement points caused by damage to the cable.

4.Earthquake monitoring

By using a sensor network composed of a large number of interconnected miniature sensor nodes, it is possible to conduct uninterrupted high-precision data collection in different environments. The use of low-power wireless communication modules and wireless communication protocols can extend the life of sensor networks for a long time. The practicability of the sensor network is guaranteed.

Compared with the traditional network, the most obvious feature of the wireless sensor network can be summarized in "self-organization, self-healing". These characteristics enable the wireless sensor network to adapt to the complex and changeable environment to monitor the harsh environment areas that are difficult to reach by humans. The wireless sensor network node is small in size and does not require an on-site cable power supply, which is very convenient for flexible deployment and monitoring, and prediction of geological disasters in emergencies.

5.Building vibration detection

The cantilever part of the building will not exceed the comfort requirements due to the vibration caused by the nearby road and subway traffic. Through on-site measurement, we can collect data to verify the relationship between the vibration caused by the road and subway traffic and the main building cantilever vibration. At the same time, through the modal analysis, the damping ratio of the first few vibration modes of the main building structure under the small-amplitude pulsating vibration condition is obtained, which provides key data for the small-amplitude dynamic analysis of the structure in the future.

Ⅵ What is the role of wireless sensors in the Internet of Things

By enabling everyday objects to communicate wirelessly, we can automatically exchange data and create new efficiencies, which will have a positive impact on life and organization. The foundation of the Internet of Things is wireless sensor technology, which allows us to collect very little information about the surrounding environment for a long time. Wireless sensors can be configured to measure various variables from air temperature to vibration. Overall, there are many different types of wireless sensors on the market.

Wireless sensors can automatically exchange data and improve efficiency, thereby having a positive impact on people's lives and organizations. Many wireless networks contain hundreds (and sometimes thousands) of wireless sensors. These devices have been widely used in retail, agriculture, urban planning, security, and supply chain management industries.

1.What do wireless sensors do?

Wireless sensors collect data about local conditions and share the findings with other powerful components or platforms for further processing. Sensors are usually distributed over large geographic areas and are programmed to communicate with central hubs, gateways, and servers.

wireless sensor network

One of the main advantages of wireless sensors is that they require a low level of maintenance and require very little power to function. The sensor can support IoT applications for many years before the battery needs to be replaced or recharged.

When building a wireless network, one of the biggest problems facing developers is how to deploy wireless sensors on site. Sensors or "nodes" must be distributed in a way that supports the overall goals of network developers.

2.How to connect wireless sensors?

The two most common arrangements of wireless sensors are star and mesh topologies.

arrangements of wireless sensors

The "Mesh" topology describes a network in which sensors are connected to as many other nearby nodes as possible. As a result, data can "jump" from one node to the next without having to follow some routing or sensor hierarchy. As a result, connection problems are less harmful to network performance, because data can reach processing components through multiple paths. The mesh topology is also easy to expand because new sensors only need to be connected to existing nodes.

On the downside, the mesh topology is expensive and can be difficult to maintain. There are too many connections to create and manage, which becomes more and more challenging as the network develops.

The "star" topology describes a network where each sensor is directly connected to a central gateway or hub. These hubs obtain sensor information and transmit it to other applications for processing. In these arrangements, the nodes do not directly communicate with each other.

Compared with mesh networks, star networks are more cost-effective because fewer connections are required. However, since any new sensor must be connected to a central hub with capacity limitations, it is difficult to expand the network.

3.How did wireless sensors communicate in the past?

Several wireless standards can support sensor networks.

Until recently, cellular technology was the most common choice for wide area network (WAN) connections. However, cellular technology is expensive and consumes a lot of energy, so it is not suitable for remote, low-power devices, such as wireless sensors.

In addition to cellular technology, WiFi, Bluetooth Low Energy (BLE) and Zigbee can also support wireless sensor networks. These standards also belong to the category of "traditional wireless solutions", but have unique advantages and disadvantages.

WiFi ("Wireless Fidelity") is one of the most widely used wireless technologies in commercial offices and homes today. WiFi uses 2.4GHz and 5GHz ISM frequency bands. Because WiFi is so popular, it is relatively easy to use existing networks to use wireless sensors. However, it is difficult for WiFi signals to penetrate walls, which is disadvantageous for remote applications. Also, WiFi networks are managed by local routers, which may not always have a direct user interface for updating sensor keys.

BLE is a low-power protocol, which is different from traditional Bluetooth technology. BLE uses the 2.4GHz frequency band to transmit a small amount of information. The cost of using wireless standards is lower than WiFi. However, the same problem exists when sending data through walls or long distances. Besides, because many other devices and standards use the 2.4GHz band, BLE is susceptible to signal interference.

Zigbee is a wireless standard that relies on a mesh network to support a large number of nodes in a single network (> 65k). Zigbee is most suitable for wireless sensor networks that do not require much bandwidth. One disadvantage of Zigbee is that certain sensors must be always on to share information for processing. As a result, the total energy consumed by Zigbee exceeds today's leading standards.

4.Which communication standards control wireless sensors?

Although traditional wireless standards are effective, a new category has emerged that is more effective for wireless sensor networks. Low-power wide-area network (LPWAN) is growing as the preferred technology for remote data transmission. LPWAN can support billions of sensors and will be used in large numbers for IoT applications.

LPWAN has many advantages over traditional standards. First, because they transmit information at a much lower bit rate, they consume less power from the device. A single charge can keep the sensor alive on LPWAN for several years. LPWAN can also support sensors in a wide geographic area because data can be transmitted over long distances.

From a cost point of view, it is cheaper to deploy wireless sensors on LPWAN compared to alternative methods. Because the data rate is too low, the hardware requirements are less stringent.

There are several disadvantages to using LPWAN. LPWAN is not suitable for applications involving large data packets. Sensor networks that need to transmit more data should use larger cellular or short-range WiFi, BLE, and Zigbee networks. Besides, LPWAN uses unlicensed radio frequencies, which can be more difficult to manage from an interference perspective.

5.What is the leading LPWAN for wireless sensors today?

The three main LPWANs used for wireless sensors are LoRa, SigFox, and NB-IoT.

LoRa ("Long Range") is a widely accepted standard that uses a chirp spread spectrum modulation scheme to transmit data over long distances. LoRa is the basis of the publicly available layer specification of LoRaWAN (wireless sensors can be connected through a gateway or LoRaWAN network provider). LoRaWAN has a higher bandwidth than Sigfox, and can transmit data packets more efficiently through a noisy environment.

Using LoRaWAN, data can be sent through encrypted messages between the gateway and the network server. The server authenticates and decrypts the data finally sent to the final application. Users can send messages directly to the wireless sensor through LoRaWAN to reconfigure the device.

LoRaWAN sensors are divided into three categories based on the sensor's ability to send and receive messages. Class A devices will stay in sleep mode until there is something to send. These sensors can send uplink messages at any time, which makes them particularly useful in wireless sensor and actuator networks (WSAN).

Class B sensors have a planned window for the device to receive downlink messages from the server. Class C devices keep the message receiving window open unless they need to transmit information. Therefore, C sensors can achieve low-latency communication but consume more energy than other types of sensors.

For all these LoRaWAN sensor types, network developers must have the appropriate gateway hardware to receive data and pass information to the server.

SigFox uses ultra-narrowband transmission to connect wireless sensors directly to the base station. The standard has covered more than 55 countries/regions, and each subband in the United States can support more than 100 channels at 600 bps. However, the data packet is limited to 12 bytes, and the standard does not allow message ACK.

NB-IoT uses existing cellular tower infrastructure to provide wide coverage for low-power devices. The standard uses protective tapes for narrow passages to avoid interference and can penetrate indoor environments well. In 2018, T-Mobile increased its NB-IoT coverage through its 4G network.