Common Wiring Methods of Temperature and Humidity Sensors

With the rapid development of modern society, temperature and humidity sensors are more and more applied to our work and life. Temperature and humidity sensors are found in the food industry, file management, greenhouse, animal breeding, drug storage, and other industries. Before using the sensor, the installation and wiring process cannot be avoided. Today, let's learn about the wiring mode of the temperature and humidity sensor.

At present, the most widely used temperature and humidity sensors are RS485 temperature and humidity sensors and analog temperature and humidity sensors.

RS485 temperature and humidity sensor

RS485 is a standard that defines the electrical characteristics of drivers and receivers in Balanced Digital Multipoint Systems, which is defined by the telecommunications industry association and the electronics industry alliance. The digital communication network using this standard can effectively transmit signals in long-distance conditions and in an environment with large electronic noise. RS485 makes it possible to configure cheap local networks and multi-branch communication links.

RS485 has two-wire and four-wire connections. The four-wire system can only realize the point-to-point communication mode, which is rarely used now. Now, the two-wire connection mode is mostly used. This connection mode is a bus topology structure, and up to 32 nodes can be connected on the same bus.

RS485 wiring specification:

1. 485 signal line cannot be wired together with a power line. In the actual construction, because the wiring is carried out through pipelines, the construction party sometimes directly binds the 485 signal line and the power line together for the convenience of the diagram. Because the strong current has a strong electromagnetic signal to interfere with the weak current, the 485 signal is unstable and the communication is unstable.

1. 485 signal lines can be wired with shielded wires or unshielded wires.

1. Choose to use ordinary super class 5 shielded twisted pair, that is, network cable. It is generally recommended to choose standard 485 wire for wire, which is a shielded twisted pair. The transmission line is not a single strand of copper wire like the network cable, but multiple strands of copper wire are twisted together to form a line so that even if a small copper wire is broken, the whole use will not be affected.

1. 485 wiring with the help of 485 hubs and 485 repeaters can be arbitrarily arranged into star wiring and tree wiring. 485 wiring specification must be hand-in-hand wiring. Once it is directly laid into star connection and tree connection without the help of 485 hubs and 485 repeaters, it is easy to cause signal reflection and lead to bus instability.

1. 485 bus must be grounded.

Analog temperature and humidity sensor

The output mode of the analog temperature and humidity sensor includes the current type and voltage type. Whether it is a current type signal or a voltage type signal, it is divided into four-wire systems, three-wire systems, and two-wire systems based on the number of cables providing signal instruments and equipment. The signal wiring methods of different types are different.

Wire system is a difficulty in understanding analog quantity. Pay attention to the outgoing lines of the equipment providing signals. There are several wire systems.

1. Four-wire system

The four-wire system signal is that there are four signal lines and power lines on the equipment providing the signal. The equipment providing signals has a separate power supply, in addition to two power lines, there are also two signal lines.

1. Three-wire system

Three wire system signal refers to that there are three lines on the equipment providing signal, including signal line and power line, and the signal negative and power supply m line are common.

Compared with the four-wire system, the three-wire system has one less signal negative, and the commonly used signal source equipment is rarely a three-wire system, mostly a two-wire system and a four-wire system.

1. Two-wire system

Two wire signal means that there are only two signal lines and power lines on the equipment providing signals. Since the analog module channel generally has no power supply function, the temperature and humidity sensor instruments or equipment need to be externally connected with a 24V DC power supply.

Precautions for analog quantity wiring:

1. The sensor cable of the analog signal should be as short as possible, use a shielded twisted pair cable, try not to bend into a right angle in the process of wiring, and the shielding layer should be grounded at one end close to the signal source.

1. The analog module and the sensor should be well grounded. If possible, the two grounding terminals should be connected for grounding, otherwise, a high common mode voltage will be generated, resulting in large fluctuations in the data in the CPU.

1. The terminals of the analog module are distributed in upper and lower rows, which is easy to be confused. Pay attention to wiring. It's best to connect the lower one first and then the upper one.

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