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RS485 temperature and humidity sensor _ analog temperature and humidity sensor wiring instructions
With the rapid development of modern society, more and more temperature and humidity sensors are used in our work and life. The food industry, file management, greenhouses, animal breeding, drug storage and other industries have temperature and humidity sensors. The figure of the humidity sensor. Before the sensor is used, the installation and wiring process cannot be avoided. Today, let's take a look at the wiring method of the temperature and humidity sensor.
Currently, the most widely used temperature and humidity sensors are RS485 temperature and humidity sensors and analog temperature and humidity sensors.
1. RS485 temperature and humidity sensor
RS485 is a standard that defines the electrical characteristics of drivers and receivers in a balanced digital multipoint system. Industry alliance definition. Digital communication networks using this standard can effectively transmit signals under long-distance conditions and in environments with high electronic noise. RS485 makes it possible to configure cheap local networks and multi-branch communication links.
RS485 has two-wire system and four-wire system. The four-wire system can only realize the point-to-point communication mode, which is rarely used now. Nowadays, the two-wire connection mode is mostly used. The method is a bus topology structure, and up to 32 nodes can be connected on the same bus.
RS485 wiring specification:
1.485 signal lines cannot be routed together with power lines. In actual construction, because the wiring is routed through pipelines, sometimes the construction party directly binds the 485 signal line and the power line together for the convenience of the drawing. 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.
2.485 signal lines can use shielded wires as wiring, and can also use unshielded wires as wiring.
3. You can choose to use ordinary super Category 5 shielded twisted-pair cable, that is, network cable. The wire is generally recommended to choose the standard 485 wire, which is a shielded twisted pair. The transmission line is not a single copper wire like a network cable, but multiple copper wires are twisted together to form a wire, so that even if a small copper wire is broken It will not affect the entire use.
4.485 wiring can be arbitrarily arranged into star wiring and tree wiring with the help of 485 hubs and 485 repeaters. The 485 wiring specification is a wiring that must be hand in hand. Once the 485 hub and 485 repeater are not directly wired into star connection and tree connection, it is easy to cause signal reflection and cause the bus to be unstable.
The 5.485 bus must be grounded.
Two, analog temperature and humidity sensor
The output mode of analog temperature and humidity sensor has current type and voltage type, whether it is current type signal or voltage type signal, to provide signal The number of cables for instruments and equipment shall prevail, which are divided into three types: four-wire system, three-wire system, and two-wire system. Different types of signal wiring methods are different.
The wire system is a difficult point to understand the analog quantity. Pay attention to the outgoing line of the equipment that provides the signal. There are several wire systems. The following figure shows the wiring differences between these types of wire systems.
1. Four-wire system:
The four-wire signal is that the signal line and power line on the equipment that provide the signal have 4 lines in total. The signal-providing equipment has a separate power supply, in addition to two power lines, there are two signal lines. The wiring method of the four-wire signal is as shown in the figure below:
2, the three-wire system:
The three-wire signal refers to the equipment that provides the signal, the signal line and the power line add up 3 lines, the negative signal and the power supply M line are common lines. The wiring method of the three-wire signal is shown in the figure below:
Compared with the four-wire system, the three-wire system has one less signal negative. Four-wire system.
3. Two-wire system:
The two-wire system means that the signal line and the power line only have two lines in the equipment that provides the signal. Since the analog module channel generally has no power supply function, the temperature and humidity sensor instrument or device needs an external 24V DC power supply. The wiring of the two-wire signal is shown in the figure below:
Notes for analog wiring:
1. The sensor cable of the analog signal should be as short as possible, and shielded twisted pair should be used. Try not to bend the cable to a right angle during the wiring process. The shielding layer should be grounded at one end close to the signal source.
2. The analog module and sensor should be well grounded. If possible, the two grounding terminals should be connected to the ground. Otherwise, a high common-mode voltage will be generated, which will cause the data in the CPU to fluctuate greatly.
3. The terminals of the analog module are distributed in two rows up and down, which is easy to confuse. Pay attention to the wiring. It is best to connect the lower one first and then the upper one.
When we buy a temperature and humidity sensor, we must choose a suitable temperature and humidity sensor according to the application scenario, and carefully ask the seller about the installation and wiring methods to avoid data measurement errors caused by incorrect or missing wiring.
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