I have a small question regarding the Modbus protocol
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As shown in the figure, I have 36 instruments, and I want to connect them to the signal acquisition system using Modbus 485. For wiring, is it to simply connect the 485 outputs of each instrument together? Finally, it is output to the upper-level computer system, and each meter also needs to be assigned an address.
Firstly, as you mentioned, it is indeed possible to connect these 36 instruments using the Modbus RS485 bus, and to collect their data into a signal acquisition system. The specific wiring steps are usually as follows: 1. Wiring method: A two-wire RS485 communication cable is used, with the D+ (data positive) and D- (data negative) terminals of each instrument connected to the same bus, thereby achieving a parallel connection. This connection method is also known as the “bus-type connection” or “two-wire half-duplex communication”. 2. Termination resistance: Since RS485 communication uses differential transmission at the physical layer, 120-ohm termination resistors are typically added at both ends of the bus to reduce reflections and improve signal quality. 3. Ground connection: Theoretically, the RS485 bus does not require a ground wire, but in practical applications it is generally recommended to include one in order to reduce communication interference and improve the system’s resistance to such interference. 4. Address setting: Ensure that the device address of each instrument is unique; this can be set through the instrument’s own settings or via external devices such as host computer software. The address range for the Modbus protocol standard is from 1 to 247. 5. Selection of bus length and baud rate: Choose an appropriate baud rate and bus length based on your field environment and communication requirements. The higher the baud rate, the shorter the bus length should be, and vice versa. 6. Check the configuration: Set the communication parameters for each instrument on the host computer (such as the signal acquisition system), including address, baud rate, data bits, stop bits, and parity, to ensure they are compatible with each instrument. 7. Testing: After the system is set up, communication tests are conducted to verify that each instrument can transmit data correctly. Finally, the Modbus RTU protocol is a master-slave protocol; there can be only one master station (such as your signal acquisition system), and the slave stations (instruments) can send data only upon the request of the master station. Therefore, please ensure that this principle is followed when designing the system, and arrange communication polling properly to ensure accurate data collection. .
Okay, thank you. I think I understand.
What software do you use on your host computer? I want software
I’m not quite sure either; I work with instruments
Where did you find that image? Is anyone still doing this these days?
Isn’t Taobao available on mobile phones? A data acquisition card costs only a few dollars – don’t you people know how to program?