Issues related to RS232 and RS485 communication.
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I have a question regarding RS485 and RS232 data transmission. Figure A: Tianxin turbine flow meters are used on-site, with Tianxin accumulators used to display the data. A microcontroller PLC listens to the A and B ports of the accumulators. One of the 4 flow meters on site does not transmit any data; there is no response when inquiries are made. A laptop is connected to RS485 A and B, as shown in the diagram, and when the laptop sends a query to the flow meter, the flow meter responds. What is this fault and how can it be fixed? Figure B: In practice, a German Eichang flow meter is used; after the data is transmitted via RS232, an RS232-RS485 conversion card is employed. Occasionally, there are issues with data not being transmitted. If, as shown in the diagram, the laptop’s RX-TX-GND connections are linked to the Eichang device’s RS232 ports, then the data can be transmitted properly. What could be the reason for this? May I ask, in Figure A, would using a 120-ohm termination resistor between A and B help to solve the issue? Thank you
1. As for the issue of no communication with this number, who knows what the reason is. . . Send your brother a big WeChat red envelope, and I’ll sell the ghost to you. 2. The quality of the wire must be good. The converter needs to be good. 3. A 120Ω resistor is required. 4. Communicate at a low baud rate.
We set a longer delay time at the remote station; the distance between our two PLCs and the DCS is around 100 meters. At first, communication worked fine during configuration, but after some time one of the PLCs stopped transmitting data. It was later found that the delay times were set differently; by setting all delay times to 200, communication resumed working normally (the delay time was increased)
A 120-ohm resistor was not found, so a 100-ohm resistor was used, but the situation remained unchanged. Today, I checked the flow meter in Figure A; by using a laptop to communicate with the flow meter, the voltage between A and B increased from 0.45 V to around 1 V, and the flow meter responded by providing data. I measured the current of the 24V power supply at the flow meter on site; the operating current of the other flow meters was 35 MA, while that of this faulty flow meter was 40 MA. At first, I thought it was the host computer that couldn’t handle the traffic of that flow meter; now it seems that there’s a problem with the transmission module or the main board of that flow meter. Is my analysis correct?
I’m not sure if it’s appropriate. You can hang this watch alone and give it a try. .
Is it the last unit in series that isn’t working properly?
OP, how was this issue resolved later?:)