Hi!
I have an automation project that requires a large number of sensors (up to 30) with a measuring range from 5cm to 2m (at least). I pretend to use an S7-1200 CPU 1215C PLC and these distance sensors.
Is it possible to establish communication (using the RS485 communication protocol) between those sensors and the PLC?
If so, I would like to have some more information on how to establish that communication. I did some research and found that, by using the RS485 communication protocol, it is possible to communicate with up to 32 devices. Is this accurate? Does it mean that I only need one communication board (CB1241) to establish communication between all sensors and the S7-1200?
I also would like to know if there is any risk of interference (crosstalk between sensors), as all the sensors will operate simultaneously and relatively close to each other. If so, is there any way to avoid that? (like synchronizing the sensors) Or what is the minimum distance (or method of computing that distance) at which I could place my sensors to avoid interference?
And, one last question, do the measuring range or the resolution change significantly with the characteristics of the reflective surface?
Thank you in advance!
The short answer is yes. In the device manual, there’s a section titled “Communication Protocols”. There is also example code that you could transform into the programming language on the PLC you are using.
Of note is setting the address for each device, so they can be communicated with one by one.
It would be best to trigger each sensor as-needed to avoid false triggers, etc. The manual suggests 30mS for a reading to be available. Within one second, you could service 33 sensors.
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Ultrasonic is quite dependant on the material surface being reflected upon, though it varies with distance. Often it’s best to simply try it out.
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Thank you for your reply!
Do I need a MAX485 chip as an interface between the sensor and the communication module/board?
Could you please recommend any examples/ documentation on how to trigger each sensor as-needed?
Thank you in advance!
Hey,
Whatever development board / PLC you end up using will need RS485 as well. Demo code and guides are in the manual for triggering a request and retrieving the result.
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Thank you for your reply!
I pretend to use an S7-1200 CPU 1215C PLC and this communication module (https://www.plc-city.com/shop/en/siemens-simatic-s7-1200-communication-modules/6es7241-1ch32-0xb0.html). So, to establish communication between the sensors and the communication module, do I still need a MAX485 chip?
Thank you in advance!
