Question Regarding Micrologix and RS232 devices

[opmal7]

Hello. I am working on a project that uses an Allen Bradley Micrologix 1100 PLC. I have two devices with RS232 output (actually one is RS232, the other is RS422) that I need to integrate.

One of the devices is already integrated. We purchase an Allen Bradley cable to connect to the RS-232 port on the PLC, and splice on the wires from the RS232 device. This device is working just as we want it to.

I need to add the second device, which actually has an RS-422 serial output. However, it looks like the PLC only has the one input port for RS-232 signals. I've read in the documentation that the PLC is capable of using RS-232 or RS-485 communications, but unfortunately I'm not too familiar with these protocols.

I'm looking for advice on the best way to integrate the two signals with the PLC. Is there an add-on that I can purchase that would give me an additional serial input (that will be compatible with RS-422)? Or is there a way to combine the signals from the two devices, and use the single serial input port on the PLC to read those signals? If so, will the PLC be able to distinguish between the two devices?

Thanks in advance!

 

[dlweber]

I do not know off the top of my head if there is a device that will add rs-422 capability, but I would say do not splice the two wires together. Not only is the coms traffic different sometimes there are different voltage levels between different forms of communication, you can easily smoke a piece of hardware if that is the case.

 

[Firejo]

Hello Opma7 and welcome to the forum.
You haven’t provided enough information. What are the “RS232 devices”? Is the PLC using DF1 or Modbus RTU?
What I can tell you is that RS422 and RS232 are different version of serial communications and you can’t combine them. You will need to convert the RS422 into RS232. You would then need to integrate an RS232 splitter. This is however assuming that the protocol is half duplex. Modbus RTU by nature is half duplex however DF1 can be either full duplex or half duplex.
You need to have and provide a lot more details about the application.

 

[opmal7]

Hi guys, thanks for the quick responses.

One of the devices is a proximity sensor (outputs distance to object) and the other device is a tilt sensor (outputs angle in 3 axes). The proximity sensor is the device that is currently working. I am not sure if the PLC is using DF1 or Modbus. To be honest, I don't even know what they are. Is there a way I can check?

I wouldn't just splice the wires together and hope for it to work. I was sort of thinking along the lines of a splitter like Firejo suggested, but I'll have to check on the communication protocol of the tilt sensor.

 

[Firejo]

You’re going to need much more detail on the devices and the protocols they use. At some point you are going to need to get into the PLC and change the program. You can go online with it now and see how the port is set up. You will still need more information about the devices but knowing how the PLC’s port is configured is a good start.