Two RS232 ascii devices to ML1400

[almk]

Hi guys. I need to read data from two dryers with RS232 using ASCII string from Micrologix 1400. Have never done anything like that. I would appreciate any info and advice. Where to start? Do I need to convert RS232 to different protocol? I've read that RS 232 can be only one connected to PLC, not two.
Thanks a lot. Al

 

[gclshortt]

The protocol will determine if you can put multiple connections on the RS232. Please check the dryer protocol and see if it includes a node/unit number. This will determine if you can send the same command to both dryers, but only the dryer whose number you selected will respond.
The distances that you can go with RS232 about 15 meters, but I have gone as far as 40 meters without issue.
Regards,
Garry
http://www.accautomation.ca

 

[almk]

Thanks Garry. Dryer protocol has no node. The RS-232 port is used to monitor dryer operation from a host computer. A (1 to 1) DB-9 cable is required to connect dryer and computer. For PC connections, data is transmitted on pin 2, received on pin 3, ground is pin 5, pins 7 and 8 are jumpered at dryer. Operation is at fixed baud rate of 9,600; asynchronous format is 8 bit, no parity, 1 stop bit (“8,N,1”). This is from the manual. Al

 

[rguimond]

How frequently do you have to poll each dryer? If not too frequently, it may be possible to use a DPDT or 3PDT relay to allow you to read from either dryer, depending on whether the relay is energized or not. Your logic will have to be configured to store what you're reading in the correct data table address(es) depending on if the relay is energized or not. Cheap solution to a common problem.

 

[almk]

Thanks, I was thinking about this too. I can read every 30 seconds and store correct data in assigned registers. Just wonder if anything else could be used.

 

[Bullzi]

Just a WAG but does anyone make a addressable 232 to 485 converter? Or even a serial to Ethernet converter. I know Moxa makes one that has 4 serial ports. That way you could mutli-drop the communications. Since your device does not have a address in its program you will need to address it another way.

 

[gclshortt]

Rguimond is correct. 30 seconds is relatively long time frame. The switching relays would work.
There is nothing that I know of that will automatically switch from on port to the other with an external signal.
The next thing to do is to establish communication with the dryer using a computer. You can use terminal services or something similar to send and receive out of the computer com ports. This way you know that your communication and wiring is good.
Next hook up your dryer to the PLC. You can use your computer to listen in on the communication and display the information being sent and delivered.
Once this has been established, then wire in your switch for the second dryer. You can then modify your PLC program to turn the relay on/off and handle the communication.

Regards,
Garry
http://www.accautomation.ca

 

[jrwb4gbm]

Found this with Google. Will it do what you need?
Link:
http://www.calta.com/plc09a.htm
Or maybe this?
Link:
http://www.prosoft-technology.com/P...-Master-Slave-to-ASCII-Generic-Serial-Gateway

 

[Bullzi]

That Prosoft device looks like it would do the trick. I like their products. I would look into that if I was the OP.

 

[kolyur]

Why not just use both serial ports on the PLC, one for each dryer? The Micrologix 1400 has two and they can be controlled independently. The Ethernet port could be used for programming.

 

[almk]

I will try to work with one serial port and relay for now. Yes, I could use both serial ports, if relay will not work. Just try to keep low budget and stay away from Prosoft module. Will posted update how it is going to work. Al