Twelve sites and 1 mainstation

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Thread Starter

Calvin

I'm a mechanical engineer in a E&M company. My boss received a job which is about communication.
The following is the details:
1 mainstation : there is a computer which is used to monitor the real time data. Linux may be used as the OS. We will write a program for receive data
12 sites: there are some alarms which can be sent out a voltage signals. I intend to use the PLC as the transimtter. All the alarm signals are entered the input slot of PLC and the data is transmitted to a modem. Then pass through the 56K cable (the cables are paid only to the mainstation and no need to dial number). So we have 12 lines.

The problems: 1) Is it a effective method for communication (i mean PLC)? 2) I don't know what products can treat 12 lines(56K) to a computer. (hubs?routers? I only know they can treat for 10-base lines) 3) Can anybody tell me what is the effective and good method? If it is suitable, my company will buy the products as soon as possible.

Thank you very much

Calvin
 
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Curt Wuollet

I'm not sure I understand the question or I might be able to help more. If you need serial comms from 1 Linux box to 12 PLCs that's not a problem at all, a 16 port RocketPort board will do that with no fuss. In your Linux monitor you simply open all the ports and use the select system call in a loop to handle the data. If all the lines need modems you can buy a card from the same source with multiple modems. This is typically cheaper than seperate modems. If you want to use EtherNet as the go between, a terminal concentrator and csu/dsu's are called for. Pick which one sounds like what you are trying to do and we can talk.

Regards

cww
 
mainstation : there is a computer which is used to monitor the real time data. Linux may be used as the OS. We will write a program for receive data depends on what is good for you. Modbus from PC to PLC is commmonly used.

2) I don't know what products can treat 12 lines(56K) to a computer. (hubs?routers? I only know they can treat for 10-base lines) 3) Can anybody tell me what is the effective and good method?

There's a product called the digiboard. you can have multiple serial ports to the PC. try www.comtrol.com and look for Rocketport
 
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amora fibrianto

Calvin,

PLC is not intend as a communication device, altough it's has a built in communication port.

I assume that you will use PLC as data concentrator (RTU) from each of 12 site. then from those 12 site (12 PLC ?), the data will be sent to a PC (act as a front end server/Master Station).

I don't know what you means by '56K cable'. Is it the media of communication (cable, radio, etc) or other specification ?

But you're gonna need a modem on both PLC side and PC side. The PC must be equipped with proper software in order to communicate with remote PLC

You'd better consult to a nearby SCADA integrator in your area. they might have a better solution.

Just try to download 'Scada Application Guide' from Allen Bradley website (www.ab.com)
 
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Chrisstoffer, Herman

Calvin,

If you have just 12 serial lines to be coupled to a cental computer system you could use either one of the methodes mentioned below. Use a terminal server to couple the 12 serial lines to your
local Ethernet network and from there to your central computer system. Several products are available for this (Digi , Lantronix, etc.. just search the web for extra info) An other other option would be to extend the number of serial
ports in your central computer system. Several prodocts are also available here (Perle, etc..).
Note: be carefull with a terminal server like device which has software with it which 'simulates' serial ports on the
central computer system. Im my experience this software will do bad things to your protocol resulting in corrupt data, communication losses, etc.. The protocol to be used can be just a standard protocol like modbus.

Regards
Herman Chrisstoffer
 
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