MicroLogix 1500 and Scada system

[mpc 0]

Hi Dear all, I would like to implement a Scada system based on one existing MicroLogix1500 PLC. The PC station and MicroLogix1500 is more than 500 meters away plus there is an existing phone line between those two. My question is as following: 1. What kind of modems should I choose (dial up or leased line)? 2. What protocol should I use? 3. When there is alarms occur, could the plc dial out to PC and send data to it? 4. I found that there is a function block AWA to configure the phone number, however, I didn't figure out how to send the required data to the SCADA system. Any help will be highly appreciated.

[BobLfoot 302]

This posts raises more questions than answers for me. The ideal solution would be to run a fiber optic cable along the path of the phone line. This would allow for continuous communication between the PC and PLC. The fiber would also have bandwidth to handle the phone service and other future expansion needs. The Serial Port can be used to send ascii commands with AWA so as to dial a standard Hayes modem, but you must then place it in System Mode to connect to RSlinx or whatever OPC service your SCADA uses. And you must have logic in your SCADA to ressurect the dormant link or answer the modem call.

[paulengr 44]

This is because it's highly dependent on the SCADA system and that normally, you don't write your own protocols. You simply set up the appropriate driver and off you go. What you found is one of several ASCII commands to manipulate the serial port. This is what you'd do if you are writing your own protocol. With the distance involved (500m), and the existing hardware, there are several choices that make the most sense, with varying costs and degrees of difficulty associated with doing them: 1. Use dial-up modems on both ends. It's old school but can be done. You'd almost be gauranteed that the PLC modem would be set up as the server (answering), not the other way around. Be forewarned that if you don't have to use a phone line, try to avoid it. Dealing with the idiosyncracies of modems is not fun at all on either end of the connection. They are/were fine for dial-up PC connections but PLC's weren't really ever set up to work with modems except as an afterthought. 2. Use wireless modems. This need not be expensive. For instance, check out Aerocomm. They sell small serial port based modems for roughly $160 US per radio with a very good range on them, especially if used outdoors. Lean towards the 900 MHz models if you are penetrating walls or steel structure. The lower the frequency, the better the penetration. In this case, you'd have serial port-to-serial port communication and you could simply act as if the PLC is directly connected to the PC. If money isn't an issue, get a pair from Esteem. Much more expensive but they have lots of bells and whistles including acting as a wireless access point and converting a serial port into Ethernet as a built-in function. This approach is very simple and keeps your phone line operational for other uses. 3. You can go Ethernet. In this case, first you need a 1761 NET ENI or equivalent (Digi One IAP is another, Lantronix UDS 100-IAP is a third) to convert from serial port to Ethernet. Or you can switch from your existing Micrologix to either the 1100 or 1400 which both have built in Ethernet ports. You can use a simple serial server (Digi One SP for instance) but it is not protocol aware and you won't be able to for instance program/troubleshoot the PLC while simultaneously using your SCADA system (due to the vagaries of DF-1, the PLC can only handle connection to one device at a time). Then you will need to decide on copper or fiber. If you run Fiber, then you can make the full 500 meter distance with just one cable. You will need copper-to-fiber converters on each end. If you go with copper, then you MIGHT (depending on the quality of the phone line) be able to get away with 10 Mbps Ethernet at best. You will need a repeater (a 2 port switch) every 100 meters. This is highly dependent on whether the phone line is CAT 3 grade or not, and whether the Ethernet hardware will tolerate it. Although the cable specification for 10 Mbps Ethernet is CAT 3, a lot of current hardware (especially Cisco stuff) will reject it. You can also go with Ethernet extenders. These convert Ethernet into some sort of proprietary protocol that is tolerant of operating over a simple wire pair such as your phone line. It avoids the fun of pulling wire/fiber, and it avoids the distance limitations of off-the-shelf Ethernet. It will never be as fast as real Ethernet (it trades speed for distance) but it might be more than enough for your needs. See this web site for an example of this: http://www.bb-elec.com/product_multi_famil...p;TrailType=Top If you are familiar with Ethernet, then this approach is difficult but not impossible. Since there are protocol converters involved, setting those up can be very intimidating. This approach is much more friendly to networked systems though which don't have a dedicated PC. It adds needless complication (and costs) if you aren't going with a truly networked system. 4. Finally, you can go for RS-485. RS-232 is limited to perhaps 30 meters on a good day with very slow speeds (typically limited to less than 10 meters). RS-485 is related to RS-232 but gives you a range of several kilometers if run correctly. In this case you use your simple wire pair (phone line) again. You will have to convert the existing RS-232 signals on either end which are single-ended signalling into balanced differential signalling format. This requires a simple electrical device. These have a variety of price points. Here is an example of the more expensive models: http://www.bb-elec.com/product_family.asp?...ub&Trail=10 In this case again, you can treat the PLC and the PC as if the PLC is directly connected to a serial port of the PC. You wire the RS-232 to RS-485 converters into each end of your phone line cable, connect them both to your PC, and you are off and running. This is NOT the same thing as DH-485. DH-485 is for a "party line" system (multiple devices connected to RS-485 in a daisy chain). In addition, the RS-232/RS-485 converters may cause timing issues which will make it fail unexpectedly. If you decide to use DH-485 despite these warnings, buy exactly the devices that Rockwell recommends. Do not try to use RS-232/RS-485 converters other than the Rockwell recommended devices. Again, this adds a lot of complication to the system because you are running a real network, not just a simple point-to-point system. And you were asking for simple. In any case, if you are not absolutely familiar with RS-232, it can be maddening to just get the devices set up correctly. I strongly suggest you buy an RS-232 tester which gives you a quick way of diagnosing RS-232 problems such as this one: http://www.bb-elec.com/product.asp?sku=9PM...ub&Trail=61 The biggest problem with RS-232 tends to be getting the device types right (DTE vs DCE devices), and whether to reverse the transmit/receive lines or not. Beyond that, sometimes the "extra" signalling wires (DTR/DSR, etc.) can cause you all kinds of problems. It appears to be safest to simply hook up only the bare minimum wires (RX, TX, and signal ground) and not mess with any of the other "features". Every feature you wire up is another thing that can go wrong. If you use the above tester, simply wire up the 3 required wires and put the tester in series with the PC or PLC serial port. If both the TX and RX lights light up, then remove it and reconnect the connectors. If only one light turns on, then unwire and reverse the TX and RX wires. If you bought premade cable assemblies, then put in a null modem cable (lines 2 & 3 are cross-connected) instead.

[mpc 0]

Hi, Paulengr. I deeply appreciate for your proposal. It is a detailed solution for my application. I went through with it this morning and still have several questions need to be clear. 1. Question about phone line modem “You'd almost be guaranteed that the PLC modem would be set up as the server (answering), not the other way around.” Does it mean that only Scada PC can poll PLC but the PLC can’t poll HMI PC? 2. Question about radio modem Actually I would propose the wireless solution to my client. I found that Data-Linc SRM6000 Modem have the similar application for the RSview SCADA system in WWTP St. Augustin, Florida. And this kind of modem support DF1 full duplex protocol. My question is that where the protocol is used? (Between PC and modem) as well as (Between PLC and modem). Actually, I am not sure how to read DF1 data to PC by configuring RSlink in PC side or by OPC server or sth else. 3. Question about Ethernet extender “If you are familiar with Ethernet, then this approach is difficult but not impossible. Since there are protocol converters involved, setting those up can be very intimidating.” To my opinion, this Ethernet extender device can convert the RJ45 to RJ11, is there any other configuration need to do to use this? 4. Question about RS232/RS485 converter “RS-485 is related to RS-232 but gives you a range of several kilometers if run correctly. In this case you use your simple wire pair (phone line) again. You will have to convert the existing RS-232 signals on either end which are single-ended signaling into balanced differential signaling format. This requires a simple electrical device. ” It is a RS232/RS485 converter. Could phone line support RS485 protocol and which one should I use in phone line (2 wire RS485 or 4 wire RS485). Thanks.