SLC 5/03 remote access

[Lordzorak 0]

We have just inherited a control cabinet that has a SLC 5/03 with a Automation Direct EZ-S8C-F (RS-232 only) HMI. This will be used at a remote test location powered by a generator. There will not be any telephone or net connections at the site. I would like to see what can be done to have a remote connection to the PLC. I am not so concerned about the HMI, though it would be nice but its exclusion is not a deal breaker. Having not done this before, I have gone through several posts on the forum as well as AB's literature. In one forum post, I saw a site for cellular gateways and routers. I also have put together two possibilities through reading of how to accomplish this, but would like some sort of verification that it would work. The first thought is to use a 1761-NET-AIC with a 1761-CBL-AS03 cable to connect to the DH485 port of the processor. Then the cellular device would connect to the AIC. The other option I saw was a 1747 DPS2 port splitter which took the place of the AS03 cable, otherwise the rest is the same but allows for another RS-232 connection. I am not sure either would work or if there is a better way to accomplish it and would welcome any suggestions from those who have more experience than I. Thanks. Z

[Rod_Hackney 2]

You could upgrade the 5/03 to a SLC 5/05. The SLC5/05 would have a serial port for the existing hmi and would give you an ethernet port for programming or to establish a remote connection.

[Lordzorak 0]

I would love to upgrade to a 5/05. Unfortunately, I do not get to make such decisions. Therefore, unless it is not possible (or costs more than a 5/05), I am stuck with what I have, which is the 5/03. And judging from what Paul says, yes, everything is possible. Thanks. Z

[Ken Roach 194]

The first principle to examine (and discard) is that the DH485 protocol cannot be transported over modems of any kind; the handshaking requirements cannot be met by any asynchronous translation device (i.e. modems or USB or serial/ethernet converters). Therefore Channel 1 of the SLC-5/03 must go through some kind of converter before data can be transported to it by modem. My best idea for this setup is to install a 1747-DPS1 port splitter. The full-feature "Network" port will connect to a cellular serial modem, allowing you to connect to and go online with the SLC-5/03 controller itself. The "HMI port" of the 1747-DPS1 will connect to the EZ-Touch panel and allow that panel to make DF1 Full Duplex requests to the SLC, and receive the responses. Two possible hitches come to mind. The 1747-DPS1 only supports DF1 Full Duplex protocol at 19200 or 38400 baud. This protocol and speed is also supported by the EZ-Touch (by my brief reading of the website) but that does not necessarily mean that's what the EZ-Touch has been configured to use. Check the RSLogix 500 program for the Channel 0 configuration and it should show you what protocol and speed the Channel 0 serial port of the SLC-5/03 is set for. If you want to leave the EZ-Touch alone, you can use a DH485 to DF1 translator. The slot-mounted 1747-KE module is the Allen-Bradley device that I like because I can do all the configuration via the backplane and I don't have to maintain a configuration file. Data-Link/EquusTek have their 3500-series DF1 to DH485 externally mounted devices that perform the same function and use their small utility program to perform the configuration. Hopefully the EZ-Touch has been set for a reasonable period between reads of the SLC-5/03. If the SLC is too busy handling requests from a touchscreen HMI panel, the online performance of your cellular connection may suffer. The cellular connection is another whole ball of beeswax. Cellular networks have, in my experience, very long connection latencies, on the order of hundreds of milliseconds. When you put a data stream like DF1 Full Duplex on a cellular connection, the ability of the modem to packetize and transport individual DF1 command frames, or bursts of DF1 command frames, is very important to understand. One of the modern gurus of industrial protocols over cellular networks is Lynn Lynse. I think he's still the principal developer for Digi International's serial device business. His various blogs about industrial networking have taught me a great deal about the protocols my company's products use and how they interact with various wireless and wide-area network technologies.

[paulengr 44]

As I recall the problem with the cell phone approach is that it is not a continuous connection, and subject to lots of connection failures. I doubt that any of your proposed solutions that involve more or less continuous-style access will work. If you intend on going the cell phone route, then definitely look at Lynn Linse's web site and look at ways of doing transfers as small as a single packet. This means you'll be implementing your own protocol of some sort using the serial port or somehow adding a serial port. Second issue is distance. "Remote" is a relative term. You can get up to about 30 miles in favorable conditions with a wireless radio link. Sometimes more if you are lucky. If you can achieve line of sight then I would encourage using this approach. An example is the ConnexLink radios from Laird Technologies. These are available through Mouser (www.mouser.com). They are very simple to use and work well with the DF-1 protocol. You can even do some port multiplication if needed using for instance a Digi-One IAP or a PLC-09 Arbitrator to split the single serial port that you have. Even without line-of-sight (and this solution can make the SLC 5/05 sound inexpensive depending on how many radios are necessary), there are some wireless radios that support a "mesh" or multihop mode. For instance where I work at we have a water pump located about 7 miles from the plant. It is not line of sight at all. Instead, it goes through about 5 different radios operating in mesh mode going around corners following the pipeline. The radios are made by Elpro. These days I suggest you check into Ubiquiti instead because they have some amazing products that are relatively inexpensive.

[Lordzorak 0]

Looks like I have some reading to do today. Thanks for pointing me in the right direction. Z