Newb - comm with MicroLogix 1500 and Modicon Quantum PLC

[work_term_guy 0]

Hi, I'm on a work term in a pulp and paper mill for my engineering program at the moment and I've been throw in the deep end with PLCs. I haven't learned anything about them in school but I'm working pretty much exclusively with them now. It's intense but it's a good way to learn. My main task is to upgrade a chemical system. We are replacing an existing SLC 150 with a Modicon Quantum 14 CPU 113 03 to control a mixing unit. I had to write a program in ModSoft for the new PLC based on the old program - The first time I saw ladder logic was three weeks ago but I have finished it and it has been verified by someone else. It'll be going on the new PLC next week and hopefully it'll work alright. My problem now is that I also need to consider an additonal, new mixing unit. It has a MicroLogix 1500 controller. From this PLC, I need to send data to the Quantum so the Quantum can send this data to the DCS. My supervisor has suggested I use a 140 NOM 212 00 Modbus Plus Network Module on the Quantum rack and a MVI46-MBP Modbus Plus Communication Module for the ML 1500. I guess my questions are: 1. The Micrologix 1500 is preprogrammed and I don't have access to the ladder logic. Is there anyway to download it from the PLC? 2. How many expansion modules (I/O or communications) can the 1500 power without using a 1769-CRRx expansion cable? I have a pile of literature in front of me and all the examples show two exansion modules on the base unit. There is no space in the panel box for an expansion. I was hoping to stick the Modbus module onto the other two already there. 3. Will Modbus Plus work with these PLCs? The AB literature says to use the 1500 as an Modbus RTU Master is need FRN 9 and higher and to use it as a Modbus RTU Slave, I need a 1500 1764-LSP Series B or higher. I have a 1500 1764-LSP Series A Ver A FRN 1. 4. Are there any other/better ways to connect the two PLCs? I need to send a small amount of data, something like the status of maybe a 16 bits every scan. 5. How do I set up Modbus Plus in Modsoft? I know that I'm kind of asking for a lot of help here but any help would be greatly appreciated. Thanks, Jon

[Ken Roach 194]

Welcome to the world of industrial automation. We've got toys and gum. First understand the difference between Modbus RTU protocol and Modbus Plus protocol. Modbus RTU is a low-speed, open-standard serial protocol implemented by nearly every vendor in one way or another. Modbus Plus is a higher-speed proprietary protocol implemented only on Modicon controllers. It's largely been superceded by Modbus/TCP, which is also an open-standard protocol carried over TCP (usually on Ethernet). Let's get the specific questions out of the way. 1. You need A-B's RSLogix 500 software to upload the program out of the MicroLogix 1500. The "Starter" version will do. 2. The number of expansion modules supported by the MicroLogix 1500 base depends on the type of modules. There's a "system qualifier" downloadable from AB.com and the RSLogix 500 software also calculates power load. Three modules should be no problem. 3. The Prosoft module handles the Modbus Plus communications onboard the module, versus implementing Modbus RTU protocol on the serial port of the controller. If you do in fact use Modbus Plus, the firmware of the controller won't matter. 4..... aw, forget it, I'm tired of numbering. That particular MicroLogix 1500 is pretty old, but the good news is that MicroLogix 1500 firmware is free from AB.com. As long as you can upload and keep that program handy, you can upgrade this controller so that it supports Modbus RTU. Since the DCS system already is using Modbus RTU protocol to communicate with that Quantum controller, just hook the same communication circuit (it's probably RS485 signalling) up to the MicroLogix 1500 (you'll need the firmware upgrade and a 1761-NET-AIC isolator/converter module) and have the DCS poll data right out of the MicroLogix.

[rpraveenkum 5]

It seems to be hardware series is also older so the processor unit 1764-LSP should be replaced

[Ken Roach 194]

I don't think the Series letter of the controller matters for MicroLogix 1500. That first-model-out-the-door controller should be upgradeable to the current FRN11 firmware. In fact.... I looked up a firmware history that says that Series A Rev B, FRN 2 was the initial release of the 1764-LSP controller. You might actually have a prototype !

[rpraveenkum 5]

Ken you mean to say All FRN can be flased in processor what ever its series

[work_term_guy 0]

First off, thanks for all the responses. Secondly, since posting I put forward a suggestion to skip the using the Modbus Plus connection and transfer the control of both units to the Quantum PLC, skipping the 1500 altogether. It involves running a few cables but my supervisor and the EI guys liked the idea. With all the stuff on the Quantum, it's more future proof and a little less complicated to troubleshoot/edit the ladder logic if the need arises. I think it qualifies as my first real "engineering decision". However, I still need the ladder logic off the 1500. There's a tech working on that right now but it's not working like it should. He's using RSLinx. The guy assures me that once we download the code, I'll have the register numbers but no descriptors. Any chance those can be downloaded from the unit? Thanks again, Jon

[gravitar 3]

Descriptions aren't stored in the PLC; They only exist on your computer (or on paper once you print it :) so you'll need to find an .RSS file with descriptions or a hardcopy. I think the engineering decision you made was a good one. It is nearly always preferable to use 1 PLC instead of two, especially when they are of different make/model and would need to communicate.

[rpraveenkum 5]

Contact your eqiupment supplier ask him for the PLC original file it will have the descriptors