GE Fanuc (IP) 90-30 PLC vs RX3, RX7 PAC Systems

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This question is posed to Steve and Russ because I know their familiarity with the GE line of products; however, anyone with some insight on this topic would be greatly appreciated. The purpose for this topic is to better understand the differences between GE's PLC vs PAC systems and which system is best suited to run in a "hot/standby" mode or as a "primary and secondary" master system running in tandem. As an independent field engineer for GE Zenith Controls I have run across multiple 90-30 PLC's which run in parallel in the event that one has a failure, the other would seamlessly take over and continue to operate as designed. I have also come across some Square D Modicon systems that utilize its own "hot/standby" feature and was very impressed with the way they functioned in tandem. They have a very nice feature that allows the user to make program changes to the Primary PLC and using a keyswitch one is able to copy the updated program to the secondary PLC, which I found to be very helpful to avoid having discrepancies between the two units. With that being said I am in the beginning stages of planning two projects where redundant PLC's are a necessity and having read a little bit about GE Fanuc's new line of RX3 & RX7 programmable automation controllers (PAC's) I am curious about which type of system would best suit the needs of each of my projects. Project A: We are being contracted to control a medium voltage emergency power switchgear lineup using dry contacts to open and close utility, generator, tie and distribution breakers. The basic scope is a lineup consisting of two sections, (A&B). Each section has an individual utility breaker, an individual generator breaker, 4 distribution breakers and a tie breaker capable carrying the load of either side in the event of a power failure or a breaker malfunction. The switchgear manufacturer is responsible for providing dry contacts to allow our system to open and close breakers using 125 VDC control power. The logic itself is fairly simple; Normal Operating mode is for both utility A & B breakers to be closed the two generator breakers to be open, the tie breaker open and the load or distribution breakers feeding water treatment station pumps closed. Single Utility Power Failure: In the event of a single utility power failure, the system is designed to open the failed utility breaker and close the tie breaker with the healthy utility breaker carrying the load of the entire system. Dual Utility Power Failure: In this event the generator is called to start, both utility breakers open and both generator breakers close. As far as communication needs are concerned we are required to provide dry contacts for the customers SCADA system for approximately 120 alarm and/or status points. I would also like to provide the option for the customer to receive these points using modbus over Ethernet to give them additional flexibility. I am guessing we will have approximatly 120 inputs and outputs and may require an analog card for reading current on specific breakers. A GE Quickpanel will also be utilized for alarms, status and manual control of the breakers through the PLC. We are also required to provide the ability for manual operation using individual breaker handles. This is the basic premise of what our scope of work and what I would like to know is which type of system is best in this application, the 90-30 PLC or the RX3 PAC's. I do want to have a redundant primary/secondary controller in the event of a failure. Project B: This project is in its infant stages as far as specific details and requirements; however, I will try and describe the scope the best I can based on what is know. The project is fairly similar to the first, with the exception that we are simply controlling 3 variable speed drives that control water pumps. Our controls are simply to control these drives based on the demand for water pressure. It is my understanding that all three pumps are not needed in order to satisfy the normal demands at the facility. There will be a need for alternating logic to keep the hours on the pumps as balanced as possible. I'm assuming we will be given some type of analog information for the pressure of the system and depending on the demand at any given point we will be starting and stopping these units based on predetermined set points we are provided. Controller requirements as I know them at present; 1. Redundant controller operating in parallel (hot/standby). 2. Modbus over Ethernet capabilities for status, alarms and RMS values. 3. 15" Quickpanel for control, alarms, status, etc. On the Quickpanel I would also like to incorporate an individual graphic page for each of the three drives shwoing when its running and displaying some of the RMS values as well as control ability for the operators. 4. Analog input cards 5. This unit will be outdoors (in Arizona heat) so I would like to incorporate some type of thermo based controls to operate internal A/C, cooling system and I want a system that is rugged enough to withstand more extreme conditions (If one of the two is more suitable than the other). These are the two projects I am working on at present and I would like to get some feedback on which type of system would best fit the needs of each of the two projects. I have done some research online about the RX3 & RX7 but am not technically savvy enough to digest a lot of what I have read. If anyone has any suggestions on which system would work best for each of these projects I would appreciate it. Also Russ/Steve if either one of you guys are interested in doing the design/programming for project B I would like to discuss that with you. Thank you, Jason

[kaiser_will 65]

Both of these projects do not appear to be long logic or fast logic programs, which is the justification for Rx3i and Rx7i PACS systems. The Rx3i is the smaller platform, similar to A-B ControlLogix, whilst the Rx7i is the larger platform high-speed, multi-processor behemoth. Both platforms are superb, and support high-speed and low-speed I/O over the same backplane (backplanes have 2 I/O busses). Cost-wise, the Rx7i is much more expensive than the Rx3i. You will have to breakdown the price differences to determine if they fit into either project margin. The Rx7i is really intended for high I/O count systems with high-speed programs. These systems are often used in very critical applications. The Rx3i lineup includes a Redundancy Memory Exchange (IC695CRU320) module that is used to link Rx3i CPUs in hot standby redundancy systems. Essentially, a reflective memory module on the high-speed bus that specifically links 2 CPUs. Rx systems are built on VME (Versa Module Europa - rack mount) technology standards that have been defined over many years of industry/research work. You might want to contact your local GE-Fanuc controls distributor and get them involved. They should be able to shed a tremendous amount of light on your application, and get you linked up with GE factory integration support.

[Steve Bailey 118]

On first glance, neither of your systems appear to be so large as to need the RX7 platform. For system A I wouldn't recommend a 90-30 solution. The 90-30 is a 20 year old platform and the RX3i is its successor. In summary, I would go with the RX3i for both systems. For the details of the redundancy strategy, there are options limited more by the size of your budget than technical considerations. You can go with a simple system which just has a second CPU synchronized with the primary for bumpless transfer between the two. You can have a redundant sync link between the two CPUs. You can have redundant I/O cables from the CPUs to the field I/O. You can have redundant I/O modules. You can have redundant I/O devices. The current redundancy strategy involves a high speed "Reflective memory" module alongside each CPU. This gives you a fiber optic link between the two CPUs to share data that has to be identical in both CPUs so that either can control the I/O without any hiccups when you change which CPU is in control. The manual GFK2300 is the hardware manual for the reflective memory modles and GFK-2308 is the redundancy manual. The brochure GFA-603 is an overview. There used to be a product called Max-On which involved an ethernet sync link, but I don't know if they are still selling it. The manual for it is GFK-2409.