I come from the bldg automation business, but now am responsible for deploying small PLCs in remote plants across the country. These PLCs will talk modbus to electrical equipment like VFDs and revenue grade demand meters. The hard wired point count is not high - most points are modbus. I want the PLCs to communicate via Ethernet to a SCADA system as well so I can monitor these scattered installations from my office. If AB (micrologix), Siemens (S7-200), and say GE Fanuc walked in to Thunderdome, which one would walk out alive?

My important criteria are: memory at the PLC to maintain point trend histories if possible, ease of setting up communication with something like Genesis 32, Intellution or Wonderware, ease of setting up modbus communication with the devices, ease of programming the PLCs, durability in harsh (hot-humid-salt air and hot-dry) environments, and cost.

 

I doubt it would be Micrologix. I have a collection of dead ones I have had to replace.

Regards

cww

 

I would throw Automation Direct PLCs into that ring. They are small, reasonably priced and have Modbus ports. Look at DL-06 or DL-260 for a start.

 

If you need Modbus, why don't you consider Modbus-native PLCs? Schneider has released recently the M340, and I think it can be a good option, with a Modbus port in the CPU, and working on Unity.

 

Miguel, William, Curt,

Thank you for the feedback. I think ease of communication using Modbus is my #1 factor. Are the Schneider Modicons as easy to program as the Siemens or AB?

I have heard that the AB PLCs are a bit pricey also.

 

Hi,

Sorry for the delay. Looking at your choices the Siemens is head and shoulders above the others. There is a modbus library available for both ports on the 214XM and the 226XM, it is simple to use and reliable. There is an ethernet and internet module available (one online at http://s7-200.germainesystems.eu) Siemens also offer siplus, which is a ruggedised range, (http://www.automation.siemens.com/siplus/index_76.htm) Although only available for windows, the programming software is low cost and IEC compatible. (trial version available at http://www.automation.siemens.com/_en/s7-200/support/tools_downloads/microwin.html)

Marc Sinclair