FF and Modicon PLC's

[Dink73]

I have asked this on Controls.com, but no luck. I probably should have come here first. Problem:

We have a smallish upgrade project that we need to get running before winter sets in. 22 on/off valves, level, flow, 3 VFD's, and 5 level switches. We would very much like to try FF hardware, as the project seems well suited for testing FF at our facility. Please keep in mind that this is a critical system for us during the winter.

The people at Emerson (Fisher/Rosemount) have been kind enough to loan us a Rosemount 3420 and a selection of FF instruments to test. We use Modicon Quantum series PLC's at all of our sites, and have run into a major problem. The Quantum NOE 771-01 module will only allow us to master block 4X registers to/from the 3420 via MB TCP/IP. The 3420 will only send the real values via 4X's. Discretes must be 1X and lower, which doesn't work for us. We can read/write real values to the 3420 all day, but we can't get discrete values in/out of the PLC. The Emerson folks (great to work with) and Modicon folks don't have an answer for us. I was just about to give up and use traditional I/O until yesterday.

While trying to find a solution, I came across a card (QUCM-OE) from NR&D that I can use in place of the Modicon NOE 771-01. It will allow us to read/write 0X - 4X registers, which sounds like the solution to our problem. Since no one can provide an answer, I am going to buy 2 of them and give it a try.

Have any of you had success with FF and Modicon PLC's? If so, what was your solution? I would greatly appreciate any suggestions and solutions to this dilemma.

Thanks,

Dink73

[rezabejd]

Took us a while to see your post and get it approved . . . apologize for that.

I have no experience with the 3420 and have never been the one who looked after Quantum PLC's . . . but I'm curious how you're doing your on-off valves, and what sort of climate you're in (sounds like it might get cold?).

If you're using a two-wire fieldbus on-off solenoid-plus-limit-switch assembly, you may need to look at the temperature spec.

Very odd that a Schnieder product doesn't like to speak Modbus. Is this just a "feature" of the TCP/IP flavor? Is serial Modbus over RS485 an option?

[Dink73]

Thanks for getting back to me. We have decided to go with traditional I/O for this project, as we don't have the time to spare on something new right now.

We have decided to continue down the FF testing route though. We purchased an NR&D QUCM-OE module as a replacement for the Modicon NOE Ethernet modules. It should be here shortly, so we will be able to run some tests once our current workload winds down.

As far a temperature, yes it gets cold here. We are going to use the new Emerson FieldQ actuators. If you haven't seen them, check them out (www.FieldQ.com (http://www.FieldQ.com)). We use a lot of rack and pinion type actuators here, and the FieldQ is by far the most robust I have seen yet.

We routinely use very dry instrument air for actuators, and heat tape and insulate everything exposed to the environment. We put panel heaters in all of our outside enclosures as well. The area that these valves will live in is warm locally because they sit so close to the heat exchangers. In the event of a failure, the only need to go to their fail safe positions, and then we go to back up heat (propane) until we get the primary system on line again.

Our PLC's will talk Modbus, but we normally use Modbus Plus for all highway comms. We use NOE modules for a few MB/TCP apps. The only time we use regular Modbus is for a few stand alone Momentum controllers we have at remote panels.

[marisg]

Just out of curiosity, what type and brand of JB heater do you use?

[Dink73]

It depends on to size of the enclosure. For small enclosures, we mount Chromalox silicon strip panel mount heaters. Larger enclosures get Hoffman 500 watt heaters with fans in them. Of course the temperature ratings of the equipment in the panel are taken into consideration as well. Some of our largest enclosures have full sized HVAC units installed, typically window mount size. These are modified to accept Honeywell wireless thermostatic controls. With these, we can control multiple cabinet conditions from one "brain", as long as the distances aren't too great.