Semi-intelligent gate controls

I would like to know if mapping Micrologix as ethernet I/O would replace the messaging that I am doing now. It would be a lot easier to understand and to troubleshoot! Micrologix don`t have produced/consumed tags

OK - here goes with the description ...

I have an L73 ControlLogix sending messages to 35 (yes, 35) Micrologix 1100 fixed IO PLCS, 10 input at 120V and 6 relay output. The details are below, but in general the gate is semi-inelligent and is told to open and to close. If communications are lost, the gate closes.

The communication is a pain to manage. This PLC is communicating to 10 other controlLogix for interlocks ... plus the 35 micrologix. 45 active messages obviously won't work. So they are timed, and modularized. The timeouts are set within the MSG instruction since 30 seconds (default) just won't work. I cringe whenever I have to change anything timing or messaging in this system.

One of the most annoying parts is to check that the MAC address of the micrologix matches what the Micrologix has stored. I'm sure that I have something not-quite-right, since my counters show a dozen messages failing this test every week or so. Each micrologix, once in a while, receives a message that is not intended for it. The messages go every 2.5 seconds and I get, like I mentioned, 6 - 12 messages that are wrong per week-ish (I don't check religiously any more). Just the Micrologix. Not the other ControlLogix.

More detail, if anyone is still reading ..

Each Micrologix has a local open and a local close pushbutton, as well as an open limit switch and a close limit switch. We have 2 power inputs, one for limits and one for the Open Solenoid. Only one output and it is energize to open, fail off (close). So communications loss, power loss, etc closes witha spring in the solenoid block and hydraulics with an accumulator

Each micrologix has one 16-bit word of interlocks, that must all be '1' in order for the OPEN commands to work, either locally or on the network.

The gates have a soft DCS/Maintenance switch (local control or remote)
a soft Enable/disable (safety enable by a supervisor)
a soft Auto/manual (gate opens and closes via a level loop or not)

The gates allow product to fall from a storage area onto a conveyor belt. So opening at the wrong time makes a big mess and wastes product.

If you made it all the way through that - congratulations!

So, why do you need a Micrologix at each gate?

Could it not be remote I/O and let the ControlLogix handle the processing and logic? Or am I missing something?

I don't think MicroLogix can be mapped as Ethernet I/O, but I've never tried...

One thing that may help is to set each MicroLogix to use a read MSG instead of the ControlLogix doing 35 writes.

JohnCalderwood said:

So, why do you need a Micrologix at each gate?

Could it not be remote I/O and let the ControlLogix handle the processing and logic? Or am I missing something?

Click to expand...

The ControlLogix can handle the IO easily. It would be less work and less complication. But the designer (me) was a bit paranoid about ethernet communications running in parallel with 600 VAC cable in the same tray, for hundreds of feet. It turns out that running cat5 inside armour (teck cable) is fairly effective at suppressing the interference.

The emergency stop circuit for the longest belt is run on DC to avoid the interference, with a 1 amp load, to hedge against interference.

The distances involved are quite large. 25 are on one belt gallery, 2500 feet long. 5 more on another belt gallery 600 feet long, and the last 5 on a belt 400 feet long. There is fiber from the L73 to each `group`of gates, which has a cisco 2955 ( if you remember Cisco`s first extended temperature range switch). 6 switches, 8 ports each. Cat5 from the switch to the micrologix. The number of switches was determined by the max distance that cat5 could run.

The design used the micrologix for local intelligence, so that the gates *COULD* be opened locally if we were having trouble with the communications. You need to jumper one input on the Micrologix to tell it that `the interlocks are all OK`.

I`m just looking for options if we do an upgrade ...

Remote IO is likely the way to go. It will just be a pain to retrofit the existing hardware plates and mounting, boxes, wiring, etc.

rupej said:

I don't think MicroLogix can be mapped as Ethernet I/O, but I've never tried...

One thing that may help is to set each MicroLogix to use a read MSG instead of the ControlLogix doing 35 writes.

Click to expand...

The ControlLogix is doing READs and WRITEs, to keep it all in the same place. I violated my rule of doing only READs, for this area.

Doing the READs and WRITEs in each Micrologix would help ... but each program would then be different - different landing zones in the ControlLogix. Right now they are identical except for the IP address (not in the program) and the MAC address (held in N34 registers and manually entered)

Doing the same change to 35 programs is possible. But I have not been successful in keeping programs identical in the past. I don`t seem to have the attention span .. And after I make the change I like to prove that it still works. A storage building ... is partially full .. pretty much all of the time. So I can only re-commission about 12 of the 35 gates at any one time. I`m not good at scheduling

Ah I see, that makes sense then. In that case, my only suggestion would be to eliminate any unnecessary switches and use fiber to connect the remaining ones if the distance > 300 meters. Not sure if that's feasible for you though.

if the distance > 300 meters

Click to expand...

~300 feet... 100meters... right?

I see it a little different form what I see you have a 35 storage bins that feed on to a common conveyor 1 at a time or even several at a time.
I would use a single ControlLogix processor wit ether net I/O as needed at each bin gate
The distance should not be a problem the 300It could work if Ft barrier can easily be extended with Ethernet Extenders or the 2 port I/O modules depending on your needs
I don't see how you can make the multiple Micro 1100's work wit out a creating more problems. It could work if the gates could be controlled independently but if I read this correctly that's not the case. Lets not forget all interlocking that you need to do to make the system work.
With the right hardware you can extend ether net many miles without problems just look at the internet it goes around the world without problems.
if you need longer distance you ca use fiber optics.

GaryS said:

I see it a little different form what I see you have a 35 storage bins that feed on to a common conveyor 1 at a time or even several at a time.
I would use a single ControlLogix processor wit ether net I/O as needed at each bin gate
The distance should not be a problem the 300It could work if Ft barrier can easily be extended with Ethernet Extenders or the 2 port I/O modules depending on your needs
I don't see how you can make the multiple Micro 1100's work wit out a creating more problems. It could work if the gates could be controlled independently but if I read this correctly that's not the case. Lets not forget all interlocking that you need to do to make the system work.
With the right hardware you can extend ether net many miles without problems just look at the internet it goes around the world without problems.
if you need longer distance you ca use fiber optics.

Click to expand...

No multiple gates open at once, and you captured the essence in a simplified summary.

For the 25 gates, there are 2 different products, and each product can have 2 gates enabled to open, but only 1 gate is allowed to open at a time. Otherwise it dumps product off the sides. If one gate plugs with lumps, they use the other one until they dig down to the gate and break up the lumps with the blade of the dozer.

The 5 and 5 gates for the other 2 buildings have 2 gates enabled, but only 1 gate open at a time.

The multiple Micrologix 1100 are working now, and have been since 2009. But maintenance of the communications is not pleasant. Interlocking is done at the ControlLogix and sent to the Micrologix. The Micrologix have not needed the 'interlock bypass' input so far. All of the advantages of a local PLC are still 'available' but not yet used.

The base Micrologix ladder logic has not changed much in 9 years. I added a bit more status and alarm logging internally in about 2012.

But I have requests in my backlog to turn on our emergency beacons (warning - evacuate the area) ... that are hard-wired to an ancient relay panel now ... 40-year-old wiring strung all over the place ... undocumented junction boxes hanging in areas where the floors have been removed, or changed so that the junction boxes are hard to get to ... and the need for replacement becomes OBVIOUS ... so I need to turn on a beacon and a horn, monitor the current to verify that the beacon is running, alarm if not.

Also in the backlog is running a few sump pumps with level switches and motor current, that are in the belt gallery area as the gates, but not actually part of the gate network ... yet ... so I need some new nodes for the network ... and I need to mess with the complex multi-plexing of the messages

So there are upgrades in the future and I'm looking to see what is easier, or better, preferably both!

Are there any stories out there about problems with ethernet IO, point IO, etc ... and how to avoid them? Our networks for control and administration are separated by a firewall. I`m not using VLANs as yet - just assigned subnets and masks. The firewall handles anything that goes between subnets.

Point IO doesn't like excessive heat, so ensure to ventilate the cabinets.


If you have a lot of independent adapters, my advice is to have them all on a 192.168.1.xxx range. That way, you can set the IP via the thumb-wheels, and bubba following along at 2am can change one out without worrying about BootP.

It sounds like you want to look at Devicelogix.
Checkout 1734-8CFGDLX or 1738-8CFGDLXM12.
Then your IO can have specific functionality under comms loss, rather than just the "fail on / fail off" setting you normally get.

the_msp said:

Point IO doesn't like excessive heat, so ensure to ventilate the cabinets.

Click to expand...

The ambient in the belt gallery is 20C - 50C. The product loaded on the belt is mixed to keep it below 80C. The Cisco 2955 switches have shut down on high temp ... so I think Point IO is kind of out of the question.

If you have a lot of independent adapters, my advice is to have them all on a 192.168.1.xxx range. That way, you can set the IP via the thumb-wheels, and bubba following along at 2am can change one out without worrying about BootP.

Click to expand...

Right now we use an assigned subnet of the 10.48.xxx and I have to connect to a new micrologix with a serial cable and download the program, assigning the correct IP. If I get the wrong IP, the old-time Cisco switch does something goofy ... it connects one gate for 60 seconds, then the other for 60 seconds, and it keeps alternating. So - if I don`t remember to check - a 50% chance that the WRONG GATE opens (!!!)

Since it is not routable anyway, I will talk to our IT guy and see if he will agree to using the 192.168 group. It will have to be done on shutdown, since all gates would need to change at once.

AustralIan said:

It sounds like you want to look at Devicelogix.
Checkout 1734-8CFGDLX or 1738-8CFGDLXM12.
Then your IO can have specific functionality under comms loss, rather than just the "fail on / fail off" setting you normally get.

Click to expand...

The Point IO specs read a max of 55C ambient. We have heat issues, but that should not be a deal breaker.

I saw a couple of 120V input modules. Most stuff seems to be DC, and configurable as in or out. We have not had good luck with DC and corrosion on contacts. 24V does not seem to be enough to `burn` through contact contamination.

50V of isolation on the bus seems a bit low. Particularly with 120V power in the cabinet. Has this been a problem for anyone so far? We have had surges travel through our UPS`s (not great UPS - commercial instead of industrial) and through instrument DC power supplies and kill instruments.

Is Pointbus the new thing at Rockwell? Flex modules were sort of like toys - all plastic and easy to break. How is Pointbus holding up?

would the armor point (doesn't need a cabinet, 60°C ambient rating) work for you?

You could do a device level ring (getting rid of your ciscos and fibre), and just hope you don't lose two gates at once. To get your ring and stick to the 100m spec, you would connect every even gate on the way up and every odd gate on the way back.

AustralIan said:

would the armor point (doesn't need a cabinet, 60°C ambient rating) work for you?

You could do a device level ring (getting rid of your ciscos and fibre), and just hope you don't lose two gates at once. To get your ring and stick to the 100m spec, you would connect every even gate on the way up and every odd gate on the way back.

Click to expand...

That sounds interesting.

I need to do some reading.

In discussions with the electricians, I found out that the way that the hydraulic solenoids are implemented, you can use a welding rod to poke through a vent hole and activate the spools on the hydraulic valve without power at all. Independent of the PLC and interlocks and everything.

So I guess having a local PLC is not much of an advantage.

I am retiring in a couple of years, so I`m trying to make maintenance much easier to document. This messaging system is complex, and programming the L73 for the extra communications buffers, keeping only 6 messages active at a time ... etc ... is hard to explain without a white board and a bunch of hand-waving.