Addressing for Micrologix 1762-oa8?

[iant]

1.Grounding is always a good Idea - if there is a GND terminal it is a good Idea to use it, regardless.
2.Noise effects should be minimal - But a good thought to keep in mind

 

[Skiroy]

Thankx and these modules have no problem with being pushed next to each other without any gaps being that the heat vent or on the top,right?

 

[OkiePC]

Thankx and these modules have no problem with being pushed next to each other without any gaps being that the heat vent or on the top,right?

Right. The ventilation is vertical through all the Micrologix as far as I know. We have violated the rules in many cases with the spacing, but as long as the panel temperature is not way over spec., they will run for a long time trouble free until the plastic parts bake...The Micros are more likely to fault and need to be downloaded (or fitted with memory modules) due to brownouts or power cycles and lightning as compared to the SLC or PLC-5. All of our ML1200, and 1500 have been fitted with them to make them automatically recover from these uncontrollable events.

The book will tell you minimum spacing, but that is going to vary depending on the temperature most of all. They are pretty tough little machines. Good grounding is a great start.

You should be fine in my experience, but I don't know the size of the panel and the total wattage of its loads, nor the environment its going in. The spacing requirements are more aimed at avoiding high frequency or high voltage noise. so don't run VFD motor leads right up against the PLC if you can help it!

2. This old system is an OLD PLC-2. All the outputs are going to 120VAC pneumatic valves. With the new Micrologix PLC which is Relay Outputs,I shouldnt have to worry about shunting the outputs right?

For your relay outputs, if the circuits they're driving are solenoids it is never a bad idea to use AC snubbers or diodes for DC to handle inrush/collapsing field currents to extend contact life. I have seen 120vac solenoid valves with power ratings anywhere from 1.3 to 15 watts.

Depending on the coils, you may not need anything. Many of them have suppression or such lower power requirements that you can get 500,000 relay cycles driving them directly.

Interposing relays are highly recommended with a brick where replacing one burnt relay means replacing the controller. Interposing relays means you use nice small "easy to operate" relays (low coil power requirements) and wire them up to the PLC outputs. Those relays then have perhaps as high as 20 amp contacts to drive the "real" load. They can be plug in style relays with din rail mounted bases to make for quick and simple and cheap replacement at the end of their very finite life.

If the output is wired locally to safe loads (under 50% of the max permitted), skip the relays, but, do "know thy loads."
Paul

EDIT: another thread:
http://www.plctalk.net/qanda/showthread.php?t=61045&highlight=interposing+relays&page=2

AND: later on you can correct the original specification and switch to higher density transistor outputs for nearly infinite life of the PLC module by the use of the interposing relay as a sacrificial component doing the hard work.

 

[sthompson]

1.Anyways the mounting panel is bonded and grounded. Now I know I am going to connect the earth grouth to the Micrologix's ground terminal. But being that it will be mounted on the DIN rail,never contacting the bonded mounting panel, do I have to further ground it by running any additional wiring?

The MicroLogix 1400 has Grounding Tabs built in.

All the information you need can be found in the Hardware Manual.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1766-um001_-en-p.pdf

2.Secondly, my employer instead of buying a few 16 point modules bought several 8 point modules so now the entire length of the panel is going to be filled up. My concern is this puts the MicroLogix 1400 so it butts up to the 120VAC I/O Wiring ducts. And the last 8 point Input module(120VAC) is butted up against the wiring duct that the main 240V wiring runs through.

So am I going to run into noise issues because of these units close proximity to these wiring ducts?

You shouldn't, again MOVs or Snubbers on your Inductive Loads will help with this. Read the Hardware Manual, it covers all this.

Stu....

 

[Skiroy]

Thankx. One last important question before I dive in.

On the old PLC-2 Output Modules shown in the Pictures of the Schemo I linked, wire 10 is L1(Hot) and is jumpered to the A,B,C,D terminal groups.Then from the output terminal the wiring goes out to the device which is wired to the L2/N(wire 2).

https://dl.dropbox.com/u/96052065/schemo%202.jpg

http://dl.dropbox.com/u/96052065/schemo 1.jpg


Here is my confusion. The PLC-2 Output module then has L2 tied in at the bottom,but the newer Micrologix output modules do not. They only have VAC1 and VAC2 for L1(Hot) to supply L1 to the 2 four terminal output groups. So why no L2 like the old PLC-2 modules? Is this L2 just to power the module electronics done now through the ribbon cable in the new modules?

Heres the link of the new Output module page 8
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1762-in007_-en-p.pdf

Thankx

 

[Skiroy]

Lied one last question for now. Just gotta cover everything before I start the re wiring. The in put module,1762-IA8 has 2 Comm terminalls but says they are internally jumpered. Whats the point of the second terminal then? Just to add an extra terminal to make daisy chaining the other module's Comms toghther?

Page 8

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1762-in002_-en-p.pdf

 

[Skiroy]

For your relay outputs, if the circuits they're driving are solenoids it is never a bad idea to use AC snubbers or diodes for DC to handle inrush/collapsing field currents to extend contact life. I have seen 120vac solenoid valves with power ratings anywhere from 1.3 to 15 watts.

Depending on the coils, you may not need anything. Many of them have suppression or such lower power requirements that you can get 500,000 relay cycles driving them directly.

.

Thankx Im still new to this. But the Biggest 120VAC pneumatic valve on the machine says .38 amps. So at 120 that 45 watts rights.

My model is the AWA and the manual specs if I am reading it correctly is saying each output terminal can handle 2.5A so am I okay? The specs are on page 168

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1766-um001_-en-p.pdf

Thankx

 

[Skiroy]

Sorry for the ton of questions. But I have 42 Ins and 32 Outs to rewire and record the new addresses as I go. I hvae to make certain I get it right the first go.

 

[iant]

If you have a good numbering MC - I find to do this it is an idea
to wire with dual number - new/old
that way it can relate to old drawings also

 

[sthompson]

On the old PLC-2 Output Modules shown in the Pictures of the Schemo I linked, wire 10 is L1(Hot) and is jumpered to the A,B,C,D terminal groups.Then from the output terminal the wiring goes out to the device which is wired to the L2/N(wire 2).

Here is my confusion. The PLC-2 Output module then has L2 tied in at the bottom,but the newer Micrologix output modules do not. They only have VAC1 and VAC2 for L1(Hot) to supply L1 to the 2 four terminal output groups. So why no L2 like the old PLC-2 modules? Is this L2 just to power the module electronics done now through the ribbon cable in the new modules?

I believe the L2 was just for convenience, it is marked as Optional. It is not normally necessary for Output Cards.

Links to 1771-OAD Information;

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1771-in024_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1771-td074_-en-p.pdf

Stu....

 

[sthompson]

Lied one last question for now. Just gotta cover everything before I start the re wiring. The in put module,1762-IA8 has 2 Comm terminalls but says they are internally jumpered. Whats the point of the second terminal then? Just to add an extra terminal to make daisy chaining the other module's Comms toghther?

Most likely, but I guess you would have to ask Allen Bradley. I am sure someone will chime in here if they have direct knowledge. Be careful you don't get overwhelmed with all these small details.

Allen Bradley has pretty good Manuals and Documentation, and it is very accessible. So, Download all the pertinent Manuals, then read and follow them.

Stu....

 

[Skiroy]

What is the general rule for jumpering(daisy chaining)? I have read the Allen Bradley's wiring and grounding guilines publication and it mentions nothing about this. The machine basically has 1 step down transformer with its L1 and L2/N going to a terminal block with jumpers. I noticed they ran a seperate L1 to the PLC and to each Output module.Ofcourse within the Output module they have the 4 groups jumpered. But what differs is they just daisy chain one L2 wire to every Input module.

Essentially its all really being tapped(daisy chained) from 2 wires coming from the transformer. So my question is there a rule of thumb on daisy chaining vs using a seperate wire straight from the terminal strips regarding L1 vs L2/N?

I am looking at a different machine with a SLC 500 and they dont daisy chain anything. All L1 and L2 lines come straight from a terminal strip.

Technically I could come off the Micrologix 1400 120ACV lines that power the processor and daisy chain everything from there,right? This would be sloppy of course and difficult with the 14 awg wire though. I know you probably wouldnt want to do this if I have other analog,communication and DC module in place due to it would like cause noise with the sloppy wiring,but in this case its all AC so it really wouldnt matter,right?

 

[Skiroy]

bump on the daisy chain question. I want to do this correctly

 

[iant]

the Idea of daisy chaining is OK But if you want to change something - like fuse an output card or introduce a safety guarded supply to an output card there can be a lot of wiring.
The Idea of wiring individually from a terminal is probably the best idea.
It depends on Panel space and Job cost
- this also means you can easily loom the wiring. with daisy chain wiring,this is not so easy.

 

[iant]

I might ask you a small question - this is important in Aus.
Is your safety circuits up to date - here any change to a control cct - requires a risk analisys and probably a full hard wired safety system update.
Safety contactors and safety relays, double contact E/stops and Guard switches etc.?
May not need to be done there but worth thinking about