PLC and Terminal block and Sensor wiring selection

[DamianInRochester]

I liked your recommendation of increasing the resolution of the measurements. I will do that as well.

Regarding your wiring recommendation (shown in bottom diagram of image below, representing both sensors in transmitters).

I was wondering what advantages/disadvantages I had in my original wiring, witch was literally wired as shown in the AB manual (or at least as I understood it). It's easier that way, but seemed odd having to bypass the comm ports on the card.

Thanks again and have a good weekend (or what's left of it)!

There was nothing wrong with how you had it. I was not entirely sure how you had it, so I just gave you point to point description that I knew would work.

If I had a nickle for every time a customer swore to me that had something hooked up right, only to find that they didn't I would be a wealthy man. I take nothing for granted anymore.

 

[Lancie1]

Thanks Lancie1, but the ones I was talking about from the sample pic on first post, the blue wires in figure A, were not two inner signal wires, but a single thick wire.

Okay, if they ARE single-conductor and run to a cable tray, then probably they were specified by an electrical engineer. Engineers like to follow the National Electrical Code, which says that wires in a cable tray must have insulation for the highest voltage present in the tray. If 480 volt cables are present, then 600 volt insulation is required, not 150 volt or 300 volt. 600 volt MTW wires have thicker insulation.

 

[DamianInRochester]

Okay, if they ARE single-conductor and run to a cable tray, then probably they were specified by an electrical engineer. Engineers like to follow the National Electrical Code, which says that wires in a cable tray must have insulation for the highest voltage present in the tray. If 480 volt cables are present, then 600 volt insulation is required, not 150 volt or 300 volt. 600 volt MTW wires have thicker insulation.

Which hopefully they would not be running low level logic signals with high voltage power lines in the same tray in the first place.

 

[Lancie1]

No one likes to do that, but at times it cannot be avoided for various reasons. It is allowed by the code if the rules are followed. It is only one of many reasons for using a certain type of insulation. For example, if the wires leave the PLC and run through certain enviroments - caustic, acidic, corrosive, high-temperature, then the proper insulation must be used to meet all regulations. Unless a junction box is installed and another set of terminations are made, then the special insulation gets run all the way to the PLC.

 

[SergioB]

Dear OkiePC, The Plc Kid, JesperMP, bce123, Lancie1 and DamianInRochester ;

Thank you all for a lot of valuable tips. Very helpful info!

Sincerely,
sb

 

[SergioB]

One last question if I may...

The AB analog I/O card manual recommends the Belden 8761 Multi-Conductor - Single-Pair Cable for wiring sensors, but It's only a 2-conductor one and would like to get a 4-conductor cable instead so that I can use it for wiring 3 and 4-wire sensors.

I found a reel of Belden 5302FE Multi-Conductor - Commercial Applications on eBay and looks like a correct cable for wiring sensors.

Could you please give me your opinion about buying this cable for wiring 2-wire, 3-wire and 4-wire sensors?

Thanks a lot in advance!

 

[Lancie1]

Could you please give me your opinion about buying this cable for wiring 2-wire, 3-wire and 4-wire sensors?

For best results and fewer problems with noise on the sensor wires, make sure this Belden 5302FE cable has an outer foil or mesh shield around the 4 conductors. Even better would be if each pair is individually shielded.

Edit: I see that it has an overall shield for all 4 conductors. That will work as long as you don't use 2 for AC power or AC signals.

 

[SergioB]

I see that it has an overall shield for all 4 conductors. That will work as long as you don't use 2 for AC power or AC signals.

Thanks for reading the specs. Yes, it says that it has "Aluminum Foil-Polyester Tape w/Shorting Fold". Nope, not planning on running ac, just planning on using low current/voltage dc signals.

So you'd say this is a good quality cable?

 

[Lancie1]

Yes, it looks like good shielded signal cable.

 

[RocketTester]

For in-cabinet multi-channel runs, I like large colored ribbon cable. Amphenol Spectra-strip makes it in 16 awg to 22 awg with many conductors. It is very rugged. A problem is 5000 ft min order. You can also find "normal" ribbon cable, but w/ 22 awg wires via Digi-key and Newark. It is more rugged than it appears.

For field wires to sensors, we use multi-conductor shielded cables 22 or 24 awg, usually straight wires (un-twisted) from Belden, Alpha, Carol, etc.

Wire is amazingly expensive, so plan carefully. Some people apply Cat5 ethernet cable to industrial instrumentation since widely available and more affordable. However, it isn't super cheap. I found fiber-optic cable was actually cheaper than copper ethernet for long runs.

Smart to use distributed IO whenever you can, so you just have ethernet and a few power cables to run between blocks. We use Beckhoff EtherCAT IO, which makes that easy.

 

[SergioB]

Thanks for all the tips!

By the way, speaking of distributed systems, does anyone know how these input/output modules are used (inside the junction box)?

They are described as: Gordos-Crouzet Digital DR-Input and Output Modules.

I bought some of these junction boxes and was wondering if the modules could be of any use to me. You may see additional info and pics in full listing here.

Regards!
sb

 

[RocketTester]

Those modules are the same standard "relay board" type that have been around for >30 years from Opto22, Gordos, Potter-Brumfield, ... Yours have the same module names (IDC24, ODC24) as other manufacturers. They were often sold as an add-on to PC boards from companies like Measurement Computing and National Instruments. Yours are more convenient since they have integral screw terminals and don't require a backplane.

The enclosure looks like a sort of "homemade" solution using boxes from Rose-Bopla or similar. I expect this was a component of a low volume system, perhaps for scientific or medical.

You might find the modules at digikey.com. I expect they cost ~$10 ea. The enclosure retails higher, but unless you need it, may have little value. I am bit surprised they get $35 for such surplus equipment, but ebay has eliminated much of the "buy a pallet for $1" surplus sales of the past.

 

[SergioB]

You might find the modules at digikey.com. I expect they cost ~$10 ea. The enclosure retails higher, but unless you need it, may have little value. I am bit surprised they get $35 for such surplus equipment, but ebay has eliminated much of the "buy a pallet for $1" surplus sales of the past.

Hmm. I bought a few of them at $25 each. I basically needed some junction boxes at various places in my project and thought these were a good option. But I guess if I had talked with you before buying them, I would've offered less.

 

[DamianInRochester]

Hmm. I bought a few of them at $25 each. I basically needed some junction boxes at various places in my project and thought these were a good option. But I guess if I had talked with you before buying them, I would've offered less.

Actually for whatever the reason the prices of these have skyrocketed over the years. Allied wants almost $40 each now days. Ten years ago I was getting them for about $12 each. Even the slimline style with the replaceable element are difficult to find for less than $30 each now days.

I used to use these a lot, but the drop in cost of PLC IO and the rise in cost of external relays forced me to re-evaluate the benefits. I always keep a box of DR-ODC24 and DR-OAC for those little suprises that pop up.

 

[SergioB]

Allied wants almost $40 each now days. Ten years ago I was getting them for about $12 each. Even the slimline style with the replaceable element are difficult to find for less than $30 each now days.

I used to use these a lot, but the drop in cost of PLC IO and the rise in cost of external relays forced me to re-evaluate the benefits. I always keep a box of DR-ODC24 and DR-OAC for those little suprises that pop up.

So then I got a pretty good deal? I mean, they're used, but at $5 each (2 IDC24 and 2 ODC24), including the junction box is a good deal, no?

So are these to be used as input/output modules for micro-controller-type applications only?