You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old February 21st, 2009, 03:42 PM   #1
irondesk40
Member
United States

irondesk40 is offline
 
Join Date: Jan 2008
Location: nc
Posts: 426
analog wiring to plc pratice

Have a question about what others on this site think is the best pratice when wiring analog inputs and outputs. Have a project where I will be using a allen bradley micrologix 1100 with a 1762-of4 analog module. At the bottom of the control panel we always have a terminal strip where all field wiring coming into the panel is terminated at. I plan to desinate each analog output as AO 0, AO 1, etc.. I plan on running a two conductor shielded cable from each analog output to the terminal strip. For example, AO 1 will have a two conductor shielded cable, one of the wires will go to AO 1, the other to COM on the analog module. The two wire cable will go down to the terminal strip, which will have a terminal labeled AO 1, A0 1 Common. At the terminal strip I plan on terminating the shield to a terminal labeled PE, which is Ground. Question is , what would be the best pratice for the termination of the shield at the end of the cable that connects to the analog card. And also, when the field wiring is connected to the terminal strip at the bottom of the panel, the shield in field device cable will also be connected to the terminal labeled PE, which is frame ground.
Is this the best approach?
Thanks for any input.
  Reply With Quote
Old February 21st, 2009, 04:40 PM   #2
Gil47
Member
New Zealand

Gil47 is offline
 
Gil47's Avatar
 
Join Date: Apr 2007
Location: South Island, NewZealand
Posts: 1,244
What you describe is what most would strive for.

My best practice is use paired wires so the resultant current flow in that pair is zero,this reduces noise pickup, better still is twisted pair cable, if a screen is involved earth the screens at one point only, sleeving the other ends so they can't touch earth to create circulating earth currents.
Any unused wires in the cables need to be earthed also and again only at one point.
These would be my top 3 or 4 in that order.

Last edited by Gil47; February 21st, 2009 at 04:45 PM.
  Reply With Quote
Old February 21st, 2009, 05:12 PM   #3
bikerdude
Member
United States

bikerdude is offline
 
bikerdude's Avatar
 
Join Date: Jul 2003
Location: Indiana
Posts: 307
Irondesk40,
You didn't mention it & I've seen it done other ways, the shielded cable from the I/O module terminals to the lower terminal strip should be ran as far away from high current/high voltage wiring as possible. Ideally in it's own panduit wireway. I have heard of panduit wireways with seperate compartments but I have never used one. I'm not certian it is necessary, but we are talking best practices here. I prefer the red/black wiring colors over the white/black @ 18awg. The foil shield is a welcome feature along with the bare shield.

I never did like the "Braided" screen because it always pokes my fingers & makes me cuss.

BD
  Reply With Quote
Old February 22nd, 2009, 03:42 AM   #4
muusic_man
Member
United States

muusic_man is offline
 
Join Date: Nov 2008
Location: Delaware
Posts: 96
We specify 3 different colors of wire ducts. White (below 50 volts), grey (120 VAC), and black (480VAC). This tends to keep low level 4-20 mA away form motor lead wiring. The white duct is always on one side of the cabinet and black on the other. The grey duct catches a little of everything and is a good place to avoid sensitive signals.

Last edited by muusic_man; February 22nd, 2009 at 03:42 AM. Reason: spelling
  Reply With Quote
Old February 22nd, 2009, 02:06 PM   #5
TheStarr
Member
United States

TheStarr is offline
 
TheStarr's Avatar
 
Join Date: Jan 2009
Location: New York
Posts: 375
Sounds like you have a good plan. For DC circuits we use blue (+) and white (-) wire.

Only question now is how to terminate. Do you use crimp-on terminal ends or bare wire straight into the terminal lug?

My advice, just strip the wire and put it in. Don't twist the wire though. Some people like to twist the end to keep stray wires from poking out, but this can cause problems.

First, it adds stress to the individual wire strands. Second, it reduces the contact area betwen the wire and the terminal lug. Twisting makes the wire round, then the lug tries to smash it between two flat plates. It can break the wire and cause intermittent connections years down the road.

The crimp-on connectors can break the wire inside the insultion and you will never see it. Very hard to troubleshoot.

And as Gil47 said, only ground the shield at one end and make sure it goes to the cabinet ground, not the power supply ground. If you ground both ends you have completed the circuit. Any stray currrent flowing through the shield will actually add noise to the system.
  Reply With Quote
Old February 22nd, 2009, 06:19 PM   #6
irondesk40
Member
United States

irondesk40 is offline
 
Join Date: Jan 2008
Location: nc
Posts: 426
thanks for advice. I have attached a quick drawing of what I was thinking would be best pratice. Main question is, the end of the shield cable that connects to the analog input and output cards, I plan on cutting flush with end of cable and wrapping with heat shrink tubing, is this a good practice or should that end be connected to panel ground as well.
Attached Files
File Type: pdf analogshield Model (1).pdf (17.1 KB, 287 views)
  Reply With Quote
Old February 22nd, 2009, 06:46 PM   #7
Tharon
Member
United States

Tharon is offline
 
Join Date: Jan 2007
Location: Michigan
Posts: 1,095
Quote:
Originally Posted by TheStarr View Post
The crimp-on connectors can break the wire inside the insultion and you will never see it. Very hard to troubleshoot.
I've never had that problem with crimp on connectors. I don't even see how you can break the wire using the proper tools and crimp connector. Maybe if you were using 26 gage solid wire and some improper tools.

Using a crimp connector eliminates the problem of "hairs" and also makes it very easy to land the connection under the actual terminal without crimping onto the insulation by pushing it too far in (because of the plastic hood on the connector).

I would recommend using the crimp on connectors for how easy and clean they make the cabinet. I have 8 year old machines with them and have never had issues with wires coming loose or breaking inside the cabinet.

On the other hand, I've had dozens of issues with wires between crimped on insulation rather than wire, wires popping out of terminals, etc. when no crimp connector is used.
  Reply With Quote
Old February 23rd, 2009, 01:32 PM   #8
plc noob
Member
United States

plc noob is offline
 
plc noob's Avatar
 
Join Date: Oct 2007
Location: atlanta , georgia
Posts: 258
From my persoal experience it is better to ground all shields in the control cabinet vs the field.

Sometimes grounds get removed during maintenance of equipment and do not get reconnected correctly or sometimes not at all.

Very dangerous i know . but that does not change the fact that it does happen
  Reply With Quote
Old February 23rd, 2009, 07:42 PM   #9
TheStarr
Member
United States

TheStarr is offline
 
TheStarr's Avatar
 
Join Date: Jan 2009
Location: New York
Posts: 375
I have seen problems with the crimp connectors in "high-traffic" areas. You know that part of the panel that people are always digging in when the machine won't run.

For example, a terminal strip mounted at the bottom of the panel without much clearance to the case.

I think the crimp connectors concentrate all the bending into a specific area of the wire. Crimps work great inside plugs and jacks where they have a strain relief, like an AMP plug.

Just out in the open I think they may be more suseptible to mis-handling.
  Reply With Quote
Old February 24th, 2009, 03:47 AM   #10
Roy Matson
Member
Canada

Roy Matson is offline
 
Roy Matson's Avatar
 
Join Date: Apr 2004
Location: Vancouver
Posts: 463
Your circuit is OK for 4 wire instruments but your 2 wire instruments need +/- 24VDC also. If you looping wires down the terminal strip for example -24VDC I like to loop back to the point of origin in case a jumper falls out. You will also need short circuit protection, I prefer minature circuit breakers over fuses.
Roy
  Reply With Quote
Old July 7th, 2011, 06:57 PM   #11
syavash_rus
Member
Iran

syavash_rus is offline
 
Join Date: Jul 2011
Location: Karaj
Posts: 4
Hello every one

I have a serious problem here with two PLCs , S7-400 and S7-200. The problem is, I have a single sensor which I need to connect to both 400 and 200 CPUs. Unfortunately I have no possibility to make a network because 400 DP and MPI ports are already reserved for communicating with other PLCs and the port on the 200 is reserved for a HMI. I thought I can import the analog signal to s200 and send it to the s400 using the analog output card (232-0Hd22). But I donít know if itís possible to use an output module on the s200 as an input for an input module on a s400. Please helpÖ
By the way, the connection on the S200 output includes 3 terminals (M0 V0 I0) but the analog input card on the s400 includes only 2 wires (A+ A-)
  Reply With Quote
Old July 7th, 2011, 07:17 PM   #12
geniusintraining
Lifetime Supporting Member + Moderator
United States

geniusintraining is offline
 
geniusintraining's Avatar
 
Join Date: Jun 2005
Location: SC
Posts: 3,915
Hello syavash_rus,

You should start a new topic not a old one

You can add a profibus module to the 200 (depending on the 200) ??

Welcome to the site....
__________________
www.PLCCable.com PLC Communication Cables, PLC Trainers, Fluke Meters, Programming Lessons, MicroLogix 1400, 1100, 1000 and 1762-I/O, coming soon WERA Tools.... all your automation needs
  Reply With Quote
Old July 7th, 2011, 08:14 PM   #13
syavash_rus
Member
Iran

syavash_rus is offline
 
Join Date: Jul 2011
Location: Karaj
Posts: 4
oh sorry. thank you anyway. I can't add a new profibus module because I have no access to one in job site. I was wondering if some one could say how I can use the analog output and inputs to transfer the signal.
  Reply With Quote
Old July 7th, 2011, 08:15 PM   #14
cjd1965
Member
United Kingdom

cjd1965 is offline
 
Join Date: Apr 2007
Location: UK
Posts: 1,236
Hi
I always wire in 2 core screened cable direcly to the plc and always connect the sceen at the plc end only. cable segregation is always good too. In the field we aim for 300mm minimum segegation between power and control cables , which typically means seperate trays. In the panel this segregation is almost impossible so we use the split duct tyoe and ALWAYS route as far as possible from inverter cables etc
  Reply With Quote
Old July 8th, 2011, 07:41 AM   #15
dogleg43
Member
United States

dogleg43 is offline
 
Join Date: Dec 2005
Location: Indiana
Posts: 155
Attached is a drawing we put together to refer to when connecting analog devices.

NOTE: We didn't go to the trouble of showing the wiring as shielded-twisted-pair. That should be understood.
Attached Files
File Type: pdf Analog_Instrument_Connection_Examples Model (1).pdf (46.1 KB, 196 views)
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
A PLC simulator with analog input \ output emulation KaktusJack LIVE PLC Questions And Answers 2 February 5th, 2008 03:21 PM
Wiring? (for PLC system-but not PLC related) grnmon97 LIVE PLC Questions And Answers 12 January 4th, 2008 11:53 AM
How to calibrate a load cell & how to program mitsubishi plc for analog input M. HASSAN LIVE PLC Questions And Answers 1 February 19th, 2005 06:10 AM
AB PLC analog input card 1771 IFE diribarren LIVE PLC Questions And Answers 13 May 9th, 2003 10:40 PM
Connecting self-powered analog signal to Moore PLC shyampv LIVE PLC Questions And Answers 2 May 13th, 2002 09:49 AM


All times are GMT -5. The time now is 04:41 PM.


.