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PLCC Communication

06/04/2015 12:49 AM

Dear all,

In my PLCC communication, I have received Carrier channel fail alarm frequently??

Why this alarm came?

What are all the things I have to check to resolve this problem?

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#1

Re: PLCC Communication

06/04/2015 4:44 AM

Check the communication protocol and error logs.

If not available set up error log and protocols.

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#2

Re: PLCC Communication

06/04/2015 12:59 PM

If the failure is intermittent, that is, sometimes it works and then it just drops out, there is a more than 80% likelihood that you have a connector problem. It could be a bad crimp, bad solder joint, twisted contactor or pin, cable with too much strain etc.

I always say that in cases like this that there is no such thing as an electrical failure. It is almost assuredly mechanical, as in falling out of the plug or something less obvious.

If you can't isolate the offender, then you will just have to start replacing hardware until you eliminate the mechanical breakdown. After all, the electrons are willing but they can't perform mechanical miracles.

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#3

Re: PLCC Communication

06/05/2015 9:55 AM

Is the equipment properly rated for the environment and application it is located in? If not, get the right equipment for the application.

Fiber Optic? Or Copper?

If fiber: What are the db losses of the channel? If high db losses are present look for a loose connection or bad finish on the fiber termination(s) at the demarcation panel. Is the fiber of the correct diameter and type? Multi-mode or single-mode? Is the laser failing and/or the intensity too low?

If copper; Is the communications cable of the correct size, correct type, and length? Does the cable conductors have the correct "twist-per-inch" ratio for the application?(As already suggested.) Check for loose or corroded connections. Was the correct terminations used on the conductors and are they properly installed.

How many devices are the PLC polling? Or; How many other devices/PLC units are in the communication loop/ring? It could be that the system polling table is not set up correctly or there are too many devices on the communication network. Is the system communications speed set correctly to match all equipment capability?

Is the bandwidth of the communications system large enough to accommodate all devices currently in the system?

Is the fault due to length of package or collisions or loss of signal?

Have you invoked the system troubleshooting to find out al information available on the fault?

If unable to answer the above questions, I suggest you contact the field service group for the PLC OEM and get help in diagnosing the issue(s).

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#4
In reply to #3

Re: PLCC Communication

06/05/2015 4:02 PM

PLCC means Power Line Carrier Communications. The power conductors are used as the transmission medium of the communications system by superimposing a carrier signal on top of the power. So there would be no separate comm line, that's the entire point of it.

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#6
In reply to #4

Re: PLCC Communication

06/05/2015 6:22 PM

You may well be correct if their system is old and outdated.

I remember that type of communications well from my youth.

It would do my soul good to see one of the old systems still in operation and it would bring back some good memories.

We have not used that type of communications since the mid 80's.

Today most of our power transmission and distribution systems utilize Fiber Optic Ground (FOG) or MTO type static lines for communications with either a PLC, J-MUX, ORION, or RTAC unit at each end for control and comms.

These are multi-conductor fiber optic cables encompassed with steel, aluminum, or copper conductors and they are used as the static conductor(s) on towers and poles.

Those that do not utilize FOG/MTO usually have ADS fiber optic running at a safe distance below the overhead power conductors from tower-to-tower or pole-to-pole.

Fiber optic communication are much more reliable during storms as static buildup and lightning does not normally affect them.

If the OP is indeed working with an old Pilot Wire system, then the issue will require some very specialized troubleshooting skills that may not be easily attained in today's workplace.

I am up for a trip to wherever they are just to see the equipment and I would really enjoy invoking my old troubleshooting skills in a "real time" situation.

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#7
In reply to #4

Re: PLCC Communication

06/07/2015 12:38 AM

Maybe. OP needs to define, you know how it is with acronyms.....

...but PLC(C) is outdated, though there was one Nepalese chap with a PLC question about a legacy system some time ago here so it may still be around.

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#5

Re: PLCC Communication

06/05/2015 4:22 PM

Generally, communications errors on PLCC systems are the result of severe common mode noise in your system, or severe line notching on the power lines, where the line notch actually drops below the zero cross repeatedly. That is often caused by things with large thyristors firing in phase-angle control mode. Look for old motor drives, big power supplies, UPS systems, battery chargers, rectifiers, or even newer but defective electronics devices and things like lighting ballasts connected to the same power lines as are being used for your PLCC.

Your PLCC system will have filtering designed to avoid these kinds of issues, but filters have components that get stressed if they have to work too hard. So keep in mind that it may be a combination of events. If you change out the interface boards and it solves the problem, keep in mind that something CAUSED them to fail, so you still need to investigate everything else.

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