Plcs & their failuers


Thread Starter


I use various International PLCs & I face a memory corruption problem contineously in a PLC
from leading manufacturer from USA.
Can anybody guide me in this regrd?
I would bet you have noise on the power to the PLC, I have eliminated this type of problem with a Schaffner EMI filter on the power input to the plc and use of MOV's on all inductive loads.

Jocko Harmet

What is the environment that the PLC is in stalled in? What is the power supply voltage? Do you have large inductive loads on the same power supply? A little more information about your application would help.

Zan Von Flue

I would not generalize this to all PLC's. I personally use S5's and S7's for the past 10 years and !never! had a bad CPU memory. I believe also in AB. This is the strong part of PLC's. If I where actually having a continued problem with a PLC I would first check my programming, then I would contact the supplier and see if maybe it was a bad "series" of PLC's and there is a recall.


Eduardo Manuel C. Cipriano

I have been with Allen Bradley for almost 4 years as a Technical Support and our customer does'nt experience this because we make sure that they follow the standards set by AB and we have a customer a Cement plant as you know this kind of plant produces a lot of noise because they use a lot of High Voltage Motors if you experience some trouble in Communications try using a Fiber optic Link because it is not affected by noise producing equpment.

Email me if you have problems. Im not with the AB anymore, Im presently working with Yokogawa DCS now as SR. Systems Engr.

Eduardo Manuel C. Cipriano
Sr. System Engr.
System Engineering Department
(632) 634 7547 loc 165
email: [email protected]

Further to this the configuration details are as follows.

1.SLC 5/03 + SN MODULE (RIO network)+Panelview 900

2.SLC L40C X 6 nos hooked up on RIO network +
3.Flex I/o X 6 nos modules on RIO

Following precautions taken under system integrator & manufacturers supervision.

1.PLC metallic body isolation from control panel

2.Separate earth pit for PLC ground.(Electrical Power has separate pit)

3.PLC 220VAC power thro isolation transformer.

4.On RIO network terminating resistors.

5.MMIs communicating with SLc are powered from USER outlet power from SLC.

Other information

Totaly 10 to 15 no of sites installations.
With above precautions problem has not reduced
to 100 %.

What should be the reason?
Since AB is a largest manufacturer its little bit hard to suspect the hardware failure???



Just off the top of my head:

You say that the PLC has it's own ground. How about the MMI's and RIO equipment? Are they grounded to the same ground as the PLC, or to the main power ground? You could be getting a ground loop through the common lead or shielding of your communication lines.

There was another thread concerning SLC processors lowing their memory. Is it tied to a power cycle, by any chance? Check thru the archives of the list for suggestions on eeprom settings, etc.

--Joe Jansen

I have faced memory corruption twice, once in a 5/40 redundant system where the backup took over due to hectic startup, and non repeatition of
the problem, a chase was abandoned. A few years later in a 5/40E which was non-redundant, However the plant was under shutdown and only startup was delayed by ten minutes.

In the second instance there was a big motor which was started when this problem occurred.

I would check for any harmonics on the power supply.

The next is a problematic component in the hardware, which is difficult to believe since AB may have stringent procedures for selecting
components and also very difficult to identify.

I never had a third opportunity, so could not check further, but harmonics is a strong choice.