Freezing of IBD inputs on Allen-Bradley PLC5

S

Thread Starter

Sahay

Using RSLogix5, A PLC-5/40E was programmed. There are 2 1771-A3B I/O chassis. Second chassis has ASB adapter, 5 IBDs and 4 OW16 modules. The 1st chassis has PLC, 1785-DMC1A, 1771-MCM, 2 IFEs, 2 OFEs, 1 IBD and 2 OWs modules. Both chassis use P4 power supply modules and the I/O modules are in the above said order in chasis.

Once in a while, I find that the bottom 8 inputs (out of 16) of any one IBD module are frozen in the PLC Input Data table. The changes in field signals are reflected by the IBD module LEDs properly (on/off) but the corresponding Data Table in the PLC Input file do not change. In such a situation, I have to recycle the chassis power to make everything work properly.

This happens very randomly - on different IBDs modules and may be once in 2 to 3 months!

Can someone throw some light on this problem?
 
A

Anthony Kerstens

Is this a communications delay in RSLogix?
Have you attempted to swap out components, including the rack?

Anthony Kerstens P.Eng.
 
Hello Sahay,

I have a couple of questions about your system.

Question 1) what is the 1771-MCM module? I cannot find reference to it anywhere. Is this module the 1771-HS Motion Control Module?

Have you calculated power draw in your processor chassis? Here are the numbers I came up with based on the information you provided.

module draw qty total
-------------------------------
PLC-5/40E 3600
DMC1A 4000
MCM(1771-HS)720 1 720
IFE 750 2 1500
OFE 1500 2 3000
IBD 250 1 250
OW 700 2 1400
-----------------------------
total 14,470mA

I am assuming the MCM module is the 1771-HS Motion Control Module. I hope that you have more than 1 P4S slot mounted power supply in the chassis. If you do not I would say that is the cause of your problem. By the way the P4 power supply can deliver 8000mA of power individually.

Here is the power draw data for the Remote chassis
module draw qty total
-------------------------------
ASB 1000 1 1000
IBD 250 5 1250
OW16 1300 4 5200
-------------------------------
Total 7450mA

How hot does the ambient temperature get in the remote chassis? If ambient temp gets too hot power supply derating could be having an effect in this chassis.

One more question. What addressing scheme is being used in the chassis 2,1,or1/2 slot?


Bradley G. Hite
Vice-President
Intertech Inc.
mailto:[email protected]
ICQ# is 38746036
http://www.myplc.com
Teaching Practical Skills For a Technological World
 
M

Michael Klothe

Dear People:

The cause of this predicament is rather obvious (to me, at least). The soulution may not be so obvious at all.

The lower 8-inputs are being forced off in some way. I don't necessarily mean "forced" in the sense of forcing a bit using a force table, so much as the lower 8-bits being written to with a word which has all 0's in the word's lower 8-bits.

Other possibilities are a failure in the chassis backplane, and of course the all too obvious one of module failure.

Have their been any program changes since the onset of the problem? If the program has been changed, and the problem did not occur beforehand, the program is the obvious culprit.

If you are dead-dog certain there has been no program change whatsoever prior to the start of the problems, then I'd check the chassis backplane first (by substitution), then the module(s).

If more than one module is affected, it strong points to the backplane as that is one common element among all modles.

Regards,

Michael E. Klothe
ELECTRICAL DESIGN & CONTROL, INC.
Detroit, USA
 
B

Blake Burgess Averydennison

We had a similar problem with a remote rack of our PLC-5 system, except that our outputs were dropping out. We replaced all the components, one at a time. The last change we made was to replace the blue hose to the next rack which was only about 6 feet long with one about 15 feet long.
It's been three months since last occurrence.
Previously, we had problem about once a month.
 
Thanks. I have changed IDBs and ASB. Did not change chassis as there are 2 12-slot chassis and the problem occured on either one at a time. So, I did not suspect the chassis. However, I am going to change those too.

Sahay
 
Brad Hite wrote:
> I have a couple of questions about your system.

> Question 1) what is the 1771-MCM module? I cannot find reference to it anywhere. Is this module the 1771-HS Motion Control Module?<

Its a 3100-MCM, Prosoft module.

> Have you calculated power draw in your processor chassis? Here are the numbers I came up with based on the information you provided.<

I am using 16 Amp power for each chassis.

> module draw qty total

> -------------------------------

> PLC-5/40E 3600
> DMC1A 4000
> MCM(1771-HS)720 1 720
> IFE 750 2 1500
> OFE 1500 2 3000
> IBD 250 1 250
> OW 700 2 1400

> -----------------------------

> total 14,470mA

> I am assuming the MCM module is the 1771-HS Motion Control Module. I hope that you have more than 1 P4S slot mounted power supply in the chassis. If you do not I would say that is the cause of your problem. By the way the P4 power supply can deliver 8000mA of power individually.

> Here is the power draw data for the Remote chassis

> module draw qty total

> -------------------------------
> ASB 1000 1 1000
> IBD 250 5 1250
> OW16 1300 4 5200

> -------------------------------
> Total 7450mA

> How hot does the ambient temperature get in the remote chassis? If ambient temp gets too hot power supply derating could be having an effect in this chassis.<

Its a control room condition.

> One more question. What addressing scheme is being used in the chassis 2,1,or1/2 slot?<

Single-slot addressing used.
 
>Have their been any program changes since the onset of the problem? If the program has been changed, and the problem did not occur beforehand, the program is the obvious culprit.<

No program changes at all. This problem is seen from day one of commissioning.

>If you are dead-dog certain there has been no program change whatsoever prior to the start of the problems, then I'd check the chassis backplane first (by substitution), then the module(s). <

Only thing not changed so far is the chassis of ASB module. I am going to do that.

>If more than one module is affected, it strong points to the backplane as that is one common element among all modles.<

All IBDs sitting in both 12-slot chassis have failed one time or other. very strange!
 
This used to occur frequently after commissioning the system. Now the frequency has reduced to once in 3 months roughly (although, its a continuous process control).
 
D

Darren Tichbourne

This one kind of reminds me of a recent experience I had with a 25yr.old mini PLC-2.
It started by dropping out the run mode on occasion. Recycling the AC power would place the processor back into run mode. Then several days later , the processor would loose parts of the ladder program. I suspected the power supply might be flaky, so I swapped it out, problem came back next day... When I was in the midst of these problems I was even having a rough time simply connecting to the old plc with my T47 laptop... for the first time ever I saw an error message 'link is noisy' on the old laptops display.
To make a long story short... i ended up removing all the cards from the rack and cleaning the gold edge card connectors... a product called
Stabilant 22 (liquid) was used to recoat the gold surface, it leaves a residue so when you plug card back into rack it makes a perfect mating
connection. The problem was cured and the faithful soldier(Mini-Plc-2) from the 70's
lives on.

I know the PLC-2 specifically had built in monitoring circuitry on each of the power supply outputs. In the power-up sequence and also during normal operation, outputs are checked for possible overvoltage, undervoltage and overcurrent conditions. Detection of any of these causes supply to shut-down requiring power to be recycled...
I missed the beginning of PLC5 freezing input thread and the details... conditions when it is stopped ...run light on/off? etc etc
Perhaps I could offer some assistance ... pardon me for missing the boat on the original message.

Sincerely,

Darren Tichbourne
President, System Integrator, CET
CompuSys Solutions
___________________________________________________________
Email : [email protected]

Website: www.CompuSysSolutions.com
 
Top