Strange behaviour of the CPU

Hello,

I cant understand whats happen in the PLC 115U, CPU945.

The program in the CPU is much more complicated but I put simple example for better understanding of the problem.

example:

segment 1

A       F0.0

AN    F0.0     "always 0"

=       F0.0

AN    F0.0

=       F0.1    "always 1"

segment 2

O   F0.1                "always 1"

O   I 125.0            "sensor"

=   F188.0             "Temporary flag"

segment 3

A   F188.0              "temporary flag

JC  FB100              " ALARM"

When F188.0 become 0 there is an alarm on the machine. That is why I125.0(sensor) should be 1 for proper operation of the machine. The problem is that F188.0 becomes 0 (for a moment) when the I125.0 (sensor) is even 1.  I put F0.1(alwayas 1) in segment 2 in order to see what causes the problem(sensor or logic) and the same thing happen.

This happen from time to time.

There is hundreds of temporaty flags in the program and different flags becomes 0 in diffrents part of the program. 

What causes this mess???

Hi

it may be input card problem

don't use any flags, Try this

A I 125.0

AN I 125.0

= F 188.0

JC FB100

If it works then your input card may have some problem

iamnayak

Hi

it may be input card problem

don't use any flags, Try this

A I 125.0

AN I 125.0

= F 188.0

JC FB100

If it works then your input card may have some problem

 It isn't input card problem . I've bypassed the sensor by putting "always 1" instead of sensor in order to exclude any hardware and there is still problem. I think that something in the logic is wrong but I don't know how to find it.

Hi gregory245,

in addition to fritz suggestion :

download to cpu a new DB (DBx) (to be sure do not work with used flags )

add this code :

C DBx

AN I125.0

S D0.0

A F0.0

S D0.1

AN F0.1

S D 0.2

A F188.0

S D 0.3

And look status of DBx bit 0.0-1-2-3.

Let us know what happen.

Regards

Thank you for your help.

After compressing PLC memory the problem disappeared.

Best Regards,