Limit issue of 32768 in ControlLogix

sns · Jun 13, 2011

Hello there

I have a control logix 5555 system installed. I am having problems with the word limit of 32767 even though I've made the tag Real, float.

I did the same thing (making the int ---> float) with SLC500 and it does work till 99999.

How to do the same in control logix?

rdrast · Jun 13, 2011

A real doesn't have a limit of 32767. Nor does the native data type in Control Logix, which is a DINT.

The only place you should see a limit of 32767 would be if you are using a plain INT value, or perhaps from an I/O module set to 16 bit integer, or if you have a limit test somewhere in the program.

If you only need whole numbers, then use the DINT datatype. That can easily accommodate 99,999.

sns · Jun 13, 2011

I was using INT intially and have moved to float now but the results are the same. It is actually a controller tag, (an add instruction) serving as a totalizer.

rdrast · Jun 13, 2011

Then you still have INT's somewhere in the AOI logic, or as an In, Out, or InOut parameter.

Post a shot of your logic.

sns · Jun 13, 2011

Attached is the pic

rdrast · Jun 13, 2011

Well, I don't see an example of a limit there.

Are you getting to a point where no matter what you add, the totalizing register never increases? Because if that is the case, then you are just running up against the dynamic range limit of approximate (floating point) values. No matter where the decimal point is, you only have 7 digits of significance in an IEEE 32 bit float.

Adding 0.001 to 10000 won't get you anywhere.

sns · Jun 13, 2011

That precisely is the problem as you mention.

Any solutions?

rdrast · Jun 14, 2011

sns said:
That precisely is the problem as you mention.

Any solutions?

You could try normalizing everything to discrete units, and use a DINT for your totalizer register.

sns · Jun 14, 2011

rdrast said:
You could try normalizing everything to discrete units, and use a DINT for your totalizer register.

Thanks for the tip.

What I've done now is that I've divided the value to be added to the total by 1000 and multiplying it again by 1000 in RSview. Not the tech fix, but then it'll be reset before it ever reaches there.

Limit issue of 32768 in ControlLogix

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