RsLogix 500 Program Help

Hello all,
I need help understanding the logic concept behind this the attached file. I’ve been at it for about an hour, going on for about 21 hours without sleep starting up a new system, I think my brain is falling asleep here.

Anyways this is for a load hopper with an screw conveyor that unloads a given weight, I think N7:9 is the preset weight to be unladed from the HMI, but I don’t have a exact description.
What bothers me is the value in N7:10 it just does not calculate. I:15.2 is a analog signal from the weight system.
Any help greatly appreciated.

The SUB instruction on rung 2 is initiated by a 1-shot, meaning it will only execute ONCE each time 'Run forward' changes from OFF to ON.



-Eric

Assuming N7:10 is not written-to somewhere else, the calculation is a one-shot-rising which means if the values in either N7:8 or N7:9 change (and there is no reason to think they can't or haven't) no calculation will be done unit the next OSR trigger.

Looks like Eric got to it first....

To follow up, I think it works something like this:

When the system is started, it calculates how much to unload (N7:10) by subtracting the desired amount (N7:9) from the current scaled value (N7:8). This is only done at the start of the process (hence the one-shot). The value in N7:10 will not change until restarted.

The 'How Much to Unload' value (N7:10) is constantly subtracted from the current scaled value (N7:8) to determine how much has been unloaded.

The additional subtraction of 20 might be a 'tare' weight, or maybe to prevent emptying completely? In any case, the result goes in N7:68

Once completely unloaded (N7:68 greater than or equal to zero in rung 0), the system shuts off.

Of course, I could be wrong...



-Eric

Thanks all,
Erik I think you nailed it.