I have an issue with an inherited PLC-5 program on a 5/80E processor. I think I know what the issue is, but can't quite put it into words to explain it to others.
The program is totalizing flow values via some math in a CPT block (that uses the scan time from the PLC (S:8, around 40ms) as update the time component) this outputted snapshot value (F28:25) is then the "Source A" in an ADD block that is added to a float value (F28:280) in "Source B", then the F28:280 tag is used again as the "Dest" of the ADD block. Seems pretty standard operation for all of the PLC's at this site, and they have had no complaints in the past on data being incorrect. These totalizers were typically reset before reaching a value of 7.000 (million gallons). Recently we have been doing some testing and the totalizers appear to lose their resolution at larger values and the totalized value "slows down" even though the flow that is being totalized remains constant. They appear to stall out entirely at values approaching 16.000.
I'm thinking the small snapshot value (around 5.00E-007) is too small to register with the F28:280 Float once the totalized value it holds rolls over into two digits left of the decimal. Does this make sense? I can't think of any other reason that a Float would just quit climbing. Thanks in advance!
The program is totalizing flow values via some math in a CPT block (that uses the scan time from the PLC (S:8, around 40ms) as update the time component) this outputted snapshot value (F28:25) is then the "Source A" in an ADD block that is added to a float value (F28:280) in "Source B", then the F28:280 tag is used again as the "Dest" of the ADD block. Seems pretty standard operation for all of the PLC's at this site, and they have had no complaints in the past on data being incorrect. These totalizers were typically reset before reaching a value of 7.000 (million gallons). Recently we have been doing some testing and the totalizers appear to lose their resolution at larger values and the totalized value "slows down" even though the flow that is being totalized remains constant. They appear to stall out entirely at values approaching 16.000.
I'm thinking the small snapshot value (around 5.00E-007) is too small to register with the F28:280 Float once the totalized value it holds rolls over into two digits left of the decimal. Does this make sense? I can't think of any other reason that a Float would just quit climbing. Thanks in advance!