GE 90-30 UPCTRs

ogimoj

Member
O
Join Date
Dec 2003
Posts
22
I've got a couple of questions about the operation of up-counters in a GE 90-30:
Question #1:
if I use a &NOCON on the Reset line which is fed from the coil on the output line,
 

  |

  |%M0001  +-----+           %M0002

  +--] [--->UPCTR+-------------( )--

  |        |     |

  |        |     |

  |%M0002  |     |

  +--] [---+R    |

  |        |     |

  |        |     |

  |%R00002-+PV   |

  |        |     |

  |        +-----+

  |        %R00001

  |


in the logic following this rung, will %M0002 be true for the remainder of the program sweep (scan) on the sweep in which %M0001 increments CV to PV?
I guess the question comes down to the logic sweep sequence: is it down then across or across then down?

Question #2:
If the PV of a counter (not the counter in question 1) is 0, is the counter always done (assuming I'm never moving a negative number (or any number) into CV)? Even when the R is being held true?

Thanks,
John
 
Question 1: Yes, %M0001 will be true for one scan when the counter's accumulated value (%R0001) reaches the preset (%R0002). The logic sequence is to treat everything on the left side of the UPCTR function as data required to execute the function and everything on the right side as data controlled as a result of executing the function.

Question 2: The output of a counter is true when the accumulated value is greater than or equal to the preset value. In your example, since reset drives the accumulated value to zero, the output will be on regardless of the state of power flow at the R node.
 
Good observation Smoke, except that the example is valid.

It's true that the GE Fanuc UPCTR uses three consecutive registers. In the example, that would be %R0001, %R0002, and %R0003. The first of those registers (%R0001) is for the accumulated value. The second register (%R0002) is for the preset value. If you program a constant at the PV node of the function, the constant value will get copied into %R0002. So, it's OK to use the second of the three consecutive registers at the PV node. When you do that, you need to make sure that you provide a way to get a value into the second register.
 
Thanks for keeping an eye out for me, but I'm doing exactly what Steve mentioned: moving a value in to the PV from another location. That way, the number of counts can vary depending on other conditions.
 
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