Hi everyone,

I started to work on PIAF 2-3 weeks ago and I would like some help for an issue that I have. My objective is to construct an individual measurements control chart with PIAF analyses (expression).

The measures are vibrations and come from PI system. Below, a sample of my values:

Date | Value (mm/s) | MR |

21-juil-17 00:00:00 | 2,202375345 | |

21-juil-17 04:00:00 | 2,110626916 | 0.09174 |

21-juil-17 08:00:00 | 2,228930486 | 0.11830 |

21-juil-17 12:00:00 | 1,935820779 | 0.29310 |

21-juil-17 16:00:00 | 2,202027916 | 0.26620 |

21-juil-17 20:00:00 | 2,309684407 | 0.10765 |

22-juil-17 00:00:00 | 2,436398957 | 0.12671 |

So, I need to compute UCL (UCL = /x + 3 * /MR/1.128 ; LCL = UCL = /x - 3 * /MR/1.128).

/x is average of column value. (computed with TagAvg() like the screenshot below).

/MR is the average of the column MR. MR = |value _{i} – value _{i-1}|

My problem is to compute /MR with PIAF. I don't know how could I do this because when we use an expression we can't have the same attribute in input and in output.

Maybe you have an idea to do that (I hope).

Thank you for your time,

Simon.

Hi Simon,

If I got it right you have,

UCL = (x + 3 * MR)/1.28

LCL = (x - 3 * MR)/1.28

MR = |value

_{i}– value_{i-1}|So your main problem is how to get the delta between the current value and the previous one, right? If that's the case, there is a function called DeltaValue that does exactly what you are looking for:

I hope it helps!