I'd like you to try to determine from a set of data
which values would pass the exception test given
certain exception specifications
so if you take a look at this example here
we've got
three attributes we need to keep in mind as we look
at this set of data
that extends forward in time here
so these are PI values
for a PI tag that has
the excdevpercent setting at 2
and that excdevpercent is a measure of the dead band that we use for exception testing
and it's a measure thatís in excuse me, in percentage of range
now we also support in addition to excdevpercent
there's also an attribute called excdev in which we would simply measure it as engineering units
but in this case we specified it as excdevpercent
excdevpercent essentially is just a second way
of writing that exception deviation, that dead band
so with a span
that ends up being 200
with that span of 200 with the excdevpercent of 2 percent of span
that means in raw engineering units
it's actually going to be 2 percent of 200
that's the kind of change we are looking for
they would pass the exception test
so that would be 4 engineering units 2 percent of 200 is 4
now in addition we've got this exception maximum say at 180
that's in seconds
if that much time elapses
we will go ahead and bring in a value
whether the exception deviation
has been violated or not
now there is a point I should make about that exception max
with the exception max
if the value is at exactly 180 seconds after
in other words when that 180 seconds has expired
Then that would be something that would pass the exception test so
it's going to be a greater than or equal function that we are using here
so given that set up and given that the first value comes in at 70.3
let's take a look at how we would calculate this
now with 70.3 we add or subtract 4 engineering units to that, that's
the 2 percent of the span of 200
add or subtract 4 engineering units and that's the dead band we're looking to go beyond
so the 74.3 down to 66.3
I don't see any of these values going outside that dead band
that's not less than 66.3 that's not greater than 74.3
and this is not greater or less than but actually at this point in time if you noticed
we've got sixty one hundred twenty two
one hundred and eighty seconds at this point
one hundred and eighty seconds has expired
has passed transpired
and so that means that this value right here because it is
is greater than or equal to the exception maximum because this differential between
this time stamp and this time stamp right here
it's a 180 seconds or greater
and that means that, that will get a free ride
so at this point we start the whole thing over again now using this as the linchpin
So we are
looking for anything that is either 180 seconds out from this time stamp
or something that goes
above and below the 70.1 plus or minus 4 engineering units
and this case what would that be
that's going to be 74.1 down to 66.1
well that is not greater than 74.1 or less than 66.1
however this
is less than 66.1
that's the 70 minus 4 engineering units
so this value here
will also be
going to the snapshots so now we've got this value here
and this value here would be the next snapshot event
and then we start the whole thing over again
and now using 66
so it's 66 we are looking for something that goes either to 70 or down to 62
that doesn't make it that doesn't make it but this does this actually passes on two counts
I suppose
first of all because it's less than 62
and also it's been exactly 180 seconds
so in this case we bring this value in
so in summary
What we see is this value right here
Now this value right here
and then this value right here are the values that actually pass
the exception test