runningdelta(), but for string signals

[David Edelman]

We have string-type signals that show the current operating mode. On the historian, these signals have a compression setting of 8 hours, meaning a new value is written no later than 8 hours after the previous value was written. So during any 12 hour period, there will be 1 or 2 values written to the historian even if nothing has changed.

We are trying to count the number of changes to the string signal during a 12 hour period. For numeric signals, we can use 

$signal.remove($signal.runningdelta() == 0)
.aggregate(count(), $capsule, durationkey())

This makes sure that if the numeric signal (also with a compression setting of 8 hrs max) does not actually change during the 12 hour period, that data point will not count.

Is there an equivalent way for doing this with string signals? 

Thanks, David

[Joe Reckamp]

Hi David,

You could do the following to create a capsule per each change in signal value (regardless of string or numeric):

$signal.tocondition()

And then you could count the capsules that are created.

[David Edelman]

Thanks Joe - unfortunately this still gives a count of 1 even when there are no changes.

Intervention - Mode Chg = 

$mode.toCondition()
.aggregate(count(), $s, durationkey())

Thanks, David

[Joe Reckamp]

Hi David,

You could either:

(1) subtract 1 from the count as it will always have the starting value as a capsule, meaning the value will always be number of changes + 1

or 

(2) use $signal.tocondition().starts(), which will make the capsule only appear at the start (or specifically the time when a change is made)

[David Edelman]

13 minutes ago, Joe Reckamp said:

(2) use $signal.tocondition().starts(), which will make the capsule only appear at the start (or specifically the time when a change is made)

This seems to work in our case. Thanks!