Daily Earliest Tag Value Extraction

General Discussion
1

Hello all,

I am trying to extract a counter value once the machine is ON, at the start of the first shift.
I used query tag (cast function and MIN value involved), but in some cases, it does not work.
So, I was wondering, what different approaches can be applied?

2

You could use a value change or quality change event on your ‘Machine ON’ tag. Something like

if currentValue.value == 'ON':  //only works when value was OFF and is now ON
  //Read the odometer count tag
  count = system.tag.read('counterTagPath').value  
  //Write count to memory tag for holding start count
  system.tag.write('dailyStartCountTag',count)
3

What about querying to the min timestamp of your data?

4

Hello, JordanCClark, how such query will looks like?

5

That depends, what does your table look like? :wink:
Also, what database are you using?

6

An example may look like:

SELECT count_value 
FROM my_table
WHERE t_stamp > '2020-05-21 06:00:00'
ORDER BY t_stamp
LIMIT 1
7

You could also use less than, if you want the last value before the start of shift.

SELECT count_value 
FROM my_table
WHERE t_stamp < '2020-05-21 06:00:00'
ORDER BY t_stamp DESC
LIMIT 1
8

Got.error "incorrect syntax near LIMIT…"Strange, because the syntax seems correct.

9

What kind of database? Some don’t have LIMIT, but use TOP n instead.

10

Oh, yes, it is SQL Express.

11

The proper syntax for SQL Server Express (my case) is:
SELECT TOP 1 count_value
FROM my_table
WHERE t_stamp < ‘2020-05-21 06:00:00’
ORDER BY t_stamp DESC,

but such query will not work for me, since it uses fixed date, and I need this query to be executed every time the machine has been started, on the current date.