TIA Portal v18: How can I ADD 6 months to a date?

[Mas01]

I'm getting stuck again.

Operator enters date when calibration was performed.

I want to ADD 6 months onto that date - this will be the due date for the next calibration.

How can I add 6 months in ladder logic?

See picture for data block declaration of tags:

 

[L D[AR2P#0.0]]

Here's a function to do the job - if you want it in ladder then you will have to convert it yourself. NB tested in a S7-1500 plc.

FUNCTION "fc7_AddSixMonths" : Date
{ S7_Optimized_Access := 'FALSE' }
VERSION : 0.1
   VAR_INPUT 
      dtLast : Date;
   END_VAR

   VAR_TEMP 
      DTL1 {InstructionName := 'DTL'; LibVersion := '1.0'} : DTL;
      myDTL1 AT DTL1 : "myDTL";
      DTL2 {InstructionName := 'DTL'; LibVersion := '1.0'} : DTL;
      myDTL2 AT DTL2 : "myDTL";
   END_VAR


BEGIN
    #DTL1 := DATE_TO_DTL(IN := #dtLast);
    #DTL2 := #DTL1;
    
    #myDTL2.usMonth := #myDTL1.usMonth + 6;
    IF #myDTL2.usMonth > 12 THEN
        #myDTL2.usMonth := #myDTL2.usMonth - 12;
        #myDTL2.uiYear += 1;
    END_IF;
    
    #fc7_AddSixMonths := DTL_TO_DATE(IN := #DTL2);
END_FUNCTION

 

[L D[AR2P#0.0]]

example call:

 

[L D[AR2P#0.0]]

UDT:

TYPE "myDTL"
VERSION : 0.1
   STRUCT
      uiYear : UInt;
      usMonth : USInt;
      usDay : USInt;
      usWeekDay : USInt;
      usHour : USInt;
      usMinute : USInt;
      usSecond : USInt;
      udNanoSecond : UDInt;
   END_STRUCT;

END_TYPE

 

[Mas01]

Thanks LD.

I tried that and got these error messages (see pic).

I clearly know nothing about SCL.

 

[Mas01]

Another screenshot , if it helps:

 

[drbitboy]

 

[Mas01]

View attachment 66067

So where I've got the pink boxes, do I define them as type "Date"? I'm lost.

 

[drbitboy]

Two approaches: the one-instruction approach from the previous post; another using DTL, if you want to keep the same day-of-month less than 29.

Both handle leap-days in their own way: with the simple approach it is built-in; the complex approach simple disallows leap-days in the result.

You declare the variables as shown (DATE, DTL, USINT) in the DB window.

​

 

[drbitboy]

P.S. adding 182 days with the simple approach keeps it on the same day-of-week.

 

[mk42]

Honestly, calendar math is super hard. There are so many corner cases: leap years (except the ones that aren't), months with different numbers of days...

I think drbitboy's ideas are solid. Is 6 months-ish good enough? If so, I'd just add 30 days * 6 mo = 180 days (or the 182 or 183 from above) and move on. If not.... check for as many corner cases as you can think of. DTL makes it easy to parse the date/time, but unfortunately it isn't magic, and the PLC doesn't automatically shift everything if the month suddenly becomes 14. It just fails when you try to use the DTL later.

 

[Mas01]

Honestly, calendar math is super hard. There are so many corner cases: leap years (except the ones that aren't), months with different numbers of days...

I think drbitboy's ideas are solid. Is 6 months-ish good enough? If so, I'd just add 30 days * 6 mo = 180 days (or the 182 or 183 from above) and move on. If not.... check for as many corner cases as you can think of. DTL makes it easy to parse the date/time, but unfortunately it isn't magic, and the PLC doesn't automatically shift everything if the month suddenly becomes 14. It just fails when you try to use the DTL later.

Agreed, that's a very pragmatic approach!

 

[Lare]

Siemens 300 example from old plctalk threads.


http://www.plctalk.net/qanda/showthread.php?t=15323

 

[Lare]

Also oscat basic (S7) free library should have date_add function.



(haven't never tested it)



http://www.oscat.de/de/component/jdownloads/category/2-oscat-basic.html?Itemid=0

http://www.oscat.de/de/component/jdownloads/send/2-oscat-basic/9-oscat-basic333-en.html?Itemid=0






The function DATE_ADD add days, weeks, months, and add years to a
date. First the module adds the specifed days and weeks, then months
and fnally the years.
The input values can be both positive as well be negative. So it can also
be subtracted from a date.
Note that especially for negative input values the sum of negative values,
i.e. -3000 days does not run below 1.1.1970 because this would have an
overfow of data type DATE and undefned values are obtained.


Example: DATE_ADD(1.1.2007,3,1,-1,-2) = 11/12/2005
adds additional 3 days and 1 week and then draws 1 month
and 2 years from.