Simatic date compare

68FuryIII

Member
6
Join Date
Nov 2011
Location
Hämeenlinna
Posts
4
I have in Siemens TP270 output field "best before date" (yyyymmdd, DINT) and now i need to compare in plc (S7-400) that user can´t input date older or newer than 40 days. Any ideas how to do that o_O
 
Do you mean that the operator has to enter the date in the format "yyyymmdd" ? I.e. 20110821 for 2011-08-21 ?
If that is the case, I think it would be less error prone if you have separate inputs for year, month and day.
And does it have to be eaxctly 40 days ? If you can accept approximately 40 days, it becomes easier as you dont have to account for 28-30-31 days per month.
 
In the Standard Library you'll find under "IEC Function Blocks" FC34 - SB_DT_DT which allows you to subtract one date and time from another - that should cover what you need.
 
JesperMP said:
Do you mean that the operator has to enter the date in the format "yyyymmdd" ? I.e. 20110821 for 2011-08-21 ?
If that is the case, I think it would be less error prone if you have separate inputs for year, month and day.
And does it have to be eaxctly 40 days ? If you can accept approximately 40 days, it becomes easier as you dont have to account for 28-30-31 days per month.
Click to expand...

Hi,
Yes operator has to enter date 20110821 for 2011-08-21. That 40 days is approximately. Its not exact.
 
RMA said:
In the Standard Library you'll find under "IEC Function Blocks" FC34 - SB_DT_DT which allows you to subtract one date and time from another - that should cover what you need.
Click to expand...

Hi,
I tried FC34, but if i understand right FC34 difference output (TIME) works only for 24d_20H_31M_23S_647MS and after that result is always 0?
 
An idea.
First, check with FC34 if the difference output is greater than 24days. If yes, then subtract 24 days (FC35 SB_DT_TM), and again calculate the difference.
Then you can compare the difference with 16 days in stead of 40 days.
Not pretty but should work.
 
JesperMP said:
An idea.
First, check with FC34 if the difference output is greater than 24days. If yes, then subtract 24 days (FC35 SB_DT_TM), and again calculate the difference.
Then you can compare the difference with 16 days in stead of 40 days.
Not pretty but should work.
Click to expand...

Good idea. I´ll try that at friday when i go back to work. Thank you for answers :)
 
Just a hint.
When using time and dates on the S7 systems, try and use BCD values, not INTs.
Makes it easier to manipulate and reference.
The (S)FC's also expect BCD values.
 

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