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PLC Real Time Clock - Daylight Saving


PLC Real Time Clock - Daylight Saving
Name DaylightSaving
 
Basic Function

A lightweight Function Block to change the PLC Real Time Clock (RTC) forward and backward by 1 hour for daylight saving time (DST) according to rules set in MonthFwd / WeekNoFwd / HourFwd and MonthBack / WeekNoBack / HourBack.  This FB will always treat Sunday for DST changes.  This accounts for most of Europe and America's.

For more information about daylight saving in selected country/timezone see...

http://www.timeanddate.com/time/dst/events.html

Syntax  
File Name DaylightSaving.cxf
Applicable models CPU Unit CP1L/H, CJ1/CS1 (V3 or above), all CJ2's
Software CX-Programmer Version 5.0 or higher
Conditions for usage  
Function Description

A Function Block (FB) to take account of Daylight Saving time according Month and ‘Week number in Month’ rules. The FB will move the PLC Real Time Clock on by 1 hour at hour 'HourFwd' on the Sunday set in MonthFwd/WeekNoFwd setting – to Summer Time clock setting. At hour 'HourBack' on the Sunday set in MonthBack/WeekNoBack the clock will be put back by 1 hour.  If Month/Week/Hour rules apply in a different world timezones, then this FB can be used for southern hemisphere too.

The FB only uses the local PLC RTC and conditions set to adjust the RTC.  Timezone information is not used/required.

Kind of FB definition

Stores variables between executions. Use only one instance in a PLC application.
 

FB Precautions

For correct operation, this FB should always be ‘Enabled’ (so detection is made correctly).  It is also provided with two inputs that will allow manual increment and decrement of the RTC by 1 hour.

Internally the FB is executed for one scan at every new hour of the RTC.  This means that overall PLC scan time is kept as low as possible.

As a minimum the FB must be running on the Sunday specified in MonthFwd/WeekNoFwd at 'HourFwd' and also on the Saturday from 23:59:59 to Sunday at hour 'HourBack' specified in MonthBack/WeekNoBack.
 
The RTC ‘Day of Week’ must be set correctly. (0=Sun, 6=Sat)

Test fully in own code to ensure correct operation.
EN input condition Always On
 
  • Variable Table 

Input variables

Name Variable name Data type Default Range Description
EN

P_On

BOOL

   

Always Enable (P_On) for correct operation.

MonthFwd

 

UINT

 

1-12

Month number (1 to 12) to put RTC forward by 1 hour

WeekNoFwd

 

UINT

 

1-4
or 0

Week number in MonthFwd to put on by 1 hour.  Sunday is always used as the day of week to move clock forward. Week number can be 1 to 4. For last Sunday, set 0

HourFwd

 

UINT

 

1-23

Hour number to move forward on specified Sunday

MonthBack

 

UINT

 

1-12

Month number (1 to 12) to put RTC backward by 1 hour

WeekNoBack

 

UINT

 

1-4
or 0

Week number in MonthBack to put back by 1 hour.  Sunday is always used as the day of week to move clock backward. Week number can be 1 to 4. For last Sunday, set 0

HourBack

 

UINT

 

1-23

Hour number to move backward on specified Sunday

IncHour

Force1HrFwd

BOOL

   

Manual increment of RTC by 1 hour upon rising edge. HourForward flag is Set.

DecHour

Force1HrBack

BOOL

   

Manual decrement of RTC by 1 hour upon rising edge.  HourForward flag is Reset.

 

Output variables

Name Variable name Data type Default Range Description
ENO

ENO

BOOL

   

Unused

HourForward

HourForward

 

Retained During Power Off

 

Flag to signify if in Daylight Saving mode (NB this flag is only set automatically at MonthFwd/WeekNoFwd and reset at MonthBack/WeekNoBack). Use Manual (IncHour/DecHour) to set initially.

 

  • Revision History

 

Version Date Contents
1.00 19 March 2012 First release

 

 



Attachments

DaylightSaving.cxf - Size: 3843
DaylightSaving.pdf - Size: 206518


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Created 2012-02-19
Modified 2019-06-06
Views 13771

 

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