big help on PLC problems

[xxxitaliaxxx]

hey i need to write the ladder logic to do use the plc as a 24 hour clock as well i have to write a count down timer any help would be so much help thanks alot

 

[OZEE]

Homework???? If so, let us know what you already have... We'll help, but we won't do your homework for you.

Which PLC??

 

[Steve Bailey]

For the 24-hour clock, pick a PLC that includes a real-time clock in its function set and learn how to read it. If you try to write one in ladder logic, you will be disappointed with the accuracy, even if you are using a PLC that lets you compensate for the inherent inaccuracy of ladder logic timers.

For the countdown timer, what are you supposed to do? Do you need to display the time remaining until some event? Do you know how to do basic arithmetic like subtraction?

 

[xxxitaliaxxx]

hey no its not homework they were just some study tips that i were told were good tricks to find out how to do for future.. and yes i no how to do basic subtraction and addition.

for the count down timer i was thinking of something like a TON connected to a CTD for everytime the TON increments have 1 CTD set for 60 and display seconds like that..

for the 24 hour clock i no it has something to do with the status registry theres some kind of time on there or something like that im just not sure on how to use it

and its a allen bradley plc 5

 

[TConnolly]

Since time moves forward and never backwards, a countdown timer is implemented by subtracting the amount of time that has elapsed since some event happened from the amount of time you want to wait before doing something after that event. So, a count down timer in an AB PLC is implemented with a TON and a SUB instruction. The time remaining is T4:X.PRE-T4:X.ACC.

For the time of day, take a look in the PLC 5 addressing manual under the status file:
http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/5000-rm002_-en-p.pdf

Here is another manual you will find usefull:
http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1785-rm001_-en-p.pdf