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Dunhillstateofmind

How to interlock program based on time of day

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I need the program to be locked at 11:15 PM so that nobody can use the roll up door again until 7:25 AM. How do I do this?

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You need to provide more info.  Which PLC?  Does it have a real time clock?  You should be able to use simple comparisons to determine the time of day and prevent and output from turning on outside that window, actually pretty easily.

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not sure about Canada but in US there are NFPA guidelines for egress door operation that might affect your plans. 

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Have you thought about emergency cases?

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In general, a motorized roll up door isn't going to be an acceptable means of emergency egress, because it can't be opened during a power outage.

In my facility, every roll-up door also has an ordinary personnel door that opens outward with a crash bar and is accessible only with a key-card from the outside.   Access hours and authorization is handled through our central alarm and security system, not through any PLC-based equipment.

As noted, any PLC that's going to be used to perform time-of-day work needs a Real Time Clock feature, and comparison instructions are generally how you program features for time window limits.

The more challenging part is how you get a PLC to accurately keep time for its location, through power losses or battery failures or time drift.   Even the common method most computers use of getting the time of day from a Network Time Protocol (NTP) server on the enterprise LAN or the Internet is not built into many PLCs.

 

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2 hours ago, Ken Roach said:

is not built into many PLCs.

This is the Allen-Bradley category.  All modern ControlLogix and CompactLogix processors with an ethernet port, or any with an EN2T/3T/4T in the chassis, can be easily configured to sync to IEEE-488 Precision Time Protocol, like you get from a GPS.  (I recommend the Time Machines TM2000B, fwiw.)  PTP will keep a Logix processor within a few microseconds of real time.  (Yes, microseconds.)  Unfortunately, the Micro8xx family's real time clock doesn't appear to have network time sync of any kind.  You'd need some ladder to do it.

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that is true but i would guess that in many cases motorized roll up door is not done using Logix series CPU. i have seen no PLCs or smart relays do the job. topic starter should confirm the hardware and software version. for all we know, it is also possible that question is asked in the wrong forum section.

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