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Retentive Timer/Counters? Beginner Question

Created by: AutoNub at: 10/11/2011 11:08 PM (4 Replies)

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10/11/2011 11:08 PM	Rate (0)
AutoNub Posts: 22 Rating: (1)	Hello! I'm trying to create a timer which keeps track of time when a condition is true, pauses when the condition goes false, and resumes when the condition goes true again. I also want the total time accumulated to be stored even after the power is shut off to the entire system, so when power is restored, if condition is true or becomes true, the timer will still resume from wherever it left off. To clarify, the only time I would want the timer to ever reset is when a programmed reset (R in the case of S_ODT, for example) condition goes true. Can anyone describe or show me an example of how to accomplish this? Thanks!
AutoNub Posts: 22 Rating: (1)
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10/12/2011 1:50 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/11/2024 Posts: 3026 Rating: (1057)	Hello AutoNub a simple search on this subject at https://support.automation.siemens.compresents you with a solution that should fit your question like an old shoe as they say: How do you program a timer that retains the time value at STOP and counts on starting at the stored value? Note that the above is only out of many other Timers and Counters related FAQ collections, which are all listed at the top the above referencedpage (and may come in handy for future related questions that you may have on this subject). I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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10/12/2011 2:54 PM	Rate (0)
AutoNub Posts: 22 Rating: (1)	For whatever reason, a simple search using Mozilla (at least on my end) produces nothing but a blank white page. Using IE, I scanned through the first 4 pages of search results and found this and I also downloaded and viewed the P_FB115.zip from your response. Unfortunately, both of these show a different type of programming from what I'm familiar with. I'm interested in finding a ladder logic solution. I also still haven't read anywhere anything about a timer or counter block which retains its value even after power is shut off to the entire system (not just the conditions, but the entire PLC unit, PC, system--everything). I'm sure I'll eventually learn the visual basic or whatever programming language is being used on the thread in my first link, but I don't have time for that this week. I'm assuming there is a simple ladder logic solution that I'm just not clear about. I'm attaching a copy and paste of my custom counting ladder logic. Please let me know if it'll do what I want. As I understand it (based on PLC glossary and google search), when the initial condition is true timer "Runtime Accumulator" will begin counting, sending a true output "1" to the "ADD_DI" function block for every second the timer condition is true. If the timer condition goes false, it will stop timing and therefore will stop outputting a true "1" signal to the ADD_DI function block. Q80.5 will reset the timer when output Q80.5 from outside network is true. If timer condition goes false and resumes after some delay, timer will start timing again and the ADD_DI function block will begin adding +1 for every second that follows, counting up from its previously stored accumulated total. The value in "Total Cell Runtime" will be retained even when the output Q of the timer "Runtime Accumulator" goes false. It will also be retained even when power to the entire system is shut off (circuit breaker, power outage, etc). Please correct me if any of the above understanding is incorrect. Thanks in advance! Attachment Custom Timer Network.JPG (1167 Downloads)
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10/19/2011 2:14 AM	Rate (0)
loryder Posts: 2 Rating: (0)	I use a similar but somewhat easier solution. If you set a clock byte in the processor (MB1 for example), then M1.5 will be a one second pulse bit. Use your true condition contact, the 1 second pulse contact and then a postive edge (p) before your ADD_DI instruction. Something like... x.x m1.5 x.y(one shot) ---\| \|--------\| \|-----------(p)--------ADD_DI Your jpg looks like it will count (ADD_DI) as long as the S_ODT is true which means it will increment by one every processor scan. Your results may be totally unpredictable. Also, if yu are using a memory word, include it in the processor retained memory range as specified in the processor hardware configuration.
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10/19/2011 2:24 AM	Rate (0)
loryder Posts: 2 Rating: (0)	Another advantage of using ADD instead of counters and the like is that Siemens counters only go to 999 of whatever you are counting. So unless you want to convert seconds to minutes to hours with adds and subtracts scattered around, an ADD network followed by a MOVE zero to the value holder works out much better IMHO. Also remember that Siemens native timers always count down from the preset value to zero, not up from zero to a preset value so to get an elapsed time can get complicated when you have to subtract the remaining time from a known value.
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